[Freeswitch-users] PCMU fallback for T.38

[Steve Underwood]

Gabriel Kuri wrote:
> once the FAX tone is detected on the PSTN side, FS receives a T.38
> re-INVITE from the provider and FS sends back a 488/Not Acceptable
> (proxy_media=false). at that point the provider than attempts fallback
> to PCMU with another reINVITE ...
>   

This part is interesting, and the subject of a discussion we had 
recently. A number of systems try that second re-invite after a 488, but 
the SIP specs say the call is pretty much dead after the 488 message is 
exchanged. Are they just hoping that maybe the other end will be 
non-compliant enough to keep the call alive, and recover its media mode, 
or haven't they read the specs?

Steve