[asterisk-users] No compatible codecs, not accepting this offer

[Markus]

For a few days now I'm getting

"chan_sip.c: No compatible codecs, not accepting this offer!"

on the CLI and in the messages log in irregular intervals. How can I 
find out what (who) is causing this? If I turn on "sip debug" I get 
flooded with SIP messages from peers/users (qualify=yes etc.) and it's 
hard to analyze.

Thanks!