Date: Tue, 07 Jan 1997 16:29:43 -0500 From: dennis <dennis@etinc.com> To: Tony Li <tli@jnx.com> Cc: isp@freebsd.org Subject: Re: FreeBSD as T1 router Message-ID: <3.0.32.19970107162940.00aab6f0@etinc.com>
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At 05:03 PM 1/6/97 -0800, you wrote: > > X.25 is just a protocol...why would one protocol work at 4Mbs and not > another? > >Well, because X.25 has a LOT more overhead. You might take a look at >what's really required. The link level has retransmissions and sliding >windows. And that's just for starters. Then, there's also the issue of >MTU.... > > There is no good reason to be able to run Frame Relay at > high speed and not X.25. > >Actually, there are some very, very good reasons. Obviously you are using the wrong hardware. With LAPB hardware, X.25 runs beautifully at high speeds. Its self-throttling, and, since its windowed, the speed of the host processes dont matter. You cant send more than a window, so slow devices just dont pass as much data. Its the way its SUPPOSED to work...protocols that is. Now I've had some real fun with a 2501 sending it single flag separated data at 2.5Mbs.... > if anything, X.25 should be more reliable because > it can be throttled by the receiver. We do X.25 at 10Mbs easily.....alas > theres not a lot of need for it :( > >Such as... there's no X.25 switch that does 10Mb/s? ;-) Because theres no market for it, not because it cant be done. many switches use the same processor that we do...but T3 is pretty uncommon overseas, and X.25 in the US...well.... >ET's serial card might do 10Mb/s, but the processor is just not there. >Unless you've started shipping 300Mhz Alpha's, and then just mebbe. ;-) And why does it take more cpu to do X.25 at 10Mbs than it does to do TCP/IP at 10Mbs? or are you saying that you need 300Mhz to do 10Mbs? With a 25mhz LAPB processor and a lightweight pentium you can run X.25 at 10Mbs...how much data you can pass depends on the speed of the receiver and what you're passing. But the processors run LAPB at 30Mbs or something (not V.35 of course)....anyone who runs soft LAPB is nuts...I've never seen one that wasnt a nightmare waiting to happen (ie...2501). I think you've been playing bit-stuffing with crappy hardware for way too long......because you seem out of the loop. Dennis
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