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Congestion window, transmission window difference

Level 1
Level 1

Hi, I`m sort of new here, and currently working on my bachelor theses. I`ve done lots of searching on various websites, but still confused about terms: Congestion window and Transmission window. Can anybody help on this topic, PLEASE?

3 Replies 3

Wilson Bonilla
Level 3
Level 3

Hello Radim.

The transmission window is the amount of data which can be in transit between two endpoints at a given  time. Because of the reliable nature of TCP, a TCP sender can transmit  only a limited amount of data before it must receive an acknowledgement  from the receiver; this is to ensure that any lost segments can be  retransmitted efficiently.

The congestion window is a variable that directly affects the transmission window, this is a value advertise by the send to the TCP peer receiver .

At any given time, the send must not send data when a congestion flag is set in the TCP header.

I hope this helps.


Wilson B

Hi Wilson,

Sorry for late reply, but yes, that helped. By the time I saw yr answer I`ve read some info about it and got a small picture about the windows. As i can see, you`re sort of proffesional in this area. Do you have any experience with Linux? regarding TCP and networking.

I really appreciate your help.


Radim H.

Joseph W. Doherty
Hall of Fame
Hall of Fame


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Have you reviewed the RFCs?