4 IEEE Wireless Communications • February 2006 he market for wireless local area network (WLAN) has
been experiencing tremendous growth in recent years, as evidenced by the fast increasing popularity of WLAN hotspots deployed in residence, enterprise, and public areas such as airports, campuses, conference venues, shopping malls, and exhibitions. Meanwhile, WLAN ser-vices are evolving from best effort data serser-vices to real-time applications with a certain level of quality of service (QoS) pro-visioning. In the near future, voice over IP (VoIP) is expect-ed to be extendexpect-ed from the Internet to the wireless domain via WLAN. An 802.11-based phone system is generally less expensive to install and support than a wired system. A sig-nificant benefit of mixing telephone traffic with data on a WLAN is that it can support user mobility and make use of a com-mon infrastructure.
However, unlike cellular networks where dedicated chan-nels are assigned to voice traffic, the voice packets in WLAN are multiplexed with other data traffic. The distributed coor-dination ffunction (DCF) is the primary operation mode of WLAN, which introduces significant delay jitter. Investiga-tion of voice packet delay/jitter performance over 802.11/DCF mode is a necessary and challenging problem. The 802.11e group is currently working on QoS support in WLAN, but the rati-fication of the standard has a long way to go. Until then, development of VoWLAN QoS proprietary schemes is essential to prioritize traffic on the network for QoS support for real-time traffic. In addition, it is necessary that voice over WLAN has handover capability across WLANs and/or hybrid WLAN-cellular networks. Improved WLAN security, WPA, and WPA2 introduce unacceptably high delays for VoWLAN during session switching, and 802.11r is going to address the issue. The next-generation wireless access technology (NGWA), such as WiMax and its mobility enhancements 802.16e and IEEE 802.20, is above the horizon. The new technology and stan-dard migration and investment protection should also be considered.
This special issue is to disseminate the state-of-the-art R&D results on VoWLAN, facilitate the deployment of VoWLAN, and bring together researchers from both academia and
indus-try in networking, wireless communications, and mobile computing, with the goal of fostering interaction among them. It is timely and valuable for those involved in the research of VoWLAN.
In the first article “Pricing VoWLAN services through a Micro-Economic Framework,” Badia et al. investigate the issue of determining an appropriate pricing strategy for voice-over-WLAN provisioning. The voice services are framed in a tunable QoS scenario. Analysis is then performed with the awareness that in a WLAN system the tariff payment deter-mines price-based access regulation. The authors also apply a micro-economic framework which considers the trade-off between perceived QoS and paid price in the users’ request. A contention-based medium access mechanism is a manda-tory part of the IEEE 802.11 standard series. In the second arti-cle, “QoS Guarantee and Provisioning at the Contention-Based Wireless MAC Layer in IEEE 802.11e Wireless LANs,” Xiao provides a survey of previous work on QoS provision-ing with contention-based medium access control (MAC). Dis-tributed admission control, data control mechanisms, bandwidth allocation, and handoff/roaming are discussed. Further research directions are also pointed out.
The next two articles focus on polling, which is an effec-tive solution for supporting real-time traffic over WLANs with stringent delay requirements. In the article “Polling-Based Protocols for Packet Voice Transport over IEEE 802.11 Wireless Local Area Networks,” Lam et al. present a survey of different polling-based protocols for supporting VoWLAN. Three key issues are discussed: managing a polling list, determining the polling sequence and reducing polling overhead. An isochronous control function (ICF) is also proposed. In the article “IEEE 802.11e Enhancements for Voice Service,” Wang et al. propose mechanisms to enhance IEEE 802.11e with voice QoS provisioning capability. The delay requirement of real-time voice is guaranteed by controlled channel access, while bandwidth efficiency can be greatly improved by overhead suppression and statistical multiplex-ing. A call admission control scheme is also presented to admit voice stations into the system with QoS guarantee.
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Admission control is essential to QoS provisioning of VoWLAN. In the article “Providing Statistical QoS Guar-antee for Voice over IP in IEEE 802.11 Wireless LANs,” Zhai et al. propose a call admission control scheme that runs over the MAC layer to support VoIP services. Voice traffic is regulated to efficiently coordinate medium contention among voice sources. Non-voice traffic is regulated by a rate control mechanism to control its impact on the perfor-mance of voice traffic. Statistical QoS guarantee for voice traffic is provided, and a stable high throughput is main-tained for non-voice traffic at the same time. In the article “A Call Admission Control Framework for Voice over WLANs,” Qian et al. present a call admission control framework called WLAN Voice Manager. The WLAN Voice Manager interacts with WLAN MAC layer protocols, soft switches (VoIP call agents), routers, and other network devices to perform end-to-end (ETE) QoS provisioning and control for VoIP calls orig-inated from WLANs. By implementing the proposed WLAN Voice Manager in the WLAN access network, a two-level ETE VoIP QoS control mechanism can be achieved.
In the final article, “Quality-Aware VoWLAN Architecture and Its Quantitative Evaluations,” Koga et al. propose a media optimization network architecture (MONA). An intercarrier handover mechanism based on a cross-layer approach using the number of layer 2 retransmissions is evaluated. Voice quality management in WLAN is also dis-cussed.
