cannot decode RTP and SKINNY VOIP capture

Hi all,

I hope someone can help, I have a Cisco uc540 system with a Ciscosf300 24 POE switch. I have interface gig 4 setup as a span port to SPAN vlan 100 (the voice VLAN).

I can see plenty of rtp and SKINNY traffic, but when i go to telephony and voip, I can see the call, the from and to numbers, the call will not decode. Have tried going to edit, preferences, protocols, rtp and capture packets outside of conversation.

Also i have tried setting a completely seperate system, a Cisco 2800 router and a catylyst switch and i still cannot decode calls.

All calls i am trying to decode are internal as this system is pre deployment.

I have also tried using a hub, still cannot decode.

Any help would be much appreciated.

I can provide captures if anyone was willing to look.

Regards

Owen