[plug] Modem disconnects

[doodli]

My serial Modem keeps on disconnecting and my ISP said it is my end 
hanging up.
Status is: connected
pppd[0]: Hangup (SIGHUP)
pppd[0]: Modem hangup
pppd[0]: Connection terminated.
pppd[0]: Connect time 114.2 minutes.
pppd[0]: Sent 1938912 bytes, received 18273866 bytes.
Status is: disconnecting
pppd[0]: Terminating on signal 15.
Status is: disconnecting
pppd[0]: Script /etc/ppp/ip-down finished (pid 9940), status = 0x0
Status is: disconnected
pppd[0]: Connect time 114.2 minutes.
pppd[0]: Sent 1938912 bytes, received 18273866 bytes.
pppd[0] died: A modem hung up the phone (exit code 16)

Have quickly searched google and the
Terminating on signal 15.

Error seems well known but nobody seems to know the why it happens.
Anybody have any ideas
Wally
doodli at beagle.com.au