TCP windowing

TCP windowing

1. TCP provides mechanisms for flow control

   • Flow control helps maintain the reliability of TCP transmission by adjusting the rate of data flow between source and destination for a given session
   • Flow control is accomplished by limiting the amount of data segments forwarded at one time and by requiring acknowledgments of receipt prior to sending more.
   • To accomplish flow control, the first thing that TCP determines is the amount of data segments that the destination device can accept
     • Window size
       • The TCP header includes a 16-bit field called the window size. This is the number of bytes that the destination device of a TCP session is able to accept and process at one time.
       • The initial window size is agreed upon during the session startup via the three-way handshake between source and destination.
       • Once agreed upon, the source device must limit the amount of data segments sent to the destination device based on the window size.
       • Only after the source device receives an acknowledgement that the data segments have been received, can it continue sending more data for the session.

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