Introduction

3GPP (3rd Generation Partnership Project) is a collaborative effort where more that 400+ members consisting of carriers, vendors and Standard bodies to specify and end-end '3rd Generation' communication system. The initial goal of the partnership was to attempt to bring competing mobile standards used across the world under one umbrella specification, that would promote interoperability and also offer a flexible architecture to be able to support new services and new access technologies. Since the final goal is rather ambitious, 3G specifications were divided into several 'Release's which started with '3G release 99' which significantly enhanced the previous mobile systems radio interfaces to be able to support higher bandwidth amongst other enhancements.

Acknowledging the exponential deployment of fixed broadband networks and emerging standards for high-bandwidth wireless networks, 3G anticipated that IP based networks were inevitable and would dominate communication in the mobile world as well, which was tradionally limited by bandwidth. To keep up with the changing times, 3G, in 'Release 5' introduced the 'IMS' (IP Multimedia Subsystem) which was an all 'IP' based 'session management' architecture. Simply put, this was the first official release where a VoIP call was supported by 3GPP. More importantly, 3GPP actually standardized on the IMS architecture for all subsequent releases and chose SIP as the protocol of choice for evolving their network to an all-IP based infrastructure.

Broadly speaking, a typical 3G system can be logically divided into 4 distinct areas:

a) Radio Access Network (RAN) - the functionality that is responsible for a mobile phone network to be able to transmit and receive radio signals.

b) IP Connectivity layer (IP-CAN) - the functionality that is required to allocate IP addresses and route IP packets to and fro.

b) Session Layer- the functionality that is responsible for session management (how does one make a call?), bearer management (how does one route media for a call) and policy management (what policies should be applied to a user or a session?). This is the heart of the 3G system.

c) Services layer - the functionality that is responsible for being able to host new applications, like push to talk, conferencing, presence and others.

Note that 'IMS' described above maps to b) Session Layer. Shown below is a logic split of the 3G system (referred to as 3G Core)

maintained by: arjun@hsc.com

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