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Publications of the Institute for Informatics
2009
Lin Cong, Guohan Lu, Yang Chen, Beixing Deng, Xing Li.What Level of Estimating Accuracy Does TCP Need and Can TCP Achieve. Poster session of the 5th ACM International Conference on emerging Networking EXperiments and Technologies (CoNEXT 2009), Rome, Italy, 2009
Martin Stiemerling, Sebastian Kiesel.A System for Peer-to-Peer Video Streaming in Resource Constrained Mobile Environments. U-NET CoNext 2009 workshop, ACM, 2009
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Peer-to-Peer based near-live video streaming is becoming more and more popular with users of xed-line broadband network access, but it is mostly unavailable to mobile users, as cellular networks, such as GPRS/UMTS, cannot meet the bitrate requirements, while other wireless technologies, such as WLAN, may be fast enough but cover only very limited areas. However, there is a small but important set of scenarios, where several mobile users in close physical proximity are interested in retrieving the same content. We propose a P2P-TV system that enables them to retrieve video chunks in a cooperative way. The coordinated and efficient usage of all wireless resources available to a group of mobile hosts is the key to enable P2P-TV in mobile environments. This paper introduces our general concept. Simulation based studies are presented to assess dierent resource allocation strategies and to demonstrate the feasibility of our approach for delivering near-live TV in resource constrained mobile environments.
Mayutan Arumaithurai, Ruediger Geib, Rene Rex, Xiaoming Fu.Pre-Congestion Notification based Flow Management in MPLS-based DiffServ Networks. The 28th IEEE International Performance Computing and Communications Conference (IPCCC 2009), Phoenix, AZ, USA, IEEE, 2009
Benjamin Zeiß , Jens Grabowski .Analyzing Response Inconsistencies in Test Suites. Proceedings of the 21st IFIP International Conference on Testing of Communicating Systems and the 9th Int. Workshop on Formal Approaches to Testing of Software (TESTCOM/FATES 2009), November 2-4 2009, Eindhoven (paper accepted),
Thomas Hornung, Wolfgang May .Semantic Annotations and Querying of Web Data Sources.
International Conference on Cooperative Information Systems
(CoopIS 2009), Vilamoura, Portugal, to appear in LNCS, Springer, page ??, 2009
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A large part of the Web, actually holding a significant portion of the useful information throughout the Web, consists of views on hidden databases, provided by numerous heterogeneous interfaces that are partly human-oriented via Web forms ("Deep Web"), and partly based on Web Services (only machine accessible). In this paper we present an approach for annotating these sources in a way that makes them citizens of the Semantic Web. We illustrate how queries can be stated in terms of the ontology, and how the annotations are used to select and access appropriate sources and to answer the queries.
Thomas Hornung, Wolfgang May .Ontology-Based Support for Graph Algorithms in Online
Exploration Workflows (Poster).
Ontologies, DataBases, and Applications of Semantics
(ODBASE 2009), Vilamoura, Portugal, to appear in LNCS, Springer, page ??, 2009
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Application domains often include notions that are inherently based on graph structures. In this paper, we propose CGDT as a comprehensive generic ontology and API for graphs, which is geared towards online exploration of potentially large graphs.
Franz Schenk , Wolfgang May .An Active Domain Node Architecture for the Semantic Web.
Ontologies, DataBases, and Applications of Semantics
(ODBASE 2009), Vilamoura, Portugal, to appear in LNCS, Springer, page ??, 2009
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We present an architecture for application nodes for the Semantic Web (SWAN). The underlying principle in SWAN is the specification of actions and events as dynamic aspects of the application. This complements the MARS framework (Modular Active Rules for the Semantic Web ), where the communication between services is based on the notions of events and (requests of) domain-level actions. Such a model allows to define workflows on the ontology level. While MARS offers the service infrastructure needed for processing the workflow, SWAN is an architecture for applications in a rule-driven environment. Basically, SWAN consists of a hybrid OWL/F-Logic knowledge base, augmented with active rules. Using SWAN, only a set of rules is needed in order to deploy a new application. A prototype implementation of the architecture exists that shows the flexibility and applicability of its concepts.
Julian Gallop, Geoff Caryer, Jens Grabowski , Tatiana Kovacikova, Thomas Rings , Stephan Schulz, Ian Stokes-Rees.Grid/Cloud Computing Interoperability, Standardization and the Next Generation Network. 13th International Conference on Intelligence in Next Generation Networks (ICIN): "Beyond the Bit Pipes" , Cite Mondiale, Bordeaux, France , Oct. 26-29 2009., 2009
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For telecom operators, the future lies in converging fixed, mobile and data services onto the Next Generation Network (NGN). This paper discusses the relationship between grid and cloud computing, identifies gaps and overlaps in existing standards and identifies how grid and cloud technology could be exploited to improve the efficiency of NGN resources and to offer new “data” services to consumers. This will enable telecom operators to manage their resources in a dynamic and optimal way by a single platform. This paper describes the approach taken by the European Telecommunications Standards Institute (ETSI) Technical Committee for grid computing (TC GRID) to identify gaps and overlaps in grid/cloud computing standards and to support the integration of grid/cloud computing with the NGN architecture.
Jianhua He, Xiaoming Fu Zuoying Tang.End-to-End Versus Hop-by-Hop Soft State Refresh for Multi-hop Signaling Systems. 17th IEEE International Conference on Network Protocols (ICNP 2009), Princeton, New Jersey, USA, IEEE, 2009
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To ensure state synchronization of signalling operations, many signaling protocol designs choose to establish “soft” state that expires if it is not refreshed. The approaches of refreshing state in multi-hop signaling system can be classified as either end-to-end (E2E) or hop-by-hop (HbH). Although both state refresh approaches have been widely used in practical signaling protocols, the design tradeoffs between state synchronization and signaling cost have not yet been fully investigated. In this paper, we investigate this issue from the perspectives of state refresh and state removal. We propose simple but effective Markov chain models for both approaches and obtain closed-form solutions which depict the state refresh performance in terms of stateconsistency and refresh message rate, as well as the state removal performance in terms of state removal delay. Simulations verify the analytical models. It is observed that the HbH approach yields much better state synchronization at the cost of higher signaling cost than the E2E approach. While the state refresh performance can be improved by increasing the values of state refresh and timeout timers, the state removal delay increases largely for both E2E and HbH approaches. The analysis here shed lights on the design of signaling protocols and the configuration of the timers to adapt to changing network conditions.
Peng Sun, Yang Chen, Beixing Deng, Xing Li.Neighbor Selection Based on TIV Severity Sort Model in Vivaldi Network Coordinate System. 17th IEEE International Conference on Network Protocols (ICNP 2009) Poster Session, Princeton, New Jersey, USA, 2009
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Network Coordinate (NC) system is an efficient andscalable mechanism to estimate the distance between Internethosts. However, the existence of Triangle Inequality Violation(TIV) decreases the accuracy of NC system. With focus onmost widely used NC system, Vivaldi, we propose an effectivemechanism of neighbor selection based on TIV Severity Sort toimprove Vivaldi performance. By sorting existing hosts based oncorresponding edges’ TIV severity, the 90th percentile relativeerror(NPRE) of Vivaldi is decreased by 13.9%. The convergencerate is improved, and the final median prediction error is 7.9%smaller.
Paper
Philip Makedonski , Helmut Neukirchen , Jens Grabowski .Validating the Behavioral Equivalence of TTCN-3 Test Cases. 2009 First International Conference on Advances in System
Testing and Validation Lifecycle (VALID 2009)
, IEEE, 2009
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Refactoring has been proven as useful means to improve the quality of source code. However, when improperly applied, it may introduce undesired changes to the observable behavior of the software. In this paper, an equivalence checking approach is presented to validate the behavior preservation after the application of refactoring in the domain of test cases specified using the Testing and Test Control Notation Version 3 (TTCN-3). The approach is based on bisimulation and incrementally checks the observable behavior of two test cases at runtime for equivalence. The approach is implemented prototypically and sample experiments are conducted to evaluate the effectiveness of the approach.
Akhtar Ali Jalbani , Jens Grabowski , Helmut Neukirchen , Benjamin Zeiß .Towards an Integrated Quality Assessment and Improvement Approach for UML Models. 14th System Design Languages Forum (SDL Forum 2009), 22-24 Sep 2009, Ruhr-University of Bochum, Germany,
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Models defined using the Unified Modeling Language (UML)are nowadays common parts of software documentations, specifications and sometimes even implementations. However, there is a broad varietyof how UML is used. Reasons can be found, for example, in the lack ofgenerally accepted modeling norms and guidelines, the semi-formal se-mantics of UML, or the complexity of the language. In practice, these factors inevitably lead to quality problems in UML models that need to beaddressed. We investigate and discuss existing work in the field of qualityassessment and improvement of UML models and present how we envision an integrated approach to quality assessment and improvement ofUML models. We assess a model with a Factor-Criteria-Metrics (FCM)based quality model, detect issues by finding smells and violated met-ric thresholds in UML models, and improve UML models by applyingrefactorings using model-to-model transformations.
Steffen Herbold , Jens Grabowski , Helmut Neukirchen .Automated Refactoring Suggestions Using the Results of Code Analysis Tools. 2009 First International Conference on Advances in System
Testing and Validation Lifecycle (VALID 2009), IEEE, 2009
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Static analysis tools are used for the detection of errors and other problems on source code level. The detected problems related to the internal structure of a software can be removed by source code transformations called refactorings. To automate such source code transformations, refactoring tools are available. In modern integrated development environments, there is a gap between the static analysis tools and the refactoring tools. This paper presents an automated approach for the improvement of the internal quality of software by using the results of code analysis tools to call a refactoring tool to remove detected problems. The approach is generic, thus allowing the combination of arbitrary tools. As a proof of concept, this approach is implemented as a plug-in for the integrated development environment Eclipse.
Jan Seedorf, Sebastian Kiesel, Martin Stiemerling.Traffic Localization for P2P-Applications: The ALTO Approach. Ninth International Conference on Peer-to-Peer Computing (IEEE P2P 2009), IEEE, 2009
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Today, most P2P applications do not consider locality on the underlying network topology when choosing their neighbors on the P2P routing layer. As a result, participating peers may experience long delays and peers’ ISPs suffer from a large amount of (costly) inter-ISP traffic. One potential solution to mitigate these problems is to have ISPs or third parties convey information regarding the underlying network topology to P2P-clients through a dedicated service. Following this approach, the IETF has recently formed an Application Layer Traffic Optimization (ALTO) working group for standardizing a protocol to enable P2P applications to obtain information regarding network layer topology. This paper comprises the problem space for such an ALTO approach, taking into account recent developments in the IETF ALTO Working Group. In particular, we will describe requirements for an ALTO protocol identified in the IETF, concrete protocols which have been proposed so far, and the overall challenges. In addition, we will discuss related issues such as privacy considerations, the relationship of an ALTO service with existing caching solutions, discovery mechanisms for an ALTO service, and security considerations.
Paper
José Júlio Alferes, Wolfgang May , Michael Eckert.Evolution and Reactivity in the Semantic Web. Semantic Techniques for the Web, The REWERSE Perspective, page ??, Springer LNCS 5500, 2009
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Evolution and reactivity in the Semantic Web address the vision and concrete need for an active Web, where data sources evolve autonomously and perceive and react to events. In 2004, when the REWERSE project started, regarding work on Evolution and Reactivity in the Semantic Web there wasn′t much more than a vision of such an active Web.
Thomas Rings , Geoff Caryer, Julian Gallop, Jens Grabowski , Tatiana Kovacikova, Stephan Schulz, Ian Stokes-Rees.Grid and Cloud Computing: Opportunities for Integration
with the Next Generation Network. Journal of Grid Computing: Special Issue on Grid Interoperability, JOGC, Volume 7, Issue 3 (ISSN 1570-7873 (Print) 1572-9814 (Online)) DOI: 10.1007/s10723-009-9132-5 , 375 - 393, Springer Netherlands, 2009
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Carrier-grade networks of the future are currently being standardized and designed under the umbrella name of Next Generation Network (NGN). The goal of NGN is to provide a more flexible network infrastructure that supports not just data and voice traffic routing, but also higher level services and interfaces for third-party enhancements. Within this paper, opportunities to integrate gridand cloud computing strategies and standards into NGN are considered. The importance of standardized interfaces and interoperability testing demanded by carrier-grade networks are discussed. Finally, a proposal how the testing methods developed at the European Telecommunications Standards Institute (ETSI) can be applied to improve the quality of standards and implementations is presented.
Paper
Zengbin Zhang, Yao Li, Yang Chen, Pei Cao, Beixing Deng, Xing Li.Understand the Unfairness of BitTorrent. In the Poster session of ACM SIGCOMM 2009 (SIGCOMM'09), 2009
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BitTorrent (BT) is the most popular P2P file-sharing application. Its tit-for-tat mechanism aims to guarantee the efficiency and fairness of sharing. However, while BT’s download efficiency has been proven, we find that the current protocol suffers seriously from unfairness, in the sense thatcertain peers will always serve as Super Peers. In this paper, we report on experiments conducted to pinpoint the cause of unfairness. The results indicate that the occurrence of Super Peer has a strong correlation with the bandwidth betweenthe initial seed and the peer, and a weak correlation with the start time of the peer.
Paper
Florian Tegeler.Interest based automated content exchange in 7DS. Technical Report IFI-TB-2009-02, Institute of Computer Science, University of Goettingen, 2009
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With the increasing storage space and performance of today′s mobile devices, users often store a large variety of content like music on their devices. We argue, that leveraging this data to extract a meaningful user interest representation on the given data can help developing next generation mobile services. The mobile device can be enabled to automatically detect and predict the usersinterest and automatically acquire such information. We are especially targeting at scenarios where the mobile device is not always connected to a global infrastructure such as the internet or a provided cellular net but moves in anoften communication disrupted manner. Typically such scenarios are referred to as mobile delay/disruption tolerant networks (mobile DTNs). We present a prototype that automatically analyzes a users content, derives the interest and exchanges data with other nodes having content of similar interest space. The two prototype media types we chose are music and news, while music represent time and location independent general user′s interest based media. News files are an example for highly time and location critical media which is not only based on the general user′s interest but has to include additional dimensionsthat can be highly dynamical. We present the general architecture of our solution and highlight some technical details of our implementation proving the flexibility and extensibility of our approach.
Jens Grabowski , Benjamin Zeiß .Quality Engineering for Test Artefacts. TAROT Summer School on Software Testing 2009, Las Navas del Marqués, Spain, July 2009,
Ralf Lübben, Guangzhi Li, Dongmei Wang, Robert Doverspike, Xiaoming Fu.Fast Rerouting for IP Multicast in Managed IPTV Networks. IEEE International Workshop on Quality of Service (IWQoS 2009), Charleston, SC, USA, 2009
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Recent deployment of IP based multimedia distribution, especially broadcast TV distribution has increased the importance of simple and fast restoration during IP network failures for service providers. In this paper, we propose and evaluate a simple but efficient method for fast rerouting of IP multicast traffic during link failures in managed IPTV networks. More specifically, we devise an algorithm for tuning IP link weights so that the multicast routing path and the unicast routing path between any two routers are failure disjoint, allowing us to use unicast IP encapsulation for undelivered multicast packets during link failures. We demonstrate that, our method can be realized with minor modification to the current multicast routing protocol (PIM-SM). We run our prototype implementation in Emulab which shows our method yields to good performance.
Paper
Changpeng Fan, Andreas Festag, Xiaoming Fu, Cornelia Kapper, Holger Karl, Mirko Schramm, Günter Schäfer (inventors).Method for carrying out a QoS-oriented handoff between a first and a second IP-based, especially mobile IPV6-based, communication path, between a mobile node (MN) and a correspondent node (CN). granted patent, No. EP20010953886, 2009
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The invention relates to a method for carrying out a QoS-oriented handoff between a first and a second IP-based, especially mobile IPv6-based, communication path, between a mobile node (MN) and a correspondent node (CN), the second communication path being part of a number of communication paths which can be accessed by the mobile node, with no, one, or a plurality of intermediate instances. The inventive method comprises at least the following steps: (a) a communication path is selected from the communication paths which can be accessed by the mobile node, as a second communication path; (b) a message (BU) is generated by the mobile node, said message containing at least one IP address which is associated with the mobile node on the basis of the selected communication path, and containing minimum quality of service requirements (QoS) in terms of the selected communication path; (c) the ability to meet at least the minimum quality of service requirements is controlled and optionally ensured by the individual intermediate instances through which the message passes successively, on the selected communication path and/or through the correspondent node. The message contains the minimum quality of service requirements for a communication from the mobile node to the correspondent node and/or vice versa. A handoff is automatically carried out between the first communication path and the second selected communication path, when at least the minimum quality of service requirements are met or the message is stopped. A notice is generated in an intermediate instance and/or in the correspondent node and is sent to the mobile node if the ability to meet the minimum quality of service requirements is not ensured.
Jens Grabowski , Philip Makedonski , Andreas Ulrich, Benjamin Zeiß .Quality Assurance for TTCN-3 Test Specifications. TTCN-3 User Conference 2009 (T3UC2009)
, European Telecommunications Standards Institute (ETSI), Sophia Antipolis (France) , 2009
Jens Grabowski , Jürgen Großmann, Friedrich-Wilhelm Schröer, Diana Serbanescu, Jacob Wieland.Testing Embedded Systems in the Automotive Industry with TTCN-3. TTCN-3 User Conference 2009 (T3UC2009), European Telecommunications Standards Institute (ETSI), Sophia Antipolis (France), 2009
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In the automotive industry, the quality assurance ofsoftware-intensive systems is still characterized by high manualportions (i.e. a low level of automation) and a multiplicity of oftenproprietary test systems and test platforms. Test specifications areoften weakly formalized and not standardized. In contrast to this, theAUTOSAR consortium opted for TTCN-3 to implement the AUTOSARconformance test suites. AUTOSAR is founded by a majority of Europeanand international car manufacturers and their suppliers to provide astandardized platform for software architectures and softwarecomponents, which is currently established in the automotive industry.While AUTOSAR tests are based on the actual version of TTCN-3, a largenumber of automotive applications feature requirements (e.g. timedbehavior, continuous behavior, closed loop control) that are notstraightforward testable by means of TTCN-3. To overcome theselimitations, a consortium from industry and academia started theresearch project "TEst specification and test Methodology for Embeddedsystems in Automobiles" (TEMEA). TEMEA started in spring 2008 and istargeted on developing a TTCN-3-based test specification and testimplementation methodology for embedded systems in automobiles.This presentation will provide an overview on the actual status of theTEMEA project including our first results in the area of testing realtime applications and continuous data streams with TTCN-3. We presenta limited set of additional TTCN-3 concepts, which enable us toprecisely define estimations on timed application and yield a solidbasis for the definition and assessment of continuous datastreams. The applicability of the concepts is demonstrated by smallexamples and a prototypical tool environment. Moreover, we willprovide an outlook on future work, especially on the consolidation ofadditional concepts dedicated for testing and assessing hybrid systemsand their temporal behavior.
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Thomas Deiss, Jens Grabowski , György Réthy, Ina Schieferdecker.The new TTCN-3 version 4.1.1. TTCN-3 User Conference 2009 (T3UC2009), European Telecommunications Standards Institute (ETSI), Sophia Antipolis (France), 2009
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The presentation will inform the audience about the new features ofTTCN-3 v4.1.1 and modifications being made. TTCN-3 v4.1.1 encompassesthe resolution for 130 change requests. The presentation willstructure the changes and point at the major additions such as themodule interface. The presentation will also review the TTCN-3 packagemechanism by which optional features can be used in TTCN-3. Currently,packages for advanced parameterization, for behavioural types, and forstatic test configurations have been developed. Although thesepackages are not yet in the approval process, the package mechanism isa major change in the language architecture of TTCN-3 and willtherefore be discussed in this presentation.
Paper
Dieter Hogrefe , Sven Anderson, Saverio Niccolini.Sipfix: A scheme for distributed sip monitoring. Proceedings of IFIP/IEEE Symposium on Integrated Management 2009 (IM2009), 2009
Lei Shi, Jing Fu, Xiaoming Fu.Loop-Free Forwarding Table Updates with Minimal Link Overflow. Proceedings of IEEE International Conference on Communications (ICC 2009), Dresden, Germany, 2009
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The forwarding paths in an IP network may change due to a link failure, network equipment maintenance or reconfiguration of link weights, then the forwarding tables in the routers need to be updated. These updates may cause transient loops and transient link overflow, if they are not performed in an appropriate order. While existing work has been done to achieve loop-free updates, transient link overflow is still a problem during the update process. In this paper, we present a method that compares the initial and final forwarding paths, and obtains the updatable nodes that do not cause any transient loop or transient link overflow. However, there is not always such kind of nodes so that the forwarding tables may not converge to the final one without causing link overflow. Therefore, we propose an algorithm to update the forwarding tables that will refrain the link overflows to a minimal level. The performance study on a real topology with two setups confirms that our approach achieves smaller link overflow than using a previously proposed approach.
