THE IMS: IP Multimedia Concepts and Services, 3rd Edition

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IP Multimedia Subsystem Architecture

This chapter introduces the reader to the Internet Protocol (IP) Multimedia Subsystem (IMS). Section 2.1 explains basic architectural concepts: for instance, we explain why bearers are separated and why the home control model was selected. Section 2.2 gives a wide overview of IMS architecture, including an introduction to different network entities and main functionalities. Section 2.3 goes deeper and shows how the entities are connected and what protocols are used between them; it also describes their relationships to other domains: IP networks, Circuit Switched Core Network (CS CN) and IP Connectivity Access Networks (IP-CAN).

2.1 Architectural Requirements

There is a set of basic requirements which guides the way in which the IMS architecture has been created and how it should evolve in the future. This section covers the most significant requirements. Third Generation Partnership Project (3GPP) IMS requirements are documented in [3GPP TS 22.228].

2.1.1 IP Multimedia Sessions

Existing communication networks are able to offer voice, video and messaging type of services using circuit-switched bearers. Naturally, end users' service offerings should not decline when users move to the packet-switched domain and start using the IMS. The IMS will take communication to the next level by offering enriched communication means see e.g. Chapter 9 and Chapter 12. IMS users are able to mix and match a variety of IP-based services in any way they choose ...