The 576 value of the MS PPP MTU is merely a default - it can be changed with a registry hack.
Expecting the tens of millions of novice computer users to set their systems for a 1500 byte MTU is irrational. Those who are knowledgeable enough to do so are generally reducing it due to "speed up your modem" articles and programs which improve interactive performance at the expense of throughput.
i think you have two things confused. raising the mtu will "speed up the modem" since you get more data for less overhead, however *lowering* the mtu will increase interactivity, since each packet is smaller, the transmit time is shorter, so the next one can get in/out sooner. you stand a better chance of getting a "word" in edgewise if the other guy is using smaller "phrases". -- |-----< "CODE WARRIOR" >-----| codewarrior@daemon.org * "ah! i see you have the internet twofsonet@graffiti.com (Andrew Brown) that goes *ping*!" andrew@crossbar.com * "information is power -- share the wealth."