Paper
Martin Stiemerling, Marcus Brunner, Sebastian Kiesel, Xiaoming Fu.TORI: User Provided Future Networking Testbeds. IEEE International Workshop on the Network of the Future, in conjunction with IEEE ICC 2009, Dresden, Germany, IEEE, 2009
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The usage of testbeds is considered a key tool for exploring the development of new protocols and network architectures in the area of network research. Testbeds, together with simulations, are the basic tool set of network researchers to drive research, but often it is impossible to get feedback from real deployments and their respective data traffic. Today’s major testbed facilities, e.g., VINI and PlanetLab, aim at emulating the behavior of large-scale networks, but they are still several orders of magnitude smaller than the deployed operational network infrastructure. We argue that it is time to extend network research beyond theoretical and testbed approaches towards a dynamic, peer-to-peer based testbed environment, similar to the approach taken by seti@home and BOINC. We aim at expanding the total number of participating nodes in an experiment and at experimenting on existing operational infrastructure with its entirely uncontrollable environment. Our vision presented in this paper, the Testbed on Real Infrastructure (TORI), includes regular end hosts (peers) in an experiment by deploying and executing the experimental software on these peers and to form an overlay network upon them. The main difference of our TORI approach compared to others is installing new technologies and testing them with the operational infrastructure.
Jun Lei, Xiaoming Fu.Interest-based Peer-to-Peer Group Management. Second IEEE/ACM International Workshop on Future Multimedia Networking (FMN 2009), Coimbra, Portugal, Springer LNCS, 2009
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Peer-to-Peer systems become popular applications but suffer from insufficient resource availability which is caused by free-riders and inefficient lookup algorithms. To address the first cause, a number of recent works have focused on providing appropriate incentive mechanisms to encourage participants to contribute their resources to the P2P systems. To improve the lookup efficiency, locality-aware peer management has been introduced into the research community. However, existing proposals attempt to optimize the service performance during the data transmission period mostly after performing the neighboring lookup, which cannot address the fundamental concern of reducing lookup traffic. Besides, existing implementations select available contributors among random neighbors suggested by a specific server. Therefore, this paper proposes interest-based peer-to-peer management (IPM) protocol to facilitate the peering lookup. Our design philosophy differs from existing work that IPM is a client-only approach and can be represented as either an alternative or a complementary to the current proposals. With additional locality-awareness considerations, IPM can reduce the lookup overhead while optimizing the P2P traffic performance. The simulation results essentially state that IPM can largely improve the efficiency and reliability of P2P media distribution systems, for instance, reduces control overhead by 50% on average and reduces average packet loss rate up to 34.7%.
Paper
Niklas Neumann, Jun Lei, Xiaoming Fu, Gong Zhang.I-PMIP: An Inter-Domain Mobility Extension for Proxy Mobile IP. in the Proceedings of 5th International Wireless Communications and Mobile Computing Conference (IWCMC 2009), Leipzip, Germany, ACM Digital Library, 2009
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Proxy Mobile IP (PMIP) provides a solution for network-based localized mobility management which in contrast to host-based mobility solutions, like Mobile IP (MIP), does not require changes to the end-hosts and avoids tunneling overhead between the mobile node and it′s network access point. Within a PMIP-enabled mobility domain, the mobile node is able to maintain the same IP address when it moves. However, if the mobile node leaves this domain the mobility support breaks. This paper proposes an extension to PMIP, called I-PMIP which allows to interconnect multiple PMIP-enabled mobility domains to provide continuous mobility support for a mobile user. I-PMIP is based on an architecture that can provide a mobile node with an anchor point that is placed very close towards the mobile. Numerical analysis show that the approach is comparable to other approaches that provide inter-domain mobility.
Paper
Fang-Chun Kuo, Kun Tan, Xiang-Yang Li, Jiansong Zhang Xiaoming Fu.XOR Rescue: Exploiting Network Coding in Lossy Wireless networks. 6th IEEE Communications Society Conference on Sensor, Mesh and Ad Hoc Communications and Networks (SECON 2009), Rome, Italy, 2009
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It is well-known that wireless links are error-prone and require retransmissions for recovering frames from errors and losses. Network coding (NC) has been proposed for more efficient MAC-layer retransmissions in WLANs. However, existing schemes employed the reception report mechanism, which is both inefficient and expensive. Furthermore, they considered neither fairness nor the effects of time-varying heterogeneous wireless networks. These issues are critical for achieving full benefit of network coding. Without addressing them, these schemes may even impair system performance. In this paper, a novel MAC-layer retransmission scheme, namely XOR Rescue(XORR) is proposed. It estimates the reception status without extra overheads and devises a new coding metric, which accommodates the effects of the frames size and the channel condition. Finally, XORR employs NC-aware fair opportunistic scheduling, which is theoretically proven to be fair, i.e. not only the service time is evenly allocated, but also it always improves the expected goodput for every wireless station. It is further verified by theoretic analyses, extensive simulations and testbed experiments. Our results show that XORR outperforms the non-coding fair opportunistic scheduling and 802.11 by 25% and 40%, respectively.
Paper
Florian Tegeler.Security Analysis of IKEv2 Session Resumption. Technical Report No. IFI-TB-2009-01, Institute of Computer Science, University of Goettingen, 2009
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This document describes the security analysis of a proposed IKEv2 Session Resumption method based on Sheffer, Y., Tschofenig, H., Dondeti, L. and Narayanan, V.: IPSec Gateway Failover Protocol (http://www.ietf.org/Internet-drafts/draft-sheffer-ipsecfailover-02.txt).
Paper
Xiaoming Fu, Pan Hui (editors).Proceedings of the 1st ACM International Workshop on Hot Topics of Planet-scale Mobility Measurement (HotPlanet'09). Krakow, Poland, ACM Press, 2009
Thomas Hornung, Wolfgang May , Georg Lausen.Process Algebra-Based Query Workflows. 21st
International Conference on Advanced Information Systems, Amsterdam, Netherlands, Springer LNCS 5565, pages 440-454, 2009
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In this paper we combine ideas from workflow processing and database query answering. Tailoring process algebras like Milner′s Calculus of Communicating Systems (CCS) to relational dataflow makes them a natural candidate for specifying data-oriented workflows in a declarative way. In addition to the classical evaluation of relational operator trees, the combination with the CCS control structures provides (guarded) alternatives and test-based iterations using recursive process fragment definitions. For the actual atomic constituents of the process, language concepts from the relational world, like queries, but also the use of abstract datatypes, e.g., graphs, can be embedded.
Jens Grabowski , Benjamin Zeiß .Modellgetriebene Softwareentwicklung und Modelltransformationen in der Praxis. 6.te studentische Informatik-Tage 2009 Göttingen (sIT2009) am 8. und 9. Mai 2009,
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Yang Chen, Xiao Wang, Xiaoxiao Song, Eng Keong Lua, Cong Shi, Beixing Deng, Xing Li.Phoenix: Towards an Accurate, Practical and Decentralized Network Coordinate System. In Proc. of 8th International IFIP-TC6 Networking Conference (Networking 2009), 2009
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Network coordinate (NC) system allows efficient Internet distance prediction with scalable measurements. Most of the NC systems are based on embedding hosts into a low dimensional Euclidean space. Unfortunately, the accuracy of predicted distances is largely hurt by the persistent occurrence of Triangle Inequality Violation (TIV) in measured Internet distances. IDES is a dot product based NC system which can tolerate the constraints of TIVs. However, it cannot guarantee the predicteddistance non-negative and its prediction accuracy is close to the Euclidean distance based NC systems. In this paper, we propose Phoenix, an accurate, practical and decentralized NC system. It adopts a weighted model adjustment to achieve better prediction accuracy while it ensures the predicted distances to be positive and usable. Our extensive Internet trace based simulation shows that Phoenix can achieve higher prediction accuracy than other representative NC systems. Furthermore, Phoenixhas fast convergence and robustness over measurement anomalies.
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Jens Nödler, Helmut Neukirchen , Jens Grabowski .A Flexible Framework for Quality Assurance of Software Artefacts --
With Applications to Java, UML, and TTCN-3 Test Specifications. 2nd International Conference on Software Testing, Verification, and Validation (ICST 2009), IEEE, 2009
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Reviews and inspections of software artefacts are able to find flaws at an early stage; however, manual review is time consuming and thus, analysis tools have been developed to automate the quality assurance of software artefacts. Usually, software analysis tools are implemented for analysing only one specific language as target and for performing only one class of analyses. Furthermore, most software analysis tools support only common programming languages, but not those domain-specific languages that are used in a test process. As a solution, a framework for software analysis is presented that is based on a flexible, yet high-level facade layer that mediates between analysis rules and the underlying target software artefact; the analysis rules are specified using high-level XQuery expressions. Hence, further rules can be quickly added and new types of software artefacts can be analysed without needing to adapt the existing analysis rules. The applicability of this approach is demonstrated by examples from using this framework to calculate metrics and detect bad smells in Java source code, in UML models, and in test specifications written using the Testing and Test Control Notation (TTCN-3).
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Steffen Herbold .Machine Learning for Software Process Analysis. Ph.D. Symposium at the 2009 International Conference on Software Testing, Verification, and Validation (ICST 2009). , Denver, Colorado, USA, 2009
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Thomas Rings .Towards systematic interoperability testing of distributed systems. Ph.D. Symposium at the 2009 International Conference on Software Testing, Verification, and Validation (ICST 2009). , Denver, Colorado, USA, 2009
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This work suggests an approach towards a systematicmethodology of developing and applying interoperabilitytests for distributed systems. The methodology includes interoperabilityassessment and dynamic interoperability testing.
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Jianhua He, Xiaoming Fu, Jie Xiang, Yan Zhang Zuoyin Tang.Routing and Scheduling for WiMAX Mesh Networks. in: Y. Zhang (ed.), WiMAX Network Planning and Optimization, Auerbach Publications, Taylor&Francis Group, USA, 2009
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The book chapter presents the recent developments and a new approach for the scheduling and (both distributed and centralized) routing issues in WiMAX mesh networks.
Paper
Jianhua He, Xiaoming Fu, Zuoyin Tang, Hisiao-Hwa Chen.End-to-End versus Hop-by-Hop State Refresh in Soft State Signaling Protocols. IEEE Communications Letters, 13(4): 268-270, IEEE, 2009
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The concept of soft state (i.e., the state that will expire unless been refreshed) has been widely used in the design of network signaling protocols. The approaches of refreshing state in multi-hop networks can be classified to end-to-end (E2E) and hop-by-hop (HbH) refreshes. In this article we propose an effective Markov chain based analytical model for both E2E and HbH refresh approaches. Simulations verify the analytical models, which can be used to study the impacts of link characteristics on the performance (e.g., state synchronization and message overhead), as a guide on configuration and optimization of soft state signaling protocols.
Paper
Florian Tegeler, Jun Lei, Xiaoming Fu.A Unified Security Backplane for Trust and Reputation Systems in Decentralized Networks. IEEE INFOCOM 2009 Student Workshop, 2009
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Trust and Reputation (TR) systems are a recently proposed means to address free-rider issues in decentralized networks such as P2P, DTNs, and wireless mesh networks. Basically, TR systems identify malicious node behaviors by observation and direct interaction experience. However, these systems often lack a security framework to prevent a variety of attacks, such as identity spoofing or capturing and false reports on nodes behavior. We present a security backplane preventing such attacks by providing authentication, non-repudiation and other security services without predetermining the exact TR algorithm on node interaction selection and the metrics on the evaluation of nodes. Utilizing this security framework, multiple proposed algorithms such as Scrubber, Eigentrust, CONFIDENT or pricing systems can be implemented with increased and flexible security properties.
Paper
Mayutan Arumaithurai, Ruediger Geib, Rene Rex, Xiaoming Fu.An encoding method to signal 3 states with a single PCN bit. IEEE INFOCOM 2009 Student Workshop, 2009
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Pre-Congestion Notification (PCN) is currently being developed by the IETF to provide admission control in DiffServ networks for non-elastic flows. Various marking schemes are being proposed as part of this effort. We evaluate a new marking behaviour that could be used to signal three different states by means of a single bit. This scheme is of interest to networks operating with MPLS as the Label QoS coding space is limited to three EXP bits. Similar to the ECN standard for MPLS, this research assumes that just two codepoints will be available to indicate different congestion states. Of these two codepoints, one would be used to differentiate between PCN and non-PCN traffic and the other would be used for PCN marking. This paper outlines the approach and presents the advantages and limitations of the proposal using the evaluations performed. A comparison of the method with a two bit PCN marking approach is also studied.
Paper
Yang Chen, Yongqiang Xiong, Xiaohui Shi, Jiwen Zhu, Beixing Deng, Xing Li.Pharos: Accurate and Decentralised Network Coordinate System. IET Communications, 539-548, 2009
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Network coordinates (NC) system is an efficient mechanism for Internet distance prediction with scalable measurements. The intrinsical cause for the unsatisfactory accuracy of the simulation-based NC algorithms has been identified. Then Pharos, a fully decentralised and hierarchical scheme, is proposed to solve this problem. Pharos leverages multiple coordinate sets at different distance scales, with the right scalebeing chosen for prediction each time. We evaluate the performance of Pharos system with the King data set and latency data from PlanetLab, and compare it with the representative NC system, Vivaldi. The experimental results show that Pharos greatly outperforms Vivaldi in Internet distance prediction without adding any significant overhead. Our extensive evaluation results also demonstrate that Pharos can significantly improvethe performance in distributed Internet applications, such as overlay multicast and server selection.
Paper
Thomas Hornung, Wolfgang May .Deep Web Queries in a Semantic Web Environment. 2nd
Workshop on Advances in Accessing Deep Web (ADW 2009), Poznan, Poland, LNBIP 37, pages 39-50, 2009
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Access to Deep Web sources is concerned with querying data that is hidden behind Web forms and primarily not accessible by common query languages. Web forms do not contain any type information, and it thus follows that Deep Web sources only work on string data in its rudimentary form. In this paper, we demonstrate how Semantic Web technologies can be used to first lift Deep Web sources to the level of databases with a precise schema and strong typing information and finally to the level of Semantic Web applications. A special focus in this context is on handling measurements, units and dimensions, which is an important issue when data from multiple Deep Web sources is declaratively combined for more involved querying tasks.
Jens Grabowski .Anmerkungen zur Langlebigkeit von Testartefakten. 1. Workshop für langlebige und zukunftsfähige Softwaresysteme 2009 (LaZuSo 2009) am 2. März 2009, im Rahmen der SE 2009 in Kaiserslautern,
Paper
Martin Stiemerling, Sebastian Kiesel.ALTO H1/H2 Protocol. Internet Engineering Task Force, Internet draft (draft-stiemerling-alto-h1h2-protocol-00) , work in progress, Application Level Transport Optimization (ALTO) Working Group, 2009
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Many Internet applications are used to access resources, uch as pieces of information or server processes, which are available in several equivalent replicas on different hosts. This includes, but is not limited to, peer-to-peer file sharing applications. The goal of Application-Layer Traffic Optimization (ALTO) is to provide guidance to applications, which have to select one or several hosts from a set of candidates, that are able to provide a desired resource. This memo proposes one possible way of implementing the ALTO protocol, called H1H2. The H1H2 protocol is a client/server protocols between end hosts and ALTO servers that allows two different ways of exchanging data between the server and the client.
Wolfgang May .A Database-Based Service for Handling Logical Variable
Bindings. Workshop Database-as-a-Service, Münster, Germany, , pages 13-25, 2009
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The paper discusses the use of a database as a service that supports applications whose data flow is based on sets of tuples of variable bindings, as e.g., in logic-based frameworks like Datalog and similar rule-based approaches. The service also supports cooperative work of different services on the bindings, thus replacing the need for actual exchange of potentially large sets of data during workflows. The concrete usage scenario of the service is in a distributed environment for processing ECA (Event-Condition-Action) rules and processes over relational states.
Jens Grabowski .Qualitätssicherung für Testspezifikationen am Beispiel der standardisierten Testing and Test Control Notation (TTCN-3). Softwareforen Leipzig, User Group (1. Arbeitstreffen)
"Softwaretest und Qualitätsmanagement" am 5./6. Februar 2009 in Leipzig,
Paper
Xiaoming Fu , Dieter Hogrefe , Henning Schulzrinne, Hannes Tschofenig, Christian Dickmann.Overhead and Performance Study of the General Internet Signaling Transport (GIST) Protocol. ACM/IEEE Transactions on Networking, 17(1): 158-171, 2009
Xiaoming Fu, Henning Schulzrinne, Hannes Tschofenig, Christian Dickmann, Dieter Hogrefe.Overhead and Performance Study of the General Internet Signaling Transport (GIST) Protocol. ACM/IEEE Transactions on Networking, 17(1): 158-171, 2009
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The General Internet Signaling Transport (GIST) protocol is currently being developed as the base protocol component in the IETF Next Steps In Signaling (NSIS) protocol stack to support a variety of signaling applications. We present our study on the protocol overhead and performance aspects of GIST. We quantify network-layer protocol overhead and observe the effects of enhanced modularity and security in GIST. We developed a first open source GIST implementation at the University of Goettingen, and study its performance in a Linux testbed. A GIST node serving 45,000 signaling sessions is found to consume average only 1.1 ms for processing a signaling message and 2.4 KB of memory for managing a session. Individual routines in the GIST code are instrumented to obtain a detailed profile of their contributions to the overall system processing. Important factors in determining performance, such as the number of sessions, state management, refresh frequency, timer management and signaling message size are further discussed. We investigate several mechanisms to improve GIST performance so that it is comparable to an RSVP implementation.
Paper
Xiaoming Fu (ed.).Biannual Report of Computer Networks Group at the University of Göttingen (2007-08). 2009
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A (bi)annual report series for the Computer Networks Group at the University of Göttingen intends to review the most relevant and important research results and other achievements and activities performed by the research group. The present report summarizes 2007-2008, the first period that the group got lounched.
Paper
Deguang Le, Xiaoming Fu, Dieter Hogrefe.A Cross-Layer Approach for Improving TCP Performance in Mobile Environments. Wireless Personal Communications, Springer Verlag, 2009
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Network-layer mobility protocols have been developed to keep continuous connectivity for mobile hosts while transparent to the higher layers. However, Due to its distinct characteristics of different from traditional TCP/IP environment, mobility poses substantial impacts on TCP performance in mobile environments. This paper proposes a new cross-layer approach, by introducing a mobility detection element in the network layer which interacts with the transport layer to optimize TCP operations. As changes are only made to the endpoints, this approach preserves the end-to-end semantics of TCP. Different from most exiting works, which utilize either transport or network layer alone without much cross-layer cooperation, our approach allows the use of mobility information in TCP. We analytically compare this approach against existing approaches and show that our approach outperforms prior approaches in terms of effective data resumption time. Through performance simulations, our approach demonstrates that it can effectively improve TCP performance in Mobile IPv6-based mobile environments.
Paper
Jun Lei, Lei Shi, Xiaoming Fu.An Experimental Analysis of Joost Peer-to-Peer VoD Service. Peer-to-Peer Networking and Applications (in press), Springer Verlag, 2009
2008
Niklas Neumann, Xiaoming Fu.Diameter WebAuth: An AAA-based Identity Management Framework for Web Applications. The 51th Annual IEEE Global Telecommunications Conference (GLOBECOM 2008), Computer and Communications Network Security Symposium, New Orleans, LA, USA, IEEE, 2008
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With an increasing number of personalized information and services offered on the Internet, especially the World WideWeb, effective identity management solutions are demanded by application providers. Instead of a web-based stand-alone approach, we extend existing network-based AAA mechanisms to be usable for identity management by web applications. Our proposal, Diameter WebAuth, allows to seamlessly integrate web-based services into a Diameter infrastructure for authentication, authorization, credit-control and identity management purposes. Diameter WebAuth offers comparable features to web-based identity management solutions, benefits from the maturity and wide deployment of the Diameter protocol, and takes advantage of existing AAA setups.
Paper
Mayutan Arumaithurai, Xiaoming Fu, Bernd Schloer, Hannes Tschofenig.Performance Study of the NSIS QoS-NSLP Protocol. The 51th Annual IEEE Global Telecommunications Conference (GLOBECOM 2008), Next Generation Networks, Protocols, and Services Symposium, New Orleans, LA, USA, IEEE, 2008
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This paper presents an evaluation of the Quality of Service Signalling Layer Protocol (QoS-NSLP) of the NSIS (Next Steps In Signalling) protocol suite. The QoS-NSLP in combination with the NSIS Transport Layer Protocol (NTLP) is proposed by the Internet Engineering Task Force (IETF) as an alternative to the Resource reSerVation Protocol (RSVP). We describe our implementations of the software architecture, both on a network simulator and on a Linux implementation. Both implementations are used in a complimentary manner to illustrate the performance of the QoS-NSLP protocol. The results show the performance of QoS-NSLP with respect to resource consumption, packet processing time, session set up time, refresh interval and protocol overhead. Furthermore, we analyse the protocol performance during route change scenarios.
Paper
Jan Seedorf, Frank Ruwolt, Martin Stiemerling, Saverio Niccolini.Evaluating P2PSIP under Attack: An Emulative Study. IEEE Globecom 2008, New Orleans, LA, USA, 2008
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Recently, establishing a VoIP call using a P2P network instead of regular SIP-servers has been proposed; this novel approach to SIP-signaling is commonly referred to as P2PSIP and technically based on a Distributed Hash Table (DHT). P2P networks are advantageous with respect to reliability and scalability. However, securing DHTs against adversary nodes which intentionally interrupt functionality of the network remains a major research problem. In particular, even if a trusted enrollment server is used for secure identifier assignment of participating nodes, attacks on overlay routing by malicious nodes that have successfully joined the network can still severely degrade the lookup service of the DHT.To gain insight into the ability of callers to reach callees during such attacks on DHT-routing, we present the first P2PSIP implementation that enables to emulate adversary nodes as well as the injection of a large amount of lookup requests (i.e., SIP-Invite requests) in an automated way. Further, we implemented several secure DHT routing algorithms and investigated their effect on the success rate of lookups and the maximum call-setup time in an infiltrated P2PSIP network. In general, our system provides the ability to analyze attacker behavior as well as future novel security techniques in an actual P2PSIP environment with comparably low effort.
