T38 switchover over CM SIP trunk

Unanswered Question
Feb 4th, 2014
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Hi,


We have problems with T38 switchover over SIP trunk between CM clusters.


Here is the setup:

ITSP---sip---CM1---sip---CM2---sip---ATA187

MTP required is checked only on sip trunk between CM2 and ATA, both CM clusters run version 9.1.2.11900-12


Problem:

On the outgoing FAX call to ITSP, we get reINVITE with 2 m-lines in SDP (m=audio and m=image) which is transparently passed back to ATA187;

ATA responds with m=audio 0 RTP/AVP and m=image xxxxx utptl t38, then CM2 sends SDP with m=image xxxxx udptl t38 and m=image 0 udptl t38 to CM1, CM1 sends same SDP to ITSP. Fax call fails.


My question is if reINVITE from ITSP is regular, and why CM changes SDP.

Any help is welcome.


Tnx,

Rok

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