HighSpeed TCP (HSTCP) is a

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 ...

protocol defined in RFC 3649 for

Transport 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 ...

(TCP). Standard TCP performs poorly in networks with a large

bandwidth-delay product In data communications, the bandwidth-delay product is the product of a data link's capacity (in bits per second) and its round-trip delay time (in seconds). The result, an amount of data measured in bits (or bytes), is equivalent to the maximum ...

. It is unable to fully utilize available bandwidth. HSTCP makes minor modifications to standard TCP's congestion control mechanism to overcome this limitation.

Algorithm

When an ACK is received (in

congestion avoidance 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 ...

), the window is increased by

a(w)/w

and when a loss is detected through triple duplicate acknowledgments, the window equals

(1-b(w))w

, where w is the current window size. When the congestion window is small, HSTCP behaves exactly like standard TCP so a(w) is 1 and b(w) is 0.5. When TCP's congestion window is beyond a certain threshold, a(w) and b(w) become functions of the current window size. In this region, as the congestion window increases, the value of a(w) increases and the value of b(w) decreases. This means that HSTCP's window will grow faster than standard TCP and also recover from losses more quickly. This behavior allows HSTCP to be friendly to standard TCP flows in normal networks and also to quickly utilize available bandwidth in networks with large bandwidth delay products. HSTCP has the same slow start/timeout behavior as standard TCP. Since only the congestion control mechanism is modified, HSTCP can be used with other TCP options like SACK. In real implementations, determining the increase and decrease parameters given a current window size is implemented as a lookup table.

References

{{Reflist

External links

HSTCP
Home Page. TCP congestion control

Algorithm

See also

References

External links