MNP modems

[lauren at RAND-UNIX.ARPA]

While I can't comment on the transparency or lack of it within MNP
(I don't have enough info) I do know that one aspect of the advertising
of these modems could really cause problems for naive users.  Often
the manufacturers imply that since the MNP protocol is error correcting,
you don't have to worry about any other error-correcting software.
This is almost always NOT the case.  The fact that the data path between
modems may be error free says nothing about lost data between the
modem and the CPU, especially on small or busy systems, where loss can
occur at bps rates as low as 2400.  Usually the modem makers offer
flow control like ^S/^Q (which definitely isn't transparent and isn't
sufficient to avoid losing some data on many systems) to try
reduce this problem.  But it isn't enough, and many (most) systems
don't support alternate flow control systems in any case.  So while those
modems may theoretically protect "part" of the path, they do not
provide the full range of control and coordination that their advertising
frequently implies.  A surprise for the unwary.

--Lauren--