From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Doug Graham" Date: Sat, 05 Sep 2009 04:54:31 +0000 Subject: Re: [PATCH 0/2] Re: Do piggybacked ACKs work Message-Id: <4AA1EF07.20009@nortel.com> List-Id: References: <1251131172-20602-1-git-send-email-vladislav.yasevich@hp.com> In-Reply-To: <1251131172-20602-1-git-send-email-vladislav.yasevich@hp.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-sctp@vger.kernel.org > > Sorry, haven't had a lot of time to play with this until now. The > behaviour for > small unfragmented message looks fine, but if the message has to be > fragmented, > things don't look so good. I'm ping-ponging a 1500 byte message > around: client > sends 1500 bytes, server reads that and replies with the same message, > client > reads the reply then sleeps 2 seconds before doing it all over again. > I see no > piggybacking happening at all. A typical cycle looks like: > > 12 2.007226 10.0.0.248 10.0.0.249 SCTP DATA (TSN 7376) > 13 2.007268 10.0.0.248 10.0.0.249 SCTP DATA (TSN 7377) > 14 2.007313 10.0.0.249 10.0.0.248 SCTP SACK (TSN 7377) > 15 2.007390 10.0.0.249 10.0.0.248 SCTP SACK (TSN 7377) > 16 2.007542 10.0.0.249 10.0.0.248 SCTP DATA > 17 2.007567 10.0.0.249 10.0.0.248 SCTP DATA > 18 2.007615 10.0.0.248 10.0.0.249 SCTP SACK > 19 2.007661 10.0.0.248 10.0.0.249 SCTP SACK > > Those back-to-back SACKs look wasteful too. One should have done the > job, > although I suppose I can't be sure that SACKs aren't crossing DATA > on the wire. But the real mystery is why the SACKs were > sent immediately after the DATA was received. Looks like delayed SACKs > might be broken, although they are working for unfragmented messages. > It just occurred to me to check the TSNs too, and I've redone the annotation in the trace above with those. So the back-to-back SACKs are duplicates: both acknowledge the second data chunk (so they could not have crossed DATA on the wire). --Doug