Paper
Xiaoming Fu, Dieter Hogrefe, Henning Schulzrinne.Forschungsrichtungen der Internettechnologie - Kein Tempolimit für die Datenautobahn. Georg Augusta, special issue on Mathematics and Computer Science Year 2008, Vol. 6, 112-118, pages , 2008
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Selected research fields on Internet technologies are presented and open issues and ongoing topics, as a result of the discussions in the 1st Columbia-Göttingen Workshop on Internet Research.
Paper
Steffen Herbold .Nachweis von Feature Freezes durch Clustering. IWSM / MetriKon / Mensura 2008, November 18-19 2008, Munich, Germany,
Paper
Philip Makedonski .Equivalence Checking of TTCN-3 Test Case Behavior. Masterarbeit im Studiengang Angewandte Informatik am Institut für Informatik, ZFI-MSC-2008-16, ISSN 1612-6793, Zentrum für Informatik, Georg-August-Universität Göttingen, 2008.,
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Previous work has shown that refactoring can be used to improve the internal quality of TTCN-3 test cases. However, refactorings and their improper application are susceptible to introducing unintentional changes to the observable behavior of test cases. An approach to validate that refactorings and their application are indeed behavior preserving is proposed in this thesis. The original unrefactored and the refactored test cases will be checked forequivalent observable behavior. The approach is based on bisimulation, and is applied on the fly to manage the state-space explosion problem. A prototypical implementation of the proposed approach is presented briefly, along with selected examples to illustrate its application and prove its applicability.
Paper
Tseno Tsenov, Hannes Tschofenig, Xiaoming Fu, Cedric Aoun, Elwyn Davies.GIST State Machine. Internet Engineering Task Force, Internet draft (draft-ietf-nsis-ntlp-statemachine-05), work in progress, Next Steps in Signaling (NSIS) Working Group, 2008
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This document describes the state machines for the General Internet Signaling Transport (GIST). The states of GIST nodes for a given flow and their transitions are presented in order to illustrate how GIST may be implemented.
Paper
Xiaoming Fu, Christian Dickmann, Jon Crowcroft.General Internet Signaling Transport (GIST) over SCTP. Internet Engineering Task Force, Next Steps in Signaling (NSIS) Working Group, 2008
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The General Internet Signaling Transport (GIST) protocol currently uses TCP or TLS over TCP for connection mode operation. This document describes the usage of GIST over the Stream Control Transmission Protocol (SCTP). The use of SCTP can take the advantage of features provided by SCTP, namely streaming-based transport, support of multiple streams to avoid head of line blocking, and the support of multi-homing to provide network level fault tolerance. Additionally, the support for the Partial Reliability Extension of SCTP is discussed.
Niklas Neumann, Ralf Lübben, Mayutan Arumaithurai, Xiaoming Fu.Decoupling Congestion Control Using Traffic Aggregates and Middleboxes. IEEE International Conference on Network Protocols (ICNP 2008), poster session, Orlando, FL, USA, 2008
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A rise in numbers of large bandwith-delay product links and an increasing heterogeneity of IP networks bring new challenges for the existing congestion control mechanisms. Congestion control mechanisms are traditionally end-to-end oriented. This makes them slow to react on high delay links and inaccurate if the flow traverses heterogeneous network segments that have different jitter, or packet loss rates. Furthermore, the slow start which TCP uses as part of its congestion control is slow to react on high bandwith-delay product links and makes it hard for short-lived flows to develop fully.We propose to decouple the end-to-end congestion control mechanisms by introducing middleboxes to create dedicated congestion control segments within the network. Within those segments congestion control mechanisms can be deployed that are specifically adapted to the particular properties of this segment.
Paper
Niklas Steinleitner.Firewall Traversal in Mobile IPv6 Networks. PhD thesis, Faculty of Mathematics and Computer Science, University of Goettingen, Germany, 2008
Benedikt Schäffler.Implementation and Analysis of HTTP Enabled Location Delivery and Location-to-Service Translation Clients for IP-based Emergency Calls. Bachelor's thesis, No. ZFI-BSc-2008-04, Center of Computational Sciences, University of Goettingen, Germany, 2008
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Nowadays, location-based services such as location specific advertisements and emergency services are becoming very popular. This thesis looks at one such service namely the Emergency Context Resolution with Internet Technologies (ECRIT) framework. This is the first attempt to realize emergency calls in an IP based infrastructure. This thesis studies the HTTP Enabled Location Delivery protocol (HELD) and the Location-to-Service Translation protocol (LoST), the two basic elements of the ECRIT framework. In this respect a HELD client and LoST client are implemented. The HELD client requests the location of a device whereas the LoST client uses this location to request a local emergency service. Furthermore, three different scenarios of the ECRIT framework are developed in which the HELD client and the LoST client collaborate to do IP based emergency calls. These three scenarios are analyzed with regards to pros and cons with the objective of determining one final solution. Furthermore, a performance analysis of both clients was executed to determine how the device, the clients are running on, affects their processing time.
Paper
Oliver Fritzen , Wolfgang May , Franz Schenk .Markup and Component Interoperability for Active Rules.
The Second International Conference on
Web Reasoning and Rule Systems, Karlsruhe, Germany, LNCS 5341, Springer, pages 197-204, 2008
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We present -on the base of previous papers- a framework for markup, interchange, execution, and interoperability of Active Rules, namely, Event-Condition-Action (ECA) Rules over semantically different sublanguages for expressing events, conditions, and actions. The contribution of the present paper is the extension of the MARS meta model of component languages to a meta model of services and an informational infrastructure that is required for a most general framework for specifying and executing active rules over heterogeneous languages. The approach is implemented in the MARS prototype.
Benjamin Zeiß , Andreas Ulrich, Jens Grabowski .Constructing Test Behavior Models Using Simulated System Answers for the Analysis of Test Behavior Anomalies. Model-based Testing 2008 (MOTES 08). Lecture Notes in Informatics (LNI) 133/134, Köllen Verlag, Bonn, 2008
Edith Werner , Sergei Polonski, Jens Grabowski .Using Learning Techniques to Generate System Models for Online Testing. Model-based Testing 2008 (MOTES 08). Lecture Notes in Informatics (LNI) 133, Seite 183-186, Gesellschaft für Informatik (to appear), ISSN 1617-5468, ISBN 978-3-88579-227-7 , Köllen Verlag, 2008
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Today’s software systems are mostly modular and have to be changeable. However, the testing of such systems becomes difficult, especially when changes are applied after deployment. One way to passively test such a system is to check whether the observed traces are accepted by a system model. In this paper, we present a method to generate a model of the System Under Test from its test cases. We adapt Angluin’s algorithm for learning finite automata to the special case of learning from traces obtained from test cases and provide the promising results of our experiment.
Steffen Herbold .Detection of feature freezes using clustering algorithms. Masterarbeit im Studiengang Angewandte Informatik am Institut für Informatik, ZFI-BM-2008-12, ISSN 1612-6793,
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Software development is complex and not easy to quantify. An approach to quantify certain aspects of a software and software development are metrics. Software metrics map a possibly abstract attribute of a software to a value. To analyze the software project itself, is is possible to use metric data, that is measured at different versions of a project. The aim of this thesis is to determine whether such metric data can be used to analyze software projects using machine learning techniques. To obtain this kind of metric data, a way to mine metric data about different versions of a software from its archive is shown as part of this thesis. The aim is to detect a feature freeze using only this metric data. To do this, the k-means clustering algorithm is used, to divide the measured versions into those, that took place before the feature freeze and those that were afterwards. The experiment successfully detected a feature freeze in the tests candidates.
Paper
Xiaoming Fu, Martin Stiemerling, Henning Schulzrinne.Implications and Control of Middleboxes in the Internet. IEEE Network, Special Issue on Implications and Control of Middleboxes in the Internet, 2008
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Middleboxes in the Internet have been explored, sometimes quite controversially, in operations, standardization, and the research community for more than 10 years. The main concern, on one hand, has been their contradicting nature to the Internet′s end-to-end principle. On the other hand, middleboxes were introduced in the Internet for various reasons. In this special issue we are pleased to introduce a series of state-of-the-art articles on this specific area. These articles cover the subject from a variety of perspectives, offering the readers an understanding of the issues and implications of various middleboxes in the Internet, including their control mechanisms.
Paper
Erik Behrends , Oliver Fritzen , Wolfgang May .Integrating and Querying Distributed XML Data via XLink. Information Systems , volume 6, number 33, pages 508-566, Elsevier, 2008
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XML instances are not necessarily self-contained but may have connections to remote XML data residing on other servers. In this paper, we show that -in spite of its minor support and use in the XML world- the XLink language provides a powerful mechanism for expressing such links both from the modeling point of view and for actually querying interlinked XML data: In our dbxlink approach, the links are not seen as explicit links (where the users must be aware of the links and traverse them explicitly in their queries), but define views that combine into a logical, transparent XML model which serves as an external schema and can be queried by XPath/XQuery. We motivate the underlying modeling and give a concise and declarative specification as an XML-to-XML mapping. We also describe the implementation of the model as an extension of the eXist XML database system. The approach can be applied both for distribution of data and for integration of data from autonomous sources.
Helmut Neukirchen , Benjamin Zeiß , Jens Grabowski .An Approach to Quality Engineering of TTCN-3 Test Specifications. International Journal on Software Tools for Technology Transfer (STTT), Volume 10, Issue 4. (ISSN 1433-2779) DOI: 10.1007/s10009-008-0075-0 , 309-326, Springer, 2008
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Experience with the development and maintenanceof large test suites specified using the Testing andTest Control Notation (TTCN-3) has shown that it is difficultto construct tests that are concise with respect to qualityaspects such as maintainability or usability. The ISO/IECstandard 9126 defines a general software quality model thatsubstantiates the term "quality" with characteristics and subcharacteristics.The domain of test specifications, however,requires an adaption of this general model. To apply it to specificlanguages such as TTCN-3, it needs to be instantiated.In this paper, we present an instantiation of this model as wellas an approach to assess and improve test specifications. Theassessment is based on metrics and the identification of codesmells. The quality improvement is based on refactoring. Examplemeasurements using our TTCN-3 tool TRex demonstratehow this procedure is applied in practice.
Paper
Jun Lei, Xiaoming Fu.Evaluating the benefits of introducing PMIPv6 for localized mobility management. in the Proceedings of International Wireless Communications and Mobile Computing Conference 2008 (IWCMC 2008), Crete, Greece, Pages 74-80, IEEE, 2008
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Abstract—Since recent years, it has been recognized that using global mobility protocol for managing localized mobility causes a number of problems, such as a long registration delay. To overcome these problems, Proxy Mobile IPv6 is proposed, which can avoid tunneling overhead over the air and support for hosts without an involvement in the mobility management. In this paper, we first discuss the recent localized mobility proposals and explore three major benefits that PMIPv6 can bring. In particular, we evaluate two aspects of the handover performance through a simple mathematical model for Fast Handovers for MIPv6, Hierarchical MIPv6, Fast handovers for HMIPv6 and PMIPv6. These analytical studies show that PMIPv6 may cause high handover latency if the local mobility anchor is located far from the current mobility access gateway. Therefore, some enhancements for PMIPv6 are suggested to further reduce the handover latency. The analysis ascertains that F-PMIPv6 is a promising mobility scheme to efficiently manage the localized mobility.
Paper
Jun Lei, Xiaoming Fu, Dieter Hogrefe.D-MORE: Dynamic Mesh-based Overlay Peer-to-Peer Infrastructure. Technical Report No. IFI-TB-2008-02, Institute of Computer Science, University of Goettingen, Goettingen, Germany, 2008
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Traditionally, Internet Service Providers (ISPs) haveto interconnect with content providers to provide network servicesto customers. Current business model that connectivityand bandwidth become commodities has motivated ISPs todistribute content and other application-specific services to theircustomers using their own infrastructure. It is desirable forISPs to economize existing infrastructure to support a varietyof applications and services.We propose a dynamic mesh-based overlay peer-to-peer infrastructureand illustrate its two examples usage cases among otherpotentials. We describe several key techniques, namely capacityclassification, locality-awareness and incentive mechanisms forconstruction of the tiered infrastructure. Through extensivesimulations, we show D-MORE scales well with an increasingnumber of hosts, in terms of control overhead, link stress anddata path length, for supporting media distribution services.We propose further improvements to enhance the D-MOREperformance, which brings up to 35% network resource savingsand up to 200% control overhead reduction in our simulations.
Paper
Fang-Chun Kuo, Kun Tan, Xiang-Yang Li, Jiansong Zhang, Xiaoming Fu.Network coding-aware fair opportunisic scheduling in wireless networks. Technical Report No. IFI-TB-2008-03, Institute of Computer Science, University of Goettingen, Goettingen, Germany, 2008
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Users increasingly depend on WLAN for business and entertainment. It is well-recognized that wireless links are prone to errors. Previous work, ER, proposed to use network coding (NC) for providing more efficient MAC-layer retransmission scheme in WLAN. However, it uses inefficient and costly reception report scheme and does not consider the effect of heterogeneous and time-varying wireless conditions and fairness. These issues are critical for getting full benefits of network coding. We show that, without addressing them, NC may even cause negative effect on the system. In this paper, we present a novel MAC-layer retransmission scheme, namely XORR, which uses reception estimation without extra overhead and adopts NC-aware opportunistic scheduling with maintaining temporal fairness in WLAN. We prove our NC-aware scheduling algorithm is fair and it will always improve the expected goodput for each wireless clients. We further verify XORR with extensive simulation as well as experiment studies and find that our scheme outperforms traditional opportunistic scheduling (without NC) and 802.11 about 25% and 40%, respectively.
Paper
Eduard Enriquez.Software Reliability Engineering im Infotainment. Masterarbeit an der Georg-August Universität Göttingen, Institut für Wirtschaftsinformatik, Göttingen, 2008
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Software reliability is a criterion for software quality. In order to measure software reliability, one must utilize software reliability models. This requires the use of stochastic reliability analyses which have hardly been utilized in practice. Reliability is important, as unreliable software can lead to customer dissatisfaction and lead to increased costs. The focus of the following paper will be placed on the use of software reliability models in regard to error-data in embedded software for BMW infotainmentinstruments of varying complexity. First, the characteristics of error-data were analysed and appropriate software reliability models – specifically non-homogeneous poisson process models – chosen. These models were then utilized and the results interpreted and compared. The goals of the use of software reliability models were to estimate the current reliability, to predict future remaining errors, to determine test-end criteria and thereby provide important information for test management.
Paper
Jun Lei.Media Distribution using Overlay Multicast and Peer-to-Peer Technologies. PhD thesis, Faculty of Mathematics, University of Goettingen, Germany, 2008
Helmut Neukirchen , Benjamin Zeiß , Jens Grabowski , Paul Baker, Dominic Evans.Quality assurance for TTCN-3 test specifications. Software Testing, Verification and Reliability (STVR), Volume 18, Issue 2. (ISSN 0960-0833) DOI: 10.1002/stvr.379 , 71-97, Wiley, 2008
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Comprehensive testing of modern communication systems often requires largeand complex test suites, which have to be maintained throughout the systemlife-cycle. Industrial experience, with those written using the standardisedTesting and Test Control Notation (TTCN-3), has shown that this maintenanceis a non-trivial task and its burden can be reduced by means of appropriateconcepts and tool support. To this aim, Motorola has collaborated withthe University of Göttingen to develop TRex, an open-source TTCN-3 developmentenvironment, which notably provides suitable metrics and refactoringsto enable the assessment and automatic restructuring of test suites. This articlepresents concepts like metrics and refactoring for the quality assuranceof TTCN-3 test suites and their implementation provided by the TRex tool.These means make it far easier to construct and maintain TTCN-3 tests thatare concise and optimally balanced with respect to maintainability qualitycharacteristics.
Paper
Benjamin Zeiß , Andreas Ulrich.Analysis of TTCN-3 Test Cases. TTCN-3 User Conference 2008 (T3UC), June 3-6 2008, Madrid, Spain,
Benjamin Zeiß , Jens Grabowski .Reverse-Engineering Test Behavior Models for the Analysis of Structural Anomalies. TESTCOM/FATES 2008 Short Papers, June 10-13 2008, Tokyo,
TEMEA Consortium (Fraunhofer FOKUS, Fraunhofer FIRST, IT Power Consultants, Testing Technologies, Fourth Project Consulting, Universität Göttingen).The TEMEA project. TTCN-3 User Conference 2008 (T3UC), June 3-6 2008, Madrid, Spain,
Sufian Hameed.Evaluation and Improvement of Security in ZigBee Networks. Institute of Informatik, RWTH Aachen, 2008
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ZigBee, an increasingly adopted WSN standard, is the upcoming standard for simple, short-range, low-footprint and low-power wireless connectivity. It is a specification of high level communication protocol suits on top of IEEE 802.15.4 developed by ZigBee Alliance. Typicalapplication areas of ZigBee include industrial control, health care, energy metering, commercial building automation and home automation.With the expected growth in ZigBee implementations and the evolution of broader sensor network applications, the topic of security has become highly pronounced. Key distribution and establishment serves as an important pillar for all the basic security services such as, e.g. confidentiality, authentication or access control as it provides the secrets necessary to enable the basic security services. Many security architectures, including ZigBee, are based on centralized approach using a central authority for key establishments (KE). Other approaches propose the use of distributed KE protocols. Both solutions present different issues like scalability, computational requirements, multi-hop scenarios where the central authority being distant or single point of failure. Further application of security burdens the data flow with increased packet size and computations, resulting in delays and communication bottlenecks.Within this thesis we evaluated the performance of ZigBee medical network for the centralized key establishment (KE) and different security levels and modes as specified by ZigBee. For evaluation via simulations, we have implemented all proposed mechanisms in Network Simulator (NS2) allowing us to simulate specific scenarios with real settings.With centralized architecture Trust Center (TC) is responsible for the key distribution and establishment. This results in long delays for key establishment in large multi hops networks. For improvement we introduced, analyzed and simulated the ZigBee operation when keyestablishment is carried out in a distributed way. The results show that the system performs faster and in a more reliable way. Finally, we optimized different security parameters used to provide basic security services such confidentiality or authentication to reduce the security overhead. In special, the refreshness counters used for replay protection are optimized using last bit optimization technique [MiniSec], resulting in reduction of transmission overheads and energy consumptions.
Sergei Polonski.Learning of protocol-based automata. Masterarbeit im Studiengang Angewandte Informatik am Institut für Informatik, GAUG-ZFI-MSC-2008-09, ISSN 1612-6793, Zentrum für Informatik, Georg-August-Universität Göttingen, 2008
Paper
TEMEA Consortium (Fraunhofer FOKUS, Fraunhofer FIRST, IT Power Consultants, Testing Technologies, Fourth Project Consulting, Universität Göttingen).Testspezifikationstechnologie und -methodik für eingebettete Echtzeitsysteme im Automobil (TEMEA). Werbeflyer für das TEMEA Projekt. Berlin, April 2008,
Paper
Swen Weiland.TCP Performance Enhancement in Wireless Environments: Prototyping in Linux. Bachelor's thesis, No. GAUG-ZFI-BSC-2008-05, Center of Computational Science, University of Goettingen, Goettingen, Germany, 2008
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In recent years, wireless communication gets more and more popular. Future wireless standards will reach throughputs much higher than 100 Mbit/sec on link layer. However, wireless channels, as compared to wired lines, exhibit different characteristics due to fading, interference, and so on. For transport control protocol (TCP), the misinterpretation of packet loss due to wireless channel characteristic as network congestion results in suboptimal performance. There are many different approaches to enhance TCP over wireless networks, especially for slow and lossy links such as satellite connections. This thesis evaluates “TCP Snoop” as one of these approaches for high transfer rates. Finding, using and implementing effective capturing, buffering and tracking of TCP communication were the objectives to solve. A general and transparent TCP proxy with “TCP Snoop” behavior was implemented during the work for this thesis. The TCP proxy runs on an intermediate Linux host which connects wired and wireless networks as a prototype user space application with a modular design.Different traffic capture methods are compared in portability and performance. A full TCP connection tracking is described and implemented. Design patterns and methods that proofed their benefit in practice were applied and sometimes partially modified to fit into the needs of the transparent TCP proxy. The modular design makes exchanging a low level module such as the data traffic capture module possible. Porting the implementation to another operating system, another platform like embedded systems which are used as wireless LAN routers or changing the TCP enhancement method are also eased by the modular design.The results show that a transparent TCP proxy or other traffic modifying implementation should not reside in the user space for performance reasons. A kernel space implementation or even better a dedicated hardware like a network processor platform should be used for such implementations.
