STUN Config for Cisco / Linksys Handsets Print

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STUN server address:


A STUN server is normally used if you're experiencing call problems such as "one way" audio, where you might hear the caller, but they can't hear you, or vice versa. This is normally caused by a Network Address Translation (NAT) problem in your local network, and the use of our STUN server will help overcome the issue.

In simple terms, a STUN server assists your extension's handset find and know it's external IP address, so that the correct traversal of audio can be completed between both parties in a call.

Enabling the use STUN depends on the type of handset you're using. Some examples are:


Cisco / Linksys SPA Range

Log into your phone via a web browser. Click Admin > Advanced.

On the "SIP" tab, there are two sections you will need to attend to.

Scroll to the RTP Parameters section.

RTP Packet Size: 0.020

Then, scroll to the bottom of the page and look for the NAT Support Parameters section.

Leaving all other settings at default, make the following changes:

- Handle VIA received: yes

- Insert VIA received: yes

- Substitute VIA Addr: yes

- STUN Enable: yes

- STUN Server:

- EXT RTP Port Min: leave blank

- Handle VIA rport: yes

- Insert VIA rport: yes

- Send Resp To Src Port: yes

- STUN Test Enable: no

- EXT IP: leave blank

- NAT Keep Alive Intvl: 15

Now, on an Extension or Line tab, make the following changes under the NAT Settings section:

- NAT Mapping Enable: yes

- NAT Keep Alive Enable: yes

Scroll down to the Proxy and Registration section, and make the following adjustments:

- Proxy:

- Use Outbound Proxy: yes

- Outbound Proxy:

- Use OB Proxy In Dialog: yes

Click "Submit All Changes" to save your new settings, and you should now find that the one-way audio issue is resolved.


Bear in mind that using STUN varies the behaviour of a handset, in that it needs to call to the STUN server before it will take a call.

On the Cisco/Linksys range of handsets, you'll see this in a pronounced way with the screen indicating the handset is contacting the STUN server before the call lights begin to flash, for example, an incoming call.

It's only when the lights are flashing that you can answer the call.

This is normal and expected behaviour, but requires some user adjustment to get used to it.


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