Create a new RTP, working profile, under Configure/Protocol Development/RTP (tab)...
1. Once under the Protocol Development/RTP (tab), click on 'New'; give your new profile a name.
2. Select and/or set, all the variables as needed (in all the available tabs)... i.e. Audio, Jitter buffer size, Codec, etc.
3. For RFC2833, make sure to enable it under the 'Out of Band' tab.
4. Once done with setting up this new, working profile, you will need to apply it in your test setup (in place of the default RTP profile)... globally, under Configure/Protocol Selection/Channels; or specifically to a Set (of channels) under Call Sequence/Partition & Timing/Protocols/RTP Protocol.