Handoffs in Cellular Wireless Networks: The Daedalus Implementation and Experience

Network protocols in cellular wireless data networks must update routes as a mobile host moves between cells. These routing updates combined with some associated state changes are called handoffs. Most current handoff schemes in wireless networks result in data loss or large variations in packet delivery times. Unfortunately, many applications, such as real-time multimedia applications and reliable transport protocols, adapt to long term estimates of end-to-end delay and loss. Violations and rapid fluctuations of these estimates caused by handoff processing often result in degraded performance. For example, loss during handoff adversely affects TCP performance [4], and high packet loss and variable delays result in poor real-time multimedia performance. In this paper, we describe a multicast-based protocol that eliminates data loss and incurs negligible delays during a handoff. The basic technique of the algorithm is to anticipate a handoff using wireless network information in the form of received signal strengths and to multicast data destined for the mobile host to nearby base stations in advance. This routing, combined with intelligent buffering techniques at the base stations, enables very rapid routing updates and eliminates data loss without the use of explicit data forwarding. We have implemented this protocol using IP Multicast and Mobile IP-like routing. In our implementation, handoffs typically take between 8 and 15 ms to complete and result in no data loss.     

A Hybrid Adaptive Wireless Channel Access Protocol for Multimedia Personal Communication Systems

This paper proposes a new medium access protocol (MAC) protocol for futurewireless multimedia personal communication systems, denoted hybrid andadaptive multiple access control (HAMAC) protocol. The HAMAC protocolintegrates fixed assignment TDMA protocol, reservation-based protocols, andcontention-based protocols into a single wireless network so as tosimultaneously and efficiently support various classes of traffic such asconstant-bit-rate (CBR), variable-bit-rate (VBR), and available-bit-rate (ABR)traffic. In particular, the HAMAC protocol uses a novel preservationslot technique to overcome the packet contention overhead in packetreservation multiple access (PRMA) like protocols, while keeping mostisochronous service features of TDMA protocols to serve voice and CBR trafficstreams. A preservation slot is a very short slot which is used torepresent a CBR connection when the traffic in the CBR connection is in asilent period in which there is no meaningful data to transmit. Due to thevery short length of the preservation slot, it only takes minimalportion of the bandwidth pre-allocated to the CBR connection, so that theremaining bandwidth can be freed for other connections to use. When the CBRsource becomes active again, the preservation slot is replaced bynormal data slots without any reservation operation, extra delay, orsignificant bandwidth loss. Consequently, the guaranteed service andsimplified signaling features of TDMA protocols, together with the adaptivebandwidth allocation features of PRMA-like protocols, are both realized in theHAMAC protocol. We have analyzed the performance of the HAMAC protocol usingextensive simulations. The results show that the HAMAC protocol can achievevery low loss rates for various multimedia traffic with stringent quality ofservice (QoS) requirements and outperforms state-of-the-art PRMA-likeprotocols. As a result, the HAMAC protocol appears to be a good candidate forfuture generation multimedia personal communication systems.     

一种支持QoS的拓扑自适应动态组播路由算法

YAM、QoSMIC、DSDMR等一类支持QoS的动态组播路由算法允许组播成员动态地加入和离开，同时为接收方提供多个可选择的组播接入路径，以满足不同应用的QoS需求。但这些算法普遍存在控制信令开销大和结点加入时延长，可扩展性不好等问题。本文在分析这些算法的基础上，提出改进的支持QoS的动态组播路由算法，即拓扑自适应动态组播路由（Topology Adaptive Dynamic Multicast Routing，TADMR）算法。该算法避免了以往算法中大部分盲目的路径搜索，并使结点加入时延不再受限于固定的等待时钟，而与网络拓扑相自适应。性能分析和仿真结果表明，该算法具有较低的控制信令开销和结点加入时延，适用于各种网络规模和群组规模，具有良好的可扩展性。     

一种适于视频点播业务的QoS协商方法

提出了一种新的采用资源预约的ＱｏＳ的协商方法（ＮＡＦＵＲ）,该方法可使服务的开始时间和服务的请求时间相分离,并允许用户设定所需服务的持续时间。若所要求的ＱｏＳ在发出服务请求时不能被支持,则可计算出用户能够以指定的ＱｏＳ开始接受服务的最早时间,ＮＡＦＵＲ还有助于：（１）通过提供用户更我的选择,增加系统的灵活性;（２）通过鼓励资源共享,提高对系统资源的利用和系统的有效性。另外,该方法还能实现：（１）一     

