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

Raj Kumaradass rajkumaradass at gmail.com
Fri Oct 25 10:28:12 UTC 2013

Hi Murali,

The failure of the T38 switch over on the PSTN side should not cause the
call to fail and the session should continue with previously negotiated
media characteristics(Per RFC3261).


On Wed, Oct 23, 2013 at 5:08 PM, Murali Natesh <murali87ece at gmail.com>wrote:

> 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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