TCP congestion control
1. Congestion control is different from flow control. The latter acts on the receiver to ensure that the receiver has time to receive data. The former acts on the network to prevent too much data from congesting the network and avoid excessive network load.
2. Slow start algorithm: The
slow start algorithm is to slowly expand the sending window at the beginning of the transmission to avoid network congestion caused by the transmission of a large amount of data at the beginning.
Specific steps:
(1) Initially set the congestion window of the connection to 1MSS
(2) Multiply the window size by two every time an RTT is passed
(3) When the window size is greater than the threshold, the congestion avoidance algorithm will be started
3. Congestion avoidance algorithm The
congestion avoidance algorithm is to increase the size of each RTT window by one, so as to avoid exponential growth leading to network congestion, and slowly adjust the size to the best value
If network congestion occurs, then:
(1) Set the threshold to half of the current congestion window
(2) Set the congestion window to 1MSS
(3) Start the congestion avoidance algorithm
Supplement: RTT (Round-Trip Time): Round trip delay. It is an important performance indicator in a computer network. It represents the total time delay experienced from the start of sending data at the sender until the sender receives the confirmation from the receiver (the receiver sends the confirmation immediately after receiving the data).