[asterisk-dev] fallback to audio faxing when T.38 INVITE fail with 488/606 Not acceptable

[Kristijan Vrban]

Hello, i use 1.4 asterisk (1.4.28 and svn) to make T.38 passthrough
between a Siemens hiQ9200 (british telecom) and an asterisk 1.6.2 with
app_fax/spandsp as T.38 termination endpoint.
this is working. But in the case that the hiQ9200 reply our T.38
INVITE with a  606 Not Acceptable, the 1.4 asterisk just hangup up,
and does not ACK this reply to fallback to audio faxing.

I this behavior intentionally? Or is this case just not considered?

draft-ietf-sipping-realtimefax-01 says:

> 6.2. Unsuccessful T.38 fax scenario -
>
>                                     - 488/606 rsp & G.711 fallback
>
>
>    This section represents an unsuccessful SIP T.38 fax call:  when the
>    emitting gateway does not support T.38 fax relay, it SHOULD respond
>    with either a ��488 Not Acceptable Here�� response or a ��606 Not
>
>    Acceptable�� response to indicate that some aspects of the session
>    description are not acceptable.  The terminating gateway SHOULD
>    react by proposing a fallback to G.711 fax pass-through with special
>
>    codec characteristics -
>                          -silence suppression OFF.  The message details
>    in this section make use of the generic SDP attribute silenceSupp
>    defined in RFC3108
>


Kristijan