Content for TS 23.333 Word version: 17.1.0
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6.2.23 Rate adaptation for media endpoints |R13| p. 131
The signalling flow shown in Figure 6.2.23.1 gives an example for a multimedia conference establishment ("dial-in" conference procedure) when rate adaptation for media endpoints using the "a=bw-info" SDP attribute (defined in clause 19 of TS 26.114 to negotiate the additional bandwidth properties) is supported by the MRFC and the MRFP.
Figure 6.2.23.1: Multimedia conference establishment ("dial-in" procedure) with support of the enhanced bandwidth negotiation mechanism
(⇒ copy of original 3GPP image)
(⇒ copy of original 3GPP image)
The procedure in the Figure 6.2.23.1 is described step-by-step with an emphasis on the additional aspects for the MRFC and the MRFP of the rate adaptation for media endpoints using the enhanced bandwidth negotiation mechanism.
Step 1.
The signalling flow shown in Figure 6.2.23.2 gives an example for a multimedia conference establishment ("dial-out" conference procedure) when the rate adaptation for media endpoints using the enhanced bandwidth negotiation mechanism is supported by the MRFC and the MRFP.
The MRFC receives the SIP INVITE request with the SDP offer containing for the offered payload types "a=bw-info" SDP attribute lines.
Step 2.
The MRFC selects the payload type from the received SDP offer. The received SDP offer contained "a=bw-info" attribute(s) lines for the selected payload type.
Step 3. - 5.
The MRFC uses the "Reserve and Configure IMS resources" procedure to request media resources and for the selected payload type (codec and codec configurations) the MRFC provides to the MRFP the "Additional Bandwidth Properties" information element containing in the remote descriptor "a=bw-info" SDP attribute lines describing the bandwidth range which the MRFP will use in the sending direction towards the conference participant and which correspond to "a=bw-info" SDP attribute lines indicating receiving direction in the received SDP offer in step 1.
The encoder in the MRFP will use media bandwidth range for rate adaptation (i.e. to select an appropriate encoding and redundancy) when transcoding media streams.
Step 6.
The MRFC inserts in the SDP answer the IP address and RTP port received from the MRFP and for the selected payload type the "a=bw-info" SDP attribute lines.
Step 7.
The MRFC sends towards the conference participant the 200 (OK) final response (or 18x provisional response) to the SIP INVITE request with the SDP answer containing for the selected payload type "a=bw-info" SDP attribute lines.
Figure 6.2.23.2: Multimedia conference establishment ("dial-out" procedure) with support of the enhanced bandwidth negotiation mechanism
(⇒ copy of original 3GPP image)
(⇒ copy of original 3GPP image)
The procedure in the Figure 6.2.23.2 is described step-by-step with an emphasis on the additional aspects for the MRFC and the MRFP of the rate adaptation for media endpoints using the enhanced bandwidth negotiation mechanism.
Step 1.
The MRFC receives a trigger to create an ad-hoc conference.
Step 2.
Based on the local configuration the MRFC creates "a=bw-info" SDP attribute(s) for the offered payload types.
Step 3. - 5.
The MRFC uses the "Reserve IMS resources" procedure to request resources from the MRFP.
Step 6.
The MRFC inserts in the SDP offer the IP address and RTP port received from the MRFP and for the offered payload types the "a=bw-info" SDP attribute lines created in step 2.
Step 7.
The MRFC sends the SIP INVITE request with the SDP offer containing for the offered payload types "a=bw-info" SDP attribute lines towards the conference participant.
Step 8.
The MRFC receives the 200 (OK) final response (or 18x provisional response) to the SIP INVITE request with the SDP answer containing for the selected payload type "a=bw-info" SDP attribute lines.
Step 9. - 11.
The MRFC uses the "Configure IMS resources" procedure to configure media resources and for the selected payload type the MRFC provides to the MRFP the "Additional Bandwidth Properties" information element containing in the remote descriptor "a=bw-info" SDP attribute lines with the values received in step 8 describing the bandwidth range which the MRFP will use in the sending direction towards the conference participant and which correspond to "a=bw-info" SDP attribute lines indicating receiving direction in the received SDP answer in step 8.
The encoder in the MRFP will use media bandwidth range for rate adaptation (i.e. to select an appropriate encoding and redundancy) when transcoding media streams.
