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ACADEMIC YEAR	1998
NAME	NISHIDA, Yoshifumi
TITLE	Autonomous Congestion Control Scheme for Wide-area Packet-switched Networks
ABSTRACT	This paper discribes autonomouns congestion control schemes for wide area packet-switched networks. As the importance of wide area networks grows, Internet continues to increase its size and diversity. Although the costs of communication devices become low, constructing and maintaining large scale networks such as transcontinental networks still incurs large costs. In this situation, the importance of the technologies that supply maximum network resource to network users with minimum costs is increased. Congestion control schemes which have the ability to use network resources efficiently, is required to play important role in large scale networks. In large-scale autonomouns distributed networks such as Internet, the autonomous congestion control by end systems becomes pricipal part of congestion control system entire networks. However, the TCP(Transmission Control Protocol) that is used current Internet as the congestion control scheme by end systems, was not designed for the world wide networks. The environment surrounding the Internet has been changed drastically in recent years. Due to the rapid advancement of communication technology, as the communication devices grows its trasmit rate and diversity, the characteristic of Internet becomes complex. Furthermore, due to emergence of commercial services, more reliability is required to the large area networks. In this paper, we propose two autonomous congestion control schemes: ``Smooth Slow-start'' and ``Packer-pair TCP''. By implementing these schemes in TCP, our schemes have backward-compatibility with existing congestion control scheme in current Internet. This compatibiliy enables Internet to transit our congestion control scheme by degrees. The smooth slow-start disperse burst of data transmission which occur in data transmission in long delay networks. Smooth slow-start uses timer interrupt routine which is provided by operating systems. The disperse algorithm of smooth slow-start uses linear congruential sequence which is used for generating uniform random numbers. Smooth slow-start provide a solution to the problem of data transmission in long delay networks. The packet-pair TCP is a congestion control scheme which combines packet pair scheme which is used for bandwidth estimation with TCP. Packet pair TCP executes packet pair probing during data transmission and decides congestion control strategy from the result of the probing. To use accurate bandwidth estimation mechanism, packet pair TCP is able to decide transmission rate which is suitable for communication paths. Packet pair TCP is able to reduce retransmission of data and establish efficient data transmission. Furthermore, by using bandwidth estimation sheme, packet pair TCP is able to detect asymmetric networks which differentiate the path for data packets from the path for acknowledgement packets. Packet pair TCP changes congestion control algorithm in asymmetric communication. Due to this algorithm, packet pair TCP is able to establish efficient data transmission in asymmetric networks, although current TCP is not able to adapt to asymmetric networks adequately. To establish fair share of network resource, packet pair TCP adopts R.Jain's algorithm. By using this scheme, packet pair TCP enables TCP connections to cooperate with each other and to attain to equilibrium when each connection shares equal resources. We analized the effect of our schemes by using experiment over simulation and real networks. Compared with normal TCP, smooth slow-start attained between 15% and 40% improvement of transmission performance Packet pair TCP was demonstrated to be between 4% and 10% more efficient in symmetric communication and between 6% and 30% more efficient in asymmetric communication. In addition to improvement of transmission performance, the packet-pair TCP reduces retransmission of data between 4% and 10%. As the results, packet pair TCP is able to use network resources efficiently. Furthermore, compared with TCPVegas, which is discussed as new congestion control scheme, our scheme was demonstrated to be more efficient in asymmetric communication and in high-congested situation and fair share of network resource.
CONTACT	To obtain the whole paper, please contact; Yoshifumi Nishida, nishida@csl.sony.co.jp Sony Computer Science Laboratories Takanawa Muse Building 3-14-13 Higashi-Gotanda, Shinagawa-ku, Tokyo 141-0022 Japan

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