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Technical Reports of the Institute for Informatics
2009
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.
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
2008
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.
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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
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.
2007
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
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
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
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
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 , 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
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
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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
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.
Xiaoming Fu , Fang-Chun Kuo , Hannes Tschofenig, Fabian Meyer.Comparison Studies between Pre-Shared Key and Public Key Exchange Mechanisms for Transport Layer Security (TLS). Technical Report No. IFI-TB-2006-01, Institute for Informatics, University of Göttingen, Göttingen, Germany, 2006
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The public-key based handshake process of TLS is regarded as part of bottleneck that significantly degrades the performance. The pre-shared key based key exchange mechanisms for TLS were recently standardized by the IETF for avoiding or reducing the cryptographic operations in public-key based mechanisms. However, so far there is no performance measurement for pre-shared key based key exchange suites available. In this paper, we present a systematic analysis of performance comparison between the pre-shared key exchange mechanisms and the standard public key exchange mechanisms in TLS. Our performance metrics are the processing time in both slow and fast processor machines as well as the transmitted data amount for a handshake establishment. Furthermore, the interaction of 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. It has been observed that pre-shared key based mechanisms perform better than the standard public key based mechanisms.
Paper
Fang-Chun Kuo, Hannes Tschofenig, Fabian Meyer, Xiaoming Fu.Comparison Studies between Pre-Shared Key and Public Key Exchange Mechanisms for Transport Layer Security (TLS). Technical Report No. IFI-TB-2006-01, Institute of Computer Science, University of Göttingen, Göttingen, Germany, 2006
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The public-key based handshake process of TLS is regarded as part of bottleneck that significantly degrades the performance. The pre-shared key based key exchange mechanisms for TLS were recently standardized by the IETF for avoiding or reducing the cryptographic operations in public-key based mechanisms. However, so far there is no performance measurement for pre-shared key based key exchange suites available. In this paper, we present a systematic analysis of performance comparison between the pre-shared key exchange mechanisms and the standard public key exchange mechanisms in TLS. Our performance metrics are the processing time in both slow and fast processor machines as well as the transmitted data amount for a handshake establishment. Furthermore, the interaction of 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. It has been observed that pre-shared key based mechanisms perform better than the standard public key based mechanisms.
Paper
2005
Xiaoming Fu , Henning Schulzrinne, Hannes Tschofenig, Jochen Eisl.A Quality-of-Service Resource Allocation Client for CASP. Technical Report No. TB-IFI-2005-07, Institute for Informatics, University of Goettingen, Germany, 2005
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Signaling resource reservations is one of the possible applications of the Cross-Application Signaling Protocol (CASP). This document describes a client protocol that supports per-flow resource reservationin both sender- and receiver-directed modes operation.
Paper
Xiaoming Fu , Hannes Tschofenig, Henning Schulzrinne, Robert Hancock, Andrew McDonald.Security Implications of the Session Identifier. Technical Report No. TB-IFI-2005-08, Institute for Informatics, University of Goettingen, Germany, 2005
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As one result of the analysis activities in the NSIS group it was realized that mobility and the ability to change the flow identifier causes problems with existing QoS reservations. To be able to associate a signaling message with existing state an identifier other than the flow identifier had to be used. Such an abstraction is achieved with the session identifier which allows identification of established state independently of the flow characteristics.Although the introduction of a session identifier sounds simple and beneficial, it introduces a problem which is subsequently referred to as the session ownership problem.This document describes the session ownership problem, the implications for an NSIS protocol and summarizes already discussed solutions.
Paper
Jun Lei, Ingo Juchem, Xiaoming Fu, Dieter Hogrefe.Architectural Thoughts and Requirements Considerations on Video Streaming over the Internet. Technical Report No. IFI-TB-2005-06, Institute of Computer Science, University of Goettingen, Germany, 2005
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With increasing demands of multimedia information over the Internet, video streaming has been received explosive attentions. With respect to the real-time nature of video streaming, instable bandwidth, latency, noise, packet loss, retransmission and out of order packet delivery are all problems that can affect video streaming over the Internet. However, the traditional Internet traffic is not sensitive to these problems. Based on the general video streaming architecture, we give out some considerations on design and architectural mechanisms, namely, media server, media compression, media QoS control, media distribution services, media security mechanisms and protocol stacks for video streaming. For each of these areas, we present some existing methods and implementations. Then we propose architecture via overlay multicast integrated with proxy caching to achieve efficiency, flexibility and scalability. Finally, we conclude this issue and point out the research direction.
