Multimedia Broadcast/Multicast Service User Services

Description

MBMS User Services are the top-level services offered to end users over the MBMS framework. According to 3GPP TS 22.246 and TS 26.346, an MBMS User Service is an application-level service that may be delivered using one or more MBMS bearer services and one or more broadcast and/or multicast sessions. This layered architecture separates the user service (what the user consumes) from the bearer service (how the data is transported) and the session (the actual radio transmission).

The concept of a user service is central to the MBMS architecture because it allows a single logical service — such as a mobile TV channel, a software update feed, or a live sports event — to be composed of multiple media streams and delivered over multiple bearers. For example, a streaming video service might use one bearer for the video component and another for the audio component, or it might use multiple sessions to provide different quality levels or to cover different geographic areas. The user service abstraction hides this complexity from the end user and from the application layer.

Each MBMS User Service is described by a User Service Description (USD), which is part of the Service Announcement metadata. The USD contains information about the service, including the service identifier, the delivery method (download or streaming), the media presentation description, the session descriptions, and the associated delivery procedures. The USD is typically delivered via HTTP or via MBMS itself, and it enables the UE to discover and initiate the service.

The relationship between user services and bearer services is many-to-many. A single user service may use multiple bearer services, and a single bearer service may carry data for multiple user services. This flexibility allows network operators to optimize resource usage by multiplexing different services onto the same bearer when appropriate. The mapping is defined in the USD and is used by the UE during the initiation procedure.

MBMS User Services can be categorized into two main delivery methods: download delivery and streaming delivery. Download delivery uses the FLUTE protocol to deliver files, with optional file repair and reception reporting. Streaming delivery uses RTP/RTCP for continuous media, with support for synchronization and error resilience. Both methods can be protected using MBMS security mechanisms.

In the context of 5G, the MBMS User Service concept has been extended to support the 5G MBS architecture, where user services can be delivered via 5G multicast/broadcast sessions. The fundamental principle of separating user services from bearer services remains, but the underlying transport and session management are adapted to the 5G core network and NR radio interface.

Purpose & Motivation

The MBMS User Service concept was created to provide a clear separation between the services that users consume and the underlying transport mechanisms. Before this abstraction, MBMS services were more tightly coupled to specific bearers, making it difficult to compose complex services from multiple media components or to adapt delivery to different network conditions.

The introduction of user services in Rel-8 (aligned with the EPS MBMS enhancements) allowed operators to offer rich multimedia services that could span multiple bearers and sessions, while keeping the user experience seamless. It also enabled the reuse of existing IETF protocols and web technologies for service announcement and delivery, reducing the need for proprietary solutions.

Furthermore, the user service abstraction supports service continuity and mobility, as the UE can maintain the user service context even when the underlying bearer changes (e.g., due to cell reselection or handover). This is essential for delivering broadcast/multicast services to mobile users without interruption. The concept also facilitates charging and policy control, as the user service can be associated with a particular QoS profile and charging model, independent of the bearer details.