Date: 21 Jun 1998 15:21:54 -0400 From: Robert Sanders <rsanders@mindspring.net> To: hackers@FreeBSD.ORG Subject: Re: TweakDUN Message-ID: <knzpf68srx.fsf@xena.mindspring.com> In-Reply-To: bmah@CA.Sandia.GOV's message of "Fri, 19 Jun 1998 23:44:51 -0700" References: <Pine.BSF.3.96.980619220851.25847A-100000@super-g.inch.com> <199806200644.XAA24111@stennis.ca.sandia.gov>
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bmah@CA.Sandia.GOV (Bruce A. Mah) writes: > I don't use dialups very often nowadays, but I dimly remember trying to > negotiate a *smaller* MTU on a downlink, in order to try to get better > interactive performance (mumble mumble, use IP TOS bits and smarter queueing, Reordering packets doesn't help on a dialup link if you have a bulk transfer going with 1500 byte packets. Even if you put "interactive" priority packets at the head of the queue, you may already have a 1500 byte packet in progress. Worse, most modems have significant local buffering to accomodate MNP/v.42bis compression so there may be even *more* than one packet's worth of delay depending on exactly how close to the wire the queuing algorithm lives. Some people have proposed "fragmenting" the packets at layer 2 (or 2.5, whatever PPP is) with MP so that interactive packets can be inserted into the middle, but I can't say off the top of my head whether that's going to be any more efficient than just using IP fragmentation and/or a small MSS. Somebody else already pointed out that VJ header compression significantly reduces packet overhead. On the other hand, with my network architect's hat on I don't like the idea of tripling the rate of packets per sec through already busy major exchanges and core routers. regards, -- Robert To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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