[asterisk-users] T.38 pass-through 488 handling problem

[Steve Underwood]

Klaus Darilion wrote:
> Atis Lezdins schrieb:
>   
>> On Mon, Jun 8, 2009 at 2:06 PM, Klaus
>> Darilion<klaus.mailinglists at pernau.at> wrote:
>>     
>>> Hi!
>>>
>>> I have the following problem with Asterisk 1.4.23:
>>>
>>>
>>> ATA w/ T.38             Asterisk          ATA w/o T.38
>>>     --------INVITE-------->
>>>                             --------INVITE-------->
>>>                             <-------200OK----------
>>>     <-------200OK----------
>>>     --------ACK----------->
>>>                             --------ACK----------->
>>>
>>>
>>>     --------INVITE w/T.38->
>>>                             ------INVITE w/ T.38-->
>>>                             <-----488--------------
>>>                             ------ACK------------->
>>>                             ------BYE------------->
>>>                             <-----200--------------
>>>
>>> Asterisk does not forward the 488 back to the caller, but hangs up the
>>> callee's call leg. Further, the caller's call leg will not be hung up.
>>>
>>> Is somebody aware of this problem and a fix?
>>>
>>>       
>> T.38 passthrough is possible if BOTH devices support T.38, so Asterisk
>> don't have to transcode anything.
>>
>> You could try 1.6 with some gateway app (don't remember if there
>> exists any and in what state), or just write a RxFax which would then
>> generate call with TxFax.
>>     
>
> That's not the problem. Asterisk should just relay back the 488 so that 
> Faxing happens with g.711.
>   
There seems to be a common misconception about 488. It represents an 
irrevocable failure of the call. Once a 488 is sent the call is 
essentially dead. A number of systems are able to continue beyond a 488, 
and allow further renegotation to another codec, but that it 
non-standard behaviour. The correct thing is to offer the options of 
T.38, u-law and A-law. If the other side can't do T.38, it should accept 
u-law or A-law. If it says 488, your dead.

Steve