goldstein@DELNI.DEC.COM.UUCP (06/06/86)
While it may be interesting to speculate over why MNP Class 3 and DDCMP
work slowly together, I've gotta ask, WHY BOTHER? Both DDCMP and MNP
are error-detecting Data Link Layer (OSI model Layer 2) protocols.
DDCMP has been around a lot longer, and is typically implemented in
the host computer (i.e., on the DMR board in a VAX). MNP is implemented
in the modem, and handles terminal traffic, which (by definition, since
async terminals don't correct for errors) could use the help. But
running them both together is a waste, since DDCMP will correct the same
errors that MNP is trying to correct, so if you have MNP on, DDCMP will
never see an error (if MNP works as well). You also have overhead
from each protocols' checksum field.
So turn off MNP when using DDCMP! Turn it back on when running async
terminals. One good data link layer at a time is enough.
fred