SIP Trunks problems

[bpafc]

We are having severe issues with a customer suffering one way transmission during telephone calls on SIP trunks. They have a Panasonic KXTDA 30 with a SIP trunk card and 4 SIP trunks supplied by Entanet. The one way transmission is random, can happen on incoming or outgoing, be either way ie caller or called party cant hear, any time of the day, any length of call, any number of lines being used at the same time. We have started to eliminate things but this is difficult and taking a lot of time. We have changed the Trunk card on the PBX, we have changed the db level between the card and the trunk aswell. Our network guys have also started to adjust the MTU on the router but only marginally and we really wonder if changing this would help anyway. My main query is to find out what causes one way transmission on VoIP calls? The randomness of the fault really hampers our work and we would like an idea of where we can channel our efforts

Thank you

 

[Sympology]

Are there any firewalls in the way? Ports may be open in one direction only, dependant on what sets up the call, could open the port. It may be that a few calls can get through, then further calls are blocked as the ports are closed.

Only the truly stupid believe they know everything.
Stu.. 2004