Subject: Re: [Tsvwg] Eifel draft and usage of time-stamps.

From: "sanjay kaniyar" <[email-masked]>
Date: Sun, 13 Jan 2002 16:40:12 -0800

Interesting example, Pasi.

>As Andrei pointed out to me, many implementations use a different (fixed?)
>version of timestamps which avoid this problem.

Can you please describe the rules for the fixed version?

Sanjay.

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From: Pasi Sarolahti <[email-masked]>
Date: Mon, 14 Jan 2002 09:19:29 +0200

On Monday 14 January 2002 02:40, sanjay kaniyar wrote:

> >As Andrei pointed out to me, many implementations use a different
> > (fixed?) version of timestamps which avoid this problem.
>

The original RFC 1323 has the following rule:

(2)  If Last.ACK.sent falls within the range of sequence numbers
     of an incoming segment:

     SEG.SEQ <= Last.ACK.sent < SEG.SEQ + SEG.LEN

     then the TSval from the segment is copied to TS.Recent;
     otherwise, the TSval is ignored.

Whereas an expired draft to update RFC 1323 available at
http://www.kohala.com/start/tcplw-extensions.txt changes the 
abovementioned condition to:

     SEG.TSval >= TSrecent and SEG.SEQ <= Last.ACK.sent

The latter condition would update TSrecent when incoming segment has 
already been received, for example because the sender has retransmitted 
the segment due to lost ACK. In my example, using the latter alternative 
the timestamp of the retransmission would have been echoed back and Eifel 
sender would not have considered the retransmission spurious, thus 
retransmitting the unacknowledged segments.

- - Pasi

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http://www.cs.helsinki.fi/u/sarolaht/