is@beverly.rhein.de writes:
> Has anybody looked at this?

I don't know, but SACK is one of the most important developments in
TCP in years. In conditions where more than a couple of packets in a
row drop, ordinary TCP dies a horrible death, but TCP with SACK keeps
on working. SACK is about to become an IETF standard, and it would be
a Very Very Very Good Thing if we put it into our kernels.

.pm

>    ----------------------------------------------------------------------
>    From: Hari Balakrishnan <hari@cs.berkeley.edu>
>    To: end2end-interest@ISI.EDU, tcplw@bsdi.com
>    Subject: TCP SACK implementation available
>    Date: Wed, 10 Jul 1996 13:41:17 -0700
> 
>    An implementation of the TCP SACK option based on the Jan. '96 IETF Draft 
>    (Mathis/Mahdavi/Floyd/Romanow) is available from:
> 
>    ftp://daedalus.cs.berkeley.edu/pub/tcpsack/
> 
>    The implementation is in the BSD/OS 2.1 kernel and is alpha code.
>    Source modifications to tcpdump (to handle SACKs) are also
>    included, as is a BSDI binary. Some (minor) additions and
>    modifications are planned to the kernel code in the near future.
>    This version of SACK has been in operation for several weeks now at
>    UC Berkeley (as part of the Daedalus project testbed,
>    http://daedalus.cs.berkeley.edu/), and for a few days now for
>    cross-country transfers.  Preliminary cross-country experiments
>    performed over the last week across 16-18 Internet hops indicate a
>    throughput improvement of between 30 and 50% on average over Reno,
>    without violating any of the standard congestion control and
>    avoidance mechanisms of TCP.
> 
>    Many thanks to Sally Floyd (LBNL), Srini Seshan (IBM), Vern Paxson
>    (LBNL), and Randy Katz (UCB) for several suggestions, comments and
>    help.
> 
>    Please send any comments, suggestions, bug reports, etc. to
>    hari@cs.berkeley.edu
> 
> Sounds promising to have a starting point for an implementation, (or
> maybe even and endpoint) given that my packed drop rate to/from pain
> is around 50% during the week.
> 
> Regards,
> 	Ignatios
>