T46G media negotiation problem

[f.ammollo]

Good morning,

we are experiencing a media negotiation problem with a T46G phone using firmware 28.72.0.25.

We are using the phone in this scenario to achieve 3rd party call control activation of a call:

INVITE w/o SDP with Call-Info answer-after=0 header
200 OK (sendrecv)
ACK (sendonly)

then we request on that call leg a REFER to the intended final destination and the phone generates a new INVITE, which contains the following SDP:

Jul 29 17:10:47 SIP [518]: SDL <6+info > [000] v=0^M
Jul 29 17:10:47 SIP [518]: SDL <6+info > [000] o=- 20003 20003 IN IP4 10.77.37.202^M
Jul 29 17:10:47 SIP [518]: SDL <6+info > [000] s=SDP data^M
Jul 29 17:10:47 SIP [518]: SDL <6+info > [000] c=IN IP4 10.77.37.202^M
Jul 29 17:10:47 SIP [518]: SDL <6+info > [000] t=0 0^M
Jul 29 17:10:47 SIP [518]: SDL <6+info > [000] m=audio 11786 RTP/AVP 0 8 18 9 101^M
Jul 29 17:10:47 SIP [518]: SDL <6+info > [000] a=rtpmap:0 PCMU/8000^M
Jul 29 17:10:47 SIP [518]: SDL <6+info > [000] a=rtpmap:8 PCMA/8000^M
Jul 29 17:10:47 SIP [518]: SDL <6+info > [000] a=rtpmap:18 G729/8000^M
Jul 29 17:10:47 SIP [518]: SDL <6+info > [000] a=fmtp:18 annexb=no^M
Jul 29 17:10:47 SIP [518]: SDL <6+info > [000] a=rtpmap:9 G722/8000^M
Jul 29 17:10:47 SIP [518]: SDL <6+info > [000] a=fmtp:101 0-15^M
Jul 29 17:10:47 SIP [518]: SDL <6+info > [000] a=rtpmap:101 telephone-event/8000^M
Jul 29 17:10:47 SIP [518]: SDL <6+info > [000] a=ptime:20^M
Jul 29 17:10:47 SIP [518]: SDL <6+info > [000] a=sendrecv^M

The INVITE is answered with a 200 OK containing the following SDP:

Jul 29 17:10:52 SIP [518]: SDL <6+info > [000] v=0^M
Jul 29 17:10:52 SIP [518]: SDL <6+info > [000] o=- 20003 1406653852 IN IP4 10.77.38.229^M
Jul 29 17:10:52 SIP [518]: SDL <6+info > [000] s=Opal SIP Session^M
Jul 29 17:10:52 SIP [518]: SDL <6+info > [000] c=IN IP4 10.77.38.229^M
Jul 29 17:10:52 SIP [518]: SDL <6+info > [000] t=0 0^M
Jul 29 17:10:52 SIP [518]: SDL <6+info > [000] m=audio 5052 RTP/AVP 101 18^M
Jul 29 17:10:52 SIP [518]: SDL <6+info > [000] a=rtpmap:101 telephone-event/8000^M
Jul 29 17:10:52 SIP [518]: SDL <6+info > [000] a=fmtp:101 0-15^M
Jul 29 17:10:52 SIP [518]: SDL <6+info > [000] a=rtpmap:18 G729/8000^M

and something in that SDP is considered wrong by the phone, because, after sending the ACK, it outputs the following line:

Jul 29 17:10:52 SIP [518]: SUA <4+warnin> [000] neg media fail, terminated

and then sends a BYE.

The only thing I had doubts about was the order of the codecs in the media format list in the response, which is listed in a different order (101 18) than in the (filtered by me) offer (18 101), so I checked out RFC 3264 and, although it is not RECOMMENDED, it seems to be legitimate.

Please note that we have three different phone models here: a T20P, a T28P and a T46G; the problem was present on both the T20P and the T46G, not on the T28P (it already has the latest firmware) and the problem disappeared from the T20P too after a firmware upgrade to the latest one.

Is a T46G official new firmware release actualy planned for the end of this month (ad I read in another forum)? Could it also solve this problem as it was solved by upgrading the T20P firmware?

Thank you in advance.

Best regards,
Fabrizio Ammollol