Recently the Gabcast people changed over suppliers and were forced to use the g726 codec on the IAX link. This caused me a few issues because I could not work out how to get my Grandstread to negotiate the correct codec… Finally solved it as follows:
-
Enabled the g726 codec via the “Asterisk IAX Settings” in “System Administration” section.
-
Add the following code in custom extensions file ("/etc/asterisk/extensions_custom.conf") to force use of the g726 codec for gabcast calls only.
;********** start **********
[gabcast-custom]
exten => _X.,1,SetVar,IAX_CODEC=g726
; end of [gabcast-custom]
; ********** end **********
I am now online again so hope this helps others who may be as foxed as I was 
Regards
-DJ