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

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Introduction

1.1 What is the Internet Protocol Multimedia Subsystem (IMS)?

Fixed and mobile networks have gone through a major transition in the past 20 years. In the mobile world, first-generation (1G) systems were introduced in the mid-1980s. These networks offered basic services for users. The main emphasis was on speech and speech-related services. Second-generation (2G) systems in the 1990s brought some data services and more sophisticated supplementary services to the users. The third generation (3G and 3.5G) and its evolution (LTE) is now enabling faster data rates and various multimedia services. In the fixed side, traditional Public Switched Telephone Network (PSTN) and Integrated Services Digital Network (ISDN) networks have dominated traditional voice and video communication. In recent years the usage of the Internet has exploded and more and more users are taking advantage of faster and cheaper Internet connection such as Asymmetric Digital Subscriber Line (ADSL). These types of Internet connections enable always-on connectivity, which is a necessity for people to start using real-time communication means – e.g., chatting applications, online gaming, Voice over IP (VoIP).

At the moment we are experiencing the fast convergence of fixed and mobile worlds as the penetration of mobile devices is increasing on a yearly basis. These mobile devices have large, high-precision displays, they have built-in cameras and a lot of resources for applications. They are always-on ...