Paper
Henning Schulzrinne, Hannes Tschofenig, Xiaoming Fu, Jochen Eisl.A Quality-of-Service Resource Allocation Client for CASP. Technical Report No. TB-IFI-2005-07, Institute of Computer Science, University of Goettingen, Germany, 2005
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Signaling resource reservations is one of the possible applications of the Cross-Application Signaling Protocol (CASP). This document describes a client protocol that supports per-flow resource reservationin both sender- and receiver-directed modes operation.
Paper
Hannes Tschofenig, Henning Schulzrinne, Robert Hancock, Andrew McDonald, Xiaoming Fu.Security Implications of the Session Identifier. Technical Report No. TB-IFI-2005-08, Institute of Computer Science, University of Goettingen, Germany, 2005
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As one result of the analysis activities in the NSIS group it was realized that mobility and the ability to change the flow identifier causes problems with existing QoS reservations. To be able to associate a signaling message with existing state an identifier other than the flow identifier had to be used. Such an abstraction is achieved with the session identifier which allows identification of established state independently of the flow characteristics.Although the introduction of a session identifier sounds simple and beneficial, it introduces a problem which is subsequently referred to as the session ownership problem.This document describes the session ownership problem, the implications for an NSIS protocol and summarizes already discussed solutions.
Paper
Xiaoming Fu , Dieter Hogrefe , Deguang Le , Xiaoyuan Gu.E2T: End-to-End Tunneling Extension to Mobile IPv6. Technical Report No. IFI-TB-2005-05, Institute for Informatics, University of Göttingen, 2005
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In the standard Mobile IPv6, route optimization or bidirectional tunnelling through the home agent show inefficiency in per-packet forwarding, especially when both communicating endpoints are mobile. To be scalable and compatible, mobile devices? packets should be forwarded in a way 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 mobile devices.In this paper, following a performance analysis of Mobile IPv6 routing mechanisms, we present the E2T - an extension to Mobile IPv6 for routing packets. It reduces per-packet forwarding cost for the communications of mobile devices. With this approach, packets are routed thorough end-to-end tunnelling between communicating endpoints, which requires little change to Mobile IPv6, but allows more efficient forwarding behavior. The numerical analysis and simulation results show it requires less overhead than the standard route optimization and it helps to achieve a low end-to-end traffic delay.
Paper
Deguang Le, Xiaoming Fu, Xiaoyuan Gu, Dieter Hogrefe.E2T: End-to-End Tunneling Extension to Mobile IPv6. Technical Report No. IFI-TB-2005-05, Institute of Computer Science, University of Göttingen, Göttingen, Germany, 2005
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In the standard Mobile IPv6, route optimization or bidirectional tunnelling through the home agent show inefficiency in per-packet forwarding, especially when both communicating endpoints are mobile. To be scalable and compatible, mobile devices? packets should be forwarded in a way 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 mobile devices.In this paper, following a performance analysis of Mobile IPv6 routing mechanisms, we present the E2T - an extension to Mobile IPv6 for routing packets. It reduces per-packet forwarding cost for the communications of mobile devices. With this approach, packets are routed thorough end-to-end tunnelling between communicating endpoints, which requires little change to Mobile IPv6, but allows more efficient forwarding behavior. The numerical analysis and simulation results show it requires less overhead than the standard route optimization and it helps to achieve a low end-to-end traffic delay.
