FAST TCP is a variant of TCP networking protocol, developed at the California Institute of Technology, with a congestion control algorithm especially targeted at high-speed, long-distance links. It is compatible with existing TCP algorithms, requiring modification only to the computer which is sending data. The Transmission Control Protocol (TCP) is a virtual circuit protocol that is one of the core protocols of the Internet protocol suite, often simply referred to as TCP/IP. Using TCP, applications on networked hosts can create connections to one another, over which they can exchange streams of data using... It has been suggested that this article or section be merged with protocol (computing). ... The California Institute of Technology (commonly referred to as Caltech)[1] is a private, coeducational university located in Pasadena, California, in the United States. ... The TCP uses a network congestion avoidance algorithm that includes various aspects of an additive-increase-multiplicative-decrease (AIMD) scheme, with other schemes such as slow-start in order to achieve congestion avoidance. ... A BlueGene supercomputer cabinet. ... In general, data consist of propositions that reflect reality. ...

Principles of operation

The role of congestion control is to moderate the rate at which data is transmitted, according to the capacity of the network and the rate at which other users are transmitting. Like TCP Vegas, FAST TCP uses queueing delay instead of loss probability as a congestion signal. A telecommunications network is a network of telecommunications links arranged so that messages may be passed from one part of the network to another over multiple links. ... TCP Vegas is a TCP congestion control, or network congestion avoidance, algorithm that emphasizes packet delay, rather than packet loss, as a signal to help determine the rate at which to send packets. ... In computer engineering, a queueing delay is the time a job waits in a queue until it can be executed. ... This page meets Wikipedias criteria for speedy deletion. ...

Most current congestion control algorithms detect congestion and slow down when they discover that packets are being dropped, so that the average sending rate depends on the loss probability. This has two drawbacks. First, low loss probabilities are required to sustain high data rates; in the case of TCP Reno, very low loss probabilities are required, but even new variants such as H-TCP, BIC and HS-TCP required loss rates lower than those provided by most wireless wide area networks. Moreover, packet loss only provides a single bit of information about the congestion level, whereas delay is a continuous quantity and in principle provides more information about the network. A wide area network or WAN is a computer network covering a broad geographical area. ...

A FAST TCP flow seeks to maintain a constant number of packets in queues throughout the network. The number of packets in queues is estimated by measuring the difference between the observed round trip time (RTT) and the base RTT, defined as the round trip time when there is no queueing. The base RTT is estimated as the minimum observed RTT for the connection. If too few packets are queued, the sending rate is increased, while if too many are queued, the rate is decreased. In this respect, it is a direct descendant of TCP Vegas. In telecommunications, the term round-trip delay time or round-trip time (RTT) has the following meanings: The elapsed time for transit of a signal over a closed circuit, or time elapsed for a message to a remote place and back again. ...

The difference between TCP Vegas and FAST TCP lies in the way in which the rate is adjusted when the number of packets stored is too small or large. TCP Vegas makes fixed size adjustments to the rate, independent of how far the current rate is from the target rate. FAST TCP makes larger steps when the system is further from equilibrium and smaller steps near equilibrium. This improves the speed of convergence and the stability.

Strengths and weaknesses

Delay-based algorithms can, in principle, maintain a constant window size, avoiding the oscillations inherent in loss-based algorithms. However, they also detect congestion earlier than loss-based algorithms, since delay corresponds to partially filled buffers, while loss results from totally filled buffers. This can be either a strength or a weakness. If the only protocol used in a network is delay-based, then the inefficiency of loss can be avoided; however, if loss-based and delay-based protocols share the network, then delay-based algorithms tend to be less aggressive. This can be overcome by suitable choice of parameters, leading to complex interactions studied by Tang et al.

Delay measurements are also subject to jitter as a result of operating system scheduling, or bus contention. An operating system (OS) is a computer program that manages the hardware and software resources of a computer. ... In computer architecture, a bus is a subsystem that transfers data or power between computer components inside a computer or between computers and typically is controlled by device driver software. ...

Whether the strengths or weaknesses prevail is not clear, and depends in large part on the particular scenario.

Intellectual property

Unlike most TCP variants, FAST is protected by several patents^[1][2]. Instead of seeking standardization by the IETF, the inventors of FAST, notably Steven Low and Cheng Jin, are seeking to commercialize it through the company FastSoft. The Internet Engineering Task Force (IETF) is charged with developing and promoting Internet standards. ...

Name

The name FAST TCP is a recursive acronym for Fast AQM Scalable TCP, where AQM stands for Active Queue Management, and TCP stands for Transmission Control Protocol. A recursive acronym (or occasionally recursive initialism) is an abbreviation which refers to itself in the expression for which it stands. ...

References

• FAST TCP: motivation, architecture, algorithms, performance David X. Wei, Cheng Jin, Steven H. Low and Sanjay Hegde. IEEE/ACM Trans. on Networking, to appear in 2007.
• FAST TCP: from theory to experiments Cheng Jin, David X. Wei, Steven H. Low, G. Buhrmaster, J. Bunn, D. H. Choe, R. L. A. Cottrell, J. C. Doyle, W. Feng, O. Martin, H. Newman, F. Paganini, S. Ravot, S. Singh. IEEE Network, 19(1):4-11, January/February 2005.
• Network Equilibrium of heterogeneous congestion control protocols Ao Tang, Jiantao Wang, Steven H. Low and Mung Chiang. Proc. IEEE Infocom, Miami, FL, March 2005.

1. ^ Jin, Cheng; Low, Steven H.; Wei, Xiaoliang (2005-01-27). Method and apparatus for network congestion control. United States Patent & Trademark Office. Retrieved on 2006-11-05.
2. ^ Jin, Cheng; Low, Steven H.; Wei, David X.; Wydrowski, Bartek; Tang, Ao; Choe, Hyojeong (2006-03-09). Method and apparatus for network congestion control using queue control and one-way delay measurements. United States Patent & Trademark Office. Retrieved on 2006-11-05.

2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ... January 27 is the 27th day of the year in the Gregorian calendar. ... The United States Patent and Trademark Office (PTO or USPTO) is an agency in the United States Department of Commerce that provides patent and trademark protection to inventors and businesses for their inventions and corporate and product identification. ... For the Manfred Mann album, see 2006 (album). ... November 5 is the 309th day of the year (310th in leap years) in the Gregorian Calendar, with 56 days remaining. ... For the Manfred Mann album, see 2006 (album). ... March 9 is the 68th day of the year in the Gregorian Calendar (69th in Leap years). ... The United States Patent and Trademark Office (PTO or USPTO) is an agency in the United States Department of Commerce that provides patent and trademark protection to inventors and businesses for their inventions and corporate and product identification. ... For the Manfred Mann album, see 2006 (album). ... November 5 is the 309th day of the year (310th in leap years) in the Gregorian Calendar, with 56 days remaining. ...

See also

• H-TCP
• BIC TCP
• HSTCP

This article or section does not cite its references or sources. ... BIC TCP (Binary Increase Congestion control) is another implementation of TCP with a optimized congestion control algorithm for high speed networks with high latency (LFN: Long Fat Networks). ... HighSpeed TCP also called HSTCP is a new congestion control algorithm for TCP protocol. ...

External links

• FAST Homepage
• Supercomputing 2005 Bandwidth Challenge