Wireless IPv6 Networking - WINE

Wireless IPv6 Networking - WINE Zach D. Shelby1, Tommi Saarinen1, Petri Mähönen1, Diego Melpignano2,Alan Marshall3, Luis Muňoz 4 1

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VTT Electronics, Oulu Finland [[email protected]] Philips Research, Monza Italy [[email protected]] 3 Queens University of Belfast [[email protected]] 4 University of Cantabria [[email protected]]

Abstract: The WINE project has one overall theme. Seamless optimisation of IPv6 over wireless networks. Research is under way on using a Performance Enhancing Proxy (PEP) architecture to improve performance. A solution for micro-mobility is proposed, which provides intra-domain roaming. Finally, support for Differentiated Services is integrated into this architecture. This paper describes the overall architecture of a Wireless Adaptation Layer (WAL), developed in the WINE project. The WAL approach allows different wireless access networks to interface to the future Internet services (including QoS aware services) through a common interface. The proposed architecture is described including simulation and implementation issues.

1. Introduction Research work over the past decade has pointed out the unique characteristics of wireless links on connectionless networks. The performance of TCP over wireless links has been shown both analytically and practically to be poor [1][3][7]. The throughput of IP traffic can be degraded by lossy, slow, or delayed wireless links. This has led to many suggestions for improving the performance of the TCP/IP protocol suite over radio links. Link layer techniques are described in [6][8]., while new versions of TCP have been developed and analysed [2][4][5]. Wireless MAC protocols have also been analysed for improving TCP performance [9]. Header compression schemes are aimed at improving throughput over slow and lossy links [11]. While all of these proposals aim to improve the performance of IP over wireless links, these techniques have so far not been applied together in order to improve throughput over many different wireless links. This paper introduces the concept of a Wireless Adaptation Layer (WAL). The WAL attempts to to bring together these methods in a flexible and implementable framework. The problem of Intra-domain mobility is not related directly to link characteristics, but rather to handoffs and routing for mobile terminals. While Mobile IP can be used to support inter-domain mobility, it cannot cope with fast handoffs between access points within a domain. This is particularly relevant whenever small pico-cellular networks are used to provide high-speed wireless access to the core network (i.e. future Internet), as handoffs will occur much more frequently. Bridging solutions at the link layer can perform hard handoffs in a homogeneous network, but cannot handoff to another network type (technology). Research into network layer intra-domain mobility has recently been very active [14][15]. In this work Cellular IP [13] has been chosen to integrate into the WINE architecture. Improvements for supporting IPv6 will be dealt with and published in a future work. The WINE architecture is also exploring more advanced Intra-domain solutions as in [17]. An important feature of wireless IP is the support and provision of service differentiation in order to support multiple classes of service (voice, video, data etc) over the same wireless access network. Although some wireless technologies provide priority levels, IP does not currently take advantage of them. The WAL integrates IP service classes to take advantage of wireless interface priority levels. This will follow the differentiated services architecture [18]. The packet scheduling discipline employed (in both the access point and in the user's mobile terminal) has a major effect on the provision of Quality of Service (QoS), and also on the efficiency of the wireless link. In order to

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provide a flexible architecture that can support a diverse range of mobile terminals, a hierarchical scheduling approach is used. This allows more complex scheduling schemes (e.g. WFQ) to be employed for those terminals with a range of service classes, and simple schedulers (e.g. FIFO) to be used for those mobile terminals which have only a best effort service class.

1.1. Research Methods Simulation is used to develop models of the new protocols developed in WINE. This includes models for the Wireless Adaptation Model and Cellular IP. Test bed measurements are compared with simulation results using iterations to improve model accuracy. Implementations of the protocols are completed to show basic functionality and performance. Simulation is then used to look at scalability of performance, which is otherwise difficult in a test bed. This approach also allows the impact of new applications to a assessed, as well as the development of new algorithms and enhancements in the WINE architecture.