Paper
Rene Soltwisch , Florian Tegeler.Review of CasperFDR Analysis of the IDKE Protocol. Technical Report No. IFI-TB-2005-04, Institute for Informatics, University of Göttingen, Germany, 2005
Florian Tegeler, Rene Soltwisch.Review of CasperFDR Analysis of the IDKE Protocol. Technical Report No. IFI-TB-2005-04, Institute of Computer Science, University of Göttingen, Germany, 2005
Xiaoming Fu , Niklas Steinleitner , Jan Demter, Christian Dickmann, Henning Peters.Performance Analysis of the TCP/IP Stack of Linux Kernel 2.6.9. Technical Report No. IFI-TB-2005-03, Institute for Informatics, University of Göttingen, Germany, 2005
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This document reports the project "performance study of the TCP/IP stack for the Linux kernel" which we performed during the practical course Computer Networks in winter semester 2004/05, including its design, implementation and performance results. We analysed the packet processing time traversing each layer of the Linux kernel 2.6.9 TCP/IP stack (socket, TCP/UDP, IP and Ethernet) and the influence of multi-threading and different packet sizes. The design is based on the idea of inserting probing points via hooks in the kernel code and export timing data to a userspace application. A packet generator and analysis tools were also developed. The results demonstrate a number of key concepts in TCP/IP networking, such as layering, user-system interface, connection versus datagram modes, processing routines and their overhead in different layers. Some preliminary results reveal the system has its bottlenecks in different situations, and our tools released under GPL-license have been designed in such a way that allows easy extensibility for other networking diagnostics purposes.
Paper
Jan Demter, Christian Dickmann, Henning Peters, Niklas Steinleitner, Xiaoming Fu.Performance Analysis of the TCP/IP Stack of Linux Kernel 2.6.9. Technical Report No. IFI-TB-2005-03, Institute of Computer Science, University of Göttingen, Germany, 2005
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This document reports the project "performance study of the TCP/IP stack for the Linux kernel" which we performed during the practical course Computer Networks in winter semester 2004/05, including its design, implementation and performance results. We analysed the packet processing time traversing each layer of the Linux kernel 2.6.9 TCP/IP stack (socket, TCP/UDP, IP and Ethernet) and the influence of multi-threading and different packet sizes. The design is based on the idea of inserting probing points via hooks in the kernel code and export timing data to a userspace application. A packet generator and analysis tools were also developed. The results demonstrate a number of key concepts in TCP/IP networking, such as layering, user-system interface, connection versus datagram modes, processing routines and their overhead in different layers. Some preliminary results reveal the system has its bottlenecks in different situations, and our tools released under GPL-license have been designed in such a way that allows easy extensibility for other networking diagnostics purposes.
Paper
Xiaoming Fu , Dieter Hogrefe , Deguang Le .A Review of Mobility Support Paradigms for the Internet. Technical Report No. IFI-TB-2005-01, Institute for Informatics, University of Göttingen, 2005
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With the development of mobile communication and Internet technology, there is a strong need to provide connectivity for roaming devices to communicate to other communication end points in the Internet at any time and anywhere. The key issue of this vision is how to support mobility in TCP/IP networks. In this paper, we review the TCP/IP protocol stack and analyze the problems associated with it in a mobile environment. We then investigate the mobility support techniques and existing solutions to provide mobility support in the Internet. We classify the proposed solutions based on the protocol layers and present examples for each category. We also provide a comparison of the different solutions belonging to different categories and in the same category, including their advantages and disadvantages, and conclude that there is no single solution perfectly addresses mobility support for the Internet.
Paper
Deguang Le, Xiaoming Fu, Dieter Hogrefe.A Review of Mobility Support Paradigms for the Internet. Technical Report No. IFI-TB-2005-01, Institute of Computer Science, University of Göttingen, 2005
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With the development of mobile communication and Internet technology, there is a strong need to provide connectivity for roaming devices to communicate to other communication end points in the Internet at any time and anywhere. The key issue of this vision is how to support mobility in TCP/IP networks. In this paper, we review the TCP/IP protocol stack and analyze the problems associated with it in a mobile environment. We then investigate the mobility support techniques and existing solutions to provide mobility support in the Internet. We classify the proposed solutions based on the protocol layers and present examples for each category. We also provide a comparison of the different solutions belonging to different categories and in the same category, including their advantages and disadvantages, and conclude that there is no single solution perfectly addresses mobility support for the Internet.
Paper
2004
Dieter Hogrefe , Rene Soltwisch .A Survey on Network Security - 2004. Technische Berichte des Instituts für Informatik an der Georg-August-Universität Göttingen, 2004
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Network Security Report from Network Security seminar hold in Wintersemester 2003/04, University Goettingen, Germany.