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Nikunj Modi.Performance Evaluation of TCP Variants over UMTS Networks. Master's thesis, No. GAUG-ZFI-MSC-2008-06, Zentrum fuer Informatik, Universitaet Goettingen, 2008
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With the evolution of 3G technologies like Universal Mobile Telecommunication System (UMTS), the usage of TCP has become more popular for a reliable end-to-end (e2e) data delivery. However, as TCP was initially designed for wired networks and therefore it suffers performance degradation due to the radio signal getting affected by fading, shadowing and interference. There are many strategies proposed by the research community on how to improve the perfor-mance of TCP over wireless links such as introducing link-layer retrans-mission, explicitly notifying the sender ofnetwork conditions or using new variants of TCP.As UMTS network is growing at very fast pace, optimization of various internal component of its wireless network is very important. One of the optimization is the introduction of High Speed Downlink Packet Access (HSDPA). This architecture not only allows higher data rates but also more reliable data transfer by the introduction of Hybrid ARQ (HARQ). With this enhancement in UMTS network, it becomes very vital to see the performance of TCP in such a network. Therefore in this thesis we try to evaluate two aspect of UMTS network: first, the impact of HSDPA parameters like scheduling algorithm and RLC/MAC-hs buffer size on overall performance of the TCP and second, to study the behavior of two categories of TCP: loss based and delay based. Our simulation shows that delay based TCP tends to perform better than loss based TCP in our selected scenarios. The simulations are performed in network simulator NS-2 using an e2e network model for enhanced UMTS (EURANE).
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Xiaodong Yang, Thomas J. Owens.Intersystem Soft Handover for Converged DVB-H and UMTS Networks. IEEE Transactions on Vehicular Technology, 57(3): 1887-1898, 2008
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Digital video broadcasting for handhelds (DVB-H) is the standard for broadcasting Internet Protocol (IP) data services to mobile portable devices. To provide interactive services for DVB-H, the Universal Mobile Telecommunications System (UMTS) can be used as a terrestrial interaction channel for the unidirectional DVB-H network. The converged DVB-H and UMTS network can be used to address the congestion problems due to the limited multimedia channel accesses of the UMTS network. In the converged network, intersystem soft handover between DVB-H and UMTS is needed for an optimum radio resource allocation, which reduces network operation cost while providing the required quality of service. This paper deals with the intersystem soft handover between DVB-H and UMTS in such a converged network. The converged network structure is presented. A novel soft handover scheme is proposed and evaluated. After considering the network operation cost, the performance tradeoff between the network quality of service and the network operation cost for the intersystem soft handover in the converged network is modeled using a stochastic tree and analyzed using a numerical simulation. The results show that the proposed algorithm is feasible and has the potential to be used for implementation in the real environment.
Paper
Thomas Rings , Helmut Neukirchen , Jens Grabowski .Testing Grid Application Workflows Using TTCN-3. Proceedings of the 2008 International Conference on Software Testing, Verification, and Validation (ICST 2008).
Lillehammer , Norway, April 9-11 2008. DOI: 10.1109/ICST.2008.24 , 210-219, IEEE Computer Society, 2008
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The collective and coordinated usage of distributed resourcesfor joint problem solutions within dynamic virtualorganizations can be realized with the Grid computing technology.For distributing and solving a task, a Grid applicationinvolves a complex workflow of dividing a task intosmaller sub-tasks, scheduling and submitting jobs for solvingthose sub-tasks, and eventually collecting and combiningthe results of the sub-tasks into a final result. The qualityassurance of Grid applications is a challenge due to thehighly distributed nature of the Grid environment in whichthe Grid application is deployed. This paper investigatesthe applicability of the Testing and Test Control Notation(TTCN-3) for testing the workflows of distributed Grid applications.To this aim, a case study has been created thatconsists of a distributed Grid application which includes atypical Grid application workflow; as the main contribution,this case study contains a corresponding distributedTTCN-3 test suite that tests the correct execution of theGrid application workflow. To demonstrate the adaptationof the abstract TTCN-3 test suite to a specific Grid environment,corresponding reusable test adapters have been implementedfor the Grid middleware Globus Toolkit 4 (GT4).The realized test system demonstrates that TTCN-3 is applicablefor testing the workflow of distributed Grid applications.
Paper
Ina Schieferdecker, Jens Grabowski , Theofanis Vassiliou-Gioles, George Din.The Test Technology TTCN-3. Formal Methods and Testing. Lecture Notes in Computer Science (LNCS ) 4949, DOI: 10.1007/978-3-540-78917-8_10, 292-319, Springer-Verlag, Berlin Heidelberg, 2008
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The Testing and Test Control Notation (TTCN-3) is a widely established test technology traditionally used in the telecommunication domain. In its new version, TTCN-3 has a wider scope and applicability. It can be applied not only for testing the conformance and interoperability of communication protocols but also for testing the functionality, interoperation and performance of software-based systems in general. Therefore, TTCN-3 is nowadays used in other domains such as automotive, railways, avionics, or security systems. This chapter introduces the concepts of the TTCN-3 language and provides examples of its practical use.
Takako Sanda, Xiaoming Fu, Seong-Ho Jeong, Jukka Manner, Hannes Tschofenig.Applicability Statement of NSIS Protocols in Mobile Environments. Internet Engineering Task Force, Internet draft (draft-ietf-nsis-applicability-mobility-signaling-10), work in progress, Next Steps in Signaling (NSIS) Working Group, 2008
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Mobility of an IP-based node affects routing paths, and as a result, can have a significant effect on the protocol operation and state management. This draft discusses the effects mobility can cause to the NSIS protocol suite, and how the protocols operate in different scenarios, with mobility management protocols.
Xiaodong Yang.Handover in DVB-H: Investigations and Analysis. 168 pages, Springer Verlag, 2008
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This book gives a detail description of the handover issues in DVB-H networks, in converged DVB-H/UMTS networks and in hybrid DVB-H/DMB-T networks. Besides, the DVB-H signalling information including ESG is discussed. The current status and the future research directions of DVB-H and DVB-H handover are presented so that the readers can also get an overview of the research methods being used.Although this book is research focused, it also gives a detail introduction to the basic concepts such as handover, time slicing, ESG, etc.. This book is written in a way that even people without prior knowledge of DVB-H can easily understand. At the end of each chapter there are some questions and there are solutions to those questions at the end of the book.This book can be used by researchers, engineers, academics, regulatory bodies and business managers as a reference book, or by university students as a text book or a reference book.
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Helmut Neukirchen .Quality Assurance for TTCN-3 Test Specifications. Software Testing Day at Tampere University of Technology (Testauspäivä TTY) 2008, Finland, March 26, 2008,
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Introduction into the test specification and test implementation language TTCN-3; Assessment of internal quality of TTCN-3 test suites using metrics and code smells; Automation of quality assessment and improvement using the open source Refactorings and Metrics Tool TRex; Results from assessing and improving TTCN-3 test suites standardised by ETSI.
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Omar Alfandi , Henrik Brosenne , Patryk Chamuczynski , Dieter Hogrefe , Constantin Werner .Performance Study of PANA Pre-authentication for Interdomain Handover. The Fourth International Conference on Networking and Services (ICNS 2008), Gosier, Guadeloupe, 2008
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To provide seamless mobility to the wireless user, acontinuous connection to the Internet is required while moving from one administration domain to another. To enable continuous connectivity, one prerequisite is the incorporation of seamless handover. The make-before-break approach facilitates seamless handover by means of executing an authentication to a new domain simultaneously while maintaining connection to current domain. The connection is only terminated after the handover to the new domain is successfully completed.However, the duration of the authentication is critical forthe handover process because if the mobile nodes move veryfast the remaining amount of time of connection to the current domain can become very limited. Therefore, it is a vital issue for seamless mobility to study the authentication performance of a pre-authentication framework.In this paper we model an authentication infrastructureand consider a scenario in which a high number of nodeshandover to a new administration domain. The simulation of the authentication process shows the relation between authentication performance and traffic intensity. Furthermore we identify some critical points and potential bottlenecks of this pre-authentication approach.
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Michael Cohrs.Implementation and Evaluation of the Peer-to-Peer-Protocol (P2PP) for P2PSIP. Master's thesis, No. ZFI-BM-2008-04, Zentrum fuer Informatik, Universitaet Goettingen, 2008
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The peer-to-peer networking paradigm, as opposed to client-server architectures, is attractive for many fields of applications. Recently, various developments led to its adoption for real-time multimedia applications like, e.g., Internet telephony. SIP, a well-established Internet standard in this field that is usually relying on central servers, is to be reformed with peer-to-peer techniques, leading to the first Internet standard carrying ?P2P? in its name.The goal of this thesis is to introduce P2PSIP and conduct a prototype implementation of a proposed P2PSIP protocol that is used for the maintenance and data communication between peers in a P2PSIP overlay network. The result has been complemented with basic SIP functionality and analyzed regarding its functionality, performance and real-world applicability.
Edith Werner , Jens Grabowski , Stefan Troschütz, Benjamin Zeiß .A TTCN-3-based Web Service Test Framework. Testing of Software - From Research to Practice 2008 (Workshop in conjunction with the GI-conference Software Engineering 2008), February 19, 2008, Garching, Germany,
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The increased usage of Web services for critical applications introduces a growing need for efficient testing approaches to assure their quality. The Testing and Test Control Notation (TTCN-3) is a standardised testing language that is well suited for black-box testing of distributed systems such as Web services. Also due to its abstract test specification methodology, it allows easy adaptation to different Webservice frameworks or platforms. This paper presents a mapping from the Web Service Description Language (WSDL) to TTCN-3 and a corresponding automated translator.
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Martin Stiemerling, Hannes Tschofenig, Cedric Aoun, Elwyn Davies.NAT/Firewall NSIS Signaling Layer Protocol (NSLP). Internet Engineering Task Force, Internet draft (draft-ietf-nsis-nslp-natfw-18), work in progress, Next Steps in Signaling (NSIS) Working Group, 2008
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This memo defines the NSIS Signaling Layer Protocol (NSLP) for Network Address Translators (NATs) and firewalls. This NSLP allows hosts to signal on the data path for NATs and firewalls to be configured according to the needs of the application data flows. It enables hosts behind NATs to obtain a public reachable address and hosts behind firewalls to receive data traffic. The overall architecture is given by the framework and requirements defined by the Next Steps in Signaling (NSIS) working group. The network scenarios, the protocol itself, and examples for path-coupled signaling are given in this memo.
D. Wing, S. Niccolini, Martin Stiemerling, Hannes Tschofenig.Spam Score for SIP. Internet draft (work in progress), IETF, 2008
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This document defines a mechanism for SIP proxies to communicate a spam score to downstream SIP proxies and SIP user agents so they can provide alternate call routing or call handling.
Martin Stiemerling, Xiaoming Fu, Marcus Brunner.A Network Virtualisation Concept Based on Ambient Networks SATO System. 1. GI/ITG Fachgespraech Virtualisierung, Paderborn, Germany, pages 33 - 36, 2008
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Network virtualization can be one way of fixing the shortcomings of today?s Internet but also open the venue for new, unforeseen applications. In this extended abstract, we present a novel approach for network virtualisation based on the Service-Aware Transport Overlay (SATO) concept of Ambient Networks. SATOs introduce on-demand overlay creation and new interfaces to ease applications to use overlays.
Xiaoming Fu, Dieter Hogrefe (editors).Reports of Advanced Topics in Computer Networking and Mobile Communications (Summer 2004 - Winter 2006/2007). Technical Report No. IFI-TB-2008-01, Institute of Computer Science, University of Goettingen, Goettingen, Germany, 2008
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This technical report includes the final reports written by students for seminars from summer semester 2004 to winter semester 2006/07 on advanced topics in computer networking/Internet research and mobile communications, including mobile, ad hoc, sensor networks and location-based systems; wireless networks, security and performance optimization issues; mobile applications and mobile devices; overlay, peer-to-peer and application layer multicast, as well as delay tolerant networks.
Omar Alfandi , Henrik Brosenne , Dieter Hogrefe , Constantin Werner .Fast Re-Authentication for Inter-Domain Handover using Context Transfer. The International Conference on Information Networking 2008 (ICOIN 2008), Busan, Korea, 2008
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The exponential growth of wireless mobile systems in recent years has created strong demand to handover between different administration domains. Such movement suffers from limited resources such as limited bandwidth and high latency. Furthermore, authentication is the key factor when providing mobile roaming services, so fast re-authentication is one of the important issues to achieve a short overall handover delay. Therefore, it is important to develop techniques that utilize the available bandwidth efficiently. One way of utilizing the wireless resources efficiently is by transferring the required context that authenticates the user in new visited domain of the running session rather than establishing the connection from scratch. Current approaches only consider a repeated authentication process run for a new visited domain and therefore, can potentially introduce high latency by communicating with authorization services of a home domain. In this paper, we propose a novel way to authenticate a mobile node without the necessity to communicate with the home domain while maintaining a high level of security. We provide an overview of the method, show the improvement to related approaches in terms of message flows and discuss security aspects.
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Florian Tegeler.Security Analysis, Prototype Implementation and Performance Evaluation of a New IPSec Session Resumption Method. Zentrum fuer Informatik, Universitaet Goettingen, Master's Thesis, No. ZFI-BM-2008-01, 2008
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In the current communication infrastructure a variety of services are already based on the Internet Protocol (IP) and effort is taken to put the mobile communication as well into the IP framework. Many of these services like voice over IP or online banking require an increased level of security and privacy, and therefore demanding a wide application of security suits as IPSec. These connections are typically secured by keys derived from a key negotiation process run with the IKEv2 key negotiation protocol. This process is computationally heavy; ideally it should be performed as rarely as possible. The computational complexity could grow to a severe problem in mobile environments where a base station is handling hundreds or thousands of mobile nodes and the gateway fails for any reason. If the gateway fails and recovers later, all IPSec capable devices will try to resume their session immediately by renegotiating keys and potentially overload the gateways resources by doing that in parallel. Furthermore the total number of clients a base station can handle is reduced when sessions to end host fail temporarily due to e.g. communication distortions etc. Every time re-keying is necessary.In this thesis a server side stateless IPSec session resumption approach developed by Sheffer et al is presented and analysed. The session?s state including the master secret as the source for further keying material is stored in an encrypted ticket which can later be used to quickly resume the session. A formal security analysis based on CSP algebra interpreted with the CasperFDR toolkit was performed and it could be shown that no new security threats are introduced by altering the IKEv2 communication sequence and storing the state inside a ticket. Furthermore, a prototype of the ticket based session resumption was implemented into an existing open source Linux IKEv2 daemon and the performance evaluation showed a significant reduction in the session resumption time. Overall, this thesis illustrates the new ticket based session resumption approach, verifies it via a formal security toolkit and proves the significant reduction of the time required to resume a session in a prototype implementation.
Paper
Erik Behrends , Oliver Fritzen , Wolfgang May , Franz Schenk .Event Algebras and Process Algebras in ECA Rules. , number 82, pages 237-263, IOS Press, 2008
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We describe how Event-Condition-Action (ECA) rules can be combined with event algebras like SNOOP for specification of the event part, and process algebras like CCS for specification of the action part to obtain a powerful, declarative formalism that also covers intuitively procedural tasks in an appropriate way. Since these formalisms have a concise formal semantics, verification and other kinds of reasoning about such specifications are possible. Using a rule markup with cleanly distinguished rule components allows for such a compositional approach. The approach is currently under implementation in the MARS (Modular Active Rules for the Semantic Web) Framework.
Sven Anderson , Dieter Hogrefe .Mouse trapping: A flow data reduction method. ICIMP ’08: Proceedings of the 2008 The Third International Conference on Internet Monitoring and Protection, Pages 17–22, 2008
Xiaoming Fu , Dieter Hogrefe , Henning Schulzrinne, Hannes Tschofenig, Christian Dickmann.Overhead and Performance Study of the General Internet Signaling Transport (GIST) Protocol. IEEE INFOCOM 2006, Bacelona, Spain, IEEE, 2008
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The General Internet Signaling Transport (GIST) protocol is currently being developed as the base protocol component in the IETF Next Steps In Signaling (NSIS) protocol stack to support a variety of signaling applications. In this paper we present our study on the protocol overhead and performance aspects of GIST. We quantify network-layer protocol overhead and observe the effects of enhanced modularity and security in GIST. We developed a first open source GIST implementation at the University of Göttingen, and study its performance in a Linux testbed. A GIST node serving 45,000 signaling sessions is found to consume small amounts of CPU and memory (on average 1.1ms for processing a signaling message and 2.4KB memory for a session). Individual routines in the GIST code are instrumented to obtain a detailed profile of their contributions to the overall system processing. Important factors in determining performance, such as the number of sessions, state management, refresh frequency, timer management and signaling message size are further discussed. We investigate several mechanisms to improve GIST performance so as to be comparable with an RSVP implementation.
Paper
Fang-Chun Kuo, Xiaoming Fu.Probe-aided MulTCP: An Aggregate Congestion Control Mechanism. ACM SIGCOMM Computer Communication Review, Vol. 38, No. 1, Pages 19-28, ACM, 2008
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An aggregate congestion control mechanism, namely Probe-Aided MulTCP (PA-MulTCP), is proposed in this paper. It is based on MulTCP, a proposal for enabling an aggregate to emulate the behavior of multiple concurrent TCP connections. The objective of PA-MulTCP is to ensure the fair sharing of the bottleneck bandwidth between the aggregate and other TCP or TCP-friendly flows while keeping lightweightness and responsiveness. Unlike MulTCP, there are two congestion window loops in PA-MulTCP, namely the probe window loop and the adjusting window loop. The probe window loop constantly probes the congestion situation and the adjusting window loop dynamically adjusts the congestion window size for the arriving and leaving flows within the aggregate. Our simulations demonstrate that PA-MulTCP is more stable and fairer than MulTCP over a wide range of the weight N in steady conditions as well as in varying congestion conditions. PA-MulTCP is responsive to flow-arriving/leaving and thus reduces the latency of short-lived transfers. Furthermore, PA-MulTCP is lightweight, since it enjoys above advantages at the cost of only an extra probe window loop, which has a marginal influence on the implementation complexity. Finally, the design of PA-MulTCP decouples the congestion management from the other functionalities in the aggregate flow management. As a result, PA-MulTCP could be potentially applied to a wider range of scenarios, e.g. wireless TCP proxies, edge-to-edge overlays, QoS provisioning and mass data transport.
Paper
2007
Martin Stiemerling, Marcus Brunner.A Peer-to-Peer SIP System based on Service-Aware Transport Overlays. Praxis der Informationsverarbeitung und Kommunikation (PIK), Special Issue on Voice over IP, Volume 30, No. 4, 2007
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The Session Initiation Protocol (SIP) traditionally establishes and manages its sessions with centralized servers, which have been challenged by issues with TCP/IP networks right from its beginning, for instance, issues with NAT traversal or network congestions. On the other hand, there are peer-to-peer and overlay techniques that potentially can make SIP working better under various network conditions. Overlay networks can provide a good abstraction from the real network, thus hiding the presence of NATs. Some proposals on peer-to-peer SIP have been recently presented. While these proposals attempted to solve a subset of challenges faced by traditional SIP, such as removing the centralized SIP entities, there is to the best of our knowledge no single solution offering a comprehensive view of the peer-to-peer SIP architecture and operation. This paper presents a novel approach for a peer-to-peer SIP system, using overlay techniques for signalling and media transport in the Internet. This system is based on the Ambient Networks Service-Aware Transport Overlay (SATO) system. The proposed system replaces the traditional SIP proxy/registrar function with a distributed lookup mechanism, adding overlay functionality to the SIP signalling and to the RTP traffic. Moreover, different from previous proposals, our approach deliberately places media/packet relays into the SIP/RTP paths, which allows an efficient session management and media communication.
Paper
Qazi Mussabbir, Wenbing Yao, Zeyun Niu, Xiaoming Fu.Optimized FMIPv6 Using IEEE802.21 MIH Services in Vehicular Networks. IEEE Transactions on Vehicular Technology, Special Issue on Vehicular Communications Networks, Volume 56, Issue 6, Pages 3397 - 3407, IEEE, 2007
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In this paper, we optimize the handover procedure in Fast Handover for Mobile IPv6 (FMIPv6) protocol by using IEEE 802.21 Media Independent Handover (MIH) services. FMIPv6 is used to enhance the performance of handovers in Mobile IPv6 (MIPv6) and its basic extension for Network Mobility (NEMO), the fundamental mobility management protocols used in vehicular networks. With the aid of the lower three layers? information of the mobile node/router (MN/MR) and the neighboring access networks, we tackle the radio access discovery and candidate Access Router (AR) discovery issues of FMIPv6. We introduce an ?Information Element Container? to store static and dynamic Layer 2 (L2) and Layer 3 (L3) information of neighboring access networks, and propose to use a special cache maintained by the MN/MR to reduce the anticipation time in FMIPv6, thus increasing the probability of the predictive mode of the FMIPv6 operation. Furthermore, we propose a cross-layer mechanism for making intelligent handover decisions in FMIPv6. Lower layer information of the available links obtained by MIH services as well as the higher layer information such as quality of service parameter requirements of the applications are used by a Policy Engine (PE) to make intelligent handover decision. We will show through analysis and simulations of the signaling procedure that the overall expected handover (both L2 and L3) latency in FMIPv6 can be significantly reduced in the proposed mechanism.
