I upgraded to Asterisk 1.6 some time ago, but didn’t think anything was wrong until recently. Calls coming in from Callcentric didn’t work: I received no audio. Everything had been working fine with Asterisk 1.4. I don’t get many calls, so initially I dismissed this as a temporary problem. Calls from my other four carriers kept working fine.
After some research, I noticed the following settings suggested by Callcentric:
session-timers=refuse session-expires=180 session-minse=90 session-refresher=uas
I’ve placed this in the [general] section of sip.conf, because calls from Callcentric arrive from multiple servers and the way Asterisk handles SRV records, only one of the servers ends up mapping into the per-carrier context at any given time. It doesn’t seem to have an adverse effect on calls from other carriers. (It is just turning off functionality new to 1.6, and setting some sensible defaults.)