B.14 Coverage and Handoff Enhancements using Multimedia error robustness feature (CHEM)

29.5143GPP5G SystemPolicy Authorization ServiceRelease 18Stage 3TS

As a network option, the P-CSCF may support the PCC procedures in the present clause to handle the Coverage and Handoff Enhancements using Multimedia error robustness feature (CHEM).

NOTE: When the CHEM feature is supported, improved error robustness might be enabled by packet-loss handling procedures of the codec, codec mode, or codec configuration to avoid, delay, or reduce the need to handoff a terminal due to degradation in the media quality. Communicating the level of robustness of the media to the network enables the eNB to use this information to determine a threshold for when the terminal should be handed off to another cell, domain (circuit-switched vs. packet-switched), or radio access technology.

When a session is initiated or modified the P-CSCF supporting the CHEM feature shall derive the "maxPacketLossRateDl" attribute and "maxPacketLossRateUl" attribute based on the PLR_adapt and maxe2e-PLR attribute values in both the SDP offer and/or SDP answer to determine the maximum tolerable end-to-end PLR budget distributed across the uplink and downlink in a media transport path as described in 3GPP TS 29.513 [7] clause 7.2.3.

Upon reception of SDP offer and answer, the P-CSCF should check whether "a= PLR_adapt" line is present in both SDP offer and answer to derive "maxPacketLossRateDl" attribute and "maxPacketLossRateUl" attribute in "medComponents" attribute else "maxPacketLossRateDl" and "maxPacketLossRateUl" attributes are not included by the P-CSCF.

The originating P-CSCF should derive "maxPacketLossRateDl" attribute to the maximum value of MaxPacketLossRateDl among all the RTP payload types. For each RTP payload type MaxPacketLossRateDl is computed as described in 3GPP TS 29.513 [7] clause 7.2.3.

– If maxe2e-PLR is included in the SDP offer then the MaxPacketLossRateDl for a payload type is derived as value of maxe2e-PLR in the SDP offer minus maxUL-PLR in the SDP answer if present else the MaxPacketLossRateDlis ½ maxe2e-PLR value present in the SDP offer.

– If maxe2e-PLR is not included in the SDP offer then the MaxPacketLossRateDl for a payload type is derived from the default value in end-to-end Maximum End-to-End Packet Loss Rate for the decoder of the RTP payload type as recommended in 3GPP TS 26.114 [30]clause X.1.2 for application layer redundancy or X.1.1 for partial redundancy minus maxUL-PLR in the SDP answer if present else the MaxPacketLossRateDl ½ default value in end-to-end Maximum End-to-End Packet Loss Rate for the decoder of the RTP payload type as recommended in 3GPP TS 26.114 [30] clause X.1.2 for application layer redundancy or X.1.1 for partial redundancy.

The originating P-CSCF should derive "maxPacketLossRateUl" attribute to the maximum value of MaxPacketLossRateUl among all the RTP payload types. For each RTP payload type MaxPacketLossRateUl is computed as described in 3GPP TS 29.513 [7] clause 7.2.3.

– If maxe2e-PLR is included in the SDP answer then the MaxPacketLossRateUl for a payload type is derived as value of maxe2e-PLR in the SDP answer minus maxDL-PLR in the SDP answer if present else the MaxPacketLossRateUl is ½ maxe2e-PLR value present in the SDP answer.

– If maxe2e-PLR is not included in the SDP answer then the MaxPacketLossRateUl for a payload type is derived as the ½ default value in end-to-end Maximum End-to-End Packet Loss Rate for the decoder of the RTP payload type as recommended in 3GPP TS 26.114 [30] clause X.1.2 for application layer redundancy or X.1.1 for partial redundancy.

The terminating P-CSCF should derive "maxPacketLossRateDl" attribute to the maximum value of MaxPacketLossRateDl among all the RTP payload types. For each RTP payload type MaxPacketLossRateDl is computed as described in 3GPP TS 29.513 [7] clause 7.2.3.

– If maxe2e-PLR is included in the SDP answer then the MaxPacketLossRateDl for a payload type is derived as value of maxDL-PLR in the SDP answer if present else the MaxPacketLossRateDl is ½ maxe2e-PLR value present in the SDP answer.

– If maxe2e-PLR is not included in the SDP answer then the MaxPacketLossRateDl for a payload type is derived as the ½ default value in end-to-end Maximum End-to-End Packet Loss Rate for the decoder of the RTP payload type as recommended in 3GPP TS 26.114 [30] clause X.1.2 for application layer redundancy or X.1.1 for partial redundancy.

The terminating P-CSCF should derive "maxPacketLossRateUl" attribute to the maximum value of MaxPacketLossRateUl among all the RTP payload types. For each RTP payload type MaxPacketLossRateUl is computed as described in 3GPP TS 29.513 [7] clause 7.2.3.

– If maxe2e-PLR is included in the SDP offer then the MaxPacketLossRateUl for a payload type is derived as value of maxUL-PLR in the SDP answer if present else the MaxPacketLossRateUl is ½ maxe2e-PLR value present in the SDP offer.

– If maxe2e-PLR is not included in the SDP offer then the MaxPacketLossRateUl for a payload type is derived as the ½ default value in end-to-end Maximum End-to-End Packet Loss Rate for the decoder of the RTP payload type as recommended in 3GPP TS 26.114 [30] clause X.1.2 for application layer redundancy or X.1.1 for partial redundancy.