Hi,
It's not congestion as we have other customers on the same service at the same exchange, we do have an open ticket and have spoken to the customer, we have also called a few other customers on the same exchange to see if they are having the same issues and none of them do. The other thing with this customers fault is the latency goes up at about the same time, it does look like congestion but we would expect others on the same exchange to report the same issues. Very odd! This is our with the carriers at the moment.
Ah, yeah - doesn't sound like congestion then. If it's not affecting other customers then it is rather odd. Does the modem resync? If it does then one option might be to try DMT if their modem is compatible:
http://dmt.mhilfe.de/
If you have SRA on your systems then it would lend credence to that. Otherwise if there's no resyncing I would wonder how long a modem will hold on before giving up. If it's tenacious perhaps it'll put up with a lot of errors instead?