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The TCP-Friendly Website Introduction This website summarizes some of the recent work on congestion control algorithms for non-TCP based applications, with a specific focus on those congestion control schemes that use the "TCP-friendly" equation, (that is, maintaining the arrival rate to at most some constant over the square root of the packet loss rate). All applications, no matter how large or small, should perform adaptive congestion control. There are several reasons for this: Applications which perform congestion control make more efficient use of the network and should generally see better performance because of it. Applications which adapt to the network are capable of running over a much wider range bandwidths and are hence more useful in the Internet. Congestion control algorithms prevent the network from entering Congestive Collapse. Congestive Collapse is a situation where, although the network links are being heavily utilized, very little useful work is being done. (Think of metropolitan traffic gridlock...) The network will soon begin to require applications to perform congestion control, and those applications which do not perform congestion control will be harshly penalized by the network (probably in the form of preferentially dropping their packets during times of congestion). A number of recent efforts have studied TCP-Friendly means of congestion control for non-TCP applications. This website is a compendium of known research on the subject. As with other websites of this sort, it is largely maintained by contributions from the community, so if you know of work in this area, please send it along to us. Current research: The TCP-Friendly algorithm and experiences with it. TCP performance and the 1/sqrt(p) algorithm.

• J. Mahdavi, S. Floyd, TCP-Friendly Unicast Rate-Based Flow Control, Technical note sent to the end2end-interest mailing list, January 8, 1997.
  This short web paper describes a simple algorithm which can be used by rate-based applications and should share bandwidth fairly with TCP connections.

• Adaptive Applications Support BOF (adapts). This BOF on the subject was held at the 40th IETF, December 9, 1997, in Washington D.C.

• T. Turletti, Parisis, J. Bolot, Experiments with a Layered Transmission Scheme over the Internet.
  This paper outlines some experimental results using a TCP-friendly rate control algorithm in an audio application.

• D. Sisalem, H. Schulzrinne, The Loss-Delay Adjustment Algorithm: A TCP-friendly Adaptation Scheme, Network and Operating System Support for Digital Audio and Video (NOSSDAV), Cambridge, UK, July 8-10, 1998.
  This paper presents the loss-delay based adjustment algorithm (LDA) for adapting the transmission rate of multimedia applications to the congestion level of the network. The LDA algorithm was designed to reduce losses and improve utilization in a TCP-friendly way that avoids starving competing TCP connections. It relies on the end-to-end Real Time Transport Protocol (RTP) for feedback information. In addition, we enhanced RTP with functionalities for determining the bottleneck bandwidth of a connection.

• D. Sisalem, F. Emanuel, H. Schulzrinne, The Direct Adjustment Algorithm: A TCP-Friendly Adaptation Scheme
  This study presents a new scheme for adapting the transmission rate of multimedia applications to the congestion level of the network. The scheme is called the direct adjustment algorithm (DAA). It is based on the TCP congestion control mechanisms and relies on the end-to-end Real Time transport Protocol (RTP) for feedback information. Our investigations of the DAA scheme suggest the efficiency of the scheme in utilizing network resources and decreasing loss ratios. Also, the scheme is shown to be fair towards competing TCP traffic.

• Lorenzo Vicisano, Luigi Rizzo (Pisa) and Jon Crowcroft, TCP-like Congestion Control for Layered Multicast Data Transfer. To appear in INFOCOM 98.
  This paper presents a congestion control algorithm for layered multicast traffic that is based on the TCP-friendly equation in combination with synchronization points and sender-initiated probes.

• W. Tan and A. Zakhor, Error Resilient Packet Video for the Internet (postscript), submitted to ICIP 98. This work is described further on Dan Tan's web page on Real-time Internet Video Transport.
  This paper describes experiments with an Internet video transport scheme that combines a low-delay TCP-friendly transport protocol with an error-resilient layered compression mechanism.

• Reza Rejaie, Mark Handley, and Deborah Estrin, RAP: An End-to-end Rate-based Congestion Control Mechanism for Realtime Streams in the Internet (postscript). To appear in IEEE INFOCOMM 99 .
  This paper presents RAP, an end-to-end rate-based congestion control mechanism based on an additive-increase, multiplicative-decrease algorithm that exhibits TCP-friendly behavior over a large time-scale.

• Jitendra Padhye, Jim Kurose, Don Towsley and Rajeev Koodli, A TCP-Friendly Rate Adjustment Protocol for Continuous Media Flows over Best Effort Networks, UMass-CMPSCI Technical Report TR 98-04, October 1998.
  This paper presents a congestion control algorithm for unicast traffic using the authors' modified version of the TCP-friendly equation. After each round of M time units, the sender estimates the roundtrip time. If any packets were lost in that round, then the sender sets the sending rate to that specified by the TCP-friendly equation for the loss rate experienced during that round. If no packets were lost in that round, then the sender doubles the sending rate. Simulations and experiments explore the behavior of this algorithm. The use of fixed rounds is a baseline policy against which alternate techniques for estimation of the packet loss rate will be compared.

