Date: Fri, 11 Jul 1997 17:13:32 -0700 From: Eddie Fry <eddie@eaznet.com> To: freebsd-isp@freebsd.org Subject: Re: T1/T3 Upgrade Options? Message-ID: <33C6CC2C.F1B@eaznet.com> References: <3.0.32.19970711171140.00e09220@etinc.com>
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dennis wrote: > > At 11:37 AM 7/11/97 -0400, you wrote: > >>>> A major factor to consider is that its very difficult to do 86Mbs (T3 is > >>>> full duplex) with an addon card on the PCI bus because the sustained > >>>> throughput rate is often pretty low. Other bus masters (ethernets, for > >>>> example) will futhur reduce the burst capability. While PCI bursts to > >>>> 128MB/s, very few PC products have sustained throughput rates over > 100Mb/s. > >>>> If you have a 100Mbs ethernet card on the same bus (you'd have to) the > >>>> number is cut in half. plus bus masters can't be controlled so you have > >>>> contention issues. > >>> > >>> Contention issues I'll agree with for the most part, however.. My > >>> calculations are (correct me if I'm wrong): > >>> > >>> T3 Card = ~12Mbytes/sec [ 90Mbits/sec] > >>> Ether = ~25Mbytes/sec [100Mbits/sec] > >>> ============= > >>> ~37Mbytes/sec > >>> > >>> 132 Mbytes/sec - PCI bus > >>> - 37 Mbytes/sec - Interfaces > >>> ================ > >>> 95 Mbytes/sec - Left to play with. > >> > >> Because you have no clue how the PCI bus really works (and that burst > >> rates are not sustainable), your Math is totally invalid. > >> Remember that ISA is a 64Mb/s medium and if you get 30Mb/s you > >> are lucky....the numbers are even more dramaticly worse when you add > >> bursts to the formula as with PCI. > > > >Invalid? I doubt it... In "real-life", how often do *MOST* T3 connections > >"sustain" 45Mbit/sec throughput in each direction? > > this depends on who your selling to. If you're building a card for little > weenie ISPs who only have 4Mb/s requirements, then maybe. But I think > that big ISPs have pretty busy links, and we're only talking about 2 or > 3 large, consecutive packets to potentially have a problem. > > >In "real-life", how > >often do ethernet cards "sustain" 100Mbit/sec throughput in each direction? > >I think my figures are right on the money, however.. Let's assume for a > >minute that you can only achieve 50% throughput on the PCI bus for whatever > >reason.. Assuming that the ethernet and the T3 card were running full tilt > >(Very, very unlikely in most situations) then with 1 ethernet and 1 T3 port > >you still have ((132Mbytes/2)-37Mbytes) = 29 Mbytes left over just for > >lolly-gagging around... > > "Bursts" are typically only a few words, so the rate you are using is just > totally invalid for this computation. > > 50% is still pretty good (sustained 2 cycle accesses)...and still bursts so > only a few words...... > > > > >> Ah, if life was only as easy as your trivial account of the world! > > > >This sounds a little bit sarcastic Dennis... This would *really* encourage > >me to purchase your products. A "Your a dumb-ass, we're not" attitude. > > Its very sarcastic :-) > > YOU'RE the one with the "you dont know what you're talking about" attitude, > which is OK if you're right, but you're not. Have you designed a PCI card > lately? > > Dennis Can you guys take your personal jabs off this list? I'm not saying your discussion isn't relevant, but the personal jabs are not needed. Thanks, Eddie
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