DTMF Indication over HD Audio Codecs

When performing DTMF transcoding while HD Audio codecs are present, Oracle® Enterprise Session Border Controller accounts for telephone-event tone indication at clock rates that match those of the HD audio codecs.

The telephone-event tone indication's clock rate, when sent alongside an HD codec, must match the audio codec's clock rate. While many non-HD codecs use 8000 Hz clock rates, HD codecs can use clock rates of 16000 Hz. Transcoding processing takes these two telephone-event clock rates into account when performing SDP manipulation. If the wrong clock rate is used, RFC2833 telephone-event indications may be relayed incorrectly.

On the ingress side of the call, if a telephone-event is received, and no audio codec with a matching clock rate is received, the ingress-side SDP response will have the unmatched telephone-event removed.

If the allow-codec parameter uses the :no tag to remove the last of an audio codec that matches a telephone-event (8000 or 16000) from SDP, then the telephone-event of that clock rate (if present) will be removed from the SDP too.

When codec policy dictates to add AMR-WB, and the received SDP contains PCMU/PCMA and telephone-event (8000), the SDP offer sent from the egress interface will include telephone-event (16000)

If rfc2833-mode is set to preferred, the Oracle® Enterprise Session Border Controller adds telephone-event 16000 to outbound SDP if AMR-WB is present in the outbound SDP.

On the egress side of the call if the SDP contains a telephone-event without an audio codec with a matching clock rate, an appropriate audio codec will be added. If codec policy adds a telephone-event, then the SBC analyzes the audio codecs in the outbound SDP and ensures that matching telephone events (8000 and/or 16000) are present.

Once the Oracle® Enterprise Session Border Controller determines the SDP to forward, the order of telephone-event clock rates will be modified to match the order of audio codec rates. Thus if AMR-WB is the top codec followed by codecs with 8000 Hz clock rates, the telephone-event with a clock rate of 16000 Hz will be listed above telephone-events with 8000 Hz clock rates.