Special Issue on Performance Issues in Mobile Computing Bo Li Computer Science Department Hong Kong Univ. of Science & Technology bli@cs.ust.hk Kazem Sohraby Lucent Technologies, Bell Labs sohraby@lucent.com We have witnessed a recent phenomenal development and rapid deployment of mobile wireless services. This special issue of the Performance Evaluation Review (PER) is dedicated to the performance aspect of mobile wireless computing, which is a collection of four papers addressing different aspects of mobile computing with respect to supporting data services. The first paper by Ming Feng and Yi-Bing Lin from National Chiao-Tung University presents a wireless web access algorithm for WAP (wireless application protocol) caching proxy or handheld devices. The objectives are to reduce the data access delay and to improve the cache efficiency using prediction. The introduced L-access algorithm probes the server every L access for possible update based on the data access pattern. The results obtained from the analysis demonstrated that the L-access algorithm can more effectively tune to the data expiration time than the existing TTL-based algorithms, thus better caching efficiency can be achieved. The second paper on the investigation of ad hoc mobile network performance, by C.-K. Toh, Richard Chen, Minar Delwar and Donald Alien from Georgia Tech, presents a comprehensive study on the performance of ad hoc wireless networks based on an experiment testbed. A wide variety of performance measures including throughput, end-to-end delay, and route discovery times are obtained. In addition, the impact of the packet size and beaconing intervals are also examined. The third paper, by Tanja Lang and Daniel Floreani from University of Southern Australia investigates the performance of TCP in wireless environments. In particular two major parts of the TCP are examined including error detection and congestion control mechanisms. The authors implemented a variety of error detection and congestion controls commonly used by adopting a modular design approach. The performance in terms of throughput, transfer time, timeout, number of retransmissions and link utilization are determined over lossy links with high propagation. The results demonstrate the trade-off in different combination of error detection and congestion control strategies. The last paper by Vikrant A. Chitre and John N. Daigle from University of Mississippi, examines the performance of GPRS (General Packet Radio Service) systems with respect to supporting IP-based Interact services under a variety of user scenarios including continuously backlogged users, HTFP users, and mixed type of traffic. Performance in term of system throughput and delay are obtained as a function of various parameters such as the number of user sessions, number of contention slots, and message length. It has been a pleasure for us in putting this special issue together. There were also a number of other time papers that could not be selected due to the space limitation. We would like to take this opportunity to thank all the authors for their contributions, and also thank Professor Scott Leutenegger for his suggestion of the topic, and his assistance during the preparation of this special issue.

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