Verizon Communications is testing Nortel's IP multimedia subsystem (IMS) architecture in its labs, evaluating the technology for its potential to provide converged voice, data and video services over its new fiber-to-the-premises networks.

Nortel said today that Verizon is conducting a multi-stage trial of its call session control function (CSCF) and home subscriber server (HSS) core elements as well as various application servers, looking to integrate the next-generation architecture in Verizon's existing Nortel-built softswitch network. While the initial trials will focus on the applications for the consumer fiber networks Verizon is rolling out in various parts of the country, later stages of the trial could explore the technology's implications for the entire network, including full wireline/wireless convergence between Verizon and Verizon Wireless, Nortel officials said.

While Lucent Technologies recently won a string of IMS contracts with BellSouth, SBC Communications, Cingular Wireless and Sprint, a Verizon win for Nortel would instantly put the Canadian vendor into the top tier of IMS technology suppliers. Verizon is not only the country's largest carrier, its 56% ownership stake of Verizon Wireless would make Nortel the likely candidate to build out the CDMA carrier's IMS infrastructure, just as Lucent won both deals with SBC and BellSouth after securing the Cingular contract.

Rob Scheible, Nortel's senior manager of IP multimedia networks, said Nortel's trials with Verizon stand out from others because it employs the entire IMS architecture form network layer to application layer to control plane. Many other carriers are merely testing a single application like push-to-talk or video conferencing that will eventually be integrated into an overall IMS architecture or are only deploying specific elements of the IMS control plane tier.

"We're focused on a true IMS architecture," Scheible said. "A lot of the IMS announcements we've seen are really only focused on a single application, but they're not built on a true IMS standards-based architecture."

Nortel already has an edge in Verizon's next-generation network. The vendor is Verizon's largest softswitch vendor and has deployed the call servers and gateways that control 3.8 million line ports on Verizon's voice-over-IP network. Verizon is now looking to take that existing core and set of initial applications into the IMS domain, Scheible said.

The CSCF and HSS elements are the heart of the IMS architecture, sitting apart from other network elements controlling every transaction and session over the network from a point up high. The CSCF is akin to a network 'traffic cop' directing every session to its proper application or set of applications, while the HSS is a central repository of all customer information. By setting those two elements apart, IMS creates a services-based architecture where applications become building blocks in the network instead of siloed applications. Verizon can use the Nortel solution to build unified applications from originally isolated services. For instance, it does something as simple as display caller ID on the TV screen while a customer is watching normal programming. If it seeks to be more ambitious, it can extend wireless applications like push-to-talk or MMS over the wireline network, breaking down the now formidable barrier between wireless and wireline telecommunications.

Those convergence plans are still a mystery though. While Verizon has been discussing IMS, Verizon Wireless has been quiet about any possible core migration plans. If the Verizons do, however, embrace wireless/wireline convergence, Nortel claims it would be an ideal partner. Many vendors are focused on the applications side of IMS but only give lip service to the convergence aspects, said Sita Lowman, director of IMS application product line management and marketing. Nortel is one of the few vendors that is offering a common core solution, obviating the need to deploy separate architectures for separate networks, and its installed base of core infrastructure, both wireless and wireline, make it a logical choice for carriers exploring convergence, Lowman said.

"We're very much focused on convergence because that's what our customers want," Lowman said.