In closing, the guest editors would like to thank all the authors who responded to the Call for Papers, regardless of whether their papers have been included in this issue or not due to space limitations. The editors would also like to acknowledge the contribution of many experts who participated in the review pro-cess, and provided helpful and valuable suggestions to the authors on improving the content and presentation of the articles. The advice and support of Dr. M. Zorzi, Editor-in-Chief of IEEE Wireless Communications, and the assistance of Sue Lange are greatly appreciated.
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IOGRAPHIESXUEMIN(SHERMAN) SHEN[M’97, SM’02] ([email protected]) received a B.Sc. (1982) degree from Dalian Maritime University, China, and M.Sc. (1987) and Ph.D. (1990) degrees from Rutgers University, New Jersey, all in electrical engineering. Currently, he is with the Department of Electrical and Computer Engineering, University of Waterloo, Canada, where he is a pro-fessor and associate chair for graduate studies. His research focuses on mobility and resource management in interconnected wireless/wireline net-works, UWB wireless communications systems, wireless security, and ad hoc and sensor networks. He is a co-author of two books, and has published more
than 200 papers and book chapters in wireless communications and net-works, control, and filtering. He was Technical Co-Chair for IEEE GLOBECOM ’03, ISPAN ’04, QShine ’05, IEEE Broadnets ’05, and WirelessCom ’05, and is Spe-cial Track Chair of the 2005 IFIP Networking Conference. He serves as Associ-ate Editor for IEEE Transactions on Wireless Communications; IEEE Transactions on Vehicular Technology; Computer Networks; ACM/Wireless Networks; Wireless Communications and Mobile Computing (Wiley); and International Journal Computer and Applications. He has also served as Guest Editor for IEEE JSAC, IEEE Wireless Communications, and IEEE Commu-nications Magazine. He received the Premier’s Research Excellence Award (PREA) in 2003 from the Province of Ontario, Canada, for demonstrated excellence of scientific and academic contributions, and the Distinguished Performance Award in 2002 from the Faculty of Engineering, University of Waterloo, for outstanding contributions in teaching, scholarship, and service.
YI-BINGLIN[F] ([email protected]) is chair professor of the Department
of Computer Science and Information Engineering (CSIE), National Chiao Tung University (NCTU). He also serves as vice president of the Office of Research and Development, NCTU. He is a senior technical editor of IEEE Network, an editor of IEEE Transactions on Wireless Communications, an associate editor of IEEE Transactions on Vehicular Technology, an editor of IEEE Wireless Communications, an editor of ACM/Baltzer Wireless Networks, Pro-gram Chair for the 8th Workshop on Distributed and Parallel Simulation, General Chair for the 9th Workshop on Distributed and Parallel Simulation, Program Chair for the 2nd International Mobile Computing Conference, Guest Editor for the ACM/Baltzer MONET special issue on Personal Commu-nications, a Guest Editor for IEEE Transactions on Computers special issue on Mobile Computing, a Guest Editor for IEEE Transactions on Computers spe-cial issue on Wireless Internet, and a Guest Editor for IEEE Communications Magazine special issue on Active, Programmable, and Mobile Code Network-ing. He is co-author of the book Wireless and Mobile Network Architecture (with Imrich Chlamtac; Wiley). He received 1997, 1999, and 2001 Distinguished Research Awards from National Science Council, ROC; 2004 K.-T. Li Outstanding Award; 2005 Pan WY Distinguished Research Award; 2005 Teco Award; and the 1998 Outstanding Youth Electrical Engineer Award from CIEE, ROC. He also received the NCTU Outstanding Teaching Award in 2002. He is an adjunct research fellow of Academia Sinica, and an adjunct chair professor of Providence University. He is an ACM Fellow, an AAAS Fellow, and IEE Fel-low.
AI-CHUNPANG([email protected]) received B.S., M.S., and Ph.D.
degrees in computer science and information engineering from National Chiao Tung University, Taiwan, in 1996, 1998, and 2002, respectively. She joined the Department of Computer Science and Information Engineering (CSIE), Nation-al Taiwan University (NTU), Taipei, Taiwan, as an assistant professor in 2002. From August 2004 to July 2005 she served as an assistant professor at the Graduate Institute of Networking and Multimedia (INM), and an adjunct assistant professor at CSIE/NTU, Taipei, Taiwan. Currently, she is an associate professor with INM and CSIE of NTU, Taipei, Taiwan. Her research interests include design and analysis of personal communications services networks, mobile com-puting, voice over IP, and performance modeling.
JIANPINGPAN[M] ([email protected]) is currently an assistant professor of computer science at the University of Victoria, British Columbia, Canada. He received his B.S. and Ph.D. degrees in computer science from Southeast University, Nanjing, China, in 1994 and 1998, respectively. From 1999 to 2001 he was a postdoctoral fellow and then research associate at the University of Water-loo, Ontario, Canada; from 2001 to 2005 he was a member of research staff at Fujitsu Labs and a research scientist at NTT MCL in Silicon Valley, Califor-nia. His area of specialization is distributed systems and networks, and his recent research interests include protocols for advanced networking, perfor-mance analysis of networked systems, and applied network security. He is a mem-ber of the ACM.