2. Wireless Adaptation Layer

Figure 1 - Wireless Adaptation Layer

The Wireless Adaptation Layer is located between the network and data link layers. This mechanism is called a Performance Enhancing Proxy and has been explored in the IETF pilc working group [19]. If the WAL is located on only one end of a wireless medium, it can run in asymmetrical mode. If located on all nodes of the wireless medium it operates in symmetrical mode with full functionality. The WAL itself is an architecture for implementing IP performance improving techniques and protocols. The WAL can examine IP traffic along with current wireless conditions to choose the most appropriate performance enhancements. Using these inputs, the WAL architecture applies the appropriate modules on each packet. Modules can implement either symmetrical or asymmetrical

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techniques. Both classical link layer protocols and transport protocol specific techniques can be applied in this fashion, along with service differentiation techniques. A wide range of link and transport layer protocol modules can be supported. Protocol enhancements such as SNOOP, TCP link outage protection, and Forward Error Correction (FEC) will be implemented. Classical link layer techniques such as Automatic Repeat reQuest (ARQ) and IP header compression may be applied to selected flows which can benefit from these techniques. Specialised functions such as differentiated service mappings to many wireless links, and the addition of service differentiation across shared wireless mediums are also possible. In theory, this architecture could be used to build a complete data link control, or even medium access control for a generic radio interface or software radio. The wide range of Internet protocol enhancements can be applied through the WAL architecture. Currently these enhancements are applied alone and in a proprietary manner. Combining multiple protocol enhancements along with the intelligence to apply them to the correct packets offers the potential for much more efficient wireless link, and the capability to support multiple services over those links. The previous work of Protocol Boosters [16] has been done to apply protocol specific techniques. The WAL goes further to combine protocol specific, link layer, and service differentiation techniques taking wireless conditions into account.

2.1. Wireless SNMP In order to take advantage of the knowledge of wireless conditions from many different wireless networking technologies, a consistent way to present those conditions is needed. We introduce wireless SNMP to solve this problem. Wireless SNMP uses a collection of Management Information Bases (MIB) related to IP over wireless; Wireless interface MIB, Wireless Adaptation Layer MIB, and Intra-domain mobility MIB. This problem has been approached in the strictly Ad-Hoc network sense in [10]. Statistics are collected from the wireless interface, WAL, and Intra-domain mobility MIBs and is stored by an SNMP agent. These MIBs are then available for use by the WAL in order to make intelligent decisions for implementing performance enhancements. Standard practices such as management and configuration are also possible through the SNMP agent.

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3. Intra-domain Mobility

Figure 2 - Example micro-mobility architecture

Mobile IP provides roaming functionality for mobile terminal over the entire Internet. This protocol is employed when a vertical handoff takes place, i.e. when a user moves from one IP domain to a completely different one. Mobile IP provides for the user to keep it's IP address even while in a foreign network, and ensures all traffic will still reach the user. However, mobility within a single domain between wireless access points or cellular base stations is not handled by mobile IP. In order to efficiently track mobile users as they roam between access points and to deliver IP packets to them, an Intra-domain mobility protocol is needed. This type of mobility protocol is basically a soft state routing protocol distributed across the access network. The goal is to provide seamless service with a low amount of overhead while maintaining mobile IP transparency. In the WINE architecture, the Cellular IP protocol [13] will be integrated to perform these functions. Route updates as users move across access points is done using soft-state routing and paging updates. Efficiency is maintained with idle user states. Semi-soft handoffs can be accomplished using buffering techniques. Part of this work will involve modifications of Cellular IP to take advantage of IPv6.

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4. Service Differentiation Many Wireless LAN devices support various levels of prioritisation for traffic. However there is currently no universal method for Internet QoS architectures to take advantage of this. The WAL can include functionality to classify traffic by the IP ToS or DS value. The traffic classifier in the Access point WALs can therefore be interfaced to existing core network protocols such as DiffServ. This traffic can then be mapped to the appropriate priority level of the wireless interface. Most importantly, this can be done using the WAL over many wireless interfaces. For wireless LAN technologies which do not provide priority levels, the WAL can also provide service class differentiation. The access point WAL can co-ordinate the WALs of other nodes to provide differentiation across the medium. This is achieved using hierarchical queuing and scheduling techniques.

