Wireshark-users: Re: [Wireshark-users] TCP Window Size and MTU/MSS
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From: Sake Blok <sake@xxxxxxxxxx>
Date: Thu, 10 Feb 2011 15:04:26 +0100
On 10 feb 2011, at 14:20, neerav panwar wrote:

> I have seen whatever be the receive window size, TCP sens ack after 2 or 3 packets of any length. It doesn't receive data as per window size.
> Exa: If receive window size is 64000 bytes and MSS/MTU is 1460 then ACK should come after 64000/1460 packets. But receiver always sends ack 
> after 2 or 3 packets maximum.
> The changes done on tcpackfrequency doesn't pay off on a windows XP.
> What is the way decrease the number of ACKs over the link?


See RFC 2581 part 4.2 :

   The delayed ACK algorithm specified in [Bra89] SHOULD be used by a
   TCP receiver.  When used, a TCP receiver MUST NOT excessively delay
   acknowledgments.  Specifically, an ACK SHOULD be generated for at
   least every second full-sized segment, and MUST be generated within
   500 ms of the arrival of the first unacknowledged packet.

(http://www.faqs.org/rfcs/rfc2581.html)

Cheers,


Sake