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. The 5GMSd Client is a logical function and its subfunctions may be distributed within the UE according to implementation choice.
5GMSd AF and 5GMSd AS are Data Network (DN) functions and communicate with the UE via the User Plane Function (UPF) using the N6 reference point 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, and may perform additional functions such as consumption and QoE metrics collection and reporting. 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, including the distribution of 5GMSd AS functionality between different physical hosts, for example in a Content Delivery Network (CDN).
The 5GMSd AS in this release supports the following features:
Content Hosting, including:
Ingesting media content from a 5GMSd Application Provider at reference point M2d.
Caching media content to reduce the need to ingest the same content repeatedly at reference point M2d.
A generic framework for content preparation.
Geographic restrictions on content access by the Media Player at reference point M4d ("geofencing").
Domain Name aliasing at reference point M4d.
Support for server certificates at reference point M4d.
URL path rewriting at reference point M4d.
URL signing at reference point M4d.
5GMSd Application Provider: External application or content-specific media functionality, e.g., media creation, encoding and formatting that uses 5GMSd interfaces 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 which enables the 5GMSd Application Provider to provision the usage of the 5G Media Streaming System for downlink media streaming 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, reporting 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): aapplication 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.