*BSD News Article 73919


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From: sthaug@nethelp.no (Steinar Haug)
Newsgroups: comp.os.linux.networking,comp.unix.bsd.netbsd.misc,comp.unix.bsd.freebsd.misc
Subject: Re: Selective Hole NAK (Was: Re: TCP latency)
Date: 16 Jul 1996 17:25:04 GMT
Organization: Nethelp Consulting, Trondheim, Norway
Lines: 41
Message-ID: <4sgj9g$43t@verdi.nethelp.no>
References: <4paedl$4bm@engnews2.eng.sun.com> <31DC8EBA.41C67EA6@dyson.iquest.net>
	<4rlf6i$c5f@linux.cs.helsinki.fi> <31DEA3A3.41C67EA6@dyson.iquest.net>
	<Du681x.2Gy@kroete2.freinet.de> <31DFEB02.41C67EA6@dyson.iquest.net>
	<4rpdtn$30b@symiserver2.symantec.com>
	<x7ohlq78wt.fsf@oberon.di.fc.ul.pt>
	<Pine.LNX.3.91.960709020017.19115I-100000@reflections.mindspring.com>
	<x74tnfn35s.fsf@oberon.di.fc.ul.pt>
	<4s33mj$fv2@innocence.interface-business.de>
	<x7ivbrddzu.fsf@oberon.di.fc.ul.pt>
	<SOUVA.96Jul16134620@aibn58.astro.uni-bonn.de>
NNTP-Posting-Host: trane.uninett.no
In-reply-to: souva@aibn58.astro.uni-bonn.de's message of Tue, 16 Jul 1996 11:46:20 GMT
Xref: euryale.cc.adfa.oz.au comp.os.linux.networking:45431 comp.unix.bsd.netbsd.misc:4075 comp.unix.bsd.freebsd.misc:23750

[Ignatios Souvatzis]

|      TCP itself as a very poor behaviour if you have > 50% packet loss on a
|      link. By design TCP assumes that links (physical links) have a low packet
|   
|   This is true for classical TCP. However, some RFC (was it 1323(?))
|   proposes a mechanism to selectively NAK holes in the stream, which
|   would help. I'm not aware wether this is implemented anywhere.

You may find the following of interest.

Steinar Haug, Nethelp consulting, sthaug@nethelp.no
----------------------------------------------------------------------
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 

-- Hari Balakrishnan.