Calls are extablishing fine between the Nortel and CUCM users over ISDN E1 PRI and vise versa.

However When the IP Phone calls the PBX Phone the PBX phone rings fine and the call is established but you cannot hear the PBX phone ringing through your IP Phone its just silence and then PBX user answers.

When a PBX phone calls an IP Phone the call establsihes fine and you can hear the remote IP Phone Ringing through PBX Phone.

Conclusion: When IP phone calls PBX Phone theres silence but the PBX phone does ring at the remote end.

Thanks