Date: Sun, 15 Dec 2002 12:44:54 +1030 From: Greg 'groggy' Lehey <grog@FreeBSD.org> To: Bsd Neophyte <bsdneophyte@yahoo.com> Cc: FreeBSD Questions <questions@FreeBSD.org> Subject: Re: Hubs and switches (was: uninformed qstn...) Message-ID: <20021215021454.GA53628@wantadilla.lemis.com> In-Reply-To: <20021215020733.46093.qmail@web20106.mail.yahoo.com> References: <20021215012545.GB144@wantadilla.lemis.com> <20021215020733.46093.qmail@web20106.mail.yahoo.com>
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On Saturday, 14 December 2002 at 18:07:33 -0800, Bsd Neophyte wrote: > > --- Greg 'groggy' Lehey <grog@FreeBSD.org> wrote: >> I'm not sure you meant to write what you did, but I'm not 100% I >> understand. But yes, latency isn't an issue. Even if it is, switches >> still win. > > My point is that generic switches are not faster than hubs, because of the > added latency associated with the store-and-forward method. Cisco 2900's > have the ability to do both types of switching. > >> I tried a test here between two machines on my network. In each case, >> the data went via the Cisco 2900 switch and then either via a hub or a >> second switch. The remote machine has a 10 Mb/s interface. Here are >> the results (average ping time): >> >> Switch, normal ping: 0.756 ms >> Hub, normal ping: 0.744 ms >> >> Switch, 1500 bytes: 4.251 ms >> Hub, 1500 bytes: 4.004 ms >> >> Switch, 1500 bytes, load: 4.244 ms >> Hub, 1500 bytes, load: 4.513 ms >> >> The "load" was a single concurrent tar over the network. I must say >> I'm impressed how little degradation there was, but it's clear that >> the latency savings on a hub are more than offset by its performance >> under load. > > I would offer the rebuttal that when you look at costs, having a hub > deal with 12-16 nodes would more than suffice. For some definition of "suffice". But why? > For example, a new catalyst 2912, depending on options, will run you > between $2000-$5200, while a 12 port fast ethernet hub will run you > about $200-$300. If you spend that much money on a hub, you're really wasting it. As discussed on this thread, you can buy 16 port switches for under $100. > BTW, I don't know if your switch is configured for cut-through > switching or store-and-forward. If it is set for store-and-forward, > I'd suggest you change it to cut-through. I don't care. We're looking at a difference of 200 µs here. > I suppose if there isn't a big price difference between a generic > switch and a hub, the switch would seem to be a better bet. There isn't, and that's the point we've all been making. Greg -- When replying to this message, please copy the original recipients. If you don't, I may ignore the reply or reply to the original recipients. For more information, see http://www.lemis.com/questions.html See complete headers for address and phone numbers To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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