Formally, the IP Multimedia Subsystem (IMS) is defined as: "... a new core network ‘domain' (i.e. a new mobile network infrastructure composed of a number of discreet elements)."
This definition is from the 3G Partnership Project (3GPP) and has been further embraced by the 3GPP2, the European Telecommunications Standards Institute (ETSI), and the WiMax Forum. This definition, however, is not only vague, but certainly does not do IMS justice. IMS is a whole new way to deliver multimedia (voice, video, data, etc.) regardless of the device (mobile phone, landline phone, cable, Internet, etc.) or the access medium (cellular, WiFi, Broadband, fixed-line, etc.), and will change the way all of us relate to our increasingly digital world.
This paper is written to achieve two main goals: to explain the basic vision/need for the IMS architecture and to give the reader a high-level understanding of how it works. In the end, the overarching goal is to help educate the reader on this burgeoning and powerful technology change.