Paper
Martin Stiemerling, Marcus Brunner.Peer-to-Peer SIP Implementation Report. Internet Engineering Task Force, Internet draft (draft-stiemerling-p2psip-impl-02), work in progress, Peer-to-Peer SIP (P2PSIP) Working Group, 2007
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This memo is an implementation report about the peer-to-peer SIP system developed in the European IST Ambient Networks research project. This system replaces the traditional SIP proxy-registrar function with a distributed lookup mechanism, adds overlay functionality to the SIP signalling and to RTP traffic, takes care about media/packet relay lookup and insertion into the SIP/RTP paths, plus automatic adaptation of the voice transmission according to changing network conditions. Standard, unmodified SIP user agents are used for communication. The presented system is work in progress and this memo is an attempt to gather IETF community feedback about the described approach.
David Weiss.Performance Evaluation of a Novel Overlay Multicast Protocol. Bachelor's thesis, No. ZFI-BM-2007-11, Zentrum fuer Informatik, Universitaet Goettingen, 2007
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The demand for high-bandwidth media streaming over the Internet is growing. For large groups of receivers, media streaming places a heavy burden on the network. IP Multicast can alleviate this problem, but it is not widely deployed. In recent years, application layer multicast and overlay multicast have been proposed as alternatives. However, there are still concerns about the efficiency, scalability and deployment of these architectures.In this thesis, a novel application layer multicast approach, called the Dynamic Mesh-based Overlay Multicast Protocol (DMMP), is evaluated. DMMP establishes an overlay network core consisting of super nodes, which are end-hosts with particularly high capacities. Each super node manages a cluster of non-super nodes. We use network simulations to analyze the performance of DMMP. For that purpose, we have implemented a DMMP module in OverSim. OverSim is an overlay network simulation framework based on OMNeT++.We compare DMMP with NICE, a well-known application layer multicast protocol, that is claimed to achieve low link stress and low control overhead. We experiment with groups of up to 2048 members. Our results indicate that DMMP can achieve comparable service quality with less control overhead, and that DMMP has the potential to scale to a high number of receivers.
Paper
Niklas Neumann.Diameter WebAuth: An AAA-based Identity Management Framework for Web Applications. Master's Thesis, No. ZFI-BM-2007-39, Zentrum fuer Informatik, Universitaet Goettingen, 2007
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Every day countless users are accessing various personal and personalized information on the Internet, especially the World Wide Web. In order to provide each user proper access, web applications need to be able to establish the user′s identity. Identity management is a concept to unify and facilitate such user identification.The objective of this thesis is to introduce and explore identity management in web applications. First, existing identity management approaches are analyzed and evaluated. Based on the results of this evaluation, a new AAA-based identity management framework, the so-called Diameter WebAuth, is proposed. The proposal is based on the Diameter protocol and intended for an easy deployment in web applications. By using Diameter as basis, the proposal takes advantage of existing Diameter functions and specifications and can be seamlessly integrated into existing Diameter setups. Diameter WebAuth provides features comparable to web-based identity management solutions such as OpenID, the Liberty Alliance project and Microsoft CardSpace.
Paper
Paul Baker, Zhen Ru Dai, Jens Grabowski , Oystein Haugen, Ina Schieferdecker, Clay E. Williams.Model-Driven Testing - Using the UML Testing Profile. ISBN 978-3-540-72562-6, Springer-Verlag, Berlin Heidelberg, 2007
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Written by the original members of an industry standardization group, this book shows you how to use UML to test complex software systems.It is the definitive reference for the only UML-based test specification language, written by the creators of that language.It is supported by an Internet site that provides information on the latest tools and uses of the profile.The authors introduce UTP step-by-step, using a case study that illustrates how UTP can be used for test modeling and test specification.You’ll learn how UTP concepts can be used for functional and non-functional testing, with example applications and best practices for user-interfaces and service oriented architectures.Model-driven development has become the most important new paradigm in software development and has already demonstrated considerable impact in reducing time to market and improving product quality.However, the development of high-quality systems not only requires systematic development processes but also systematic test processes.This book is about systematic, model-driven test processes in the context of UML.
Jens Nödler.An XML-based Approach for Software Analysis -- Applied to Detect Bad Smells in TTCN-3 Test Suites. Masterarbeit im Studiengang Angewandte Informatik am Institut für Informatik, ZFI-BM-2007-36, ISSN 1612-6793, Zentrum für Informatik, Georg-August-Universität Göttingen, 2007
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This thesis presents an XML-based approach for software analysis. Patternsin software artefacts which should be found by the analysis are describedusing the declarative XML query language XQuery. Implementationand design of a software analysis framework are presented. The design ofthe framework allows patterns to be described in a generic, abstract, andreusable way. The framework is customised for the detection of places insource codes which should be refactored, so-called bad smells. As a casestudy, the framework is used to detect bad smells in test suites written inthe testing language TTCN-3.
Paper
Deguang Le, Jun Lei, Xiaoming Fu.A New Decentralized Mobility Management Service Architecture for IPv6-based Networks. in Proceedings of the 3rd ACM International Workshop on Wireless Multimedia Networking and Performance Modeling (WMuNeP'07), in conjunction with the 10th ACM/IEEE International Symposium on Modeling, Analysis and Simulation of Wireless and Mobile Systems (MSWiM'07), Chania, Crete Island, Greece, ACM Press, New York, NY, USA, 2007
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In Mobile IPv6, the home network - through a designated home agent - is responsible for distributing all traffic from/to the mobile node in the default bidirectional tunneling mode, when the mobile node is connected to a foreign network. This approach not only lacks sufficient scalability and efficiency of delivery, but also poses a heavy burden on the home network and the global Internet. In this paper we propose a new decentralized mobility management service (DMMS) architecture to address this issue. The idea is to employ a local mobility agent in each access network, which handles node mobility based on local movement information, so that the ongoing communication can be maintained efficiently and scalable without relying on centralized traffic distributing entities.
Paper
Niklas Steinleitner, Xiaoming Fu, Dieter Hogrefe, Thomas Schreck, Hannes Tschofenig.An NSIS-based Approach for Firewall Traversal in Mobile IPv6 Networks. Third Annual International Wireless Internet Conference (WICON 2007), Austin, Texas, USA, ACM Press, 2007
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Firewalls have been successfully deployed in today?s network infrastructure in various environments and will also be used in IPv6 networks. However, most of the current firewalls do not support Mobile IPv6, the best known standardized solution for mobility support in IPv6. As a result, Mobile IPv6 traffic will be most likely dropped when used without an appropriate firewall traversal solution.This paper describes the problems and impacts of having firewalls in Mobile IPv6 environments and presents a firewall traversal solution based on the IETF?s Next Steps In Signaling framework to address these issues. Compared with other candidates such as STUN, TURN, ICE, ALG, MIDCOMand COPS, this approach does not rely on specific firewall placements and can be applied in various operational modes without additional introducing entities. In this paper we also explore security aspects since they are typically difficult to handle.
Paper
Jun Lei, Lei Shi, Xiaoming Fu.An Experimental Analysis of Joost Peer-to-Peer VoD Service. Technical Report No. IFI-TB-2007-03, Institute of Computer Science, University of Goettingen, Goettingen, Germany, 2007
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Most of the current Video-on-Demand (VoD) systems rely on content distribution networks or some local streaming proxies. While these traditional systems offer a means for media delivery and streaming, they also pose a significant performance challenge in terms of scalability and service delay as the number of clients increases. To solve this issue, peer-to-peer (P2P) technologies have been applied to support the VoD systems. Joost is one of such systems for distributing TV shows or other forms of video over the Internet. However, like Skype in its early stage, the mechanisms behind Joost are still unrevealed.The main purpose of this paper is therefore to study the underlying Joost architecture and its key components, and analyze its media streaming behaviors and peer management mechanisms through close investigations on Joost network traffic. With three envisioned typical scenarios we have further studied the Joost performance in terms of locality awareness, bandwidth capacity and VoD functionalities. Based on extensive experiments, we infer that Joost is a server-assisted peer-to-peer VoD system. It mainly relies on a set of delicate infrastructure nodes (e.g. content servers) for video distribution. To our best knowledge, this paper is the first analytical and performance study on commercial P2P VoD services.
Paper
Bernd Schloer.Implementation and Performance Evaluation of the IETF QoS NSLP Protocol. Master's thesis, No. GAUG-ZFI-BM-2007-37, Center for Informatics, University of Goettingen, Germany, 2007
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The main focus of this thesis is an open source implementation of the NSIS QoS NSLP with the support of signalling IntServ Controlled Load Service and its evaluation. The implementation was done in a research project at the University of Goettingen. Several software design features were introduced during the implementation work which yields in a stable and timely responsive application. The design features include a state machine, a traffic control interface and a timer library which together cover the whole functionality of the implementation.
Paper
Clemens Dubian , Wolfgang May .Design and Usage of an IT-System for workplace management
with ergonomic analysis under health protection aspects.
Enterprise Modelling and Information Systems Architectures -
Concepts and Applications, St.Goar, Germany, GI LNI 119, pages 163-176, 2007
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This article describes an information system for analysis anddescription of workplaces under the aspects of health protection andergonomic risks, which is currently being developed at VolkswagenwerkKassel. The system provides an in-strument for matching ergonomic risks ofworkplaces with work limitations of employees for an efficient assignmentof employees to appropriate workplaces. It integrates data from severalexisting systems and collects additional data. The collection andmaintenance of data is accomplished by an analysis team and by the teamleaders in the factory.
Edith Werner , Jens Grabowski , Helmut Neukirchen , Nils Röttger, Stephan Waack, Benjamin Zeiß .TTCN-3 Quality Engineering: Using Learning Techniques to Evaluate Metric Sets. Proceedings of 13th System Design Language Forum (SDL Forum 2007), 18-21 September 2007, Paris, Lecture Notes in Computer Science (LNCS) 4745. DOI: 10.1007/978-3-540-74984-4_4 , 56-70, Springer, Heidelberg, 2007
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Software metrics are an essential means to assess softwarequality. For the assessment of software quality, typically sets of complementingmetrics are used since individual metrics cover only isolatedquality aspects rather than a quality characteristic as a whole. The choiceof the metrics within such metric sets, however, is non-trivial. Metricsmay intuitively appear to be complementing, but they often are in factnon-orthogonal, i.e. the information they provide may overlap to someextent. In the past, such redundant metrics have been identified, for example,by statistical correlation methods. This paper presents, based onmachine learning, a novel approach to minimise sets of metrics by identifyingand removing metrics which have little effect on the overall qualityassessment. To demonstrate the application of this approach, results froman experiment are provided. In this experiment, a set of metrics that isused to assess the analysability of test suites that are specified using theTesting and Test Control Notation (TTCN-3) is investigated.
Paper
Thomas Rings .Testing Grid Applications Using TTCN-3. Masterarbeit im Studiengang Angewandte Informatik am Institut für Informatik, ZFI-BM-2007-27, ISSN 1612-6793, Zentrum für Informatik, Georg-August-Universität Göttingen, 2007
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The collective and coordinated usage of resources for joint problem solutions withindynamic virtual organizations across different institutes is realized with the Gridcomputing technology. Since the deployment of Grid computing grows, the quality ofGrid computing environments and Grid applications has to be assured. An importantconstituent of quality assurance is testing.This thesis investigates the applicability of the Testing and Test Control Notationversion 3 (TTCN-3) for testing Grid applications. As case study of this thesis, testcases implemented in TTCN-3 have been applied to an application running in a Gridcomputing environment.A description of the implemented example Grid application that is tested withTTCN-3 is covered by this thesis. The main focus of the thesis is on the realizationof a basic TTCN-3 test system and its test harness in order to check the correctnessof the application that runs in a Grid environment. The realized tests demonstratethat TTCN-3 is applicable for distributed testing in Grid environments. The Gridenvironment used in the case study is the Instant-Grid. It is based on the Grid middlewareGlobus Toolkit.
Paper
John-Patrick Wowra.RTP over Datagram TLS. Master's thesis, No. GAUG-ZFI-BM-2007-28, Center for Informatics, University of Goettingen, 2007
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The popularity of Internet Telephony has been rising continuously in recent years. With a rising number of users inevitably the number of malicious users rises as well. Hence security is a major concern for Internet Telephony.Commonly RTP is used with Internet Telephony for transmission and reception of audio and video data. Traditionally, RTP runs over UDP, and RTP traf?c is in most cases transmitted without any protection.Datagram TLS is a modi?ed version of TLS that functions properly over datagram transport. This thesis studies an RTP extension based on DTLS, and includes conduction of a prototype implementation and further analysis of the design towards securing RTP and thus Internet Telephony.
Paper
Heiko Kattenstroth, Wolfgang May , Franz Schenk .Combining OWL with F-Logic Rules and Defaults.
International Workshop on Applications of Logic Programming
to the Web, Semantic Web and Semantic Web Services (ALPSWS07), Porto, Portugal, CEUR online proceedings available at
, pages 60-75, 2007
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We describe the combination of OWL and F-Logic for the architecture of Semantic Web application nodes. The approach has been implemented by combining an existing Jena-based architecture with an external Florid instance. The approach is based on a loose coupling where the F-Logic rules are used for e.g., role-value-maps, closed-world-reasoning, (stratified) negation, aggregation, and definition of answer views; additionally the default inheritance of F-Logic can be exploited.
Xiaoming Fu , Dieter Hogrefe , Jun Lei , Jianrong Tan.Comparative Studies on Authentication and Key Exchange Methods for 802.11 Wireless LAN. Computers & Security, Volume 26, Issue 5, Pages 401-409, Elsevier, 2007
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IEEE 802.11 wireless LAN has become one of the hot topics on the design and development of network access technologies. In particular, its authentication and key exchange (AKE) aspects, which form a vital building block for modern security mechanisms, deserve further investigation. In this paper we first identify the general requirements used for WLAN authentication and key exchange (AKE) methods, and then classify them into three levels (mandatory, recommended, and additional operational requirements). We present a review of issues and proposed solutions for AKE in 802.11 WLANs. Three types of existing methods for addressing AKE issues are identified, namely, the legacy, layered and access control-based AKE methods. Then, we compare these methods against the identified requirements. Based on the analysis, a multi-layer AKE framework is proposed, together with a set of design guidelines, which aims at a flexible, extensible and efficient security as well as easy deployment.
Paper
RolA. Burger, Giovanni Iacovoni, Cliff Reader, Xiaoming Fu, Xiaodong Yang, Wang Hui.An overview of digital TV standards in China. Proceedings of ChinaCom 2007, Shanghai, China, Special Session on Digital Broadcasting and Mobile Convergence, IEEE, 2007
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This paper presents an updated overview of the different proposed standards on the market for mobile TV in China as of June 2007 and analyzes the different trade-offs, strengths and weaknesses. Furthermore the used video codecs are compared with special emphasis on the usage in mobile TV in China.
Paper
Jun Lei, Xiaoming Fu, Dieter Hogrefe, Jianrong Tan.Comparative Studies on Authentication and Key Exchange Methods for 802.11 Wireless LAN. Computers & Security, Volume 26, Issue 5, Pages 401-409, Elsevier, 2007
Read abstract
IEEE 802.11 wireless LAN has become one of the hot topics on the design and development of network access technologies. In particular, its authentication and key exchange (AKE) aspects, which form a vital building block for modern security mechanisms, deserve further investigation. In this paper we first identify the general requirements used for WLAN authentication and key exchange (AKE) methods, and then classify them into three levels (mandatory, recommended, and additional operational requirements). We present a review of issues and proposed solutions for AKE in 802.11 WLANs. Three types of existing methods for addressing AKE issues are identified, namely, the legacy, layered and access control-based AKE methods. Then, we compare these methods against the identified requirements. Based on the analysis, a multi-layer AKE framework is proposed, together with a set of design guidelines, which aims at a flexible, extensible and efficient security as well as easy deployment.
Paper
Changpeng Fan, Andreas Festag, Xiaoming Fu, Cornelia Kapper, Holger Karl, Mirko Schramm, Günter Schäfer (inventors).Method for carrying out a QoS-oriented handoff between a first and a second IP-based, especially mobile IPV6-based, communication path, between a mobile node (MN) and a correspondent node (CN). granted patent, No. AU2001276315, 2007
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The invention relates to a method for carrying out a QoS-oriented handoff between a first and a second IP-based, especially mobile IPv6-based, communication path, between a mobile node (MN) and a correspondent node (CN), the second communication path being part of a number of communication paths which can be accessed by the mobile node, with no, one, or a plurality of intermediate instances. The inventive method comprises at least the following steps: (a) a communication path is selected from the communication paths which can be accessed by the mobile node, as a second communication path; (b) a message (BU) is generated by the mobile node, said message containing at least one IP address which is associated with the mobile node on the basis of the selected communication path, and containing minimum quality of service requirements (QoS) in terms of the selected communication path; (c) the ability to meet at least the minimum quality of service requirements is controlled and optionally ensured by the individual intermediate instances through which the message passes successively, on the selected communication path and/or through the correspondent node. The message contains the minimum quality of service requirements for a communication from the mobile node to the correspondent node and/or vice versa. A handoff is automatically carried out between the first communication path and the second selected communication path, when at least the minimum quality of service requirements are met or the message is stopped. A notice is generated in an intermediate instance and/or in the correspondent node and is sent to the mobile node if the ability to meet the minimum quality of service requirements is not ensured.
Helmut Neukirchen , Benjamin Zeiß .Automation of Refactoring and Refactoring Suggestions
for TTCN-3 Test Suites -- The TRex TTCN-3 Refactoring and Metrics Tool. 1st Workshop on Refactoring Tools held in conjunction with 21st European Conference on Object-Oriented Programming (ECOOP 2007), July 31st 2007, Berlin,
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Refactoring is not only useful for source code of implementations, but as wellfor test specifications. The open source TRex tool automates the application of refactoringsand the detection of refactoring opportunities for test suites that are specified using thestandardised Testing and Test Control Notation (TTCN-3). Depending on the refactoring,the behaviour preserving transformations may include syntax tree transformations and directmodification of the source code; for suggesting refactorings, metrics are calculated andcode smell patterns are detected.
Paper
Helmut Neukirchen , Benjamin Zeiß .Automation of Refactoring and Refactoring Suggestions
for TTCN-3 Test Suites -- The TRex TTCN-3 Refactoring and Metrics Tool (Extended Abstract). Proceedings of the 1st Workshop on Refactoring Tools held in conjunction with 21st European Conference on Object-Oriented Programming (ECOOP 2007), July 31st 2007, Berlin. (Editors: Danny Dig, Michael Cebulla). Technical Report No 2007-8, Technische Universität Berlin, Fakultät IV - Elektrotechnik und Informatik, ISSN 1436-9915,
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Refactoring is not only useful for source code of implementations, but as wellfor test specifications. The open source TRex tool automates the application of refactoringsand the detection of refactoring opportunities for test suites that are specified using thestandardised Testing and Test Control Notation (TTCN-3). Depending on the refactoring,the behaviour preserving transformations may include syntax tree transformations and directmodification of the source code; for suggesting refactorings, metrics are calculated andcode smell patterns are detected.
Paper
Helmut Neukirchen , Martin Bisanz .Utilising Code Smells to Detect Quality Problems in TTCN-3 Test Suites. Proceedings of the 19th IFIP International Conference on Testing of Communicating Systems and 7th International Workshop on Formal Approaches to Testing of Software (TestCom/FATES 2007),
June 26-29 2007, Tallinn, Estonia. Lecture Notes in Computer Science (LNCS ) 4581. DOI: 978-3-540-73066-8_16 , 228-243, Springer, Heidelberg, 2007
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Today, test suites of several ten thousand lines of code arespecified using the Testing and Test Control Notation (TTCN-3). Experienceshows that the resulting test suites suffer from quality problemswith respect to internal quality aspects like usability, maintainability, orreusability. Therefore, a quality assessment of TTCN-3 test suites is desirable.A powerful approach to detect quality problems in source codeis the identification of code smells. Code smells are patterns of inappropriatelanguage usage that is error-prone or may lead to quality problems.This paper presents a quality assessment approach for TTCN-3test suites which is based on TTCN-3 code smells: To this aim, variousTTCN-3 code smells have been identified and collected in a catalogue;the detection of instances of TTCN-3 code smells in test suites has beenautomated by a tool. The applicability of this approach is demonstratedby providing results from the quality assessment of several standardisedTTCN-3 test suites.
Paper
Stefan Troschütz.Web Service Test Framework with TTCN-3. Masterarbeit im Studiengang Angewandte Informatik am Institut für Informatik, ZFI-BM-2007-14, ISSN 1612-6793, Zentrum für Informatik, Georg-August-Universität Göttingen, 2007,
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Web services are standards-based software systems designed to facilitate interoperableapplication-to-application integration over a network. The broadening adoption of Webservices and especially their use for business purposes or critical applications introducea growing need for efficient testing approaches that allow assuring the correctness andinteroperability of Web services.This thesis presents a framework for the testing of Web services with the standardizedtest specification and implementation language TTCN-3. Foremost, the mapping of aWeb service description to a TTCN-3 abstract test suite, which facilitates basic testingof the Web service, is discussed in detail. A time-saving automation of the proposedmapping implemented as a Java console application is introduced afterwards. Finally,the enhancement of TTworkbench Basic, a TTCN-3 test development and executionenvironment, for Web service testing is presented. The implemented extension enablesthe execution of a TTCN-3 abstract test suite derived from a Web service description. Inaddition, it provides dialog-based wizards for using the automation of the mapping fromwithin TTworkbench or defining new, more complex test cases.
