have found others in the community (via newsgroups) experiencing apparently
identical issue (see below for url).  persist option of pppd is being used to
allow the pppd process to linger after a link down event, and try to
automatically recover the link when the other end comes back.  after several
(hundreds) of ppp link up/down cycles, pppd is unable to recover when the other
end comes back -- messages are issued to syslog, as described in: 
--- http://www.uwsg.iu.edu/hypermail/linux/kernel/0208.3/0305.html ---
kill the failing pppd process, start a new one, and ppp communications resume.
tried (latest) errata kernel (2.4.18-18.8), which exhibits the same results. 
----------
Action by: jgiles
Issue Registered