26.1143GPPIP Multimedia Subsystem (IMS)Media handling and interactionMultimedia telephonyRelease 18TS
The robustness of media to packet loss can be affected by the following factors in the MTSI terminal:
– codec mode
– application layer redundancy
– packet loss concealment implementation
– dejitter buffer implementation
The above factors are considered to be part of the codec configuration.
The level of robustness can affect the coverage area of the service in a network. Furthermore, communicating the level of robustness of the media to the network enables the eNB/gNB 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.
The MTSI terminal may support the coverage and handover enhancements using the multimedia error robustness (CHEM) feature specified in this clause. When CHEM is supported by terminals, the terminals exchange packet loss rate (PLR) information via specified SDP parameters. A PCF/PCRF may use these SDP PLR values to set handover thresholds in their local eNB/gNBs.
In the procedures specified in the rest of this clause, whenever the UE estimates the packet loss rate at the media receiver, the estimate can be measured either pre-dejitter buffer or post-dejitter buffer. When packet loss rate is measured post-dejitter buffer, presentation of partial redundancy information (e.g., in EVS channel aware mode) does not count towards a correctly received packet. Unless specifically configured using the OMA-DM Management Objects, the post-de-jitter buffer PLR estimate shall be used.
The PLR_adapt attribute to be used for this feature is specified using the following ABNF:
Usage Level: media
Charset Dependent: no
plr-adapt-value = %s"ALR" / token
The "ALR" parameter is optional and may be omitted when use of Application-Level Redundancy is not supported.
The semantics of the above attribute and parameter are specified below. Unsupported parameters of the PLR_adapt attribute may be ignored.
The IANA registration information for the PLR_adapt SDP attribute is provided in Annex M.9.