RFC 2833 Scenario 1

The following ingress and egress policies are used for scenario 1.

Ingress Policy		Egress Policy
allow-codecs	* telephone-event:no	allow-codecs	* PCMA:no
add-codecs-on-egress		add-codecs-on-egress	telephone-event
order-codecs		order-codecs
force-ptime	disabled	force-ptime	disabled
packetization-time		packetization-time
dtmf-in-audio	preferred	dtmf-in-audio	preferred

1. In the following diagram, telephone event was offered by the offerer but was stripped by ingress policy. telephone-event was not added by the egress policy because the remaining audio codec in O1 was not DTMFable. G729 was the only codec forwarded on to the answerer.

   The SDP answer agreed to use the remaining audio codec, G729. A0 is unaltered by egress policy, and forwarded as the Result to the offerer. Therefore, G729 is used in both the ingress and egress realms, the call does not support RFC 2833, and the call is not transcoded.

   
2. In the following diagram, telephone event was offered by the offerer but was stripped by ingress policy. telephone-event was added by the egress policy because the remaining audio codec in O1 was DTMFable. PCMU and telephone-event are then forwarded on to the answerer. Note that the telephone-event payload type is added with the lowest available dynamic type number.
   

   This case illustrates when the answerer supports audio and RFC 2833, but the offerer supports audio with inband DTMF. The Oracle® Enterprise Session Border Controller transcodes between RFC2833 in the egress realm to in-band DTMF on the ingress realm.

3. In the following diagram, telephone event was offered by the offerer but was stripped by ingress policy. telephone-event is added by the egress policy because the remaining audio codec in O1 was DTMFable. PCMU and telephone-event are then forwarded on to the answerer. Note that the telephone-event payload type is added with the lowest available dynamic type number.
   

   The SDP answer only agreed to use PCMU. When A0 reaches the egress policy, it is passed along through the Oracle® Enterprise Session Border Controller to the offerer. Because telephone-event was not answered by the answerer and not supported in O1, it can’t be used. Transcoding is therefore not used for this call.

4. In the following diagram, telephone event was offered by the offerer and was stripped by ingress policy. Since PCMA was also stripped by the egress policy, leaving no non-signaling codecs, the call is rejected. A 500 message is sent back to the offerer.