Media Session Handler

Description

The Media Session Handler (MSH) is a core network-based function specified within the 5G Media Streaming (5GMS) framework (3GPP TS 26.501 series). It resides in the application layer, typically within the 5GMS Application Provider's domain or as a trusted application function interfacing with the 5G Core. The MSH's primary role is to act as a session controller for media delivery. It does not deliver the media content itself but orchestrates the session by interacting with the 5G Core Network's Policy Control Function (PCF) and the Media Streaming Client (MSC) in the User Equipment (UE).

Architecturally, the MSH works in tandem with the Media Distribution Function (MDF), which handles the actual content caching and delivery. When a Media Streaming Client initiates a request for a streaming service, it contacts the MSH. The MSH authenticates the client and the request, determines the appropriate media delivery policies (e.g., required bitrate, QoS levels), and negotiates these requirements with the 5G Core via the N5 interface to the PCF. This results in the establishment of a dedicated QoS Flow for the media session, ensuring the network resources are allocated according to the streaming service's needs. The MSH then provides the client with the necessary session description, typically a Media Presentation Description (MPD) for DASH-based streaming, which contains the URLs for the media segments hosted by the MDF.

During an active session, the MSH monitors the session status and can dynamically influence the delivery based on network conditions or application requests. For example, if the network detects congestion, the PCF can inform the MSH, which can then instruct the client (via the MPD) to switch to a lower bitrate representation. Conversely, if high bandwidth is available, the MSH can enable the client to switch to a higher quality stream. It also handles session events like pause, resume, and termination, ensuring proper coordination with the 5G Core to activate or release the corresponding QoS resources. The MSH thus abstracts the complexity of 5G network policy control from the media client, enabling efficient, QoS-aware, and adaptive media streaming services.

Purpose & Motivation

The Media Session Handler was introduced in 5G Release 17 as part of the 5G Media Streaming enablers to address the limitations of over-the-top (OTT) streaming in mobile environments. Prior to 5GMS, streaming clients operated independently of the underlying network, requesting content from CDNs without any coordination with the mobile operator's network. This led to inefficiencies, such as suboptimal bitrate selection during congestion, inability to guarantee quality, and no network-assisted optimizations. The MSH was created to bridge this gap, providing a standardized interface for streaming applications to leverage 5G network capabilities.

The key problem it solves is the lack of integration between application-layer streaming and network-layer QoS and policy control. By acting as a centralized session controller, the MSH allows the service provider to request specific network resources (like a guaranteed bitrate flow) for a premium streaming session. This enables truly differentiated services, such as guaranteed ultra-high-definition video or low-latency live streaming, which were difficult to assure with best-effort internet access. Its creation was motivated by the industry demand for carrier-grade streaming services, network slicing for media, and the need for more efficient use of 5G network resources for high-bandwidth applications.