I have a UC520 which is connected to an ISTP (SIP Provider). Incoming ang outgoing calls are fine.
If i receive a call from a SIP based PBX the call is rejected for a reason.
If i make the call to the specific SIP based PBX, the call works fine.
From normal phones, e.g my mobile, my home phone or even IP based PBX that uses BRI for outgoing calls everything works fine.
Any suggestions? I have upload the debug ccsip from my uc520.