IMS made its way to the U.S. with little fanfare. Announcing its vendors for an upcoming 3G rollout, Sprint briefly noted that it would be deploying the new technology in its network core. That technology, IP multimedia subsystem, or IMS, didn't generate the headlines of Sprint's announcement of $3 billion in new network spending, but nonetheless Sprint became the first carrier to commit to a converged platform and heralded the age of IMS in the U.S.

Sprint maintains the decision was an easy one. It has both wireline and wireless networks and has committed to breaking down the barrier between them. It's already done away with the notion of the FON versus the PCS network and is instead dividing its business between enterprise and consumer. According to Bob Azzi, vice president of network engineering, conceptually Sprint was already on the convergence path. It just needed the technology to get there.

“IMS is the logical direction we need to go in,” Azzi said. “It's one of the key components of maintaining and leading without data services. We would foresee the need for IMS sooner than other carriers.”

As the first major carrier to commit to a full IMS rollout, Sprint sent Lucent Technologies to the top of the pile in the IMS space. With only a handful of carriers publicly trialing IMS and even fewer committing to full deployments, Sprint's decision to put an IMS core in its network gives Lucent instant prestige. Lucent's gear, however, will be put to the test. Sprint is not only planning to use Lucent's platform as a launching pad for new services but will make it the basis of its ultimate plans for wireline/wireless integration. If those dual challenges weren't enough, Sprint has an extensive Wi-Fi footprint waiting to be linked to both its wide area mobile networks and its burgeoning voice-over-IP (VoIP) service. Finally, Sprint has many network integrations to perform in the coming years, melding Nextel's iDEN infrastructure with its own CDMA 1X systems, a process that certainly couldn't be hurt by the presence of an IMS core.

Lucent says it's up to the challenge, and it plans on using its Sprint deployment as its showcase network for its IMS platform. While the activity in IMS in recent years has focused on IP services and blending applications over the network, Lucent and other vendors are now beginning to focus on another critical function of the platform: creating a direct link between the wireless and wireline worlds.

The most basic definition of IMS is that of an enabler of data, speech and mobile network technology convergence. In essence, it fills in the gaps between all the disparate telecommunications technologies out there: the gap between the public network and cellular voice, the gap between cellular voice and cellular data and the gap between dedicated purpose-built networks and open standards-based networks. The filler in those gaps is session initiation protocol (SIP), the application layer that is intended to bridge the myriad technologies in the marketplace and the fuel behind today's commercial VoIP services.

If IMS achieves the evolutionary destiny ascribed to it, SIP will be the common language at the core of the wireless network, providing the cipher that allows all of those previously incommunicado networks to talk to one another. Though the elements of an IMS network are distributed among servers and gateways and softswitches and legacy gear, the central features of its architecture are the call session control function, which manages every single voice call and data session traversing the network, and the home subscriber server, a central repository of all customer information from phone-book settings to IM buddy lists. The session control is a sort of IP traffic cop that works hand-in-hand with the subscriber database, allowing it to see on the fly what services any given customer has available to him and to make adjustments accordingly. The session control could send a voice call to a customer's handset, his home phone or a VoIP handset operating over a Wi-Fi network, all determined by customer data loaded into the home subscriber server. In addition, the session control has the ability to layer services on the fly, adding video to an SMS or initiating a presence-based voice call off an IM client, simply by accessing multiple applications servers on the network and meshing their functions together into a single session.

The possible applications for the platform are varied. If suddenly all of the services a carrier deploys are no longer isolated on the network and allowed to inter-operate, carriers can create new services almost instantaneously. It can add video to a voice call, to an MMS or to an IM chat through settings management instead of going through the arduous process of linking together proprietary systems and creating separate databases. In addition, new applications can be deployed over the IMS network with little integration requirements, in many cases merely through a software upgrade. One of the reasons for European operators' keen interest in IMS is to lay the foundation to launch complex applications like push-to-talk without enduring a grueling network upgrade across both access network and core.

