[e2e] tcp retransmission packet size.

[David Borman]

> From: Tianbo Kuang <kuang at cpsc.ucalgary.ca>
> Subject: [e2e] tcp retransmission packet size.
> Date: Mon, 26 Nov 2001 14:56:41 -0700
...
> I noticed in a captured trace that a TCP sender actually retransmitted a
> bigger packet than the orignal one (after the ACK was dropped in the
> network). My question is,
> (1) Is this allowed by specification?

Yes.

> (2) If so, that means that a TCP receiver will always have to use the
> duplicated packet as the useful data as it contains more information. Is

No.  From RFC 793, page 53:

  When a segment overlaps other already received segments we reconstruct
  the segment to contain just the new data, and adjust the header fields
  to be consistent.

So, the duplicate data is trimmed off and just the new data is
processed.

		-David Borman, dab at bsdi.com