On Wed, 4 Feb 1998, Perry E. Metzger wrote:
Several people have noted to the Microsoft Support and Product groups that they want the Windows 95 PPP MTU to be set to 576 (down from 1500). this change is in Windows 98.
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accept a large MTU, no matter what Windows would like. The entire story sounds, to say the least, fishy.
I think what is really going on is that people tweaking on the MTU setting have discovered that for some unknown reason 576 just plain works better over a dialup PPP connection than ~1500 or any other value for that matter. My guess would be that it is in some way related to the packet latency generated by clocking in 1500 bytes over a ppp link (~500 ms PLUS the V.whatever overhead) A ~500 byte packet would be more like ~166 ms. I just did a real-world check of these numbers, and they seem pretty close to reality for a 28.8 connection. They're a little high for a 33.6. (real 33.6 numbers were 250 (total clock+v.?) and 412 for 500 and 1500 respectively) Now it's been a while since I looked at latency vs transfer rates, so maybe someone who works on this on an everyday basis would like to comment on what ~200 more ms of latency on a 28.8 link would do to throughput end-to-end across the net (totals of something like 350 and 512 ms end-to-end). I'm pretty certain though, that the common "myth" that 576 works better because of end-to-end MTU's is just that - a myth. My network is all 1500 or better - not sure if I've EVER seen anything less than 1500 or not in the last few years, but I doubt it. - Forrest W. Christian (forrestc@imach.com) ---------------------------------------------------------------------- iMach, Ltd., P.O. Box 5749, Helena, MT 59604 http://www.imach.com Solutions for your high-tech problems. (406)-442-6648 ----------------------------------------------------------------------