Multi-Stream Multimedia Telephony Service for IMS

Description

Multi-Stream Multimedia Telephony Service for IMS (MSMTSI) is a comprehensive service specification defined by 3GPP for delivering advanced telephony over IP Multimedia Subsystem (IMS) networks. It extends basic Voice over LTE (VoLTE) to support multiple, synchronized media components within a single SIP session. Architecturally, it relies on the IMS core (CSCFs), the Telephony Application Server (TAS), and the Media Resource Function (MRF) for control and media processing. The service uses the Session Description Protocol (SDP) for complex media negotiation, allowing endpoints to advertise, add, remove, and modify multiple media streams dynamically during a call. For example, a typical MSMTSI session could include a primary audio stream for speech, a primary video stream for user camera feed, and a secondary video stream for screen sharing or a presentation, all synchronized and managed as a cohesive call. Key protocols involved are SIP for session control and RTCP for media stream synchronization and quality feedback. The Media Resource Function Processor (MRFP) can be used for advanced services like mixing media streams or providing tones and announcements. MSMTSI defines detailed procedures for session establishment, modification (adding a video stream mid-call), and termination, ensuring interoperability between devices and networks from different vendors. It also specifies quality of service (QoS) mechanisms, leveraging the Policy and Charging Control (PCC) architecture to ensure appropriate bearer resources are allocated for each media stream type, guaranteeing a high-quality user experience.

Purpose & Motivation

MSMTSI was created to standardize and enrich the multimedia telephony experience beyond simple voice and basic video calls. Prior to its specification, multimedia services were often proprietary, leading to fragmentation and lack of interoperability between different operators and devices. The problem it solves is the need for a carrier-grade, standardized service that can support complex, multi-stream communications like video calls with content sharing, which are essential for business collaboration and enhanced consumer services. Its development was motivated by the convergence of telecom and IT services and the desire to offer feature-rich, interoperable communication as a competitive alternative to over-the-top (OTT) applications. By basing it on IMS, MSMTSI allows operators to offer advanced, billable services with guaranteed quality, integrated with other IMS services like presence and messaging. It provides the technical foundation for commercial Rich Communication Services (RCS) and future immersive communication experiences.