Multimedia Broadcast Multicast Service Streaming Delivery Method

Description

The MBMS streaming delivery method is a key service enabler in 3GPP Multimedia Broadcast Multicast Service (MBMS) that allows for the delivery of continuous media, such as real-time video and audio, to multiple users simultaneously. It is one of the two primary delivery methods in MBMS, the other being file delivery. Streaming delivery is designed for content that is consumed in real-time, where the media is played out as it is received, without the need for complete download before playback. This makes it ideal for live broadcasts, such as sports events, news, and emergency alerts.

Technically, the MBMS streaming delivery method operates by establishing an MBMS streaming session, which is a unidirectional bearer that carries the media stream from the Broadcast Multicast Service Center (BM-SC) to the User Equipment (UE). The media is typically encoded using codecs such as H.264/AVC for video and AAC for audio, and is packetized according to the Real-time Transport Protocol (RTP) over UDP/IP. The BM-SC is responsible for ingesting the content, performing any necessary transcoding or rate adaptation, and then distributing it to the MBMS Gateway (MBMS-GW) and subsequently to the radio access network for transmission.

The streaming session is characterized by a set of parameters that define the quality of service, such as bitrate, latency, and error resilience. These parameters are signaled to the UE via the MBMS Service Announcement, allowing the UE to configure its receiver appropriately. The UE's MBMS client sets up the streaming session, buffers the incoming media, and plays it out to the user. The streaming delivery method supports both broadcast and multicast modes. In broadcast mode, the content is transmitted to all UEs in a service area, while in multicast mode, only UEs that have joined the multicast group receive the content. This flexibility allows operators to tailor the delivery to the target audience.

One of the key challenges in streaming delivery over MBMS is ensuring robust reception in varying radio conditions. To address this, MBMS employs techniques such as application-layer forward error correction (FEC) and retransmissions. FEC adds redundancy to the media stream, allowing the UE to recover from packet losses without requiring retransmissions, which is crucial in a broadcast environment where feedback is limited. In later releases, more advanced FEC schemes and adaptive streaming techniques have been introduced to further improve quality and efficiency. For example, Dynamic Adaptive Streaming over HTTP (DASH) can be used in conjunction with MBMS to provide adaptive bitrate streaming.

The MBMS streaming delivery method is specified in 3GPP TS 26.346 (MBMS User Services), TS 26.237 (IMS-based PSS and MBMS User Service), and other related specifications. It has evolved over releases to support higher resolutions, lower latency, and better error resilience. In 5G, the concept has been extended to the 5G Multicast Broadcast Service (MBS), which aims to provide similar streaming capabilities with enhanced performance. The streaming delivery method remains a vital tool for operators to deliver live content efficiently, leveraging the broadcast nature of the cellular network to reach many users at once without overwhelming the network with individual unicast streams.

Purpose & Motivation

The MBMS streaming delivery method was created to enable efficient broadcast of live media content over cellular networks. Before its introduction, delivering live video to multiple users required separate unicast streams for each user, which consumed significant network resources and limited scalability. As mobile networks evolved to support higher data rates, the demand for mobile TV and live streaming grew, necessitating a more efficient approach. MBMS streaming delivery addresses this by allowing a single stream to be transmitted to many users simultaneously, dramatically reducing the load on the core network and radio access network.

Historically, the first version of MBMS in Release 6 included support for streaming delivery, but it was limited in terms of codecs and quality. Release 8 introduced the MBMS streaming delivery method as a formalized concept, with improved specifications and support for more advanced codecs. This coincided with the rise of smartphones and the increasing popularity of video streaming. The method was designed to be flexible, supporting both broadcast and multicast modes, and to be robust against packet loss through the use of FEC.

The motivation for streaming delivery also includes the need for real-time content, such as emergency alerts and live events. Unlike file delivery, which can tolerate delays, streaming requires timely delivery to ensure a good user experience. The MBMS streaming delivery method provides the necessary mechanisms to meet these requirements, including synchronization and buffering. Over time, it has been enhanced to support adaptive streaming and integration with IMS-based services, further expanding its applicability. In 5G, the principles of MBMS streaming delivery are being carried forward into MBS, ensuring that operators can continue to offer efficient live streaming services.