There are many reasons apart from these that ppp fails to connect and/or
operate properly.
Look in the PPP FAQ (which is really a series of questions and
answers). This is a very comprehensive document and the answers ARE
there! From my own (sad) experience, if the answer to your
problems is not there, the problem is NOT ppp's fault! In my case I was
using an ELF kernel that I had not upgraded to the appropriate
kernel modules. I only wasted about 2 days (and most of one night)
cursing what had been a perfect PPP server before the light dawned!
Free eBook: 