• B. Whetten, J. Conlan, A Rate Based Congestion Control Scheme for Reliable Multicast. Technical White Paper, GlobalCast Communications, October 1998.
  This paper includes an evaluation of the adaptive range of congestion control characterized by of the TCP-friendly equation.

• Floyd, S., Connections with Multiple Congested Gateways in Packet-Switched Networks Part 1: One-way Traffic. Computer Communication Review, Vol.21, No.5, October 1991, p. 30-47.
  Section 5 of this paper introduces a simple "steady-state" model for analyzing additive-increase/multiplicative-decrease algorithms, and explores the relationship between the steady-state packet drop rate and connection roundtrip times, numbers of congested gateways, and window increase/decrease algorithms.

• Floyd, S., and Jacobson, V., On Traffic Phase Effects in Packet-Switched Gateways (compressed postscript, pdf). Internetworking: Research and Experience, V.3 N.3, September 1992, p.115-156.
  Section 3.3 of this paper discusses the relationship between TCP throughput and roundtrip times, and discusses a modified TCP window increase algorithm that would eliminate the dependence on the roundtrip time.

• T. Ott, J.H.B. Kemperman, M. Mathis, The Stationary Behavior of Ideal TCP Congestion Avoidance.
  This paper provides a detailed derivation of the 1/sqrt(p) performance model for TCP Congestion Avoidance. August 1996.

• T. Ott, J.H.B. Kemperman, M. Mathis, Window Size Behavior in TCP/IP with Constant Loss Probability.
  This paper is very similar in content to Stationary Behavior (above). November, 1996.

• Floyd, S., and Fall, K., Promoting the Use of End-to-End Congestion Control in the Internet. IEEE/ACM Transactions on Networking, August 1999.
  The Appendix of this paper discusses the "TCP-friendly" equation in some detail, gives the derivation in a simple "steady-state" model, and compares the equation with results from simulations.

• T. V. Lakshman, U. Madhow, B. Suter, Window-based Error Recovery and Flow Control with a Slow Acknowledgement Channel: a Study of TCP/IP Performance, Proceedings of Infocom '97, April 1997.
  Section 3.4 of this paper derives the formula for throughput vs. loss taking into account reverse path congestion. The constant in the p^(-1/2) result is modified by the ratio of transmission time of data packets divided by transmission time of ack packets.

• Henderson, T. and E. Sahouria, Improving Fairness of TCP Congestion Avoidance, Class project (WORK IN PROGRESS), May 1997.
  This paper explores the relationship between TCP throughput and roundtrip times for a range of TCP window increase/decrease algorithms.

• T. V. Lakshman, U. Madhow, The Performance of Networks with High Bandwidth-delay Products and Random Loss, IEEE/ACM Transactions on Networking, June 1997.
  Section 4 of this paper derives an approximate formula for loss vs. throughput. Section 5 has an approximate analysis of multiple TCP connections with different round-trip times sharing a bottleneck link.

• M. Mathis, J. Semke, J. Mahdavi, T. Ott, "The Macroscopic Behavior of the TCP Congestion Avoidance Algorithm",Computer Communication Review, volume 27, number3, July 1997.
  This paper compares TCP performance to the inverse-square-root of packet-loss model.

• Balakrishnan, H., How do Different Congestion Control and Avoidance Policies Influence Packet Loss Rates?, December 1997.
  While throughput is proportional to 1/sqrt(p) for additive-increase/multiplicative-decrease window algorithms, for "p" the packet drop rate, throughput is proportional to 1/p for multiplicative-increase/multiplicative-decrease, additive-increase/additive-decrease, and additive-decrease/multiplicative-increase algorithms. (URL to be posted shortly.)

• Padhye, J., Firoiu, V., Towsley, D., and Kurose, J., Modeling TCP Throughput: a Simple Model and its Empirical Validation, UMASS CMPSCI Tech Report TR98-008, Feb. 1998.
  This paper gives a characterization of TCP's steady state throughput, as a function of loss rate and RTT, that takes into account retransmit timeouts.

• J. Padhye, V. Firoiu and D. Towsley, A Stochastic Model of TCP Reno Congestion Avoidance and Control, Technical Report 99-02, Department of Computer Science, University of Massachusetts, Amherst.
  This report provides an in-depth stochastic analysis following the ideas in TR98-008 above.

Revised: Wednesday, 17-Feb-99 10:50:47 EST
URL: http://www.psc.edu/networking/tcp_friendly.html