I have a SIP TRUNK (PEER, no login needed), wont receive calls from outside (it can make them no issue), i hear you all saying its a firewall issue, and i believe it is INSIDE THE GRANDSTREAM due to some security isse.
UCM6208, both ports are SWITCH mode: (single IP address, one port in use)
- When making a call outside from a deskphone through the UCM to an outside number, works fine, HOWEVER if the call is dropped from the receiving party (my mobile) the call is never dropped in the UCM (no SIP message received from the ISP).
- When calling the number (from my mobile to the VoIP SIP at the ISP) it never gets to the UCM (no SIP message gets to the UCM).
The same firewall rules work fine for FREEPBX (just changed the internal IP address on the rule)
The UCM6208 works fine with a SIP Trunk that needs login (as expected as the T-sync was started from the UCM end and logs in every 60 seconds).
I seem to remember reading something about the WAN / LAN being different for this, i cant find any documentation from Grandstream, there SIP config has the PEERs logging in.
I am still looking now, i just had a failed migration from freePBX over this.