A lot of talk in wireless and wireline circles lately has centered on the convergence of both networks and services, exploring future opportunities made possible by IP Multimedia Susbsystems (IMS). Ronald Gruia, program leader and senior strategic analyst at Frost & Sullivan, explains what IMS is and what it can do.  IMS: Brains for Tomorrow’s Network? The common theme at "Next Generation Networks" and related tradeshows recently has been discussion – at almost fever pitch – of IP Multimedia Subsystems, or IMS.  All major equipment manufacturers are talking up their IMS offerings, application vendors are boasting of IMS compliance, and even service providers are thinking about offering some IMS services.But what exactly is IMS? It is an access protocol- and device-agnostic specification that allows convergence between wireline and wireless network architectures.  This framework enables wireline, wireless and cable operators to offer a new generation of rich voice, video and multimedia services across both legacy circuit-switched and new packet-switched networking infrastructures. In essence, IMS enables next-generation service networks. Break the StovepipeThe traditional approach to services in the legacy circuit-switched PSTN was based on a vertical "stovepipe" architecture, in which common functions are replicated for each application. This approach proved to be inflexible in delivering new applications quickly and efficiently. Typically, the proprietary hardware and software were sold as a service node, which meant that common functions such as charging, list management, routing and provisioning kept being implemented separately in each different application. This in turn led to a lot of duplication, scalability concerns, and systems integration issues. Since the IMS architecture addresses many of these problems, it is not surprising this acronym has been hogging the attention of the trade press, recent conferences and standardization groups around the world. Wireless OriginOriginally born in the mobile world as a 3GPP (3rd Generation Partnership Project) standard, the IMS concept has quickly evolved into much more than just a wireless specification, with active involvement from standards bodies such as the IETF, ITU, ETSI, and even Cable Labs.  These organizations hold that IMS is a blueprint for an IP multimedia and telephony core network system consisting of logical functions such as session control, connection control and applications or services that can deliver voice and data services.  Furthermore, IMS is a framework of logical (not physical) entities that defines a three-layered approach to services:• Access / transport • Core / control • Application / services The access-agnostic nature of the specification makes it one of the most ambitious and comprehensive standardization efforts to date, specifically addressing the evolution to next-generation telecom infrastructures.  IMS utilizes packet technologies for underlying transport and relies upon SIP for call signaling between the various components.One of the main advantages of IMS is the reuse of common functions (such as QoS, presence and billing) and the integration of these common functions in a horizontal fashion. These functions can be reused for many different applications. The benefits of IMS are manifold:• Lower capital and operational expenditures;  • Shorter time-to-market, the new product introduction lifecycle can go down from two years to just three to five months;  • Higher revenue per user, due to the creation of new "blended lifestyle services" enabling users to mix and match services (e.g. push-to-talk, video sharing, voice messaging, instant messaging, and voice conferencing);  • Flexible Service Oriented Architecture, enabling service providers to build their own services or mix-and-match apps in trying to come up with a custom suite;  • Sharing of functions across several applications (e.g. voice calling, instant messaging, presence, push-to-talk over cellular, and picture messaging);  • Increased customer retention; • One framework for any kind of access (wireless, wireline or cable) and any kind of traffic—VoIP, data, multimedia;  • Creation of "combinational" services (e.g. location and presence). IMS is a still-evolving technology for which carriers must develop a long-term strategic plan. Many service providers have already begun evaluating IMS, with some trials and ongoing deployment efforts, including Sprint (Cisco, Ericsson and Lucent), mm02 (Siemens), Telecom Italia Mobile (Nokia) and Telefonica (Ericsson). In addition, at press time Bell South was expected to announce soon the winner of its IMS sweepstakes, with vendors such as Lucent, Sonus and Tekelec vying for parts of the contract. Although IMS was born in the wireless world, fixed-line service providers have shown active interest. IMS can be a great delivery mechanism to enable mobile calls to roam seamlessly onto a fixed network. Obviously, this can be part of a strategy for fixed-line carriers to win back some of the minutes lost to wireless operators over the past few years. Moreover, wireline carriers are not limited by constraints faced by wireless operators such as extra bandwidth requirements, radio and handset availability, and Quality of Service.  Service Decomposition Service decomposition is not a new idea; arguably, the AIN (Advanced Intelligent Network) introduced that concept. But the lofty goals of AIN were never achieved. What hope is there for IMS? This time around there is hope that the benefits of horizontal integration might be realized, given that SIP and XML are widely known, thereby shortening the required investment of a programmer to develop new applications.  Moreover, the value chain is much more fragmented now, enabling the carriers to play vendors off against each other and pick best-of-breed solutions. Finally the standard interfaces make it easier to replace a non-performing or non-cooperating vendor. Nonetheless, in order for IMS to deliver all its benefits, carriers must flatten their organizational structures, creating horizontal groups focused in specific areas rather than the current status-quo vertical silos. This shift represents a profound change in strategic management, and might require quite some time to be realized. It is a powerful manifestation of the disruptive nature of IMS, a technology that undoubtedly will cause the redefinition of industries and business models.  Ronald Gruia is program leader and senior strategic analyst at Frost & Sullivan covering Emerging Communications Solutions. He can be reached at email@example.com.