Study on media handling aspects of Radio Access Network (RAN) delay budget reporting in Multimedia Telephony Service for Internet Protocol (IP) Multimedia Subsystem (IMS) (MTSI)
The present document investigates several MTSI enhancements relevant to the media handling aspects of RAN delay budget reporting. More specifically, the following MTSI enhancements are addressed, and the related gap analysis and conclusions are documented:
1) Potential recommendations for MTSI on the available mechanisms in TS 26.114 to determine the content of UEAssistanceInformation messages with delay budget report information including:
- Relevant end-to-end quality metrics (e.g., round-trip time (RTT), packet loss ratio (PLR), jitter, etc.) in MTSI and other relevant information that can be used to trigger UEAssistanceInformation messages.
- Suitable conditions on the end-to-end delay and jitter to determine:
- if UE should send UEAssistanceInformation with delay budget report information, e.g., suitable RTT thresholds (i.e., with RTT determined by using RTCP sender and receiver reports),
- what kind of information may be included in the UEAssistanceInformation messages based on the available information at the MTSI client.
2) Potential recommendations on how RAN-level delay budget reporting works in conjunction with existing media adaptation behaviours in TS 26.114 for MTSI. Relevant media adaptation behaviours include:
- Codec rate or mode adaptation via CMR / RTCP-APP messages (for voice).
- Use of application layer redundancy for increased reliability.
- Use of packet bundling (a.k.a. frame aggregation).
In particular, potential recommendations are studied on when and how the UEs should use RAN-based delay adjustment mechanisms in an end-to-end fashion also accounting for local radio conditions and when UEs may activate and perform media-layer adaptation. The recommendations provided are flexible enough to enable implementations to optimize how relevant metrics and information, including non-standardized information, are used by the UE.
3) Identification and definition of potential new formats for real-time signalling of delay budget information from an MTSI receiver to an MTSI sender during a multimedia telephony session are also considered.
Furthermore, end-to-end performance evaluations for MTSI are presented, based on end-to-end metrics such as delay, jitter and packet loss rate, in conjunction with RAN-level air interface delay considerations toward developing potential recommendations on MTSI for the areas above.