Migration

Description

In the context of 3GPP Mission Critical (MC) services, 'Migration' refers to the capability of an MC Service user to obtain MC service directly from a partner MC system. This allows a user to continue using mission-critical applications such as MCPTT (Mission Critical Push-to-Talk), MCVideo, or MCData even when they are outside the coverage of their home MC system or when their home system is temporarily unavailable. The partner MC system is a separate MC service provider that has a trust relationship and interoperability agreement with the user's home system.

Migration is a key feature for ensuring service continuity and resilience in mission-critical communications. It is defined in specifications such as TS 23.280 (Common functional architecture for MC services), TS 23.779 (Functional architecture and information flows for MC services), and TS 23.781 (Mission Critical Data). The mechanism involves the user's MC client discovering and registering with a partner MC system, which then provides the service. The home MC system may still be involved for authorization, policy, and charging, but the actual media and signalling may be handled by the partner system.

The concept evolved from the initial MCPTT-specific definition in Rel-13, where migration meant obtaining service from an MCPTT system where no MCPTT user profile exists for that user. This was later generalized to cover all MC services and to explicitly involve a partner MC system. The migration procedure typically includes steps such as service discovery, authentication and authorization with the partner system, and establishment of the necessary bearers and signalling connections. Security and privacy are paramount, so the partner system must verify the user's credentials and ensure that the user is authorized to receive the service.

Migration is distinct from roaming, although it may be used in roaming scenarios. While roaming typically involves the user's home network providing services through a visited network, migration allows the user to directly obtain services from a partner network, which may be necessary when the home network is not reachable or when the partner network offers better coverage or capabilities. This makes migration an essential tool for public safety and other mission-critical users who require reliable communications in all circumstances.

Purpose & Motivation

Migration exists to address the need for mission-critical service continuity when users are outside their home network's coverage or when their home network is unavailable. In public safety and other mission-critical scenarios, reliable communication is essential, and any interruption can have severe consequences. Traditional roaming may not be sufficient because it relies on the home network's involvement, which may be impossible if the home network is down or if there is no roaming agreement. Migration allows a user to directly obtain service from a partner MC system, ensuring that communication can continue.

The concept was introduced in Rel-13 as part of the initial MCPTT specifications. At that time, it was defined narrowly as obtaining service from an MCPTT system where no user profile exists. This addressed the scenario where a user from one MCPTT system needs to use another MCPTT system, perhaps during a large-scale incident where mutual aid is required. Over time, the definition was broadened to cover all MC services and to explicitly involve a partner MC system, reflecting the evolution of MC services from MCPTT to a suite of applications including MCVideo and MCData.

Migration solves the problem of interoperability between different MC service providers. It enables seamless service across organizational boundaries, which is crucial for multi-agency responses. It also provides a fallback mechanism when the home system is unavailable, enhancing the resilience of the overall MC service. By standardizing the procedures for migration, 3GPP ensures that different vendors' implementations can interoperate, which is vital for the success of mission-critical communications.