We have a campus radio station which uses comrex blue box devices to broadcast audio. These comrex devices work fine over direct telco analog lines but have various problems on our VOIP system. I have it connected to a VG 202, have modem passthrough enabled everywhere. Calls connect and seem to stay connected but constantly 'retrain' during which there are silences in the broadcast. I contacted the comrex vendor and they were not very helpful, just indicated it will not work over VOIP. Why? Is there any way to make this work? It uses a synchronous POTS codec. Is there any tweaking/tuning that can be done either on the VG 202 or gateway routers (all MGCP) to improve performance?
Call traces do not indicate problem, CDR does not show jitter/lost packets/latency, etc...
According to comrex documentation retraining occurs 'if codec loses sync' or 'if it senses errors on line'.
Any help would be appreciated. I have been pulling my hair out on this!