Paper
Jun Lei, Xiaoming Fu.Evaluating the Benefits of Introducing PMIPv6 for Localized Mobility Management. Technical Report No. IFI-TB-2007-02, Institute of Computer Science, University of Goettingen, Goettingen, Germany, 2007
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Since recent years, it has been recognized that using global mobility protocol for managing localized mobility causes a number of problems, such as long registration delay. To overcome these problems, host-based and network-based localized mobility approaches have been proposed. Moreover, network based mobility management is more desirable since it requires no host software stack changes. Proxy Mobile IPv6 (PMIPv6) provides a solution for network-based mobility management that can avoid tunneling overhead over the air and support for hosts without an involvement in the mobility management.We first review the localized mobility proposals and explore three major benefits that PMIPv6 can bring. In particular, we evaluate two aspects of the handover performance through a mathematical model for Fast Handovers for MIPv6 (FMIPv6), Hierarchical MIPv6 (HMIPv6), Fast handovers for HMIPv6 (F-HMIPv6) and PMIPv6. These analytical studies show that PMIPv6 may cause high handover latency if the local mobility anchor (LMA) is located far from the current mobility access gateway (MAG).In this paper, we therefore propose an enhancement for PMIPv6, so-called fast handovers for PMIPv6 (F-PMIPv6) to further reduce the handover latency. The analysis result ascertains that F-PMIPv6 is a promising mobility scheme to efficiently manage the localized mobility.
Paper
Enrico Franconi, Michael Kifer, Wolfgang May .4th European Semantic
Web Conference (ESWC 2007). ,
, 2007
Wolfgang May .MARS: Modular Active Rules in the Semantic Web. Guest talk, , 2007
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In dem Vortrag wird ein im Rahmen der "Working Group I5: ′Evolutionand Reactivity′" des EU NoE "REWERSE - Reasoning on the Web with Rulesand Semantics" entwickelter Ansatz zur Beschreibung undImplementierung von Verhalten im Semantic Web beschrieben.
Erik Behrends , Oliver Fritzen , Tobias Knabke, Wolfgang May , Franz Schenk .Rule-Based Active Domain Brokering for the Semantic Web.
The First International Conference on
Web Reasoning and Rule Systems, Innsbruck, Austria, LNCS 4524, Springer, pages 259-268, 2007
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We investigate the use of domain ontologies that also include actions and events of that domain. Such ontologies do not only cover the static aspects of an ontology, but also activities and behavior in the given domain. We analyze what information has to be contained in such an ontology and show that large parts of the behavior can be expressed preferably by rules. We show how the tasks can be integrated and handled by a service infrastructure in the Semantic Web.
Jens Grabowski , Helmut Neukirchen , Ina Schieferdecker, Diana Vega, Benjamin Zeiß .An ISO 9126-based Quality Model to Assess the Quality of TTCN-3 Test Specifications. TTCN-3 User Conference 2007 (T3UC), 29 May-1 June 2007, Stockholm, Sweden,
Lei Shi , Peter Sjödin.A VLAN Ethernet Backplane for Distributed Network Systems. IEEE Workshop on High Performance Switching and Routing (HPSR) 2007, New York, USA, IEEE, 2007
Paper
Lei Shi, Peter Sjödin.A VLAN Ethernet Backplane for Distributed Network Systems. IEEE Workshop on High Performance Switching and Routing (HPSR) 2007, New York, USA, IEEE, 2007
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In a network system, such as a router or a switch, it is difficult to achieve flexibility and performance at the same time. We propose an architecture that consists of network processors for packet processing and a VLAN-based Ethernet backplane for switching. This allows us to use flexible network processors for packet processing functions, and still exploit the cost-effectiveness of Ethernet to achieve switching capacity. We propose an architecture where we use VLAN tagging for internal traffic management, and also for distributed packet forwarding decisions between ingress and egress units. We describe our implementation of this system and report performance analysis, were we find that we can achieve near line rate performance in a system with Gigabit Ethernet ports, and that internal memory management is important for network processor performance.
Paper
Helmut Neukirchen .Pattern-Based Quality Assessment of TTCN-3 Test Suites. Software & Systems Quality Conferences 2007 International (ICSTEST), 25th--27th April 2007, Düsseldorf, Germany,
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The Testing and Test Control Notation (TTCN-3) is a language for test specification and test implementation which has been standardised by the European Telecommunications Standards Institute (ETSI) and the International Telecommunication Union (ITU). Experience has demonstrated that large industrial size TTCN-3 test suites suffer from the same quality problems like any ordinary source code of larger implementations does. For example, code duplication, unused variables, or high complexity lead to low quality in terms of readability, re-usability, and maintainability. While such internal quality issues have been investigated for source code of implementation languages, assessment of the internal quality of test suites has not been well studied, yet.One recent approach for the quality assessment of TTCN-3 test suites is the application of test metrics. However, such size and structural metrics are sometimes not powerful enough to detect certain issues. While metrics are able to locate e.g. unused definitions or complex code, they cannot detect advanced internal quality problems, e.g. code duplication or anomalies in control or data flow. In addition to our previous results based on test metrics, we present therefore our latest results on applying a more powerful pattern-based approach of quality assessment and issue detection for TTCN-3 test suites. To this aim, we have developed a catalogue of more than 30 so called TTCN-3 "smells" which are patterns of inappropriate usage of TTCN-3. Examples from this catalogue are: duplicate branches in alternative behaviour, usage of hard coded values, unreachable code, violation of naming conventions, not setting a test verdict in a test case, or asymmetric activation/deactivation of TTCN-3 defaults. By associating TTCN-3 refactorings to these "smells", we are not only able to detect issues, but even provide support for removing issues. For this, we have developed an accom-panying catalogue of TTCN-3 refactorings which includes instructions how to restructure test suites without changing their external behaviour. As a result, we are not only able to assess the internal quality of TTCN-3 test suites, but also to improve their internal quality.The effort for applying our approach is significantly reduced by providing corresponding tool support: TRex is an open-source TTCN-3 Refactoring and Metrics tool which is freely available as an Eclipse plug-in on its website. We present latest results from applying our TTCN-3 smell catalogue and the TRex tool to huge real-word TTCN-3 test suites which have been standardised by ETSI for testing implementations of the SIP and IPv6 protocol.Our approach of using pattern-based detection of issues in TTCN-3 test suites immediately helps users of TTCN-3 to assess the quality of their test suites and to locate and to avoid issues in TTCN-3 test suites. The overall approach which consists not only of pattern-based issue detection, but also of TTCN-3 metrics and TTCN-3 refactoring, has been put into practice by our TRex TTCN-3 Refactoring and Metrics Tool. TRex and the underlying concepts have been developed together with Motorola Labs UK, where this approach is used to assess and improve the quality of industrial size TTCN-3 test suites.
Paper
Benjamin Zeiß .A Refactoring Tool for TTCN-3. 6th Exchange of Experience on Testing at Siemens AG, München/Neuperlach, 17th April 2007,
Benjamin Zeiß , Diana Vega, Ina Schieferdecker, Helmut Neukirchen , Jens Grabowski .Applying the ISO 9126 Quality Model to Test Specifications -- Exemplified for TTCN-3 Test Specifications. Software Engineering 2007 (SE 2007). Lecture Notes in Informatics (LNI) 105. Copyright Gesellschaft für Informatik, 231-242, Köllen Verlag, Bonn, 2007
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Quality models are needed to evaluate and set goals for the quality of asoftware product. The international ISO/IEC standard 9126 defines a general qualitymodel for software products. Software is developed in different domains and the usageof the ISO/IEC quality model requires an instantiation for each concrete domain. Onespecial domain is the development and maintenance of test specifications. Test specificationsfor testing, e.g. the Internet Protocol version 6 (IPv6) or the Session InitiationProtocol (SIP), reach sizes of more than 40.000 lines of test code. Such large testspecifications require strict quality assurance. In this paper, we present an adaptationof the ISO/IEC 9126 quality model to test specifications and show its instantiation fortest specifications written in the Testing and Test Control Notation (TTCN-3). Examplemeasurements of the standardised SIP test suite demonstrate the applicability ofour approach.
Paper
Xiaoming Fu , Christian Dickmann, Jon Crowcroft.General Internet Signaling Transport (GIST) over SCTP. Internet Engineering Task Force, Next Steps in Signaling (NSIS) Working Group, 2007
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The General Internet Signaling Transport (GIST) protocol currently uses TCP or TLS over TCP for connection mode operation. This document describes the usage of GIST over the Stream Control Transmission Protocol (SCTP). The use of SCTP can take the advantage of features provided by SCTP, namely streaming-based transport, support of multiple streams to avoid head of line blocking, and the support of multi-homing to provide network level fault tolerance. Additionally, the support for the Partial Reliability Extension of SCTP is discussed.
Ivano Guardini, Xiaoming Fu.ENABLE QoS Services for Large Operational IP Mobility Networks. Presented at the 1st OpenNet Workshop, Brussels, Belgium, 2007
Xiaoming Fu , Dieter Hogrefe , Deguang Le , Xiaoyuan Gu.E2T: End-to-End Tunnelling Extension to Mobile IPv6. in Proceedings of the 4th IEEE Consumer Communications and Networking Conference (CCNC 2007), Las Vegas, Nevada, USA, IEEE Communications Society, 2007
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In the standard Mobile IPv6 (MIPv6), the bidirectional tunnelling through the home agent or the route optimization show inefficiency in per-packet routing, especially when both communicating endpoints are mobile. To be scalable and compatible, mobile devices? packets should be routed efficiently with minimal changes to the network infrastructure. However, the current solutions do not provide any means for the end systems to perform optimized packet routing during the operation of the mobile devices. In this paper, we present an end-to-end tunnelling extension to MIPv6 (E2T) for mobile routing packets, which reduces the per-packet routing cost for the communications of mobile devices through the lower packet routing overhead. Besides, our approach requires little change to MIPv6, but allows the more efficient routing behavior with the shorter end-to-end transmission latency between communicating endpoints. The simulation results show our approach is suitable for real-time multimedia applications.
Paper
Xiaoming Fu , Dieter Hogrefe , Jun Lei .DMMP: A New Dynamic Mesh-based Overlay Multicast Protocol Framework. Proceedings of the 2007 IEEE Consumer Communications and Networking Conference - Workshop on Peer-to-Peer Multicasting (P2PM 2007), Las Vegas, Nevada, USA, IEEE Communications Society, 2007
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Multicasting can provide an efficient way of delivering data from a sender to a group of receivers. It has received much attention over the past decade because of an increasing demand for group communication applications such as multimedia streaming. However, native IP multicast has not become widespread largely due to its technical and operational issues. To overcome these obstacles of deployment, various application layer and overlay multicast approaches have been proposed. Compared with IP multicast, they provide a new way of handling multicast without upgrading the infrastructure in a large scale. Nevertheless, they introduce a number of challenges and are still plagued with concerns on scalability, heterogeneity and dynamic performance. In this paper we propose a new protocol framework for addressing these issues, so-called the Dynamic Mesh-based Overlay Multicast Protocol or DMMP, which intends to provide an efficient and resilient multicast support by dynamically managing an overlay core comprised of end hosts. Moreover, DMMP can be used for media streaming which is contracted by a limited resource in stream supplying entities and requires good scalability and reliability. Initial analysis shows that DMMP has the potential to efficiently deliver multicast services for large groups.
Paper
Deguang Le, Xiaoming Fu, Xiaoyuan Gu, Dieter Hogrefe.E2T: End-to-End Tunnelling Extension to Mobile IPv6. in Proceedings of the 4th IEEE Consumer Communications and Networking Conference (CCNC 2007), Las Vegas, Nevada, USA, IEEE Communications Society, 2007
Read abstract
In the standard Mobile IPv6 (MIPv6), the bidirectional tunnelling through the home agent or the route optimization show inefficiency in per-packet routing, especially when both communicating endpoints are mobile. To be scalable and compatible, mobile devices? packets should be routed efficiently with minimal changes to the network infrastructure. However, the current solutions do not provide any means for the end systems to perform optimized packet routing during the operation of the mobile devices. In this paper, we present an end-to-end tunnelling extension to MIPv6 (E2T) for mobile routing packets, which reduces the per-packet routing cost for the communications of mobile devices through the lower packet routing overhead. Besides, our approach requires little change to MIPv6, but allows the more efficient routing behavior with the shorter end-to-end transmission latency between communicating endpoints. The simulation results show our approach is suitable for real-time multimedia applications.
Paper
Jun Lei, Xiaoming Fu, Dieter Hogrefe.DMMP: A New Dynamic Mesh-based Overlay Multicast Protocol Framework. Proceedings of the 2007 IEEE Consumer Communications and Networking Conference - Workshop on Peer-to-Peer Multicasting (P2PM 2007), Las Vegas, Nevada, USA, IEEE Communications Society, 2007
Read abstract
Multicasting can provide an efficient way of delivering data from a sender to a group of receivers. It has received much attention over the past decade because of an increasing demand for group communication applications such as multimedia streaming. However, native IP multicast has not become widespread largely due to its technical and operational issues. To overcome these obstacles of deployment, various application layer and overlay multicast approaches have been proposed. Compared with IP multicast, they provide a new way of handling multicast without upgrading the infrastructure in a large scale. Nevertheless, they introduce a number of challenges and are still plagued with concerns on scalability, heterogeneity and dynamic performance. In this paper we propose a new protocol framework for addressing these issues, so-called the Dynamic Mesh-based Overlay Multicast Protocol or DMMP, which intends to provide an efficient and resilient multicast support by dynamically managing an overlay core comprised of end hosts. Moreover, DMMP can be used for media streaming which is contracted by a limited resource in stream supplying entities and requires good scalability and reliability. Initial analysis shows that DMMP has the potential to efficiently deliver multicast services for large groups.
Paper
Telemaco Melia , D. Corujo, A. de la Oliva, A. Vidal, R. Aguiar, I. Soto.Impact of heterogeneous network controlled handovers on multi-mode mobile device design. WCNC 2007 (IEEE Wireless Communications and Networking Conference), 2007
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The availability of multiple technologies, withmicro and macro wireless cells, for network access combinedwith terminals capable of exploiting such diversity in wirelessaccess requires the development of new mechanisms foroptimized handover procedures. Appealing solutions shouldsupport network controlled handovers through heterogeneoustechnologies, preferably combined with a cross-layers two/threedesign. The IEEE 802.21 working group is currentlystandardizing the methods and the protocol potentially able toprovide such a solution. In this paper we analyze the impact ofsignaling timing on network controlled handovers execution andperformance in this environment. Through an extensivesimulation study, we obtain results, that can be exploited in bothterminal and handover procedure designs.
Paper
Fang-Chun Kuo, Xiaoming Fu.Probe-Aided MulTCP: An Aggregate Congestion Control Mechanism. Technical Report No. IFI-TB-2007-01, Institute of Computer Science, University of Goettingen, Goettingen, Germany, 2007
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A number of new application scenarios, e.g. mobile/wireless TCP proxies, edge to edge overlays, QoS provisioning and mass data transport, are calling for aggregate flow management. In this paper we show that applying a single flowshare to an aggregate flow will result in unfairness in the bandwidth sharing between the aggregate traffic and the background flows sharing the same bottleneck. To overcome this problem, we propose an aggregate congestion control mechanism, namely probe-aided MulTCP, which dynamically adjusts the congestion window loop to support multiple flowshares for an aggregate. The probe-aided MulTCP differs from existing works, such as MPAT, CP, MulTCP, in the following aspects. Firstly, our simulations show that against the traditional MulTCP the probe-aided MulTCP could maintain relatively stable, smooth and fair performance over a wide range of weight N in steady conditions as well as in varied congestion conditions. Secondly, an adjusting window loop is introduced to constantly probe the congestion situation and dynamically adjust the congestion window size for the newly arriving and leaving flows within the aggregate. This integration of congestion information improves the startup performance for new arriving flows, especially for short-lived ones. Thus, the probe-aided MulTCP is lightweight since only one extra probe window loop is used. Our extensive simulation studies show that with the probe-aided MulTCP, the improved performance and fairness will overweight the complexity caused by two congestion window loops.
Paper
2006
Benjamin Zeiß , Helmut Neukirchen , Jens Grabowski , Dominic Evans, Paul Baker.Refactoring and Metrics for TTCN-3 Test Suites. System Analysis and Modeling: Language Profiles. 5th International Workshop, SAM 2006, Kaiserslautern, Germany, May 31 - June 2, 2006, Revised Selected Papers. Lecture Notes in Computer Science (LNCS ) 4320. DOI: 10.1007/11951148_10 , 148-165, Springer, 2006
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Experience with the development and maintenance of testsuites has shown that the Testing and Test Control Notation (TTCN-3)provides very good concepts for adequate test specification. However, experiencehas also demonstrated that during either the migration of legacytest suites to TTCN-3, or the development of large TTCN-3 test specifications,users have found it is difficult to construct TTCN-3 tests thatare concise with respect to readability, usability, and maintainability.To address these issues, this paper investigates refactoring and metricsfor TTCN-3. Refactoring restructures a test suite systematically withoutchanging its behaviour. Complementary metrics are used to assess thequality of TTCN-3 test suites. For automation, a tool called TRex hasbeen developed that supports refactoring and metrics for TTCN-3.
Paper
Martin Bisanz .Pattern-based Smell Detection in TTCN-3 Test Suites. Masterarbeit im Studiengang Angewandte Informatik am Institut für Informatik, ZFI-BM-2006-44, ISSN 1612-6793, Zentrum für Informatik, Georg-August-Universität Göttingen, 2006
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TTCN-3 is a specification and implementation language for software tests. Just like any ordinarysoftware, software tests can suffer from many quality problems. Software Engineeringprovides means and techniques to counteract these problems and to increase the quality ofsoftware in many respects. Refactoring is such a technique which is used to enhance theinternal structure of code and to increase its readability, maintainability and comprehensiveness.Code parts in need of refactoring are referred to as "code smells". Refactorings forTTCN-3 test suites have already been investigated. In this thesis the concept of code smellsis applied to TTCN-3. A catalog of code smells for TTCN-3 is presented, and each smellis connected to a corresponding counter measure. In addition, a tool for automated codesmell detection is introduced together with results of applying this tool on existing TTCN-3test suites.
Paper
Xiaoming Fu , Dieter Hogrefe , Hannes Tschofenig.Beyond QoS Signaling: a Generic IP Signaling Framework. Computer Networks, Volume 50, Issue 17, pages 3416-3433, Elsevier, 2006
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This paper describes the design principles and an introduction of a framework and protocols for generic IP signaling, namely the Cross-Application Signaling Protocol (CASP) and its signaling applications. While reusing certain features of the existing RSVP protocol, CASP overcomes its shortcomings and may be deployed as a replacement technology to provide simpler, mobility-supported, more extensible and more secure signaling services in IP based networks. This paper discusses challenges of today?s IP signaling protocols and addresses fundamentals and key aspects of CASP and its current signaling applications. In addition, a comparison with previous signaling protocol proposals and an outlook of future work in this area are also given.
Paper
Dieter Hogrefe , Constantin Werner , Sebastian Kraatz.A UML Profile for Communicating Systems. in: Gotzhein, Reed: System Analysis and Modeling: Language Profiles, 5th International Workshop, SAM 2006, Kaiserslautern, Germany, May 31 - June 2, 2006, Revised Selected Papers, pp. 1-18, Springer Verlag, 2006
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This paper presents a UML 2 profile for communicating systems. It is driven by the experience of SDL and uses formal constraints for profile definition and mapping rules by means of OCL. It features language elements for high-level specification and description of Internet communication and signaling protocols where SDL is not optimally suited. Due to its support of several concrete notations, this profile is aligned to work with several UML 2 compliant modeling tools. In addition, an implementation by an XSLT-based mapping from UML to behavioral and structural SDL specifications is available. The intention of the paper is to present the main work done which is defining an actual profile and mapping this to SDL.
