Type of
Transmission Control Protocol
The Transmission Control Protocol (TCP) is one of the main protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the entire suite is commonly ...
which is designed to provide much higher throughput and
scalability
Scalability is the property of a system to handle a growing amount of work by adding resources to the system.
In an economic context, a scalable business model implies that a company can increase sales given increased resources. For example, a ...
.
Standard TCP recommendations as pe
RFC 2581an
RFC 5681call for congestion window to be halved for each packet lost. Effectively, this process keeps halving the throughput until
packet loss
Packet loss occurs when one or more packets of data travelling across a computer network fail to reach their destination. Packet loss is either caused by errors in data transmission, typically across wireless networks, or network congestion.Kur ...
stops. Once the packet loss subsides, slow start kicks in to ramp the speed back up. When the window sizes are small, say 1 Mbit/s @ 200 ms round trip time and the window is about 20 packets, this recovery time is quite fast—on the order of a few seconds. But as transfer speeds approach 1 Gbit/s, the recovery time becomes half an hour and for 10 Gbit/s it's over 4 hours.
Scalable TCP modifies the
congestion control algorithm
Network congestion in data networking and queueing theory is the reduced quality of service that occurs when a network node or link is carrying more data than it can handle. Typical effects include queueing delay, packet loss or the blocking of ...
. Instead of halving the congestion window size, each packet loss decreases the congestion window by a small fraction (a factor of 1/8 instead of Standard TCP's 1/2) until packet loss stops. When packet loss stops, the rate is ramped up at a slow fixed rate (one packet is added for every one hundred successful acknowledgements) instead of the Standard TCP rate that's the inverse of the congestion window size (thus very large windows take a long time to recover). This helps reduce the recovery time on 10 Gbit/s links from 4+ hours (using Standard TCP) to less than 15 seconds when the round trip time is 200 milliseconds.
See also
*
UDP-based Data Transfer Protocol
UDP-based Data Transfer Protocol (UDT), is a high-performance data transfer protocol designed for transferring large volumetric datasets over high-speed wide area networks. Such settings are typically disadvantageous for the more common TCP proto ...
References
External links
Scalable TCP DetailsCERN Paper About Scalable TCP
Internet protocols
TCP congestion control
Transport layer protocols
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