When sending a packet (segment), a station includes in the TCP header the
current size of its receive window. In your example, the sender is saying
that its receive window is 28765 bytes. The station is saying, "you can
send me 28765 bytes without stopping and waiting for an acknowledgement."
That's about 20 1500-byte packets. That's not really very big when you
consider the low cost of memory these days. (Buffer size is based on
available memory.)
If you study a protocol analyzer trace, you may see the receive window size
shrink as the station's receive buffers start to fill up. Probably an
application will come along, though, and grab the received bytes, clearing
up space in the buffer. So the station will acknowledge some data and slide
its window back open.
You can see evidence of the sending window also by tracking TCP sequence
numbers. The size of the sending window is determined by the recipient's
receive window. It's easier to just track receive windows because a station
explicitly specifies the number of bytes in its receive window on every
packet it sends.
Priscilla
At 12:05 PM 10/17/00, Billy Monroe wrote:
>Hello:
>
>Is there any way to see the size of the (sliding) window when transmiting a
>TCP packet ?
>
>I saw a "Window" field using a sniffer and the number was big 28765...
>Please correct me if I am wrong: I believe that is the buffer of the
>receiving station.
>
>Thanks,
>
>Ronaldo
>
>
>
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Priscilla Oppenheimer
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