Last night, I noticed two instances where my modem ppp link became inactive;
the lights on the modem indicated that everything was normal except that CTS
was not being asserted, and sure enough, TD was flickering (for a while)
until the modem deasserted DTR.  Shortly thereafter, it hung up.  PPP restarted
by itself, but it managed to happen twice in a row.  I changed the port baud
rate from 57.6K to 38.4K (hoping to stress the flow control logic less) but
I don't know for certain that it helped (since I went to bed right afterward).

If anyone has changed the com driver recently (like since June; I am now
running Sunday's sources), it would probably be good for them to desk-check
any changes they might have made in this area...