Codecs for some internal calls

Hello everyone! This is my first post in this forum, so hope it goes ok! (excuse my english, please!)

I have a setup whith a PBX in central office, and some extensions are located in branch offices. I have VPN’s connecting this branch offices with central site, and have succesfully installed this extensions through the VPN. I’m having problems with quality of calls between one of the sites and some extensions in the central site. So I have two questions:

First is about debugging: How can I determine wich codec is being used in a particular call between extensions.
Second is about configuration: How can I force a codec for selected calls.

Thanks for any help in advance!!!

Hi, if you run ‘sip show channels’ from the asterisk manager you can see the codec being used on the channel.

You can set the codec for sip peers in the sip.conf file by using:


disallow=all disallows all codecs and allow=ulaw overrides this to allow the ulaw codec only

Mattk thanks for your answer. I’ve configured the system (it’s based on freepbx), and I’ll begin testing.
I was able to see some info with sip show channels, but i was wondering about a tethereal o tcpdump fitler to help me debug the issue.