Date: Sun, 30 May 1999 17:59:46 +0200 (MET DST) From: Luigi Rizzo <luigi@labinfo.iet.unipi.it> To: dgilbert@velocet.ca (David Gilbert) Cc: dgilbert@velocet.ca, wollman@khavrinen.lcs.mit.edu, freebsd-net@FreeBSD.ORG Subject: Re: Linux and Solaris tcp beating FreeBSD 4:1 Message-ID: <199905301559.RAA17069@labinfo.iet.unipi.it> In-Reply-To: <14161.30204.750053.989577@trooper.velocet.ca> from "David Gilbert" at May 30, 99 01:31:21 pm
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> Luigi> one wonders what is your config and why you have high losses > Luigi> (congestion or what ?). Lowering the MTU in some cases might > Luigi> help because it keeps more packets in flight and lets fast > Luigi> retransmit act earlier. > > As I explained in my first message, we're providing our selves with > ADSL. Since we are further than we should be from the other end, we either i did not see it or i missed that part -- sorry. > only barely get a connection. However, this gives us 816K up and 680K > down for about $10/month. It is worth some optimization on the link. > Fast retransmit is an something that reacts in less than a second? it reacts at the third duplicate ack, meaning 3 good packets after a loss. If you manage to have st least 4-5 pkts in flight you have a chance to trigger fast restransmit. Furthermore short packets in your case might reduce the pkt loss rate (for a given BER). In your case all standard TCP mechanisms will help very little, because they are end-2-end and furthermore they assume congestion-related loss, not noise-related loss. SACK probably won't help you because SACK need support on both sides (which is actually end-to-end for the way they work). short timeouts might be a solution in your case, but only in one direction unless you have access to _both_ sides of the ADSL link. If you have access to both sides of the adsl link, i think you might more effectively implement link-level retransmits (i am not sure, but it might be that ppp already does this). It could be a relatively simple project to implement within a FreeBSD-based router or bridge cheers luigi -----------------------------------+------------------------------------- Luigi RIZZO, luigi@iet.unipi.it . Dip. di Ing. dell'Informazione http://www.iet.unipi.it/~luigi/ . Universita` di Pisa TEL/FAX: +39-050-568.533/522 . via Diotisalvi 2, 56126 PISA (Italy) http://www.iet.unipi.it/~luigi/ngc99/ ==== First International Workshop on Networked Group Communication ==== -----------------------------------+------------------------------------- To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
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