Date: Fri, 11 Jul 1997 11:37:26 -0400 (EDT) From: Robert Shady <rls@mail.id.net> To: dennis@etinc.com (dennis) Cc: rls@mail.id.net, isp@freebsd.org Subject: Re: T1/T3 Upgrade Options? Message-ID: <199707111537.LAA22297@server.id.net> In-Reply-To: <3.0.32.19970711111025.00c96100@etinc.com> from dennis at "Jul 11, 97 11:10:28 am"
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>>> 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? 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...
> 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.
-- Rob
===
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