I was (am) bitten by this again:

Sep 12 08:01:38 kyyhky pppd[3149]: LCP terminated by peer (Peer not
responding)

This happens when ftp'ing from gnome.labs.redhat.com.  I started gnome
installation last night and my PPP link has been going up and down all
night long because the ftp data packets block the transmission of LCP
echo packets.  pppd is too stupid to understand that receiving legal
IP packets also means the PPP link just *might* be up...

I hope this has been / will be fixed in 1.5 because the problem is
pretty annoying and there's very little you can do about it (well, you
can suspend ftp every two minutes and wait for some LCP echo packets
to get through.. ;)

LCP can be disabled, but in my experience, sometimes pppd locks up and
the LCP echo mechanism helps in getting the link restarted.

  -jm