During Rel-14, several VoLTE/ViLTE enhancement features were specified at the RAN level (as part of the LTE_VoLTE_ViLTE_enh work item) for RAN-assisted codec adaptation, VoLTE/ViLTE signalling optimization and VoLTE/ViLTE quality/coverage enhancement. In addition, media handling aspects of RAN-assisted codec adaptation functionality were specified in TS 26.114. As part of the VoLTE quality/coverage enhancement functionality, a delay budget reporting framework was specified at the RAN level so that the VoLTE coverage can be effectively enhanced by relaxing the air interface delay budget. The UE uses RRC signalling to report the delay budget information. Based on the reported delay budget information, when a UE is in good coverage, the eNB can configure longer DRX for power saving purpose or the eNB can reduce DRX cycle in order to help the remote UE and reduce end-to-end delay and jitter, since when the remote UE is in bad coverage, the local eNB of that remote UE can increase the retransmission times in order to reduce the packet loss. The present document addresses several gaps associated with the use of the RAN delay budget reporting framework requiring suitable media handling recommendations. In particular, the following questions are addressed:

• What are the available mechanisms in TS 26.114 and kinds of information available at the MTSI client that can help towards determining the content of the RAN-level UEAssistanceInformation messages with delay budget report information?
• How does RAN-level delay budget reporting work in conjunction with existing media adaptation behaviours in TS 26.114 for MTSI in an end-to-end fashion?
• What kind of MTSI signalling (if any) at the media handling level would facilitate a more coordinated and optimized use of the RAN delay budget reporting framework in an end-to-end fashion?

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.

The following documents contain provisions which, through reference in this text, constitute provisions of the present document.

• References are either specific (identified by date of publication, edition number, version number, etc.) or non-specific.
• For a specific reference, subsequent revisions do not apply.
• For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.