Return to BSD News archive
Path: euryale.cc.adfa.oz.au!newshost.anu.edu.au!harbinger.cc.monash.edu.au!munnari.OZ.AU!news.mel.connect.com.au!news.mira.net.au!inquo!news.seinf.abb.se!news.mdh.se!columba.udac.uu.se!newsfeed.sunet.se!news00.sunet.se!sunic!news99.sunet.se!news.rccn.net!master.di.fc.ul.pt!usenet
From: Pedro Roque Marques <roque@di.fc.ul.pt>
Newsgroups: comp.os.linux.networking,comp.unix.bsd.netbsd.misc,comp.unix.bsd.freebsd.misc
Subject: Re: TCP latency in the presense of RFC1323 (Was: Re: TCP latency)
Date: 18 Jul 1996 18:01:58 +0100
Organization: Faculdade de Ciencias da Universidade de Lisboa
Lines: 34
Sender: roque@oberon.di.fc.ul.pt
Message-ID: <x7g26pa41l.fsf@oberon.di.fc.ul.pt>
References: <4paedl$4bm@engnews2.eng.sun.com>
<4rlf6i$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>
<4sbrcr$rqd@enomem.lkg.dec.com>
<SOUVA.96Jul16132215@aibn58.astro.uni-bonn.de>
NNTP-Posting-Host: oberon.di.fc.ul.pt
Mime-Version: 1.0 (generated by tm-edit 7.69)
Content-Type: text/plain; charset=US-ASCII
X-Newsreader: Gnus v5.2.25/XEmacs 19.14
Xref: euryale.cc.adfa.oz.au comp.os.linux.networking:45672 comp.unix.bsd.netbsd.misc:4108 comp.unix.bsd.freebsd.misc:23907
>>>>> "Ignatios" == Ignatios Souvatzis <souva@aibn58.astro.uni-bonn.de> writes:
Ignatios> In article <4sbrcr$rqd@enomem.lkg.dec.com>
Ignatios> matt@3am-software.com (Matt Thomas) writes:
Ignatios> There are a number of problems with the way timers
Ignatios> are implemented in TCP. The first is granularity. A
Ignatios> slow/fast timeout has an inaccuarcy of up to
Ignatios> 500ms/200ms. That may cause inaccuaries to creep into
Ignatios> round-trip estimates.
Ignatios> Shouldn't this be unimportant in the presence of the
Ignatios> RFC1323 round trip _measurement_ (instead of "educated
Ignatios> guessing", which old BSD TCP did)?
No.
Where talking about completly different things. RFC 1323 changes the
precision of the input to rtt (and rto) estimatives. We are talikng about
the internal software timer that has to go off when rto msecs have elapsed
since a unacked send or {random(0,200) in BSD, delay_ack_estimate in Linux}
has elapsed since the receive of a segment.
Also actually the input is only better if
a) you have broken messurements (Linux pre 2.0 had)
b) you retransmited the segment
Ignatios> (Assuming that no other part of the networking code
Ignatios> violates layering).
Is layering a "good thing" (TM) ? :-)
regards,
Pedro.