IP phone through VPN

  Flopper 13:05 02 Dec 2008

Not sure if this is the correct forum but I have an issue in that I cannot register an IP telephone handset as part of our 'network' and use it as an extension on our system.
The handset is in China along with a PABX and other handsets and a PABX are located in England.
A ping has been done and both sets of hardware are replying. All the IP addresses and settings, etc seem OK but our phone system suppliers cannot 'see' the handset to register it.
As the phone is going through a VPN we have been told that it is not a port issue, or if any are required they are already open.
Any suggestions.

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