基于IP组播的分布式多媒体视频会议系统的设计和应用

针对IP网络在QoS方面的缺陷，根据开发小组设计的基于IP组播的分布式多媒体视频会议系统，着重介绍该会议系统在终端会议系统中的QoS解决方案，并简要讲述该会议系统在教学等方面的应用。     

QoS Guarantees in Heterogeneous Systems Consisting of IP Core Networks with Satellite Access

This paper aims at investigating the issue of differentiated QoS provision to services over a heterogeneous terrestrial-satellite infrastructure. In particular, the implementation of a dynamic mapping of the main service classes offered by IP IntServ and DiffServ models over satellite bearer services is investigated.Objective of the research is to enable mobile subscribers to access broadband services offered within a fixed IP core network, through satellite links. This has to be performed while still guaranteeing the same Quality of Service (QoS) offered by the IP IntServ and DiffServ models over the terrestrial segment. In such an environment, the considered traffics derive from multimedia applications and are characterised by real-time and non-real-time constraints as well as variable (VBR) and constant (CBR) bit-rate profiles.     

A New MAC Protocol Ensuring the Multimedia Traffic QoS for CDMA Networks

This paper describes the CDMAC, a new Medium Access Control (MAC)protocol for multimedia traffic in CDMA wireless networks. Theprotocol intends to extract the maximum capacity and flexibilityout of the CDMA scheme and at the same time guarantee the expectedQoS of different service types. CDMAC is able to maintain QoSrequirements thanks to the shaping, policing and trafficdifferentiation performed by the scheduler. Moreover, an iterativealgorithm, applied at the beginning of each frame, is used to findthe optimal power vector for all mobiles present in the system,which maximize the system capacity. The basic constraint of thecapacity maximization process is that the BER QoS of eachconnection should be fulfilled. Finally a distributedimplementation, feasible in a practical scenario, is presented.     

Wireless Ad Hoc Multicast Routing with Mobility Prediction

An ad hoc wireless network is an infrastructureless network composed of mobile hosts. The primary concerns in ad hoc networks are bandwidth limitations and unpredictable topology changes. Thus, efficient utilization of routing packets and immediate recovery of route breaks are critical in routing and multicasting protocols. A multicast scheme, On-Demand Multicast Routing Protocol (ODMRP), has been recently proposed for mobile ad hoc networks. ODMRP is a reactive (on-demand) protocol that delivers packets to destination(s) on a mesh topology using scoped flooding of data. We can apply a number of enhancements to improve the performance of ODMRP. In this paper, we propose a mobility prediction scheme to help select stable routes and to perform rerouting in anticipation of topology changes. We also introduce techniques to improve transmission reliability and eliminate route acquisition latency. The impact of our improvements is evaluated via simulation.     

Scalable Multicasting: The Core-Assisted Mesh Protocol

Most of the multicast routing protocols for ad hoc networks today are based on shared or source-based trees; however, keeping a routing tree connected for the purpose of data forwarding may lead to a substantial network overhead. A different approach to multicast routing consists of building a shared mesh for each multicast group. In multicast meshes, data packets can be accepted from any router, as opposed to trees where data packets are only accepted from routers with whom a tree branch has been established. The difference among multicast routing protocols based on meshes is in the method used to build these structures. Some mesh-based protocols require the flooding of sender or receiver announcements over the whole network. This paper presents the Core-Assisted Mesh Protocol, which uses meshes for data forwarding, and avoids flooding by generalizing the notion of core-based trees introduced for internet multicasting. Group members form the mesh of a group by sending join requests to a set of cores. Simulation experiments show that meshes can be used effectively as multicast routing structures without the need for flooding control packets.     

