CodePudding user response:
Network congestion: when the user demand for network resources, more than the server provides the number of available resources, then there is the phenomenon of congestion,If let this situation continue, network throughput is falling,
TCP provides four kinds of congestion control algorithm:
Slow start: every time after the complete transmission, CWND +=CWND
Congestion avoidance: every time after the complete transmission, CWND +=1
These two kinds of algorithms, defines a "congestion window" variables "CWND", "slow" in "slow start" algorithm is refers to the value is small; Then defines a "congestion avoidance algorithm enabled condition variables," "ssthresh", each time a data packet transmission, send number is equal to the CWND network resources, judging CWND and ssthresh first, to determine what kind of algorithm using
When the CWND & lt; Equals the ssthresh use slow start algorithm, both can, CWND & gt; Ssthresh used when congestion avoidance,
Assuming both AB forward message m1 - m9
Fast retransmission: just send something to B, if B received m3, m2 will always communicate confirm received signal, three times as long as you don't achieve A still continue to preach, to reach three times, after A will know you didn't receive the m3, then start the retransmission m3, don't need to counter after the timeout retransmission completely, there will not be mistaken for congestion situation,
Quick recovery: when B communicate three times after repeated confirmation signal, enable quick recovery algorithm
Set the CWND/=2, and then begin to execute congestion avoidance algorithm | | set ssthresh +=3
CodePudding user response:
The TCP congestion control algorithm in four1. Slow start
2. The congestion control
3. The fast retransmission
4. Quick recovery