[asterisk-dev] Asterisk 1.2 / chan_local / Polycom "302 Redirect"

[Gregory Boehnlein]

Hello,
	I'm trying to track down an issue w/ "squealing" noises on
call-redirects between a vanilla Asterisk 1.2 system, a Switchvox PBX (Rev
9525) and a Polycom 501 phone. I believe I understand the problem, but I
wanted a sanity check to my reasoning to see if I am just being stupid.

Here is the setup:

Server A: PSTN Gateway Server (SVN-branch-1.2-r90170) w/ a TE-405P
    
     SIP (G711 Ulaw)

Server B: Switchvox SMB (Rev 9525)
  
     SIP (G729)

Phone A: Polycom 501 (1.6.7 fimrware)

The call path is as follows:

1. Server A takes inbound TDM calls and forwards them to Server B using
SIP/G711U
2. Server B sends the call to the Polycom as G729
3. Polycom has the "Forward" feature enabled to an offsite number, which
sends a "302 Temporarily moved" message w/ the destination
4. Server B attempts to connect the call back to the PSTN via SIP/G711U to
Server A.

While the call is ringing, the caller hears ridiculous static, squealing
etc.. (basically codec mismatch) while until the destination user picks up,
then everything is fine. Furthermore, the following is printed out on the
Switchvox asterisk console for every frame:

1211483568 NOTICE[24529]: channel.c:2005 ast_read: Dropping incompatible
voice frame on Local/2164104184 at outgoing-5cb4,2 of format slin since our
native format has changed to ulaw
1211483568 NOTICE[24529]: channel.c:2005 ast_read: Dropping incompatible
voice frame on Local/2164104184 at outgoing-5cb4,2 of format slin since our
native format has changed to ulaw

If we use all Ulaw, this isn't an issue. It seems to be a problem when a
call is setup using G729 and then re-directed to a Ulaw channel. Perhaps the
codec is not re-negotiated on the second leg.... For fun, I tried adjusting
the "progressinband" settings (which are set to defaults all around) and
that didn't help.

Am I missing something? Or is this fundamentally retarded behavior in 1.2
that isn't fixable?

And no, I do not have the option of using G729 on between Server A and
Server B.