Paper
Xiaoming Fu , Dieter Hogrefe .Modeling Soft State Protocols with SDL. Technical Report No. IFI-TB-2004-02, Institute for Informatics, University of Göttingen, Germany, 2004
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Soft state enables new services to packet-switching networks by introducing a type of state in the network nodes which is refreshed by periodical messages otherwise expire. System designers build protocols that implement soft state concepts based on intuition or on high-level explanations believe that the design is "better" than hard state and soft state implementations should be robust, reliable and interoperable. As states in the network nodes are critical for both applications the and network infrastructure, the operations of soft state protocols, which tend to be designed more and more complex, need to be error-free and deadlock-free. Thus, verification, formal analysis and validation of these protocols become a vital task. In this paper we utilize formal techniques, specifically, Specification and Description Language (SDL) and Message Sequence Chart (MSC), for modeling, analysis and validation of general soft state protocols. We propose a general architecture of state management systems and find several points through the SDL/MSC modeling which may enrich the design, modeling and evaluation of real soft state protocols: 1) modeling these protocols using these techniques is feasible, 2) it can be possible to use these techniques to identify possible design errors and deadlocks/livelocks, which may be caused by imprecise informal specifications of these protocols.
Paper
Xiaoming Fu, Dieter Hogrefe.Modeling Soft State Protocols with SDL. Technical Report No. IFI-TB-2004-02, Institute of Computer Science, University of Göttingen, Germany, 2004
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Soft state enables new services to packet-switching networks by introducing a type of state in the network nodes which is refreshed by periodical messages otherwise expire. System designers build protocols that implement soft state concepts based on intuition or on high-level explanations believe that the design is "better" than hard state and soft state implementations should be robust, reliable and interoperable. As states in the network nodes are critical for both applications the and network infrastructure, the operations of soft state protocols, which tend to be designed more and more complex, need to be error-free and deadlock-free. Thus, verification, formal analysis and validation of these protocols become a vital task. In this paper we utilize formal techniques, specifically, Specification and Description Language (SDL) and Message Sequence Chart (MSC), for modeling, analysis and validation of general soft state protocols. We propose a general architecture of state management systems and find several points through the SDL/MSC modeling which may enrich the design, modeling and evaluation of real soft state protocols: 1) modeling these protocols using these techniques is feasible, 2) it can be possible to use these techniques to identify possible design errors and deadlocks/livelocks, which may be caused by imprecise informal specifications of these protocols.
Paper
Xiaoming Fu , Dieter Hogrefe , Sebastian Willert.Implementation and Evaluation of the Cross-Application Signaling Protocol (CASP). Technical Report No. IFI-TB-2004-001, Institute for Informatics, University of Göttingen, Germany, 2004
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In this report, we describe implementation aspects and performance results of a novel general signaling protocol for the Internet, the Cross-Application Signaling Protocol CASP). Much debate exists about the applicability of RSVP as a general signaling protocol in the Internet, particularly for its modularity, complexity, security and mobility support. Based on a layered architecture, the CASP design intends to address these challenges and unlike RSVP, it provides a simpler mechanism for reliability and security by re-using existing protocols for transporting signaling messages, and supports a wide range of signaling applications. While this concept is considered to be advantageous over RSVP signaling, the actual mechanisms and behaviors of the CASP implementation have not yet been explored. With our work, despite being still far from a final judgment, we try to shed light on this issue by presenting a first public CASP implementation and a preliminary study about its properties. Performance results show that even under heavy signaling loads, the round trip time of signaling messages is acceptable (appr. 5ms in serving more than 1000 simultaneous signaling client applications in the initiator each at a random refresh interval between 3s and 15s in our experiments), and the memory and CPU consumption of the implementation are low. Although further work will be necessary, critical design choices in CASP have been proved to be feasible.
Paper
Xiaoming Fu, Dieter Hogrefe, Sebastian Willert.Implementation and Evaluation of the Cross-Application Signaling Protocol (CASP). Technical Report No. IFI-TB-2004-001, Institute of Computer Science, University of Göttingen, Germany, 2004
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In this report, we describe implementation aspects and performance results of a novel general signaling protocol for the Internet, the Cross-Application Signaling Protocol CASP). Much debate exists about the applicability of RSVP as a general signaling protocol in the Internet, particularly for its modularity, complexity, security and mobility support. Based on a layered architecture, the CASP design intends to address these challenges and unlike RSVP, it provides a simpler mechanism for reliability and security by re-using existing protocols for transporting signaling messages, and supports a wide range of signaling applications. While this concept is considered to be advantageous over RSVP signaling, the actual mechanisms and behaviors of the CASP implementation have not yet been explored. With our work, despite being still far from a final judgment, we try to shed light on this issue by presenting a first public CASP implementation and a preliminary study about its properties. Performance results show that even under heavy signaling loads, the round trip time of signaling messages is acceptable (appr. 5ms in serving more than 1000 simultaneous signaling client applications in the initiator each at a random refresh interval between 3s and 15s in our experiments), and the memory and CPU consumption of the implementation are low. Although further work will be necessary, critical design choices in CASP have been proved to be feasible.