基于遗传算法的QoS组播路由算法的改进

QoS组播路由技术在网络技术发展中占有很重要的地位,是一种关键的技术。在分析网络模型的基础上,建立了组播问题的数学模型。遗传算法是一种经典的寻优算法,应用广泛,提出了改进的算法。并且结合改进Dijkstra算法,使算法能很好地体现实际组播路由问题的特点。试验表明,这种新的算法可靠性更高,适应了当今网络性能优化的需要。     

Efficient QoS Provisioning for Adaptive Multimedia in Mobile Communication Networks by Reinforcement Learning

The scarcity and large fluctuations of link bandwidth in wireless networks have motivated the development of adaptive multimedia services in mobile communication networks, where it is possible to increase or decrease the bandwidth of individual ongoing flows. This paper studies the issues of quality of service (QoS) provisioning in such systems. In particular, call admission control and bandwidth adaptation are formulated as a constrained Markov decision problem. The rapid growth in the number of states and the difficulty in estimating state transition probabilities in practical systems make it very difficult to employ classical methods to find the optimal policy. We present a novel approach that uses a form of discounted reward reinforcement learning known as Q-learning to solve QoS provisioning for wireless adaptive multimedia. Q-learning does not require the explicit state transition model to solve the Markov decision problem; therefore more general and realistic assumptions can be applied to the underlying system model for this approach than in previous schemes. Moreover, the proposed scheme can efficiently handle the large state space and action set of the wireless adaptive multimedia QoS provisioning problem. Handoff dropping probability and average allocated bandwidth are considered as QoS constraints in our model and can be guaranteed simultaneously. Simulation results demonstrate the effectiveness of the proposed scheme in adaptive multimedia mobile communication networks. This work is based in part on a paper presented at BroadNet's 04, San Jose, CA, Oct. 2004. Fei Yu received the M.S. degree in Computer Engineering from Beijing University of Posts and Telecommunications, P.R. China, in 1998, and the Ph.D. degree in Electrical Engineering from the University of British Columbia (UBC), Canada, in 2003. From 1998 to 1999, Dr. Yu was a system engineer at China Telecom, P.R. China, working on the planning, design and performance analysis of national SS7 and GSM networks. From 2002 to 2004, He was a research and development engineer at Ericsson Mobile Platforms, Sweden, where he worked on dual-mode UMTS/GPRS handsets. He is currently a postdoctoral research fellow at UBC. His research interests are quality of service, cross-layer design and mobility management in wireless networks. Vincent W.S. Wong (S'94-M'00) received the B.Sc. (with distinction) degree from the University of Manitoba, Winnipeg, MB, Canada, in 1994, the M.A.Sc. degree from the University of Waterloo, Waterloo, ON, Canada, in 1996, and the Ph.D. degree from the University of British Columbia (UBC), Vancouver, BC, Canada, in 2000, all in electrical engineering. From 2000 to 2001, he was a Systems Engineer at PMC-Sierra, Inc., Burnaby, BC. Since 2002, he has been with the Department of Electrical and Computer Engineering, UBC, where he is currently an Assistant Professor. His research interests are in wireless communications and networking. Dr. Wong received the Natural Science and Engineering Research Council (NSERC) postgraduate scholarship and the Fessenden Postgraduate Scholarship from Communications Research Centre, Industry Canada, during his graduate studies. Victor C.M. Leung received the B.A.Sc. (Hons.) degree in electrical engineering from the University of British Columbia (U.B.C.) in 1977, and was awarded the APEBC Gold Medal as the head of the graduating class in the Faculty of Applied Science. He attended graduate school at U.B.C. on a Natural Sciences and Engineering Research Council Postgraduate Scholarship and obtained the Ph.D. degree in electrical engineering in 1981. From 1981 to 1987, Dr. Leung was a Senior Member of Technical Staff at Microtel Pacific Research Ltd. (later renamed MPR Teltech Ltd.), specializing in the planning, design and analysis of satellite communication systems. He also held a part-time position as Visiting Assistant Professor at Simon Fraser University in 1986 and 1987. In 1988, he was a Lecturer in the Department of Electronics at the Chinese University of Hong Kong. He joined the Department of Electrical Engineering at U.B.C. in 1989, where he is a Professor, Associate Head of Graduate Affairs, holder of the TELUS Mobility Industrial Research Chair in Advanced Telecommunications Engineering, and a member of the Institute for Computing, Information and Cognitive Systems. His research interests are in the areas of architectural and protocol design and performance analysis for computer and telecommunication networks, with applications in satellite, mobile, personal communications and high speed networks. Dr. Leung is a Fellow of IEEE and a voting member of ACM. He is an editor of the IEEE Transactions on Wireless Communications, and an associate editor of the IEEE Transactions on Vehicular Technology. He has served on the technical program committees of numerous conferences, and is serving as the Technical Program Vice-Chair of IEEE WCNC 2005.