Date: Thu, 18 Jul 2002 12:16:49 +0930 From: Greg 'groggy' Lehey <grog@lemis.com> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: Garrett Wollman <wollman@lcs.mit.edu>, cvs-committers@FreeBSD.ORG, cvs-all@FreeBSD.ORG Subject: Retransmission timeouts (was: cvs commit: src/sys/netinet tcp_timer.h) Message-ID: <20020718024649.GJ40633@wantadilla.lemis.com> In-Reply-To: <200207180228.g6I2Scpv004823@apollo.backplane.com> References: <20020717185653.C82638-100000@patrocles.silby.com> <200207180102.g6I129Gw004350@apollo.backplane.com> <200207180206.g6I266ma000510@khavrinen.lcs.mit.edu> <200207180228.g6I2Scpv004823@apollo.backplane.com>
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On Wednesday, 17 July 2002 at 19:28:38 -0700, Matthew Dillon wrote: > >> >> <<On Wed, 17 Jul 2002 18:02:09 -0700 (PDT), Matthew Dillon <dillon@apollo.backplane.com> said: >> >>> Actually, >>> I think the one second minimum is absurd anyway, so no, I am not >>> going to back it out. >> >> The standard says one second, period. It's not your choice to make. >> >> -GAWollman > > I've looked through five RFCs. I have been unable to locate any > lower bound requirement fro the retransmission timeout. The best > I've found is in RFC1122, 4.2.3.1: > > The recommended upper and lower bounds on the RTO are known > to be inadequate on large internets. The lower bound SHOULD > be measured in fractions of a second (to accommodate high > speed LANs) and the upper bound should be 2*MSL, i.e., 240 > seconds. > > All the other references I've found... New Reno and the two > congestion control RFCs (one being the fast-retransmit RFC) simply > state something on the order of 2*RTT or something similar. > > RFC793 has an eample of an RTO timeout calculation where it says > > "where UBOUND is an upper bound on the timeout (e.g., 1 minute), > LBOUND is a lower bound on the timeout (e.g., 1 second), ALPHA is > a smoothing factor (e.g., .8 to .9), and BETA is a delay variance > factor (e.g., 1.3 to 2.0)." > > This is obviously NOT a requirement of any sort, and besides it is in > RFC793... an extremely old RFC (1981). I'd put money on Garrett coming up with some reference somewhere. But that's not important. Things change, and we have to change with them. This change looks like a logical adaptation to changed network speeds. If it contravenes some standard, why not make it configurable? IMO the default should be "on". Greg -- Finger grog@lemis.com for PGP public key See complete headers for address and phone numbers To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-all" in the body of the message
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