A school we look after has had a few issues with their ISP and builders recently, with several fibre breakages and power cuts as both managed to sever the respective cables on numerous occasions. The Polycom Group 300 came back up and tried to register with the VCS at the country HQ, and although the VCS saw and accepted the registration, the Polycom was insistent the it was not registered. We could see the registration request attempt and confirmation accept occur on the VCS every 30 seconds or so, but the Polycom device simply would not register.
We could ping/traceroute to the Polycom from the VCS and vice versa, so no issue with routeing. We could manually de-register the Polycom, and again after 30 seconds or so the registration would re-appear, but the Polycom unit would not show as registered. Rebooting the Polycom did not resolve the issue. It is as if the Registration Confirmation (RAS RCF) never gets to the Polycom - even though we can see the VCS send and retransmit these packets.
As a last ditch attempt, we rebooted the VCS, and lo and behold the registration was successful both on the VCS and on the Polycom, and calls could once again proceed as normal, but obviously this is not an ideal way to resolve this issue. It has occurred on at least three occasions, and each time the only thing we could do was to reboot the VCS to resolve the issue.
The Polycom is registering to a VCS-C. The network is internal, and although I am not privy to the full network infrastructure, I believe that we have asked if there are any firewalls between the endpoint and VCS-C, and the answer was negative.
We setup registrations based on an allow list determined by E.164, I can categorically state that there is no E.164 conflict. The only device to use this E.164 is the Polycom itself. Also remember that the VCS is ALLOWING the Polycom to register, it just never seem to get a acknowledgement of that from the CODEC, so times out, only to allow registration again, and again, and again..... until rebooted.
The odd thing is, that if the Polycom is registered OK, and is then powered off and powered back normally, all seems to be OK. It has only been when there has been a disruption to the service (2 network, 1 power) that this problem occurs, and can only be rectified with a VCS reboot - which is less than ideal.