Convergence – the next step

The latest buzzword in telecommunications isn’t a box, an application or a service. Instead, IMS (Internet Protocol Multimedia Subsystem) is a way of organising all those elements and more.

It’s 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 being it separates services from the underlying networks that carry them. That way services such as text messaging, voicemail and file sharing can reside on application servers anywhere and be delivered by multiple wired and wireless service providers.

“The subscriber is at the centre 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. Also, IMS should make it less expensive and risky for service providers to invest in new services, a boon to companies, he says.

IMS originated with the Third Generation Partnership Project (3GPP), which was looking for a common way for 3G mobile operators migrating from GSM to deliver data services. However, in the past year or so it has been embraced by a number of other standards bodies for both wired and wireless networks. At its core is SIP (Session Initiation Protocol), the signalling system for setting up and handling calls and data sessions which already is the standard for VoIP products.

However, the wide availability of SIP could be the downfall of IMS, says David Passmore, an analyst at Burton Group. Using enterprise communications gear or peer-to-peer software that uses SIP, users 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.

“Long term, I’m not convinced that IMS is going to be successful,” he says. “Ultimately, fat pipes may win out.”

The complexity of IMS makes the road to deployment even steeper, he says, although the architecture can be boiled down to three basic parts. They are the home subscriber server, which stores information about each user; application servers, which run the services that subscribers use; and the call session control function, which regulates how each session works and is merged with other sessions. SIP is the glue that holds all these elements together. The traditional circuit-switched telephone network can tie into IMS via gateways.

However, having all services handled on one architecture could have several benefits. One of the first windfalls is likely to be fixed-mobile convergence, providing an infrastructure for combination wi-fi/cellphones, Passmore says. IMS would also help to extend push-to-talk functions to more cellular networks.

In addition, more users could participate in a given application, such as videoconferencing, if it could be delivered to mobile devices as well as office PCs. Interoperability among service providers using IMS could bring in participants from parts of the company that use different carriers. Also, users could start multiple communications applications, such as text messaging, voice, file sharing and videoconferencing, from one software portal on a device, says Kevin Mitchell, an analyst at Infonetics Research.

That capability can already be set up in an enterprise or service provider network with Nortel’s Multimedia Communications Server (MCS) products, says Mike Doerk, Nortel’s senior manager of wireline marketing.

MCS will play the role of application server in a 3GPP-compliant Nortel IMS line-up to be released soon, he says. Reaching beyond the 3GPP standard to bring IMS to all types of networks will take more work, but Doerk believes individual vendors will be able to build such systems within a year. Interoperability among different vendors’ IMS platforms is perhaps a year or two away, he says.

Nortel rival Cisco is committed to IMS in the long term, but believes there are still issues to be worked out. The architecture as defined today isn’t secure or scalable enough, says Art Feather, manager of architectures and standards for Cisco’s mobile and wireless organisation.

However, carriers are already working on IMS. Burton Group’s Passmore says many contracts with vendors have been signed and initial deployments should come in 18–24 months, beginning in Europe.