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

Stephen James sjames_1958 at yahoo.com
Thu Oct 24 17:00:46 UTC 2013

Theoretically, after rejecting the T.38 the call should go back to G.711a no reINVITE should be required.
The PSTN trunk will not support T.38 - the Softswitch will need to convert T.38 back to G.711A before sending the PSTN.

Stephen James 
sjames_1958 at yahoo.com
We are not princes of the earth, we are the descendants of worms, and any nobility must be earned.

 From: Murali Natesh <murali87ece at gmail.com>
To: discussion at sipforum.org 
Sent: Wednesday, October 23, 2013 6:38 AM
Subject: [SIPForum-discussion] Fax call getting 488 not acceptable here

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?


2.Do we need to add any codecs in the PSTN trunk to negotiate with T.38?

Thanks and Regards

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