Foreword by Stephen Hayes
3GPP, or the Third Generation Partnership Project, was formed in late 1998 to specify the evolution of GSM into a third generation cellular system. Although much focus was placed on new higher bandwidth radio access methods, it was realized that the network infrastructure must also evolve in order to provide the rich services capable of taking advantage of higher bandwidths. The original GSM network infrastructure was very much circuit- and voice-centric. Although data capabilities were added over time the system retained much of its circuit-switched heritage and its inherent limitations. A new approach was needed.
IMS, or the IP Multimedia Subsystem, represented that new approach. The development of IMS was very much a collaborative effort between the leading cellular standards organization (3GPP) and the leading Internet standards organization (IETF). IETF provided the base technology and protocol specifications, while 3GPP developed the architectural framework and protocol integration required to provide the capabilities expected of a world-class mobile system, such as inter-operator roaming, differentiated QoS, and robust charging.
Since the initial specification of IMS, IMS has been adopted by 3GPP2 (the other major cellular standards organization) and it is the leading contender as the base of the ITU work on Next Generation Networks. In the upcoming decades an understanding of IMS will be as important and fundamental for the well-rounded telecom ...
