INTRODUCTION

1.1 Why the Internet Protocol Multimedia Subsystem 1.2 Where did it come from?

1.1 WHY THE INTERNET PROTOCOL MULTIMEDIA SUBSYSTEM New communication paradigm networking Internet Protocol (IP)-based mobile devices terminals large, high-precision displays built in cameras and a lot of resources for applications always-on-always-connected application devices

applications no longer isolated entities exchanging information more exciting applications are peer-to-peer entities, which facilitate sharing browsing whiteboard game experience two-way radio session (i.e., push to talk)

Figure 1.1 shows the key ingredient to a peer-to- peer connection between the new IP-enabled mobile devices IMS a global system used to enable applications in mobile devices to establish peer-to-peer connections

True integration of voice and data services increases productivity and overall effectiveness The development of innovative applications integrating voice, data and multimedia will create demands for new services presence multimedia chat conferencing push to talk

Figure 1.2 shows a consolidated network where the IMS introduces multimedia session control in the packet-switched domain at the same time brings circuit-switched functionality in the packet-switched domain

Traditional mobile communication system has been divided in three parts terminals radio access network (RAN) core network With IMS-based system "radio access network" should be replaced by "access network" an IMS system can be deployed over non-RANs as well

1.2 WHERE DID IT COME FROM? GPP Release 5 and Release 6

GPP RELEASE 5 AND RELEASE 6 Release 5 introduced IMS as part of 3GPP standards IMS is a standardized access-independent IP- based architecture interworks with existing voice and data networks for both fixed network users (e.g., PSTN, ISDN, Internet) mobile users (e.g., GSM, CDMA) is able to establish peer-to-peer IP communications with all types of clients with the requisite quality of services

functionalities session management complete service delivery e.g., registration, security, charging, bearer control, roaming The functional content of 3GPP Release 5 was frozen in March 2002 Release 6 is completed in 2004 Table 1.1 shows the most important features of Release 5 and the items postponed to Release 6

AKA ： Authentication and Key Agreement

3GPP has defined a finite architecture for SIP-based IP multimedia service a functionality of logical elements a description of how elements are connected selected protocols and procedures Optimization for the mobile communication environment has been designed in the form of user authentication and authorization based on mobile identities definite rules at the user network interface for compressing SIP messages security and policy control mechanisms that allow radio loss and recovery detection

IMS development is distributed to multiple working groups in 3GPP The working method has three different stages stage 1 a service description from a service user and operator point of view are evaluated stage 2 problems are broken down into functional elements and the interactions between the elements are identified

stage 3 all the protocols and procedures are defined in detail Figure 1.3 shows the most important working groups and responsibility areas that are involved in the development of IMS