应IDC实验室李瑞轩副教授邀请，国际知名学者、美国俄亥俄州立大学（Ohio State University）张晓东教授将于2006年9月6日来我校举行专题讲座。相关内容如下：
讲座时间：2006年9月6日下午3：00开始
讲座地点：东九楼B103
讲座题目：ASAP: an AS-Aware Peer-relay protocol for high quality VoIP
欢迎大家届时参加。
Title: ASAP: an AS-Aware Peer-relay protocol for high quality VoIP
Speakers: Xiaodong Zhang, Robert M. Critchfield Professor in Engineering
Abstract:
Peer-to-peer (P2P) technology has been successfully applied in Internet telephony or Voice over Internet Protocol (VoIP), such as the Skype system, where P2P is used for both searching clients and relaying voice packets. Selecting one or multiple suitable peers to relay voice packets is a critical factor for the quality, scalability and cost of a VoIP system. In this paper, we first present two sets of intensive Internet measurement results to confirm the benefits gained by peer relays in VoIP, and to investigate the performance of the Skype system. We obtain the following results: (1) many relay peer selections are suboptimal; (2) the waiting time to select a relay node can be quite long; and (3) there are a large number of unnecessary probes, resulting in heavy network traffic to limit scalability of the VoIP system. Our further analysis shows that two main reasons cause these problems. First, the peer selections do not take Autonomous System (AS) topology into consideration, and second, the complex communication relationships among peers are not well utilized. Motivated by our measurements and analysis, we propose an AS-aware peer-relay protocol called ASAP. Our objective is to significantly improve VoIP quality and system scalability with low overhead. Our intensive evaluation by trace-driven simulation shows ASAP is highly effective and easy to implement on the Internet for building large and scalable VoIP systems.
Biography:
Xiaodong Zhang is the Robert M. Critchfield Professor in Engineering, and Chairman of the Department of Computer Science and Engineering at the Ohio State University. He was the Lettie Pate Evans Professor of Computer Science, and the Department Chair at the College of William and Mary before joining Ohio State.
Since 1992, he has established and directed the High Performance Computing and Software Laboratory where he has supervised over 40 graduate students (both MS and Ph.D), post-docs, and visiting scholars. His research interests cover a wide spectrum in the areas of high performance and distributed systems. A common thread among his research projects focuses on fast data accesses and resource sharing with cost- and energy-efficient management at different levels of the memory and storage hierarchies in computer, distributed, and Internet systems. Several technical innovations and research results from his team have been adopted or being developed in commercial products and open source systems with direct impacts to our daily computing operations, including the permutation memory interleaving technique first in the Sun MicroSystems' UltraSPARC IIIi processor and then in the Sun's dual-core Gemini Processor, the token thrashing protection mechanism and the Clock-Pro page replacement algorithm for memory management in the Linux Kernel .
Xiaodong Zhang was the Program Director of Advanced Computational Research at the National Science Foundation, 2001-2004. He is the associate Editor-in-Chief of IEEE Transactions on Parallel and Distributed Systems, and is also serving on the Editorial Boards of IEEE Transactions on Computers and IEEE Micro. He is an organizer and a lecturer of the Dragon Star Lecture Program offering advanced research classes of computer science in many Chinese universities for thousands of talented graduate students every year.
Sponsored by the US National Science Foundation, and with Fred Roberts of Rutgers University, Peter Freeman and Wei Zhao of NSF, Xiaodong Zhang co-organized US NSF Senior Computer Scientist Delegation mainly consisting chairs from leading computer science departments to visit China, May 20 to June 2, 2006. The activities include to have held a US-China Computer Science Leadership Summit in Beijing, visited many universities and research institutions in Beijing, Nanjing, Shanghai, Suchow, and Xi'an, and to write a final report of the visit.
Xiaodong Zhang received his Ph.D. in Computer Science from the University of Colorado at Boulder in 1989, and his B.S. in Electrical Engineering from Beijing Polytechnic University.
Xiaodong Zhang completed his Master thesis of computer science in Colorado in 1985, under the direction of Ralph Slutz (1917-2005), who was a world-class scholar and a computer pioneer.
More information about Professor Xiaodong Zhang can be found at http://www.cse.ohio-state.edu/~zhang/
