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Setting up a direct external extension for 3CX has always been a bit of a lottery. It will work with some routers and not others. The 3CX proxu tunnel works OK but ou need a computer to use it - also if the internet connection drops either end it needs to be restarted manually sometimes.

I have used the following settings with SPA942, SPA921 and SPA504 phones with 100% success:

 

In the SIP tab

RTP Parameters

  Note the RTP port range - this must port forwarded in your router to the IP address of phone

  RTP Packet Size = 0.020

 
 NAT Support Parameters

  Handle VIA recieved = yes
  Handle VIA rport = yes
  Insert VIA recieved = yes
  Insert VIA rport = yes
  

To use STUN STUN Enable = yes
  STUN server = stun.3cx.com (or any public STUN server)
  EXT IP = blank

To use fixed IP STUN Enable = no
  STUN server = blank
  EXT IP = public IP of your 3CX system

 

Ext 1 tab


 NAT Settings

  NAT Mapping Enable = yes
  NAT Keep Alive Enable - yes

 Proxy and Registration

  Proxy = public IP of 3CX system
  Use Outbound Proxy = no

 Subscriber Information

  Display Name = display name
  User ID = extensiom number
  Password = password
  Use Auth ID = yes
  Auth ID = auth ID

 Dialplan

  Dialplan = [x*].

  (note the dot in dial plan)

 

The only downside is that you have to port forward the RTP ports in your router - this is the bit that some router allow through without forwarding.

If you want more that one phone as an external extension on the same network then change the RTP port range on the other phone(s) and forward that range to them in your router.

 

John Budden

3CX technician

Ponticello IT Solutions

01803 200402

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