Dieter Hogrefe .Internet und Kommunikation: zuverlässig, sicher, allgegenwärtig?. Vandenhoeck & Ruprecht, 2006
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Wir alle nutzen heute das Internet auf vielfältige Arten und Weisen: Bankgeschäfte, Telefonieren, Kaufen/Verkaufen, Informationen aller Art beschaffen oder Spielen. Inwieweit kann man dem Medium eigentlich trauen, das man da nutzt, wie verlässlich ist es eigentlich im Sinne der Bereitstellung eines Dienstes zu einer bestimmten Zeit an einem bestimmten Ort in der gewünschten Qualität und Sicherheit?Es ist davon auszugehen und wird sogar von den Nutzern zunehmend erwartet, dass das Internet in der Zukunft allgegenwärtig ist, wir also ständig und überall darauf Zugriff haben, so wie wir heute ständig und überall telefonieren können, wenn wir möchten, ohne auf Telefonzellen und Kleingeld angewiesen zu sein. Wenn man mal kein ?Handynetz? hat, sich z.B. in einem Funkloch befindet, wird das bereits als großer Mangel empfunden: ?Wo sind wir denn hier gelandet??. Was heute für das Telefonieren gilt, wird morgen für den Zugriff auf das Internet mit all seinen Informationsmöglichkeiten gelten. Eigentlich befinden wir uns bereits in diesem Zustand, ohne dass die Gesellschaft das wirklich realisiert. Allerdings hat der ubiquitäre (allgegenwärtige) Internetzugang derzeit noch immer Experimentiercharakter, ist also derzeit eher etwas für eingeweihte Bastler. Das wird sich allerdings ändern. Es ist dabei festzustellen, dass der ubiquitäre Internetzugang eine ökonomische Fragestellung ist, d.h. immer und überall online sein, wird generell teurer sein, als z.B. gelegentlich vom häuslichen DSL-Anschluss das Internet zu nutzen.In dieser Situation des allgegenwärtigen Internets, stellt sich schnell die berühmte ?Big Brother is watching you?-Frage: Was ist eigentlich mit Vertraulichkeit, Privatsphäre, also Sicherheit im Allgemeinen? Es gibt eine Reihe von Sicherheitsinstrumenten wie Verschlüsselung, Authentifizierung, etc., die viele von uns nutzen. Im Allgemeinen soll ein Sicherheits-Mechanismus dazu da sein, gegen böswillige Beteiligte zu schützen. Wenn man das so versteht, dann gibt es aber eine ganze Menge Sicherheitsherausforderungen, denen nicht mit herkömmlichen Instrumenten begegnet werden kann. Traditionelle Instrumente schützen typischerweise Ressourcen vor böswilligen Nutzern, indem der Zugriff nur den autorisierten Nutzern gewährt wird. Allerdings muss sich der einzelne Benutzer selbst auch oft gegen solche Beteiligte schützen, die böswillige Dienste anbieten. Technisch gesehen geht das in manchen Fällen mit Firewalls, allerdings nur auf sehr niedriger semantischer Ebene. Es geht z.B. dann nicht, wenn wir explizit Dienste in Anspruch nehmen möchten und nicht wissen, ob sie böswillig sind oder nicht. So könnte z.B. ein Informationsanbieter zu seinem eigenen Vorteil absichtlich falsche Informationen anbieten. Dagegen können die traditionellen Sicherheitsmechanismen nicht schützen.Um diesen Sicherheitsherausforderungen zu begegnen, geraten sog. Vertrauens- und Reputationssysteme immer mehr in den Blickpunkt. Man bezeichnet das neuerdings auch als ?Soft-Security? im Gegensatz zu der herkömmlichen ?Hard-Security?.
Paper
Xiaodong Yang , Jani Väre Thomas J. Owens.A Survey of Handover Algorithms in DVB-H. IEEE Communications Surveys & Tutorials, 2006
Katherine Guo, Xiaoming Fu, Jon Crowcroft (editors).MobiArch'06 - Proceedings of the First ACM/IEEE International Workshop on Mobility in the Evolving Internet Architecture. San Francisco, CA, USA, ACM Press, 2006
Steffen Wagner.Implementation and Evaluation of the Interaction between Host Identity Protocol and Session Initiation Protocol. Master's thesis, No. ZFI-BM-2006-42, Center for Informatics, University of Goettingen, Germany, 2006
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The Session Initiation Protocol (SIP) enables a pair of user agents to establish and maintain sessions. The recent proposed Host Identity Protocol (HIP) addresses the issue of multi-homing, readdressing and mobility by introducing an additional layer between the network and transport layers. The scope of this thesis is to implement the concept of exchanging the Host Identities (or Host Identity Tags) used in HIP as part of the initial SIP exchange, thus enabling the real-time communications in nomadic environments.
Paper
Xiaoming Fu, Hannes Tschofenig, Dieter Hogrefe.Beyond QoS Signaling: a Generic IP Signaling Framework. Computer Networks, Volume 50, Issue 17, pages 3416-3433, Elsevier, 2006
Read abstract
This paper describes the design principles and an introduction of a framework and protocols for generic IP signaling, namely the Cross-Application Signaling Protocol (CASP) and its signaling applications. While reusing certain features of the existing RSVP protocol, CASP overcomes its shortcomings and may be deployed as a replacement technology to provide simpler, mobility-supported, more extensible and more secure signaling services in IP based networks. This paper discusses challenges of today?s IP signaling protocols and addresses fundamentals and key aspects of CASP and its current signaling applications. In addition, a comparison with previous signaling protocol proposals and an outlook of future work in this area are also given.
Paper
Xiaodong Yang, Jani Väre, Thomas J. Owens.A Survey of Handover Algorithms in DVB-H. IEEE Communications Surveys & Tutorials, 8(4): 16-29, IEEE, 2006
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Digital Video Broadcasting for Handhelds (DVB-H) is a standard for broadcasting IP Datacast (IPDC) services to mobile handheld terminals. Based on the DVB-T standard, DVB-H adds new features such as time slicing, MPE-FEC, in-depth interleavers, mandatory cell id identifier,optional 4K-modulation mode and the use of 5 MHz bandwidth in addition to the usually used 6, 7, or 8 MHz raster. IPDC over DVB-H is proposed for ETSI to complement the DVB-H standard by combining IPDC and DVB-H in an end-to-end system. Handover in such unidirectional broadcastingnetworks is a novel issue. In the last few years since the birth of DVB-H technology, great attention has been given to the performance analysis of DVB-H mobile terminals. Handover is one of the main research topics for DVB-H in mobile scenarios. Better reception quality and greater power efficiency are considered to be the main targets of handoverresearch for DVB-H. New algorithms for different handover stages in DVB-H have been the subject of recent research and are currently being studied. Further novel algorithms need to be designed to improve the mobile reception quality. This article provides a comprehensive survey of the handover algorithms in DVB-H. A systematic evaluation and categorization approach is proposed based on the problems the algorithms solve and the handover stages being focused on. Criteria are proposed and analyzed to facilitate designing better handover algorithms for DVB-H that have been identified from the research conducted by the authors.
Paper
Jens Grabowski , Helmut Neukirchen , Benjamin Zeiß .Qualitätssicherung und Qualitätsverbesserung für TTCN-3 Testspezifikationen - Unterlagen zu einem Arbeitstreffen am Institut für Informatik der Georg-August-Universität Göttingen vom 18. Oktober 2006. Technical Report, IFI-TB-2006-06, ISSN 1611-1044, Institute for Informatics, University of Göttingen, Germany, November 2006,
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On October 18th, 2006, the Institute for Informatics at the Georg-August-University inGöttingen organized a technical meeting with the subject "Quality assurance and qualityimprovement for TTCN-3 test specifications". Participants from the Technical University ofBerlin, the University of Dortmund and the University of Göttingen presented and discussedtheir work in this field. This technical report documents the technical meeting. It includes theslides of the presentations and further unpublished material.
Paper
Helmut Neukirchen .Quality Assurance of TTCN-3 Test Suites. Universität Osnabrück, November 2006,
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The comprehensive test of modern software systems leads to large andcomplex test suites which have to be maintained throughout the systemlife-cycle. Experience with test suites written in the standardisedTesting and Test Control Notation version 3 (TTCN-3) has shown thatthe development and maintenance of test suites is a non-trivial taskwhich requires strict quality assurance.To address these issues, this talk presents appropriate means:refactoring, metrics, and "smell" detection for TTCN-3. Refactoringrestructures a test suite systematically without changing itsbehaviour. Metrics are applicable to calculate numbers which can beused to assess the overall quality of test suites, but also toidentify locations where a refactoring is worthwhile. In some cases,simple metrics are not sufficient for the latter task, but apattern-based detection of inappropriate usage of TTCN-3 (so called"smells") is required. For the automation of these tasks, the TRexopen-source tool has been developed as a plug-in for the popularEclipse platform. TRex has successfully been applied to huge TTCN-3test suites from industry and standardisation.
Paper
Telemaco Melia , Antonio De La Oliva, Ignacio Soto, Carlos Jesus Bernardos Cano, Albert Vidal.Analysis of the effect of mobile terminal speed on WLAN/3G vertical handovers. IEEE GLOBECOM 2006, San Francisco, CA, USA, 2006
Jan Demter.Prototyping and Testing of GONE - GIST Overlay Networking Extension. Bachelor's thesis, No. ZFI-BM-2006-37, Center for Computer Science, University of Goettingen, Germany, 2006
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This thesis provides an implementation of the GIST Overlay Network Extension (GONE) and its initial performance testing. GONE is an overlay network built upon the General Internet Signaling Transport (GIST) and the Stream Control Transmission Protocol (SCTP). GIST enables GONE to automatically build an overlay along a path in an IP-network with GONE-aware routers. Each GONE-aware hop forwards traffic to the next hop via an SCTP connection, making GONE resilient to path failures due to SCTP’s failover mechanism. Protection against DoS-attacks is employed by using a per-packet capability based authentication. The thesis investigates how the functionality offered by GIST can be used in implementing a path overlay. Problems with the concept of GONE surfacing during implementation and testing are pointed out and possible solutions or hints for further research and testing are given.
Paper
Erik Behrends , Oliver Fritzen , Wolfgang May , Franz Schenk , Daniel Schubert.A Framework and Components for ECA Rules in the Web (Demo).
International Conference on
Rules and Rule Markup Languages for the Semantic Web
(RuleML 2006; Demonstration Session), Athens, Georgia, USA, 2006
Erik Behrends , Oliver Fritzen , Wolfgang May , Franz Schenk .Combining ECA Rules with Process Algebras for the
Semantic Web.
International Conference on
Rules and Rule Markup Languages for the Semantic Web
(RuleML 2006), Athens, Georgia, USA, IEEE Comp. Sc. Press, pages 29-38, 2006
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We describe how Event-Condition-Action (ECA) rules can be combined with Process Algebras like CCS as specification of the action part to obtain a powerful, declarative formalism that also covers intuitively procedural tasks in an appropriate way. Since both formalisms have a concise formal semantics, verification and other kinds of reasoning about such specifications are possible. Using a rule markup with cleanly distinguished rule components allows for such a compositional approach. The approach is currently under implementation in a General ECA Framework for the Web and the Semantic Web.
Xiaoming Fu .From Resource Reservation to Extensible IP Signaling. Habilitation Thesis, Mathematische Fakultaet, Universitaet Goettingen, Goettingen, Germany, 2006
Xiaoming Fu , Dieter Hogrefe , Jun Lei .Dynamic Mesh-based overlay Multicast Protocol (DMMP). Internet Research Task Force, Internet draft (draft-lei-samrg-dmmp-01), work in progress, Scalable Adaptive Multicast (SAM) Research Group, 2006
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This document describes a Dynamic Mesh-based overlay Multicast Protocol (DMMP) to support multicast data delivery applications without relying on classic IP multicast, including multicast group management, overlay hierarchy establishment, multicast tree construction and data forwarding scheme from the source to a number of receivers. The DMMP framework builds on control plane functions which dynamically manage an overlay core and a multicast tree layer. The key idea is a number of end hosts self-organize into an overlay mesh, and dynamically maintain such a mesh. Based on the constructed mesh, some core-based clusters are built with capacity-aware trees inside. Then, a multicast tree consisting of DMMP-aware end hosts (and/or specific routers) is built on the top of the overlay core for the efficient delivery of the multicast data.
Paper
Xiaoming Fu.From Resource Reservation to Extensible IP Signaling. Habilitation Thesis, Mathematische Fakultaet, Universitaet Goettingen, Goettingen, Germany, 146 pages, 2006
Jun Lei, Xiaoming Fu, Dieter Hogrefe.Dynamic Mesh-based overlay Multicast Protocol (DMMP). Internet Research Task Force, Internet draft (draft-lei-samrg-dmmp-01), work in progress, Scalable Adaptive Multicast (SAM) Research Group, 2006
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This document describes a Dynamic Mesh-based overlay Multicast Protocol (DMMP) to support multicast data delivery applications without relying on classic IP multicast, including multicast group management, overlay hierarchy establishment, multicast tree construction and data forwarding scheme from the source to a number of receivers. The DMMP framework builds on control plane functions which dynamically manage an overlay core and a multicast tree layer. The key idea is a number of end hosts self-organize into an overlay mesh, and dynamically maintain such a mesh. Based on the constructed mesh, some core-based clusters are built with capacity-aware trees inside. Then, a multicast tree consisting of DMMP-aware end hosts (and/or specific routers) is built on the top of the overlay core for the efficient delivery of the multicast data.
Paper
Benjamin Zeiß , Helmut Neukirchen , Jens Grabowski , Dominic Evans, Paul Baker.TRex - An Open-Source Tool for Quality Assurance of TTCN-3 Test Suites. Proceedings of CONQUEST 2006 -- 9th International Conference on Quality Engineering in Software Technology, September 27-29, Berlin, Germany, dpunkt.Verlag, Heidelberg, 2006
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The comprehensive test of modern communication systems leads to large and complex test suites which have to be maintained throughout the system life-cycle. Experience with those written in the standardised Testing and Test Control Notation (TTCN-3) has shown that the maintenance of test suites is a non-trivial task and its burden can be reduced with appropriate tool support. To this aim, we have developed the TRex tool, published as open-source under the Eclipse Public License, which supports the assessment and automatic restructuring of TTCN-3 test suites by providing suitable metrics and refactorings. Besides presenting TRex and its functionality, the main contribution of this paper is the discussion of complexity metrics for TTCN-3 test suites.
Paper
Dennis Neumann.Testen der Web Services eines Lehrevaluationssystems. Bachelorbeit im Studiengang Angewandte Informatik am Institut für Informatik, ZFI-BM-2006-31, ISSN 1612-6793, Zentrum für Informatik, Georg-August-Universität Göttingen, 2006
Paper
Dieter Hogrefe , Rene Soltwisch , Constantin Werner .An Evaluation of Multi-Role Access Routers: Specification and Validation of an IDKE aware Access Router. Proceedings of the IEEE International Conference on Networks (ICON) 2006, Singapore, 2006
André Riedel , Timo Fischer.Achieving Pareto-efficient Bandwidth Allocations using a Non-Monetary Mechanism. IEEE International Conference on Innovative Computing, Information and Control (ICICIC'06), 2006
Dieter Hogrefe , André Riedel , Timo Fischer.Optimising WiMAX Business Models using Incentive Engineering. IEEE International Conference on Networks (ICON?06), 2006
Paul Baker, Dominic Evans, Jens Grabowski , Helmut Neukirchen , Benjamin Zeiß .TRex -- The Refactoring and Metrics Tool for TTCN-3 Test Specifications. Proceedings of TAIC PART 2006 (Testing: Academic & Industrial Conference - Practice And Research Techniques), Cumberland Lodge, Windsor Great Park, UK, 29th-31st August 2006. Copyright IEEE Computer Society 2006. DOI: 10.1109/TAIC-PART.2006.35 , 90-94, IEEE Computer Society, 2006
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Comprehensive testing of modern communication systems often requires large and complex test suites which then have to be maintained throughout the system life-cycle. Industrial experience, with those written in the standardised Testing and Test Control Notation (TTCN-3), has shown that this maintenance is a non-trivial task and its burden could be reduced if appropriate tool support existed. To this aim, Motorola has collaborated with the University of Göttingen to develop TRex, a TTCN-3 development environment published under the Eclipse Public License, which notably provides suitable metrics and refactorings to enable the assessment and automatic restructuring of test suites. In this paper we present the TRex tool, which will make it far easier to construct and maintain TTCN-3 tests that are concise and optimally balanced with respect to readability, usability, and maintainability.
Paper
Benjamin Zeiß , Helmut Neukirchen , Jens Grabowski , Dominic Evans, Paul Baker.TRex -- The Refactoring and Metrics Tool for TTCN-3 Test Specifications. Technical Report, IFI-TB-2006-02, ISSN 1611-1044, Institute for Informatics, University of Göttingen, Germany, August 2006,
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The comprehensive test of modern communication systems leads to large and complextest suites which have to be maintained throughout the system life-cycle. Experiencewith those written in the standardised Testing and Test Control Notation (TTCN-3) hasshown that the maintenance of test suites is a non-trivial task and its burden can bereduced with appropriate tool support. To this aim, we have developed the TRex tool,published as open-source tool under the Eclipse Public License, which supports theassessment and automatic restructuring of TTCN-3 test suites by providing suitablemetrics and refactorings. This paper presents TRex, its functionality, and its implementation.
Paper
Xiaoming Fu , Hannes Tschofenig.Securing the Next Steps in Signalling (NSIS) Protocol Suite. International Journal of Internet Protocol Technology, Volume 1, No. 4, pages 271-282, InderScience Publishers, 2006
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The Next Steps In Signalling (NSIS) protocol suite represents an extensible framework for enabling various signalling applications over IP-based networks. The framework consists of two layers that need different types of security protection; the lower layer mainly deals with the discovery of adjacent peers and establishment of channel security to protect the delivery of signalling messages between two peers, while the upper layer provides the signalling application specific functionalities. Different security properties are required at the two layers with stronger authorisation functionality at the signalling application layer. In this paper we examine how various security vulnerabilities can be utilised by an adversary, including eavesdropping, Man-In-The-Middle (MITM) attacks, fraud and Denial of Service (DoS) attacks. Moreover, we describe how to protect against a number of selected security threats and highlight some security challenges that require further research.
Paper
Hannes Tschofenig, Xiaoming Fu.Securing the Next Steps in Signalling (NSIS) Protocol Suite. International Journal of Internet Protocol Technology, Volume 1, No. 4, pages 271-282, InderScience Publishers, 2006
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The Next Steps In Signalling (NSIS) protocol suite represents an extensible framework for enabling various signalling applications over IP-based networks. The framework consists of two layers that need different types of security protection; the lower layer mainly deals with the discovery of adjacent peers and establishment of channel security to protect the delivery of signalling messages between two peers, while the upper layer provides the signalling application specific functionalities. Different security properties are required at the two layers with stronger authorisation functionality at the signalling application layer. In this paper we examine how various security vulnerabilities can be utilised by an adversary, including eavesdropping, Man-In-The-Middle (MITM) attacks, fraud and Denial of Service (DoS) attacks. Moreover, we describe how to protect against a number of selected security threats and highlight some security challenges that require further research.
Paper
Xiaoming Fu , Niklas Steinleitner , Henning Peters, Hannes Tschofenig.Implementation and Performance Study of a New NAT/Firewall Signaling Protocol. in Proceedings of the 26th International Conference on Distributed Computing Systems-Workshops (ICDCSW 2006), the 5th International Workshop on Assurance in Distributed Systems and Networks (ADSN2006), Lisboa, Portugal, IEEE Computer Society, 2006
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The NAT/Firewall NSIS Signaling Layer Protocol (NAT/FW NSLP) is a path-coupled signaling protocol for explicit Network Address Translator and firewall configuration within an extensible IP signaling framework currently being developed by the IETF Next Steps in Signaling (NSIS) working group. This new protocol allows end hosts to signal along a path to configure NATs and firewalls according to the data flow needs. In this paper we present a first open source implementation and performance evaluation of the NAT/FW NSLP protocol. The implementation utilizes a generic state machine template and can automatically generate source code for message handling classes. The performance study shows that our implementation scales well and is able to support firewall signaling for up to tens of thousands of flows in parallel even in a low-end PC testbed environment. The overall performance bottleneck is found to lie in the utilized firewall implementation, not depending on the NAT/FW NSLP implementation.
Paper
Xiaoming Fu , Dieter Hogrefe , Jun Lei .DMMP: A New Dynamic Mesh-based Overlay Multicast Protocol Framework. Technical Report No. IFI?TB?2006?05, Institute for Informatics, University of Goettingen, Germany, 2006
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Multicasting provides an efficient way of delivering data from a sender to a group of receivers. It has been gained much attention over the past decade because of an increasing demand for group communication applications such as multimedia streaming. Compared with network layer multicast solutions, recent application-layer multicast and overlay multicast approaches provide a new way of handling multicast without upgrading the infrastructure in a large scale. Meanwhile, they introduce a number of challenges and are still plagued with concerns pertaining to scalability, deployment, heterogeneity and dynamic performance. In this paper we propose a new protocol framework for relieving these issues, so-called the Dynamic Mesh-based Overlay Multicast Protocol or DMMP, which intends to provide an efficient and reliable multicast support by dynamically managing an overlay core comprised of end hosts. Although more analysis and evaluation is necessary, this paper sheds light on several identified design issues with DMMP and initially analyzes its performance.
Paper
Niklas Steinleitner, Henning Peters, Xiaoming Fu, Hannes Tschofenig.Implementation and Performance Study of a New NAT/Firewall Signaling Protocol. in Proceedings of the 26th International Conference on Distributed Computing Systems-Workshops (ICDCSW 2006), the 5th International Workshop on Assurance in Distributed Systems and Networks (ADSN2006), Lisboa, Portugal, IEEE Computer Society, 2006
Read abstract
The NAT/Firewall NSIS Signaling Layer Protocol (NAT/FW NSLP) is a path-coupled signaling protocol for explicit Network Address Translator and firewall configuration within an extensible IP signaling framework currently being developed by the IETF Next Steps in Signaling (NSIS) working group. This new protocol allows end hosts to signal along a path to configure NATs and firewalls according to the data flow needs. In this paper we present a first open source implementation and performance evaluation of the NAT/FW NSLP protocol. The implementation utilizes a generic state machine template and can automatically generate source code for message handling classes. The performance study shows that our implementation scales well and is able to support firewall signaling for up to tens of thousands of flows in parallel even in a low-end PC testbed environment. The overall performance bottleneck is found to lie in the utilized firewall implementation, not depending on the NAT/FW NSLP implementation.
