A.18 Coverage and Handoff Enhancements using Multimedia error robustness feature (CHEM)

29.2143GPPPolicy and charging control over Rx reference pointRelease 17TS

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 1: When the CHEM feature is supported, improved error robustness can 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 Max-PLR-DL AVP and Max-PLR-UL AVP 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 29.213 [9] clause 6.2.

Upon reception of SDP offer and answer, P-CSCF should check whether a= PLR_adapt line is present in both SDP offer and answer to derive Max-PLR-DL and Max-PLR-UL AVP in Media-Component-Description AVP else downlink and uplink maximum packet loss are not included by AF.

The originating P-CSCF should derive Max-PLR-DL AVP to the maximum value of Max-PLR-DL among all the RTP payload types. For each RTP payload type Max-PLR-DL is computed as described in 3GPP TS 29.213 [9] clause 6.2.

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

– If maxe2e-PLR is not included in the SDP offer then then Max-PLR-DL 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 [41] clause X.1.2 for application layer redundancy or X.1.1 for partial redundancy – maxUL-PLR in the SDP answer if present else the default value is 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 [41].

The originating P-CSCF should derive Max-PLR-UL AVP to the maximum value of Max-PLR-UL among all the RTP payload types. For each RTP payload type Max-PLR-UL is computed as described in 3GPP TS 29.213 [9] clause 6.2.

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

– If maxe2e-PLR is not included in the SDP answer then then Max-PLR-UL 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 [41] clause X.1.2 for application layer redundancy or X.1.1 for partial redundancy.

The terminating P-CSCF should derive Max-PLR-DL AVP to the maximum value of Max-PLR-DL among all the RTP payload types. For each RTP payload type Max-PLR-DL is computed as described in 3GPP TS 29.213 [9] clause 6.2.

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

– If maxe2e-PLR is not included in the SDP answer then then Max-PLR-DL 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 [41] clause X.1.2 for application layer redundancy or X.1.1 for partial redundancy.

The terminating P-CSCF should derive Max-PLR-UL AVP to the maximum value of Max-PLR-UL among all the RTP payload types. For each RTP payload type Max-PLR-UL is computed as described in 3GPP TS 29.213 [9] clause 6.2.

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

– If maxe2e-PLR is not included in the SDP offer then then Max-PLR-UL 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 [41] clause X.1.2 for application layer redundancy or X.1.1 for partial redundancy.