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This article mainly introduces what slow start in tcp congestion control refers to, has a certain reference value, interested friends can refer to, I hope you can learn a lot after reading this article, the following let the editor take you to understand it.

In the congestion control of tcp, slow start means that when the host just begins to send a message segment, the congestion window cwnd can be set to the value of the maximum message segment MSS; after each confirmation of a new message segment, the congestion window is increased by at most one MSS value; this method is used to gradually increase the congestion window cwnd of the sender.

Slow start:

The congestion window cwnd can be set to the value of the maximum message segment MSS when the host begins to send the message segment. After each acknowledgement of a new message segment is received, the congestion window is increased by up to one MSS. By using this method to gradually increase the congestion window cwnd of the sender, the rate at which packets can be injected into the network is more reasonable.

Congestion avoidance:

When the congestion window value is greater than the slow start threshold, stop using the slow start algorithm and use the congestion avoidance algorithm instead. The congestion avoidance algorithm makes the sent congestion window increase the size of a MSS for each round-trip delay RTT.

The fast retransmission algorithm stipulates:

As long as the sender receives three duplicate ACK in a row, it can conclude that a packet has been lost, and it should immediately retransmit the lost message segment without having to wait for the timeout of the retransmission timer set for the message segment.

Fast recovery algorithm:

When the sender receives three consecutive duplicate ACK, it resets the slow start threshold ssthresh

Unlike slow start, congestion window cwnd is not set to 1, but set to ssthresh

If the duplicate AVK received is n (n > 3), the cwnd is set to ssthresh

If the sending window value also allows to send a message segment, it will continue to send the message segment according to the congestion avoidance algorithm.

If you receive an ACK confirming the new message segment, reduce the cwnd to ssthresh

Multiplication decreases:

Whether in the slow start phase or the congestion avoidance phase, whenever there is a timeout (that is, a network congestion), the slow start threshold value ssthresh is set to the current congestion window value multiplied by 0.5.

When the network is congested frequently, the ssthresh value decreases rapidly to greatly reduce the number of packets injected into the network.

Add to increase:

It means that after the congestion avoidance algorithm is implemented, after receiving the confirmation of all the message segments (that is, after a round trip time), the congestion window cwnd is increased by a MSS size, so that the congestion window increases slowly, so as to prevent the network from congestion prematurely.

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