“From an end-user point of view, IMS is about allowing a person to access their personal information without worrying about what device or what media they use,” said Chris Ebert, Nokia's executive director of convergence and service enabling platforms. It isn't about whiz-bang new technologies and killer applications, Ebert added. It's about using the technologies that already exist in ways customers want to use them, not the way a rigid network architecture permits customers to use them. That flexibility in and of itself might just make IMS, in the grander scheme, the killer app.

But while those enhanced and melded IP services have captured the imagination of carriers, the previously understated convergence capabilities of the platform have started coming to the attention of operators, particularly operators in the U.S. Unlike in Europe, every U.S. operator, with the exception of T-Mobile, has an aging wireline network it hopes to leverage. There are also plenty of purely wireline operators that want to leverage other carriers' mobile networks through MVNOs. Fueled by the current craze around VoIP, wireless/wireline convergence has become such a priority in the U.S. that domestic carriers may pull an industry first and beat their European counterparts to market with IMS, said Victor Coello, a solutions manager for Siemens Communications.

“The competitiveness of the different carriers in the U.S. is driving them forward,” Coello said. “While the Europeans may be making all of the announcements on IMS, their deployments will be much longer term.”

Wireless operators may not be the only ones interested in IMS' convergence promise. There's likely little coincidence wireline carriers with aggressive business VoIP rollout plans like AT&T and Qwest have chosen Sprint as their MVNO partner — an IMS core in Sprint's network would allow them to much more easily integrate their enterprise landline offerings with Sprint's cellular wares. Most vendors claim that they've gotten almost as many calls from traditional wireline operators about IMS as they have from the usual mobile suspects.

“AT&T will want to mobilize its VPN; the MSOs will need to knit two networks together when they launch wireless service; VoIP operators want to enable roaming over Wi-Fi and cellular — these aren't just mobile operators we're talking about anymore,” said John Marinho, vice president of strategic marketing for Lucent.

The conclusion is a logical one — the IMS architecture is essentially the mirror image of a converged wireline architecture, relying on a core softswitch to route both voice and data and store the network's intelligence and media servers to supply the common applications. And the same SIP used to power VoIP and enhanced services in the wireline network is used in its wireless equivalent. It stands to reason if IMS can make services merge transparently across a differentiated wireless network, it can do the same across wired and unwired architectures.

That point where wired and unwired meet is where Lucent believes it has its competitive advantage. Lucent claims to have the only common IP platform across both wireline and wireless, using the same Accelerate softswitch and home subscriber server in both network architectures while most vendors develop separate softswitches for IMS. Lucent believes that commonality was a key reason to its Sprint win and will give the carrier an enormous benefit in competing in the convergence-centered U.S. market

“It wasn't necessary a conscious decision we made to develop a common platform,” said Jeff Cortley, Lucent's product management director for service enablement and emerging applications. “It was a natural one. We've always supported wireless and wireline companies. Consequently, we have always approached IMS as a common technology platform.”

While Lucent's architecture may give it an advantage in the convergence space, it certainly hasn't precluded other vendors from competing. In fact, vendors like Nokia and Siemens have landed their own contracts in Europe — Nokia with Telecom Italia Mobile and Siemens with KPN — for IMS-based wireline/wireless convergence. And Lucent certainly wasn't hurt in the competition for Sprint's contract by the fact that it had already provided Sprint with a packet core. Still, Sprint is by far the largest IMS contract announced so far and a key indication that the U.S. market is gearing up for convergence. When one major carrier moves in the U.S., the others are not far behind, and since many vendors haven't started marketing their platforms in the U.S., Lucent may have the advantage it claims.

“Once we get this network deployed, we think we'll create a lot of momentum in this industry for IMS,” Lucent's Marinho said. “We're trying to change the paradigm in the market today. We're changing the overall value proposition for the customer, and we're moving beyond just adding more capacity to the network.”