5. Conclusions This paper has described the introduction of a Wireless Adaptation Layer (WAL), currently under development in the WINE project IST10028. The WAL is used to connect a range of wireless access networks to the Internet via a common interface. The flexible architecture adopted in the WAL allows a wide range of performance enhancing protocols at the link, network and transport layers to be applied across a range of wireless networks. The WAL also considers the delivery of multiple classes of service over future core networks (Internet) to wireless access networks. It has been designed to support both differentiated and best effort services modes, and employs a novel hierarchical scheduling scheme in order to provide this flexibility. The WAL is currently under development, and will be applied to three testbed wireless networks: 802.11, HiperLAN2, and Bluetooth. Empirical results from these testbeds will then be used to refine simulation models of the overall network in order to assess the behavior and performance of the architecture in terms of scale, traffic load, new application support, and also for the development of new algorithms within the WAL (e.g. handoff, scheduling).

Acknowledgements The authors gratefully acknowledge the support provided by the European Union under the Framework V IST program (project ref. IST10028) for this work.

References [1] A. DeSimone, M. C. Chuah, and O. C. Yue, "Throughput Performance of Transport-Layer Protocols over Wireless LANs," in Proceedings of the IEEE GLOBECOM '93, pp. 542-549, December 1993. [2] H. Balakrishnan, S. Seshan, and R. Katz, "Improving Reliable Transport and Handoff Performance in Cellular Wireless Networks," ACM Wireless Networks, Vol. 1, December 1995. [3] R. Cáceres and L. Iftode, "Improving the Performance of Reliable Transport Protocols in Mobile Computing Environments," IEEE Journal on Selected Areas in Communications, Vol. 13, No. 5, June 1995. [4] H. Balakrishnan, V. Padmanabhan, S. Seshan, and R. Katz, "A Comparison of mechanisms for Improving TCP performance over Wireless Links," in Proceedings of ACM/SIGCOMM '96, Stanford, CA, August 1996.

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[5] B. S. Bakshi, P. Krishna, N. H. Vaidya, and D. K. Pradhan, "Improving Performance of TCP over Wireless Networks," in Proceedings of the 17th International Conference on Distributed Computing Systems, May 1997. [6] G. Xylomenos and G. C. Polyzos, "Enhancing Wireless Internet Links," in Proceedings of the ICT, June 1998. [7] G. Xylomenos and G. C. Polyzos, "TCP and UDP Performance over a Wireless LAN," in Proceedings of the IEEE INFOCOM '99, pp. 439-446, March 1999. [8] Chaskar Hemant M., Laksman T.V. and Madhow U, "TCP over Wireless with Link Level Error Control", in IEEE Transactions on networking, pp. 605-615, Vol. 7, No 5, October 1999. [9] K.Tang, M. Correa, M. Gerla, "Isolation of Wireless Ad Hoc Medium Access Mechanisms under TCP", in IEEE ICCCN, October 1999. [10] W. Chen, N. Jain, S. Singh, "ANMP: Ad Hoc Network Management Protocol", IEEE Journal on Selected Areas of Communications, pp. 1506-1531, Vol. 17, No. 8, August 1999. [11] M. Degermark, B. Nordgren, S. Pink, "IP Header Compression", RFC 2507, February 1999. [12] C. Perkins, editor, "IP mobility support", RFC 2002, October 1996. [13] A. Valko, "Cellular IP: A New Approach to Internet Host Mobility", ACM Computer Communication Review, January 1999. [14] R. Ramjee, et. al.,"HAWAII : A Domain-based Approach for Supporting Mobility in Wide-area Wireless Networks", ICNP '99. [15] C. Castelluccia, "HMIPv6: A Hierarchical Mobile IPv6 Proposal". ACM Mobile Computing and Communication Review (MC2R), April 2000. [16] D.C. Feldmeier, A.J. McAuley, J.M. Smith, D.S. Bakin, W.S. Marcus, T.M. Raleigh, "Protocol Boosters," in IEEE Journal on Selected Areas of Communication, Vol. 16, No. 3, April 1998. [17] T. Inzerilli, "SIMPLE, a Scalable Intra-domain Mobility Protocol using Local Encapsulation for Mobile IPv6 and Mobile IP", in This Conference, October 2000. [18] S. Blake, D. Black, M. Carlson, E. Davies, Z. Wang, W. Weiss, "An Architecture for Differentiated Services", RFC 2475, December 1998. [19] IETF Performance Implications of Link Characteristics (pilc), http://www.ietf.org/html.charters/pilc-charter.html, August 2000.

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