HSTCP
Encyclopedia
HighSpeed TCP is a new congestion control algorithm protocol defined in RFC 3649 for TCP. Standard TCP performs poorly in networks with a large bandwidth delay product
. It is unable to fully utilize available bandwidth. HSTCP makes minor modifications to standard TCP's congestion control mechanism to overcome this limitation.
When an ACK is received (in congestion avoidance
), the window is increased by
and when a loss is detected through triple duplicate acknowledgments, the window is decreased by 
, 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.
Bandwidth-delay product
In data communications, bandwidth-delay product refers to the product of a data link's capacity and its end-to-end delay . The result, an amount of data measured in bits , is equivalent to the maximum amount of data on the network circuit at any given time, i.e. data that has been transmitted but...
. It is unable to fully utilize available bandwidth. HSTCP makes minor modifications to standard TCP's congestion control mechanism to overcome this limitation.
When an ACK is received (in congestion avoidance
TCP congestion avoidance algorithm
Transmission Control Protocol uses a network congestion avoidance algorithm that includes various aspects of an additive increase/multiplicative decrease scheme, with other schemes such as slow-start in order to achieve congestion avoidance....
), the window is increased by
and when a loss is detected through triple duplicate acknowledgments, the window is decreased by , 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 productsBandwidth-delay product
In data communications, bandwidth-delay product refers to the product of a data link's capacity and its end-to-end delay . The result, an amount of data measured in bits , is equivalent to the maximum amount of data on the network circuit at any given time, i.e. data that has been transmitted but...
.
HSTCP has the same slow start
Slow-start
Slow-start is part of the congestion control strategy used by TCP, the data transmission protocol used by many Internet applications. Slow-start is used in conjunction with other algorithms to avoid sending more data than the network is capable of transmitting, that is, to avoid causing network...
/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.
See also
- TCP congestion avoidance algorithmTCP congestion avoidance algorithmTransmission Control Protocol uses a network congestion avoidance algorithm that includes various aspects of an additive increase/multiplicative decrease scheme, with other schemes such as slow-start in order to achieve congestion avoidance....
- Transmission Control Protocol#Development of TCP