Date: Wed, 20 Mar 1996 12:14:40 -0800 From: David Greenman <davidg@Root.COM> To: Joe Greco <jgreco@brasil.moneng.mei.com> Cc: nate@sri.MT.net (Nate Williams), freebsd-isp@freefall.freebsd.org Subject: Re: Microsoft "Get ISDN"? Message-ID: <199603202014.MAA03338@Root.COM> In-Reply-To: Your message of "Wed, 20 Mar 1996 12:19:40 CST." <199603201819.MAA29896@brasil.moneng.mei.com>
next in thread | previous in thread | raw e-mail | index | archive | help
>> > I am curious, why do you use SLIP for your dedicated connections? >> >> I don't speak for Joe, but I use SLIP (w/VJ compression) whenever >> possible since it uses less overhead and I seem to have lower latency >> and higher throughput than using both user-mode and kernel-mode PPP on >> FreeBSD boxes. > >I don't have anything to say about higher throughput since in my experience >it's only a mild difference, but the latency issue is mainly due to ppp's >default 1500 mtu. Lowering that (I know one fella who uses 296) will help >latency issues quite a bit. With 1500, you only get two or three packets >per second through the link if somebody is running a large transfer of some >sort. > >Most sites which run dedicated connections will have multiple people using >the link simultaneously, so the lower mtu gives the impression of faster >response. This hurts overall throughput mildly, buuuuut there's always a >tradeoff to be made. > >fyi: SLIP uses a 552 mtu. While this is true when using traditional modems, it is far less true when using modern modems with data compression. The modems themselves buffer a potentially large amount of data (1Kb or more of compressed data), and this will often make small MTUs perform worse in all respects because of the higher packet overhead. I know this through direct experimentation with different MTU values on several different 28.8K modems and the results of that are how I came up with the 552 value that we are currently using in FreeBSD. -DG David Greenman Core-team/Principal Architect, The FreeBSD Project
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199603202014.MAA03338>