The 5GMSd Application Provider uses 5GMSd functions for downlink streaming services. It provides a 5GMSd-Aware Application on the UE the ability to make use of 5GMSd Client and network functions using 5GMSd interfaces and APIs.
The architecture in Figure 4.2.1-1 below represents the specified 5GMSd functions within the 5G System (5GS) as defined in TS 23.501. Three main functions are defined:
5GMSd AF: An Application Function similar to that defined in TS 23.501, clause 6.2.10, dedicated to 5G Downlink Media Streaming.
5GMSd AS: An Application Server dedicated to 5G Downlink Media Streaming.
5GMSd Client: A UE internal function dedicated to 5G Downlink Media Streaming.
5GMSd AF and 5GMSd AS are Data Network (DN) functions and communicate with the UE via N6 as defined in TS 23.501.
Functions in trusted DNs are trusted by the operator's network as illustrated in Figure 4.2.3-5 of TS 23.501. Therefore, AFs in trusted DNs may directly communicate with relevant 5G Core functions.
Functions in external DNs, i.e. 5GMSd AFs in external DNs, may only communicate with 5G Core functions via the NEF using N33.
5G Media Streaming Client for downlink (5GMSd Client) on the UE: Receiver of 5GMS downlink media streaming service that may be accessed through well-defined interfaces/APIs. Alternatively, the UE may be implemented in a self-contained manner such that interfaces M6d and M7d are not exposed at all.
The 5GMSd Client contains two subfunctions:
Media Session Handler: A function on the UE that communicates with the 5GMSd AF in order to establish, control and support the delivery of a media session. The Media Session Handler may expose APIs that can be used by the 5GMSd-Aware Application.
Media Player: A function on the UE that communicates with the 5GMSd AS in order to stream the media content and may provide APIs to the 5GMSd-Aware Application for media playback and to the Media Session Handler for media session control.
5GMSd-Aware Application: The 5GMSd Client is typically controlled by an external media application, e.g. an App, which implements external application or content service provider specific logic and enables a media session to be established. The 5GMSd-Aware Application is not defined within the 5G Media Streaming specifications, but the function makes use of 5GMSd Client and network functions using 5GMSd interfaces and APIs.
5GMSd AS: An Application Server which hosts 5G media functions. Note that there may be different realizations of the 5GMSd AS, for example a Content Delivery Network (CDN).
5GMSd Application Provider: External application or content-specific media functionality, e.g., media creation, encoding and formatting that uses 5GMSd to stream media to 5GMSd-Aware applications.
5GMSd AF: An Application Function that provides various control functions to the Media Session Handler on the UE and/or to the 5GMSd Application Provider. It may relay or initiate a request for different Policy or Charging Function (PCF) treatment or interact with other network functions via the NEF.
The following interfaces are defined for 5G Downlink Media Streaming:
M1d (5GMSd Provisioning API): External API, exposed by the 5GMSd AF to provision the usage of the 5G Media Streaming System and to obtain feedback.
M2d (5GMSd Ingest API): Optional External API exposed by the 5GMSd AS used when the 5GMSd AS in the trusted DN is selected to host content for the streaming service.
M3d: (Internal and NOT SPECIFIED): Internal API used to exchange information for content hosting on a 5GMSd AS within the trusted DN.
M4d (Media Streaming APIs): APIs exposed by a 5GMSd AS to the Media Player to stream media content.
M5d (Media Session Handling API): APIs exposed by a 5GMSd AF to the Media Session Handler for media session handling, control and assistance that also include appropriate security mechanisms, e.g. authorization and authentication.
M6d (UE Media Session Handling APIs): APIs exposed by a Media Session Handler to the Media Player for client-internal communication, and exposed to the 5GMSd-Aware Application enabling it to make use of 5GMS functions.
M7d (UE Media Player APIs): APIs exposed by a Media Player to the 5GMSd-Aware Application and Media Session Handler to make use of the Media Player.
M8d: (Application API): application interface used for information exchange between the 5GMSd-Aware application and the 5GMSd Application Provider, for example to provide Service Access Information to the 5GMSd-Aware Application. This API is external to the 5G System and not specified by 5GMS.
