Linux PPP : how to debug disconnects with exit code = 16?

I'm using pppd and wvdial on my ARM Linux embedded system. I have a CDMA modem connected via a serial port and am connecting to the Verizon network. I am seeing that several times per day pppd exits with exit code 16 (see exact message from log below). How do I work out what is causing these disconnects? In particular what does the LCP terminated by peer message indicate? Feb 18 12:31:04 ts7600-47aad3 pppd: LCP terminated by peer Feb 18 12:31:04 ts7600-47aad3 pppd: Connect time 0.6 minutes. Feb 18 12:31:04 ts7600-47aad3 pppd: Sent 1044 bytes, received 0 bytes. Feb 18 12:31:04 ts7600-47aad3 pppd: restoring old default route to eth0 [1 92.168.98.1] Feb 18 12:31:07 ts7600-47aad3 pppd: Connection terminated. Feb 18 12:31:07 ts7600-47aad3 pppd: Modem hangup Feb 18 12:31:07 ts7600-47aad3 pppd: Exit. Feb 18 12:31:07 ts7600-47aad3 wvdial: Disconnecting at Tue Feb 18 12:31:07 2014 Feb 18 12:31:07 ts7600-47aad3 wvdial: The PPP daemon has died: A modem hung up t he phone (exit code = 16) Feb 18 12:31:07 ts7600-47aad3 wvdial: man pppd explains pppd error codes in more detail.