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Re: [tcpm] TCP tuning

Joe Touch <touch@ISI.EDU> Wed, 03 February 2010 22:59 UTC

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Date: Wed, 03 Feb 2010 14:59:21 -0800
From: Joe Touch <touch@ISI.EDU>
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To: Marco Mellia <mellia@tlc.polito.it>
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Subject: Re: [tcpm] TCP tuning
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Marco Mellia wrote:
...
> On the flip side,
> 
> - someone is already hacking the TCP rules:
> 
>   - google is "retransmitting" the SYN-ACK with a timeout of about
> 200ms. This causes spurious retransmission on practically all tcp
> connection on a 2.5G network (I remember a paper from FTW showing this...)
> 
>   - windows O.S. (at least XP) is triggering the fast retransmit at the
> third ACK, not at the third DUPLICATE ack
> check http://support.microsoft.com/?scid=kb%3Ben-us%3B224829&x=11&y=11
> if you don't believe it! Default value is 2 duplicate packets)
> 
>   - large initial windows are commonly seems. 16kB of initial window can
> be easily observed in any network. I suspect this is related to TCP
> Offloading Engines (TOE), that perform segmentation at the NIC, or the
> use of jumbo ethernet frames (9kB) -- the OS sees a "MSS" of 16kB (or
> 9kB), the initial windows is 1 segment => 10 (6) packets of 1500B each
> are then generated by the TOE.

See RFC2525; some of these may be candidates for 2525-bis.

Joe

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