The following subfunctions are identified as a part of a more detailed breakdown of the 5GMSd AS for stage 3 specifications:
Adaptive Bit Rate (ABR) Encoder, Encryption and Encapsulator.
Manifest (e.g. MPD) Generator and Segment (e.g. DASH) Packager.
CDN Server (e.g. Edge Servers).
DRM Server (e.g. DRM License Server).
Content Guide Server.
Replacement content server (e.g. Ad content server).
Manifest Proxy, i.e. MPD modification server.
Session Management Server.
A breakdown of 5GMSd functions in the UE is provided in clause 4.2.2 below.
The UE may include many detailed subfunctions that can be used individually or controlled individually by the 5GMSd-Aware Application. This clause breaks down several relevant identified subfunctions for which stage 3 specification is available.
The 5GMSd-Aware Application itself may include many functions that are not provided by the 5GMSd Client or by the 5G UE. Examples include service and content discovery, notifications and social network integration. The 5GMSd-Aware Application may also include functions that are equivalent to ones provided by the 5GMSd Client and may only use a subset of the 5GMSd client functions. The 5GMSd-Aware Application may act based on user input or may for example also receive remote control commands from the 5GMSd Application Provider through M8d.
With respect to Media Player functions, Figure 4.2.2-1 below shows more detailed functional components of a UE for media player functions to access the 5GMSd AS.
The following subfunctions are identified as part of a more detailed breakdown of the Media Player function:
Media Access Client: Accesses media content such as DASH-formatted media segments.
Media Decapsulation: Extracts the elementary media streams for decoding and provides media system related functions such as time synchronization, capability signalling, accessibility signalling, etc.
DRM Client (optional): When present, the DRM client might or might not be a part of the Media Player. It provides a content protection mechanism with its unique key management and key delivery system, authentication/authorization, policy enforcement and entitlement check. The DRM Client is not defined within 5G Media Streaming specifications.
Media Decryption (optional): When present, media decryption is responsible to decrypt the media samples using the keys provided in the DRM license, and further passing to the Media Decoder to enable playback of encrypted media. The media decryption and media decoding could be implemented on a general-purpose processor in software or hardware or, for a more secure and robust architecture, the decryption, decoding and rendering could be implemented on the hardware of secure processors.
Media Decoder: Decodes the media, such as audio or video.
Media Presentation and Rendering: Presents the media using an appropriate output device and enables possible interaction with the media.
With respect to the Media Session Handler, Figure 4.2.2-2 below shows more detailed functional components of a UE to access the 5GMSd AF.
The following subfunctions are identified as part of a more detailed breakdown of Media Session Handler:
Core Functions: Realization of a "session" concept for media communications, optionally spanning multiple stateless sessions. May optionally interact with network-based 5GMSd AFs.
Metrics Reporting: executes the collection and reporting of metrics.
Consumption Reporting: reports to a 5GMSd AF about the currently consumed media within the available presentation, about the UE capabilities and about the environment of the media session for potential transport optimizations by the network or consumption report analysis.
Associated Delivery Procedures: Functionalities, such as location filtering, provided by the 5GMSd Client to support the 5GMSd-Aware Application in the delivery of media presentations.
Network Assistance: downlink streaming delivery assisting functions provided by the network to the 5GMSd Client and Media Player in the form of bit rate recommendation (or throughput estimation) and/or delivery boost. Network Assistance functionality may be supported by 5GMSd AF or ANBR-based RAN signaling mechanisms.
Media control interface(s) to configure and interact with the different UE media functions.
Media control interface for media session management.
Control interface for metrics collection and reporting.
Decoded media samples are handed over to the media renderer.
Decrypted, compressed media samples are handed over to a trusted media decoder.
In case of encryption, the encrypted, compressed media samples are handed over to the DRM Client.
The Service Access Information is the set of parameters and addresses which are needed by the 5GMSd Client to activate the reception of a downlink streaming session or other 5GMSd network features.
The Service Access Information may be provided together with other service announcement information using M8d. Alternatively, the 5GMSd Client fetches the Service Access Information from the 5GMSd AF. Regardless of how it is provided, the Service Access Information contains different information, depending on the collaboration model between the 5GMS System and the 5GMSd Application Provider, and also depending on offered features. Baseline parameters are listed in Table 4.2.3-1 below: