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The IMS: IP Multimedia Concepts And Services, Second Edition by Aki Niemi, Hisham Khartabil, Georg Mayer, Miikka Poikselka

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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. IMS users are able to mix and match a variety of IP-based services in any way they choose during a single communication session. Users can integrate voice, video and text, content sharing and presence as part of their communication and can add or drop services as and when they choose. For example, two people can start a session as a voice session and later on add a game or video component to the same session.

2.1.2. IP connectivity

As the name IP Multimedia Subsystem implies, a fundamental requirement is that a device has to have IP connectivity to access it. Peer-to-peer applications require end-to-end reachability and this connectivity is easiest attainable with IP version 6 (IPv6) because IPv6 does not have address shortage. Therefore, 3GPP has arranged matters so that the IMS exclusively ...

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