> I had experiments with FreeBSD SACK implementation. FreeBSD SACK > retransmits multiple segments respond to single dupack. It breaks > "packet conservation principle". > > In OpenBSD SACK implementation, > retransmission from SACK hole is limited to single segment. > "sack_rxmit" and "sendalot" are exclusive. > > I think solution is introducing mechanism to estimate amount of > outstanding segments. For example, "pipe" alogorithm is well known. > http://www.icir.org/floyd/talks/sf-sacks-96.pdf
Note that in RFC3517 we explicitly allow sending multiple retransmits on
a "dupack". Basically, SACK allows for robustness in the face of ACK
loss and so as long as the total amount of data sent is in line with the
congestion control algorithms this is fine.
The downside is that there is the potential for increased burstiness.
We don't think this is a terribly big deal. We have recent results that
say that small scale bursting doesn't hurt the connection all that
much. See:
Ethan Blanton, Mark Allman. On the Impact of Bursting on TCP
Performance. Proceedings of the Workshop for Passive and Active
Measurement, March 2005. To appear.
http://www.icir.org/mallman/papers/burst-pam05.ps
allman
--
Mark Allman -- ICIR -- http://www.icir.org/mallman/
pgp6vmg2sB3jA.pgp
Description: PGP signature
