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NAT issues

Some of the biggest problems that plague people such as "one way audio" or "Calls dropping after XX Seconds" are caused by NAT not being correctly setup.

Make sure you have a resolvable address on the Internet.

If you don't want to pay a few bucks to get a static IP address, and are served by an ISP that periodically changes your IP address, then get an account with a dynamic DNS service such as DynDNS . Your router may already have built-in support for one or more of these services, if so, use one that your router supports and then configure your router to automatically update your dynamic address when your ISP changes your IP address. Failing that, you can set up an updater program such as inadyn, there are instructions for doing that at this blog page

Adding NAT information in  FreePBX 

All of your settings will be under Settings > Asterisk SIP settings

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Set NAT as yes

Static IP from your ISP 

Select "Static IP" and enter your external IP

Dynamic IP Updated through dynamic IP service

Select "Dynamic IP" and put the Full host name in such as  "foo.dyndns.net"

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After clicking "submit changes" and the Red Apply click "General SIP Settings" on the right menu

Local Networks

Under "NAT" you will see a box for "Local Networks" 

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Click "Submit changes" And the red "APPLY" button.

RTP Port Range

Open the SIP and RTP ports to your Asterisk server

You must make sure that you open the correct UDP ports in your router's firewall and pointed at your Asterisk server. For SIP protocol, open UDP (NOT TCP) port 5060 (SIP) AND ports 10000-20000 (RTP, which must also be defined in /etc/asterisk/rtp.conf, see below). All these ports are UDP, opening the TCP ports will NOT help anything and may expose your system needlessly. While you are in your firewall configuration, you may as well also open UDP port 4569 (IAX), since sooner or later you'll probably want to accept IAX connections.

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