Subject: [Tsvwg] question on TCP send window update

From: "Leah Shalev" <[email-masked]>
Date: Thu, 21 Nov 2002 09:56:32 +0200

Probably I am missing something vary basic about the send window update
algorithm (RFC 793).

In particular, I have a question regarding SND.WL2 variable. Apparently it
should be always equal to SND.UNA.
I was trying to figure out when can it be different (to justify its
existence). After a while, I did find one case it can be different: a
retransmitted data segment carries new acknowledge number; SND.UNA is
updated and SND.WND is not updated since SEG.SEQ < SND.WL1. Then I started
to wonder what is the state of the send window at this point: the left edge
moved, while the [old] window size did not change, so it seems that the
right edge is messed up. So I am back to my original question: why it
should be possible to have SND.WL2 different from SND.UNA.

I would appreciate any help on this.

Thanks,
Leah Shalev

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