[Asterisk-Users] codec preference

[Mark Willis]

Need some help understanding codec preferences:

I have 2 asterisk servers.
Server 1 sends calls to the PSTN and has allow=g729 allow=gsm and 
allow=ulaw in iax.conf
Server 2 receives calls and routes them to server 1. It has the same 
allow lines.
We receive calls from a phone co and route them via server 2 to server 
1. The calls originate in g729 and everything works fine.

Now I want to take calls from FWD, which delivers calls in ulaw format, 
and have them routed by server 2 to server 1, which will play back a 
.gsm file. This doesn't work, and I get these diags on server 1:

       > requested format = ulaw,
       > requested prefs = (),
       > actual format = g729,
       > host prefs = (g729|gsm|ulaw),
       > priority = mine
    -- Executing Playback("IAX2/server1 at xxx.xxx.xxx.xxx:4569-12", 
"demo-insruct") in new stack
Jun  8 09:51:55 WARNING[46848]: file.c:489 ast_openstream_full: File 
demo-insruct does not exist in any format
Jun  8 09:51:55 WARNING[46848]: file.c:793 ast_streamfile: Unable to 
open demo-insruct (format g729): No such file or directory
Jun  8 09:51:55 WARNING[46848]: app_playback.c:90 playback_exec: 
ast_streamfile failed on IAX2/server1 at xxx.xxx.xxx.xxx:4569-12 for 
demo-insruct

demo-instruct.gsm does exist in the sounds dir.

So why doesn't server1 just accept the call in ulaw and play the 
message? Why does it force the call to g729?

Mark