Local Media Playback Operation
You configure the Oracle Communications Session Border Controller (OCSBC) to generate media locally, based on configuration and signaling. You configure the triggers and media files you need; the OCSBC monitors signaling traffic for playback triggers. For the most part, operation of the local media playback feature is the same whether configured with or without the SPL options. Differences are provided herein.
The OCSBC allows for playback configurations on a session agent, realm and sip interface. It plays back media to a caller using the configuration 'closest' to that endpoint. The term 'closest' refers to the hierarchy by which the OCSBC selects the playback configuration to use for a given call. The hierarchy the OCSBC uses is session-agent, followed by realm, followed by sip-interface. To complete the notion of 'closest', consider the element's proximity to the end station initiating the call, to which the OCSBC would send the RTP.
For example, if the initiating end station is a session agent that includes a playback configuration, then the OCSBC would use that configuration. But if the endpoint is not a session agent or is a session agent without a playback configuration, the OCSBC would check that endstation's realm, then the sip-interface configurations to identify which, if any, playback trigger and media it would use.
Key operational detail on the RTP stream generated by the OCSBC playback function includes:
- The OCSBC supports local media playback as RTP or SRTP streams over IPv4 and IPv6, using UDP transport and SIP.
- The OCSBC supports local media playback over VLANs.
- The generated RTP stream complies with all relevant RTP standards, including incrementing RTP timestamp and Sequence Number, and specifying a unique SSRC.
- If applicable, the playback RTP stream continues the Payload Type, SSRC, RTP timestamp and Sequence Numbers of the original media stream.
- The OCSBC marks the first packet of the playback with the RTP marker bit.
- The
OCSBC does not create a
playback stream if:
- The initial INVITE or the 180 response includes the “P-Early-Media: inactive” or “P-Early-Media: sendonly” parameter(s).
- The 18x response includes the “P-Early-Media: inactive” or “P-Early-Media: recvonly” parameter(s).
- If playback is operating on a hairpin stream, and the scenario fires multiple playback triggers, the OCSBC plays the stream based on the configuration 'closest' to the destination.
- Once playback is in progress, the OCSBC mutes the session in the playback direction so that only the playback media can be heard.
The OCSBC stops local media playback when:
- It receives the final SIP answer from the callee, or
- If you are using the 180-force or 180-no-sdp configuration, the callee has received a SIP UPDATE with SDP and has relayed it to the caller.
External signaling and other OCSBC configuration that impacts local media playback deployments include:
- The OCSBC disables local media playback when configured to release media.
- If both 2833 generation and playback are configured on a flow, the OCSBC gives precedence to the playback feature, disabling 2833 generation.
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If you are using the 180-no-sdp configuration, the OCSBC has not received SDP from the callee, and the processed response does not contain SDP, the OCSBC adds SDP:
- The OCSBC chooses the codec based on the offer received, and after application of the ingress and egress codec policy.
- If the OCSBC has not received an offer at that time from caller (delayed offer scenario), the OCSBC disables local media playback.
- When several early dialogs are received from the called party side, the OCSBC starts and stops local media playback based on the “active” early dialog. The active dialog is the last dialog for which the OCSBC received a provisional response.
Example Call Flows
The call flow below shows local media playback injecting RBT. The applicable configuration sets the ingress realm's ringback-trigger to use 180-no-sdp. This scenario triggers only for 180 responses to initial INVITEs, not for re-INVITEs.