The latest buzzword in telecom isn't the name of a box, an application or a service. Instead, IMS is a way of organizing all those elements and more.

IP Multimedia Subsystem is an architecture that defines how IP networks should handle voice calls and data sessions. It essentially takes the place of the control infrastructure in the traditional circuit-switched telephone network, with the key difference that it separates services from the underlying networks that carry them. That way, services such as text messaging, voice mail and file sharing can reside on application servers anywhere and be delivered by multiple wired and wireless service providers. One system could hold information about the preferences and access rights of each user and made available on many others for roaming.

"The subscriber is at the center of the universe now, instead of everything revolving around the network," says Joe McGarvey, an analyst at Current Analysis. Whether users are in the office, at home or on the road, they will have access to the best possible resources and ways of communicating, according to McGarvey and other industry analysts, carriers and vendors. Plus, IMS should make it less expensive and risky for service providers to invest in new services, a boon to companies, he says.

"They're going to see a lot more interesting applications [that will be] introduced a lot more quickly than they are now," McGarvey says.

IMS originated in the Third-generation Partnership Project (3GPP), which was looking for a common way for 3G mobile operators migrating from Global System for Mobile Communications to deliver data services. However, in the past year or so it has been embraced by other standards bodies for both wired and wireless networks. At its core is Session Initiation Protocol (SIP ), a signaling system for setting up and handling calls and data sessions, which already is the standard for VoIP products. That is helping IMS gain backing from infrastructure makers, service providers and software vendors.

But the wide availability of SIP also could be the downfall of IMS, according to David Passmore, an analyst at Burton Group. Using enterprise communications gear or peer-to-peer software that uses SIP, both corporations and consumers could choose to handle their own voice or data sessions and get most of the capabilities of IMS. That would leave carriers in the role of selling pure high-speed IP connections, Passmore says.

The IDG News Service is a Network World affiliate.