Voip connection times out

[ianm]

I can set up a voip connection and everything runs fine, but after a while the voip session seems to time out. IVM does not appear to show anything in the log but the voip provider shows that the line is offline and a call to the voip number has "the service can not be connected".

Is there a setting somewhere that keeps the voip session alive when there is no activity.

I'm running an evaluation copy of 3.04 and using Gradwell voip service in the UK.