Paper
Jun Lei, Xiaoming Fu, Dieter Hogrefe.DMMP: A New Dynamic Mesh-based Overlay Multicast Protocol Framework. Technical Report No. IFI-TB-2006-05, Institute of Computer Science, University of Goettingen, Germany, 2006
Read abstract
Multicasting provides an efficient way of delivering data from a sender to a group of receivers. It has been gained much attention over the past decade because of an increasing demand for group communication applications such as multimedia streaming. Compared with network layer multicast solutions, recent application-layer multicast and overlay multicast approaches provide a new way of handling multicast without upgrading the infrastructure in a large scale. Meanwhile, they introduce a number of challenges and are still plagued with concerns pertaining to scalability, deployment, heterogeneity and dynamic performance. In this paper we propose a new protocol framework for relieving these issues, so-called the Dynamic Mesh-based Overlay Multicast Protocol or DMMP, which intends to provide an efficient and reliable multicast support by dynamically managing an overlay core comprised of end hosts. Although more analysis and evaluation is necessary, this paper sheds light on several identified design issues with DMMP and initially analyzes its performance.
Paper
Benjamin Zeiß .TRex -- An Eclipse-Based Tool for TTCN-3 Editing, Refactoring and Metrics. TTCN-3 workshop at Siemens Corporate Technology, Software & Engineering, München, June 2006,
Dieter Hogrefe , Constantin Werner , Sebastian Kraatz.UML Profile for Communicating Systems. Proceedings of SAM'06 -- Fifth Workshop on System Analysis and Modelling (formerly SDL and MSC Workshop), May 31st-June 2nd 2006, University of Kaiserslautern, Kaiserslautern, Germany, pp. 81-90, 2006
Michael Ebner , Constantin Werner , Jürgen Jähnert, Yongzheng Liang.Daidalos - A Scenario based approach from Scenarios towards Integration. Joint MAGNET Workshop, Myconos, Greece, 2006
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In the IST Daidalos Project a blueprint of the next generation Beyond 3G Systems is designed, developed and demonstrated integrating mobile and broadcast communications. Daidalos delivers pervasive end-to-end services across heterogeneous technologies. This require the development of key technologies as demonstrated by the Daidalos five key concepts which are MARQS (Mobility Management, AAA, Resource Management, QoS and Security), VID (Virtual Identity), USP (Ubiquitous and Seamless Pervasiveness), SIB (Seamless Integration of Broadcast and Federation The Daidalos results ? architectural framework, conceptual solutions, software components and sub-systems, and the overall demonstrators based on two scenarios ? will contribute to the next generation of networks. Having this goal, an appropriate methodology on how to guide the overall development process is required, which relies on formal methods and tools which closely follows a scenario based overall design defining a ?red line? along the overall work of any activity from the formal definition of a scenario down to the final integration.
Telemaco Melia , Joao Girao, Bernd Lamparter, Marco Liebsch.A Practical Approach to Provide Communication Privacy. IEEE ICC 2006, Istanbul, Turkey, 2006
Xiaodong Yang , Yong-Hua Song, Thomas J. Owens, John Cosmas, Takebumi Itagaki.Incorporating digital repeaters into the soft handover standard in digital video broadcasting for handhelds. International Journal of Services and Standards, 2(3): 238 - 256, InderScience Publishers, 2006
Read abstract
Digital Video Broadcasting for Handhelds (DVB-H) is a standard for broadcasting IP data to portable devices. This paper proposes and analyses the Repeater-Aided Soft Handover (RA_handover) algorithm for a DVB-H receiver with Multiple Input?Multiple Output (MIMO) antennas and presents the benefits of implementing the RA_handover compared with a handover process without repeaters. Simulation models are developed to analyse the RA_handover approach. It is shown that the RA_handover could greatly improve the quality of service and consume much less front-end battery power than the handover method without repeaters. This paper also provides valuable outcomes for service providers and standard policymakers.
Xiaoming Fu.Modelling Soft-State Protocols with SDL. IEE Proceedings Communications, 2006
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The notion of soft state has been introduced in packet-switched networks to achieve particular services for end-to-end communications, such as quality-of-service provisioning and configuration of stateful packet filters. Protocols built upon soft state principles were believed to be simple, however in practice they are far more complex. An important issue with such protocols is to ensure their operations to be error-free and deadlock-free. In the paper the use of formal techniques is proposed, specifically, Specification and Description Language (SDL) and Message Sequence Charts (MSCs), for modelling, analysis and validation of soft-state protocols. Based on a general state management system that identifies their most representative behaviour, an extensive study on modelling and validating soft-state protocols with SDL/MSCs is presented, and it is shown that design flaws and ambiguity introduced in informally specified, textual protocols can be avoided if a protocol is formally modelled.
Paper
Xiaodong Yang, Yong-Hua Song, Thomas J. Owens, John Cosmas, Takebumi Itagaki.Incorporating digital repeaters into the soft handover standard in digital video broadcasting for handhelds. International Journal of Services and Standards, 2(3): 238 - 256, InderScience Publishers, 2006
Read abstract
Digital Video Broadcasting for Handhelds (DVB-H) is a standard for broadcasting IP data to portable devices. This paper proposes and analyses the Repeater-Aided Soft Handover (RA_handover) algorithm for a DVB-H receiver with Multiple Input?Multiple Output (MIMO) antennas and presents the benefits of implementing the RA_handover compared with a handover process without repeaters. Simulation models are developed to analyse the RA_handover approach. It is shown that the RA_handover could greatly improve the quality of service and consume much less front-end battery power than the handover method without repeaters. This paper also provides valuable outcomes for service providers and standard policymakers.
Paper
Wolfgang May .An Ontology-Based Approach to Integrating Behavior in the Semantic Web. Second International
Workshop on Exchange and Integration of Data, Brixen-Bressanone, Italy, 2006
José Júlio Alferes, James Bailey, Wolfgang May , Uta Schwertel.Workshop on
Principles and Practice of Semantic Web Reasoning
(PPSWR 2006). , LNCS 4187, Springer, 2006
Wolfgang May , Franz Schenk , Elke von Lienen.Extending an OWL Web Node with Reactive Behavior. Workshop on
Principles and Practice of Semantic Web Reasoning
(PPSWR 2006), Budva, Montenegro, LNCS 4187, Springer, pages 134-148, 2006
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We describe an extension of an OWL knowledge base using PostgreSQL, Jena, and Pellet with active rules in form of triggers. The triggers react on atomic events on the OWL level. In contrast to ``simple′′ RDF triggers that can directly be mapped on updates on RDF triples, the extension to RDFS and OWL requires to combine reactivity with OWL reasoning. For this, ``direct′′, pre-reasoning triggers that react on update operations (often also providing support for the intended operation), and ``indirect′′, post-reasoning triggers that react on actual changes have to be distinguished. The approach has been implemented in a prototype based on the Jena framework.
Paul Baker, Dominic Evans, Jens Grabowski , Helmut Neukirchen , Benjamin Zeiß .TRex: An Eclipse plug-in tool for TTCN-3 Editing, Refactoring, and Metrics. Proceedings of 'The TTCN-3 User Conference 2006' (T3UC), 31 May - 02 June 2006, Berlin, Germany,
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This presentation describes the recent development of the TRex Eclipseplug-in to address the needs for improved TTCN-3 specification. In particular, the presentation will discuss the motivation for the tool, providing an overview of the Eclipse plug-in tool capabilities, including editing features, refactoring, and metrics.Following experiences within Motorola the presentation will introducerefactoring rules and metrics that have been specifically implemented to aid the usability and maintainability of TTCN-3 templates. Simple metrics have been introduced to aid the assessment of potential maintenance issues and refactoring rules to address usability. The refactoring rules describe systematically how to restructure TTCN-3 template specifications of a test suite without changing the behaviour of the test suite. The result is a test suite which is easier to understand and cheaper to modify.
Paper
Xiaoming Fu , Jon Crowcroft.GONE: an Infrastructure Overlay for Resilient, DoS-Limiting Networking. Proceedings of the 16th ACM International Workshop on Network and Operating Systems Support for Digital Audio and Video (NOSSDAV 2006), Newport, Rhode Island, USA, ACM, 2006
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With today′s penetration in volume and variety of information flowing across the Internet, data and services are experiencing various issues with the TCP/IP infrastructure, most notably availability, reliability and mobility. Therefore, a critical infrastructure is highly desireable, in particular for multimedia streaming applications. So far the proposed approaches have focused on applying application-layer routing and path monitoring for reliability and on enforcing stateful packet filters in hosts or network to protect against Denial of Service (DoS) attacks. Each of them solves its own aspect of the problem, trading scalability for availability and reliability among a relatively small set of nodes, yet there is no single overall solution available which addresses these issues in a large scale.We propose an alternative overlay network architecture by introducing a set of generic functions in network edges and end hosts. We conjecture that the network edge constitutes a major source of DoS, resilience and mobility issues to the network, and propose a new solution to this problem, namely the General Internet Signaling Transport (GIST) Overlay Networking Extension, or GONE. The basic idea of GONE is to create a half-permanent overlay mesh consisting of GONE-enabled edge routers, which employs capability-based DoS prevention and forwards end-to-end user traffic using the GIST messaging associations. GONE′s use of GIST on top of SCTP allows multi-homing, multi-streaming and partial reliability, while only a limited overhead for maintaining the messaging association is introduced. In addition, upon the services provided by GONE overlays, hosts are identified by their unique host identities independent of their topologies location, and simply require (de-) multiplexing instead of the traditional connection management and other complex functionality in the transport layer. As a result, this approach offers a number of advantages for upper layer end-to-end applications, including intrinsic provisioning of resilience and DoS prevention in a dynamic and nomadic environment.
Paper
Fang-Chun Kuo , Ronald YS Tee, Lajos Hanzo.Generalized Low-Density Parity-Check Coding Aided Multilevel Codes. Proc. of the VTC2006-Spring, Melbourne, Australia, 2006
Xiaoming Fu, Jon Crowcroft.GONE: an Infrastructure Overlay for Resilient, DoS-Limiting Networking. Proceedings of the 16th ACM International Workshop on Network and Operating Systems Support for Digital Audio and Video (NOSSDAV 2006), Newport, Rhode Island, USA, ACM, 2006
Read abstract
With today′s penetration in volume and variety of information flowing across the Internet, data and services are experiencing various issues with the TCP/IP infrastructure, most notably availability, reliability and mobility. Therefore, a critical infrastructure is highly desireable, in particular for multimedia streaming applications. So far the proposed approaches have focused on applying application-layer routing and path monitoring for reliability and on enforcing stateful packet filters in hosts or network to protect against Denial of Service (DoS) attacks. Each of them solves its own aspect of the problem, trading scalability for availability and reliability among a relatively small set of nodes, yet there is no single overall solution available which addresses these issues in a large scale.We propose an alternative overlay network architecture by introducing a set of generic functions in network edges and end hosts. We conjecture that the network edge constitutes a major source of DoS, resilience and mobility issues to the network, and propose a new solution to this problem, namely the General Internet Signaling Transport (GIST) Overlay Networking Extension, or GONE. The basic idea of GONE is to create a half-permanent overlay mesh consisting of GONE-enabled edge routers, which employs capability-based DoS prevention and forwards end-to-end user traffic using the GIST messaging associations. GONE′s use of GIST on top of SCTP allows multi-homing, multi-streaming and partial reliability, while only a limited overhead for maintaining the messaging association is introduced. In addition, upon the services provided by GONE overlays, hosts are identified by their unique host identities independent of their topologies location, and simply require (de-) multiplexing instead of the traditional connection management and other complex functionality in the transport layer. As a result, this approach offers a number of advantages for upper layer end-to-end applications, including intrinsic provisioning of resilience and DoS prevention in a dynamic and nomadic environment.
Paper
Wolfgang May .Reasoning im und für das Semantic Web. Semantic Web - Wege zur
vernetzten Wissensgesellschaft, pages 485-504, Springer, 2006
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Dieses Kapitel gibt zuerst einen kurzen historischen Überblick über "Reasoning", d.h., Schließen, Wissensrepräsentation und "künstliche Intelligenz". Der Hauptteil geht auf einige "Reasoning"-Mechanismen und -Konzepte, die im Semantic Web eine Rolle spielen, ein und zeigt, wie dieses "Reasoning" -unauffällig- in den Konzepten des Semantic Web zur Beschreibung von Wissensbasen enthalten ist. Weiterhin werden Reasoning-Mechanismen umrissen, die dem Zusammenspiel verschiedener Knoten im Semantic Web dienen und ein kurzes Fazit gezogen.
Benjamin Zeiß , Helmut Neukirchen , Jens Grabowski , Dominic Evans, Paul Baker.Refactoring for TTCN-3 Test Suites. Proceedings of SAM'06 --
Fifth Workshop on System Analysis and Modelling
(formerly SDL and MSC Workshop),
May 31st-June 2nd 2006,
University of Kaiserslautern,
Kaiserslautern, Germany, 2006,
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Experience with the development and maintenance of testsuites has shown that the Testing and Test Control Notation (TTCN-3)provides very good concepts for adequate test specification. However, experiencehas also demonstrated that during either the migration of legacytest suites to TTCN-3, or the development of large TTCN-3 test specifications,users have found it is difficult to construct TTCN-3 tests thatare concise with respect to readability, usability, and maintainability.To address these issues, this paper investigates refactoring for TTCN-3;systematically restructuring a test suite without changing its behaviour.Complementary metrics are suggested to assess the readability and maintainabilityof TTCN-3 test suites. For automation, a tool called TRexhas been developed that supports refactoring and metrics for TTCN-3.
Paper
Xiaoming Fu , Fang-Chun Kuo , Hannes Tschofenig, Fabian Meyer.Comparison Studies between Pre-Shared and Public Key Exchange Mechanisms for Transport Layer Security. Proceedings of the 9th IEEE Global Internet Symposium, in conjunction with IEEE INFOCOM 2006, Barcelona, Spain, pages 77-82, IEEE, 2006
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The pre-shared key based mechanisms for Transport Layer Security (TLS) were recently standardized by the IETF to extend the set of ciphersuites by utilizing existing key management infrastructures. The benefit of pre shared based mechanisms is the avoidance or reduction of the cryptographic operations used in public-key based mechanisms. However, so far there are no performance measurements for pre-shared key based ciphersuites available. In this paper, we present a systematic analysis and performance comparison between the pre-shared key exchange mechanisms and the standard public key exchange mechanisms in TLS. Our performance metrics are processingtime and transmitted amount of data for a handshake establishment. Furthermore, the interaction between the overall TLS handshake duration and the network environment is evaluated. The results for different key exchange mechanisms are comparatively studied and the design choices of pre-shared key based key exchange mechanisms have been validated. Experimental results give details about the performance improvement of the preshared key based mechanisms compared to the standard public key based mechanisms.
Paper
Fang-Chun Kuo , Lajos Hanzo.Symbol-Flipping Based Decoding of Generalized Low-Density Parity-Check Codes Constructed over GF(q). Proc. of the IEEE Wireless Communications and Networking Conference 2006, Las Vegas, NV USA, IEEE, 2006
Xiaoming Fu, Henning Schulzrinne, Hannes Tschofenig, Christian Dickmann, Dieter Hogrefe.Overhead and Performance Study of the General Internet Signaling Transport (GIST) Protocol. IEEE INFOCOM 2006, Bacelona, Spain, IEEE, 2006
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The General Internet Signaling Transport (GIST) protocol is currently being developed as the base protocol component in the IETF Next Steps In Signaling (NSIS) protocol stack to support a variety of signaling applications. In this paper we present our study on the protocol overhead and performance aspects of GIST. We quantify network-layer protocol overhead and observe the effects of enhanced modularity and security in GIST. We developed a first open source GIST implementation at the University of Göttingen, and study its performance in a Linux testbed. A GIST node serving 45,000 signaling sessions is found to consume small amounts of CPU and memory (on average 1.1ms for processing a signaling message and 2.4KB memory for a session). Individual routines in the GIST code are instrumented to obtain a detailed profile of their contributions to the overall system processing. Important factors in determining performance, such as the number of sessions, state management, refresh frequency, timer management and signaling message size are further discussed. We investigate several mechanisms to improve GIST performance so as to be comparable with an RSVP implementation.
Paper
Fang-Chun Kuo, Hannes Tschofenig, Fabian Meyer, Xiaoming Fu.Comparison Studies between Pre-Shared and Public Key Exchange Mechanisms for Transport Layer Security. Proceedings of the 9th IEEE Global Internet Symposium, in conjunction with IEEE INFOCOM 2006, Barcelona, Spain, pages 77-82, IEEE, 2006
Read abstract
The pre-shared key based mechanisms for Transport Layer Security (TLS) were recently standardized by the IETF to extend the set of ciphersuites by utilizing existing key management infrastructures. The benefit of pre shared based mechanisms is the avoidance or reduction of the cryptographic operations used in public-key based mechanisms. However, so far there are no performance measurements for pre-shared key based ciphersuites available. In this paper, we present a systematic analysis and performance comparison between the pre-shared key exchange mechanisms and the standard public key exchange mechanisms in TLS. Our performance metrics are processingtime and transmitted amount of data for a handshake establishment. Furthermore, the interaction between the overall TLS handshake duration and the network environment is evaluated. The results for different key exchange mechanisms are comparatively studied and the design choices of pre-shared key based key exchange mechanisms have been validated. Experimental results give details about the performance improvement of the preshared key based mechanisms compared to the standard public key based mechanisms.
Paper
Benjamin Zeiß .A Refactoring Tool for TTCN-3. Masterarbeit im Studiengang Angewandte Informatik am Institut für Informatik, ZFI-BM-2006-05, ISSN 1612-6793 (Tippfehlerbereinigte Version), Zentrum für Informatik, Georg-August-Universität Göttingen, 2006
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Software is continuously growing in size and getting more and more complex while developmentcycles are getting shorter. The resulting software aging effect leads to a decayin software quality causing maintainability problems and bugs. Software engineering techniqueslike modularization, object-orientation, design patterns, aspect-oriented programmingor refactoring have been developed to slow down the software aging effects, increaseflexibility and support reuse.Software tests written in the TTCN-3 core notation also suffer from the effects of softwareaging. Huge efforts are spent to maintain TTCN-3 test suites, but even standardized testsuites often consist of few files with a length of several ten-thousand lines each. Refactoringis a proven technique to systematically restructure code to improve its quality andmaintainability while preserving the semantics which can also be applied to TTCN-3.In this thesis, existing well known refactorings have been investigated for their applicabilityand a catalog with 20 specific refactorings for TTCN-3 is presented. In addition, a toolcalled TRex based on the Eclipse Platform has been implemented which provides the infrastructurefor automating TTCN-3 refactorings and corresponding sample implementationsof TTCN-3 refactorings.
Paper
Dieter Hogrefe , Constantin Werner .UML Profile for Communicating Systems. Technical Report No. IFI-TB-2006-03, Institute for Informatics, University of Goettingen, Germany, 2006
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This report presents a UML2 profile for communicating systems. It is driven by the experience of SDL and provides XMI based mapping from UML to SDL-2000 but it is not limited to SDL. It features language elements for high-level specification and description of Internet communication and signaling protocols where SDL is partly cumbersome. Due to its support of several concrete notations, this profile is aligned to work with most UML 2 compliant modeling tools. This report describes all stereotypes which are defined in this profile, gives an informal semantic description and proposes concrete notations.
Henning Peters.Analysis of NAT Approaches and Explicit Signaling for NAT Traversal. Bachelor's thesis, No. ZFI-BM-2006-09, Zentrum fuer Informatik, Universitaet Goettingen, 2006
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Network Address Translation (NAT) provides a solution for IPv4 address depletion and Internet scalability problems at large. NAT has since been unexpectedly popular, and it is in wide use today, especially in home and small office environments. Unfortunately, it has major drawbacks, most fundamental is the maintenance of states inside the network, challenging the Internet?s end-to-end principle. This thesis analyzes these very promising NAT approaches, and tries to compare the approaches with each other. Furthermore, an applicability statement for implicit and explicit NAT configuration is given and an implementation of NAT/Firewall NSLP proves the feasibility of an yet uncommon explicit signaling approach.
Paper
Erik Behrends , Oliver Fritzen , Wolfgang May .Handling Interlinked XML Instances on the Web. 10th.
Intl. Conference on Extending
Database Technology (EDBT'06), Munich, Germany, LNCS 3896, Springer, pages 792-810, 2006
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XML instances are not necessarily self-contained but may have links to remote XML data residing on other servers. Links between (autonomous) XML instances can be expressed by the XLink language; although, querying such interlinked sources is not yet actually supported.
Erik Behrends , Oliver Fritzen , Wolfgang May .Querying along XLinks in XPath/XQuery:
Situation, Applications, Perspectives.
11th International Workshop on
Foundations of Models and Languages for Data and Objects (FMLDO):
QLQP-2006 "Query Languages and Query Processing", Munich, Germany, LNCS 4254 (EDBT Workshops), Springer, pages 662-674, 2006
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This paper summarizes the situation about using XLink for connecting XML instances. We discuss applications where XLink functionality can be useful, and derive requirements how the basic XLink technology should be supported in these scenarios. We compare several proposals dealing with interlinked XML data with our dbxlink approach which is a minimal extension to XLink and XPath, and we show how its semantics can be added to arbitrary XPath-based query engines.
Erik Behrends , Oliver Fritzen , Wolfgang May , Daniel Schubert.An ECA Engine for Deploying Heterogeneous Component Languages
in the Semantic Web. EDBT-Workshop
'Reactivity on the Web', Munich, Germany, LNCS 4254 (EDBT Workshops), Springer, pages 887-898, 2006
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We describe a generic ECA service for implementing beha