Paper
2003
Michael Ebner , M. Schmitt.The TTCN-3 module and template concepts revisited. Technische Berichte des Instituts für Informatik an der Georg-August-Universität Göttingen, Institut für Informatik, Georg-August-Universität Göttingen, Germany, 2003
Paper
Xiaoming Fu , Henning Schulzrinne, Hannes Tschonfenig, Andrew McDonald.CASP ? Cross-Application Signaling Protocol. Technische Berichte des Instituts für Informatik an der Georg-August-Universität Göttingen, Institut für Informatik, Georg-August-Universität Göttingen, Germany, 2003
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CASP is a modular potocol for establishing network control state along a data path between two nodes communicating on the Internet.The signalling problem addressed by CASP is the same as the overall problem being addressed by the NSIS activities.The CASP framework is defined as a modular protocol, which includes a general purpose messaging layer (M-layer), which supports a number of client layers for particular ignalling applications (e.g. QoS, MIDCOM). In addition there is distinct, special purpose client component for next-peer discovery.
Paper
Henning Schulzrinne, Hannes Tschofenig, Xiaoming Fu, Andrew McDonald.CASP - Cross-Application Signaling Protocol. Technische Berichte des Instituts für Informatik an der Georg-August-Universität Göttingen, Institut für Informatik, Georg-August-Universität Göttingen, Germany, 2003
Read abstract
CASP is a modular potocol for establishing network control state along a data path between two nodes communicating on the Internet.The signalling problem addressed by CASP is the same as the overall problem being addressed by the NSIS activities.The CASP framework is defined as a modular protocol, which includes a general purpose messaging layer (M-layer), which supports a number of client layers for particular ignalling applications (e.g. QoS, MIDCOM). In addition there is distinct, special purpose client component for next-peer discovery.
Paper
2002
Xiaoming Fu , Cornelia Kappler, Hannes Tschofenig.Analysis on RSVP Regarding Multicast. Technische Berichte des Instituts für Informatik an der Georg-August-Universität Göttingen, Institut für Informatik, Georg-August-Universität Göttingen, Germany, 2002
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RSVP version 1 has been designed for optimum support multicast. However, in reality multicast is being used much less frequently than anticipated. Still, even for unicast (one sender, one receiver) full-fledged multicast-enabled RSVP signaling must be used. As pointed out in the NSIS requirement draft, multicast would not be necessarily required for an NSIS signaling protocol. This draft analyses ingredients of RSVP Version 1 which are affected by multicast, and derives how these ingredients may look like if multicast is not supported in the generic RSVP signaling protocol and adapt related functionalities accordingly - we call the resulting feature set "RSVP Lite", a potentially more light-weight version of RSVP.
Paper
Xiaoming Fu, Cornelia Kappler, Hannes Tschofenig.Analysis on RSVP Regarding Multicast. Technische Berichte des Instituts für Informatik an der Georg-August-Universität Göttingen, Institut für Informatik, Georg-August-Universität Göttingen, Germany, 2002
Read abstract
RSVP version 1 has been designed for optimum support multicast. However, in reality multicast is being used much less frequently than anticipated. Still, even for unicast (one sender, one receiver) full-fledged multicast-enabled RSVP signaling must be used. As pointed out in the NSIS requirement draft, multicast would not be necessarily required for an NSIS signaling protocol. This draft analyses ingredients of RSVP Version 1 which are affected by multicast, and derives how these ingredients may look like if multicast is not supported in the generic RSVP signaling protocol and adapt related functionalities accordingly - we call the resulting feature set "RSVP Lite", a potentially more light-weight version of RSVP.
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