IMac modem mystery

Question

I set up a 600MHz G3 iMac (10.3.9) for a client; the modem worked fine when I tested it, but now she says it sometimes can't connect -- about "1 time out of 15". When it doesn't connect, it will fail repeatedly ("5 or 6 times in a row") but then work okay later in the day. The ISP says there's no problem; and once when the iMac wouldn't connect she tried right then with her PC and it worked.
I've looked at the Internet Connect utility's Connection Log; where a successful connection is logged thus:
(date & time) : Version 2.0
Dialing (number)
Modem Reliable Link Established.
Modem Compression Established.
Serial connection established.
Using interface ppp0
Connect: ppp0 <--> /dev/cu.modem
... and IP & DNS numbers are listed
An unnsuccessful connection is logged thus:
Connect: ppp0 <--> /dev/cu.modem
LCP terminated by peer.
Hangup (SIGHUP).
Modem hangup.
Connection terminated.
Does anyone have any idea what this means? Is the modem going bad (I thought modems either worked or didn't work, not intermittent)? "LCP terminated by peer" sounds like something happening on the other end. Anyone know what SIGHUP means? I can replace the modem if necessary, but it's a pain so I'd like to learn what I can first.

Answer 1

Thanks for your response. As it turned out, I discovered I was able to duplicate the problem on my iBook at my house, which pretty well ruled out a cause in either the iMac or the phone line at the client's house. Consultation with the ISP determined that it was probably due to how I had the connection configured, i.e. using "[email protected]" rather than simply "username". For some reason, 90% of the time that would work, but 10% of the time it wouldn't. So I've corrected that, and we're hoping the problem won't recur. (The tech also suggested entering the DNS numbers, rather than allowing them to be retrieved automatically; he said "Macs require that," though I doubt this is true -- certainly not for EarthLink, which I use.)