15 Miscellaneous UE-internal APIs

26.5123GPP5G Media Streaming (5GMS)ProtocolsRelease 17TS

15.1 General

While the core functionality of 5GMS is specified in terms of the dedicated system interfaces and APIs that impact the UE, specified in clauses 10 to 14 (M4 to M8 respectively), certain features of 5GMS rely on interfaces and APIs that are essentially UE-internal.

Each usage of a UE-internal interface is specified in subsequent sub-clauses of the present clause.

15.2 RAN Signaling-based Network Assistance API

If RAN Signaling-based Network Assistance is supported, the Media Session Handler uses an interface to the RAN Modem (specifically, the UE MAC entity in the modem) to send and receive bit rate recommendation messages. The interface to the modem may be based on the AT commands +CGBRRREQ and +CGBRRREP as defined in [15].

Furthermore, messaging across that interface corresponds to the logical translations of the Bit Rate Recommendation and/or Bit Rate Recommendation Query messages, carried by the Recommended bit rate MAC CE, exchanged between the RAN Modem and the RAN, as specified in [13] for 5G NR and [14] for LTE. The association between the LCID for which the recommendation applies and the actual flow (including the intermediate RLC channel) is performed by the modem.

NOTE: The +C5GQOSRDP=? command may be used to get a list of CID values that are associated with QoS flows (both network and MT/TE initiated).When used for requesting a bit rate boost, the query shall not request a bit rate that may exceed the MFBR for the corresponding QoS Flow. Failure to ensure this may result in unexpected congestion-induced packet delays and dropping.

The Bit Rate Recommendation Query shall indicate the bit rate desired by the application, as described by [13] and [14]. This request may be used by the 5GMSd Media Session Handler to request for a temporary increase in bit rate for the corresponding flow (bit rate boost). The RAN responds with a Bit Rate Recommendation message that confirms the recommended bit rate after the boost grant. Once the bit rate drops again after a boost grant, the network shall inform the Media Session Handler about the new recommended bit rate by means of an ANBR message.

Whenever the Media Session Handler receives a message from the RAN Modem, corresponding to the logical translation of the Bit Rate Recommendation message for the associated RAN uplink or downlink, it shall indicate the associated bit rate recommendation to either the Media Player (via M7d, in the case of downlink streaming) or Media Streamer (via M7u, in the case of uplink streaming) function of an affiliated PDU session. Furthermore, whenever the Media Session Handler receives a request for a bit rate boost from either the Media Player (via M6d in the case of downlink streaming) or the Media Streamer (via M6u, in the case of uplink streaming) function of an affiliated PDU session, it may send a bit rate boost message to the RAN Modem. That bit rate boost request is logically translated by the modem to the Bit Rate Recommendation Query message which is then sent to the RAN on the associated RAN uplink or downlink.

It is left to the implementer of the media player to decide how to best use the bit rate recommendation and the bit rate recommendation query information for the media streaming sessions.

15.3 RAN-based Metrics Reporting API

These procedures shall be used by the Media Session Handler to control metrics reporting when such reporting is configured by the OAM via the 5G control channel.

The Media Session Handler shall subscribe to metrics configurations from the OAM according to TS 26.247 Annex L.1. This configuration may also include virtual reality metrics as specified in TS 26.118 [42] clause 9.3. When a metrics configuration is received, the Media Session Handler shall store this configuration and use it for all subsequent streaming sessions.

When a streaming session is started the Media Session Handler shall determine whether metrics from this session shall be reported. The determination shall be based on the sample percentage and streaming source filter specified in the stored metrics configuration, according to TS 26.247 Annex F.

If metrics are to be reported for the session, the Media Session Handler shall request the Media Player to create a metrics collection job. The Media Player shall return a reference to the created job, which the Media Session Handler shall use in all subsequent actions related to this job.

The Media Session Handler shall configure the metrics collection job with the set of metrics that shall be collected during the session. The format of the configuration shall be according to TS 26.247 Annex L.2, but note that only the metrics attribute in the configuration shall be used for this purpose.

The Media Session Handler shall regularly request the collected metrics from the Media Player according to the reportingInterval specified in the metrics configuration. The metrics returned by the Media Player shall use the format as described in TS 26.247 clause 10.6, and (for virtual reality media) in TS 26.118 [42] clause 9.4, and the Media Session Handler shall forward these to the OAM according to TS 26.247 Annex L.1.

When the session is finished the Media Session Handler shall delete the metrics collection job.