[SIPForum-discussion] Fax call getting 488 not acceptable here

qcorba qcorba at gmail.com
Thu Oct 24 16:02:49 UTC 2013

1. Check this
http://tools.ietf.org/html/draft-ietf-sipping-realtimefax-01.txt which
describes a scenario to fallback G711 after 488.

2. I've come across another scenario in which the re-INVITE contains both
G711 and T38 and 488 is therefore not encountered.

Murali Natesh 在 2013年10月23日星期三寫道:

> Hi guys,
> I have one fax call scenario mentioned below
> PSTN-----*SS7*------>SOFTSWITCH-------*SIP*----->SIP Trunk with customer
> PSTN user sending the fax.The audio has been established using G.711 Alaw.
>  while the called SIP user sending Re-invite with T.38 in SDP the calling
> party  giving 488 not acceptable here the ACK is given by Called SIP UA.
> It means the Calling UA not support T.38 may be the PSTN.There is no
> INVITE from Called SIP UA to continue the Session with the existing G.711
> Alaw.
> Please clarify me the following things.
> 1.Do we have to ask the Called SIP carrier to enable the fallback
> procedure from T.38 to G.711Alaw.do they need to send INVITE with
> G.711Alaw after 488 not acceptable here?
> *or*
> 2.Do we need to add any codecs in the PSTN trunk to negotiate with T.38?
> *--
> Thanks and Regards
> Murali
> *
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