Global Multimedia Mobility

Description

Global Multimedia Mobility (GMM) is a service framework defined by 3GPP to support uninterrupted multimedia communications as user equipment (UE) moves across diverse network domains and access technologies. It addresses the challenge of session continuity in heterogeneous environments, where a UE might transition between 3GPP networks (e.g., LTE, 5G NR) and non-3GPP networks (e.g., Wi-Fi, fixed broadband). GMM ensures that active multimedia sessions, such as Voice over IP (VoIP), video calls, or streaming applications, are maintained with consistent quality of service (QoS) during handovers or network changes. The framework encompasses protocols, procedures, and network functions that manage session transfer, mobility policies, and resource allocation to minimize disruption and preserve user experience.

Architecturally, GMM leverages existing 3GPP mobility management mechanisms, such as those defined for the IP Multimedia Subsystem (IMS) and Packet Data Networks (PDN). Key components include the Policy and Charging Rules Function (PCRF) for QoS policy enforcement, the Access Network Discovery and Selection Function (ANDSF) for guiding UE network selection, and IMS core elements like the Call Session Control Function (CSCF) for session control. In operation, when a UE detects an available alternative access network (e.g., moving into Wi-Fi coverage), GMM procedures may trigger a handover decision based on policies, signal strength, and service requirements. The network facilitates the transfer by establishing a parallel bearer or session path in the target network before switching the media flow, using techniques like Single Radio Voice Call Continuity (SRVCC) for voice or IMS-based session continuity for multimedia.

How it works involves coordination between the UE and network functions. Initially, the UE registers with IMS and establishes a multimedia session over the current access. As mobility events occur, the UE or network initiates handover preparation. For instance, in an LTE-to-Wi-Fi handover, the UE might use ANDSF policies to decide when to switch, then engage in authentication and resource setup with the target network via trusted non-3GPP access gateways. The IMS session is anchored in a central node (e.g., Service Centralization and Continuity Application Server), which manages the session state and redirects media flows. During the handover, QoS parameters are re-negotiated to match the new access capabilities, and buffers may be used to prevent packet loss. Specifications like 3GPP TS 23.228 and TS 24.007 detail the signaling flows, while TS 23.851 covers mobility enhancements. GMM also interacts with network-based mobility protocols like Proxy Mobile IPv6 (PMIPv6) or General Packet Radio Service (GPRS) Tunneling Protocol (GTP) to maintain IP continuity, ensuring that the UE's IP address is preserved or smoothly changed.

Purpose & Motivation

GMM was introduced to address the fragmentation in multimedia service delivery as mobile networks evolved towards all-IP architectures and heterogeneous access. Prior to its standardization, multimedia sessions were often confined to single network types (e.g., circuit-switched voice in 2G/3G), and handovers between technologies like LTE and Wi-Fi led to session drops or degraded quality. The proliferation of IMS-based services and user demand for always-on connectivity motivated the creation of GMM to enable seamless mobility, similar to how voice calls could hand over between cells in traditional networks.

Historically, with the rise of VoIP and video over LTE in Release 8 and beyond, 3GPP recognized the need for a unified approach to session continuity. Early solutions like SRVCC focused on voice but lacked comprehensive support for multimedia. GMM filled this gap by providing a framework that extended continuity to data-rich sessions, addressing limitations in prior mobility management which was primarily designed for data bearer handovers without session awareness. It solved problems like media interruption during network transitions, enabling applications like video conferencing to remain active as users moved between home, office, and mobile networks.

Furthermore, GMM facilitated convergence between 3GPP and non-3GPP networks, supporting scenarios like Wi-Fi calling and fixed-mobile integration. Its development was driven by operator desires to offload traffic to Wi-Fi while maintaining service quality, and by regulatory needs for reliable emergency communications across accesses. By standardizing procedures, GMM ensured interoperability across vendors and releases, reducing complexity for UE implementation. In later releases, it evolved to support 5G and network slicing, ensuring multimedia sessions can leverage dynamic network resources. Its purpose remains critical in today's multi-access edge computing (MEC) environments, where low-latency applications require robust mobility management.

Key Features

• Enables seamless multimedia session continuity across heterogeneous networks (e.g., LTE, Wi-Fi, 5G)
• Integrates with IMS for session control and anchoring during handovers
• Utilizes ANDSF and PCRF for policy-based access selection and QoS management
• Supports techniques like SRVCC for voice and IMS session transfer for multimedia
• Maintains IP connectivity and QoS parameters during network transitions
• Facilitates fixed-mobile convergence and Wi-Fi calling scenarios

Evolution Across Releases

Defining Specifications