G729 Codec interworking

I have a NetNet4500 connected to a Cisco Unity Express 8.6 PBX. When the PBX makes a call through teh SBC the SBC rejects the call with a 488 Not acceptable here reason.

 

From my investigations I can see that we get the following message in the sipd log

 

Jan 23 09:29:03.056 [MEDIA] INVITE 100 B<C-Completed:488> setup_media: media translation failed

Jan 23 09:29:03.056 [MEDIA] CT:0x3b912f84(2)[INVITE:100]<C-Completed:488> W Q:0x37c9adb4(2) R:0x3cfdd650(2) CX:0x36b50dbc(4)

Jan 23 09:29:03.056 [MEDIA] media=0x3d0f8220(1) create=09:29:03.055 last=09:29:03.056 exp=32000

Jan 23 09:29:03.056 [MEDIA] TXID=

 

 

Looking at the SDP in the Invite we have

 

Media Attribute (a): rtpmap:0 PCMU/8000