Hello Dave
Here is part of the problem that was raised last week below.
I just tried dialing your number and had the problem a couple of times. It seems like the call is being answered by a modem or fax machine, so maybe it’s being routed incorrectly somewhere along the way. Hopefully Fred can try dialing your number a few times and confirm that when they hear the fax / modem tones that the call either is or isn’t going across the SIP trunk. Maybe when it fails it’s not even being routed over it. If it is being routed over it is the CS1k sending it to the right extension? Just a few ideas?.
Even if it were possible for the CS1K to intermittently route the call differently (which sounds unlikely!) I don’t think the CS1K could be redirecting to a fax or modem because it doesn’t ring first – you dial and then immediately get the modem noise. If you call a fax or modem you always get a ring or two before the fax/modem picks up the call.
Here is the answer below.
The problem was due to a missing dial-peer on one of our Cisco 5400 media-gateways (we have 20+in routing at any given time).
I built a specific dial-peer for your traffic profile and added it to all routers for TDM-IP conversion, one gateways configuration did not take. I have now corrected this and checked all other routers to ensure the UAL dial-peer is in place.
The tones you were hearing was the DSP answering the call as it had no destination to route the call.
I can't give out the complete email for security reasons, but I do hope that this may point you in the right direction as the fault was located by the SIP trunking provider within their own network and it was nothing to do with the Nortel / Customer end.
All the best
Firebird Scrambler
Meridian Programmer in the UK
If it's working, then leave it alone!.