TCP - difference between Congestion window and Receive window

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I try to understand the difference between Congestion window and Receive window.

As I understand, the receiver window is a buffer where the receiver can get the packets. The same is with the Congestion window which tell us the bound of the Receiver's abilities, and change according to lost packets, etc.

So what is the diffrence between them?

2 Answers

Initially, CongWindow is set equal to one packet. It then sends the first packet into the network and waits for an acknowledgment. If the acknowledgment for this packet arrives before the timer runs out, the sender increases CongWindow by one packet and sends out two packets. Once all of these packets are acknowledged before their timeouts, CongWindow is increased by two—one for each of the acknowledged segments. Now the size of CongWindow is four packets, and thus, the sender transmits four packets. Such an exponential increase continues as long as the size of CongWindow is below the threshold and acknowledgments are received before their corresponding timeouts expire.One important difference is that CongWindow changes in size but receive window size is always constant.

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