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TA908e (3rd Gen) SIP ReINVITES and TA908 SDP Responses?

We Adtran TA908e's deployed for SIP<->PRI conversion.  This has worked great until I ran across what seems to be s singular issue so far.

The TA908 is on R10.4.5

The Softswitch is Metaswitch w/ Perimeta SBC

Our Metaswitch during a call will send a INVITE w/ SDP every 15 Minutes.  The Adtran responds with 200 OK w/ SDP.  What is odd about the Adtran's response is it increments the SESS-Version field in the origin line by one each time.

First 200OK w/ SDP from the Adtran:


v=0


o=- 1451932356 1 IN IP4 10.201.201.26


s=-


c=IN IP4 10.201.201.26


t=0 0


m=audio 10280 RTP/AVP 0 101


a=silenceSupp:off - - - -


a=rtpmap:0 PCMU/8000


a=rtpmap:101 telephone-event/8000


a=fmtp:101 0-15


15 minutes later the Metaswitch sends INVITE w/ SDP and here is the 200 OK w/SDP back from the Adtran:


v=0


o=- 1451932356 2 IN IP4 10.201.201.26


s=-


c=IN IP4 10.201.201.26


t=0 0


m=audio 10280 RTP/AVP 0 101


a=silenceSupp:off - - - -


a=rtpmap:0 PCMU/8000


a=rtpmap:101 telephone-event/8000


a=fmtp:101 0-15


15 minutes later the Metaswitch sends INVITE w/ SDP and here is the 200 OK w/ SDP back from the Adtran:


v=0


o=- 1451932356 3 IN IP4 10.201.201.26


s=-


c=IN IP4 10.201.201.26


t=0 0


m=audio 10280 RTP/AVP 0 101


a=silenceSupp:off - - - -


a=rtpmap:0 PCMU/8000


a=rtpmap:101 telephone-event/8000


a=fmtp:101 0-15


As you can in the origin line the SESS-Version flag keeps going up by 1, which wold generally indicate the attempt for new SDP Offers.

This is all part of Offer/Answer RFC3264 - https://www.ietf.org/rfc/rfc3264.txt

I have pointed out to Metaswitch the following statement:


Nearly all aspects of the session can be modified. New streams can


  be added, existing streams can be deleted, and parameters of existing


  streams can change. When issuing an offer that modifies the session,


  the "o=" line of the new SDP MUST be identical to that in the


  previous SDP, except that the version in the origin field MUST


  increment by one from the previous SDP. **If the version in the origin


  line does not increment, the SDP MUST be identical to the SDP with


  that version number.**


They are looking into this but seem to think this is an Adtran issue by incrementing session-version.

My question to any of you out there - Is Adtran in the right by Incrementing sess-version, when not necessarily required?  Adtran seems by my account to be RFC3264 Compliant for Offer/Answer, is this correct?

TIA

Kevin

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