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Calculated window size

Level 1
Level 1


I captured some TCP comunication because there is a issue with long respons of some application.

I see in some TCP packets using Wireshark:

window size value:593

{Calculated window size: 151808}

{Window size scaling factor: 256}

Can this values indicate some issue?

Or is it correct?

I have other capture when respons of application is OK and there is still the same value "window size value" and "Calculated window size"



2 Replies 2

Joseph W. Doherty
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It's correct.

Window size is only two bytes, so it cannot be larger than 64KB.  To allow larger receive windows, another byte (I think actually 7 bits) were made an option to "scale" window size by some power of two.  So if scale "says" multiply 64KB by 4, actual window size is 256KB.

Windows scaling is an option of later TCP.  Older TCP stacks don't support it, and if they don't, they revert to using window size as is.

Thank you, I was looking for the same answer, RFC 1323 has more details.

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