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Finding the FMC solution for enterprises
By Lloyd Williams, Vice President, Engineering, NewStep

Jun 14, 2007 12:10 PM

On the surface, most fixed-mobile convergence (FMC) solutions look the same. Beneath the surface however, FMC solutions can differ widely. And the differences matter, especially for enterprises.

In most FMC scenarios, users replace their mobile phones and their office or home phones with dual-mode wireless handsets. The handsets roam automatically between cellular and Wi-Fi access to voice services. Productivity increases because users can be reached at a single phone number and can access the same calling features whether they are in the office, at home, or on the road. Service quality improves because Wi-Fi reaches where cellular may not and vice versa. Phone bills shrink because many calls can travel over IP connections instead of more costly cellular links.

To deliver these benefits, every FMC solution relies on a special “convergence server” that tracks handset presence, manages handoffs between Wi-Fi and cellular, and interacts with the public infrastructure. Some FMC solutions embed the convergence server in the enterprise network, while others make it part of the service provider’s infrastructure.
Solutions based on both approaches—enterprise hosting and provider hosting—are available today. For example, the Converged Services Node from NewStep Networks supports both types of solutions. And while both approaches deliver basic FMC benefits, each also has advantages that the other lacks. A new model—federated hosting—incorporates the advantages of both approaches while also laying a foundation for flexible, economical access to future multimedia services.

FMC Basics
Basic FMC architecture is fairly simple (Figure 1). Dual-mode handsets access voice services via either a cellular link or a Wi-Fi link, depending on signal strength and other factors. The cellular link leads to a cellular network that is part of the worldwide public switched telephone network (PSTN), and voice traffic is carried using time-division multiplexing (TDM). The Wi-Fi link leads to an IP network, and voice traffic is carried using voice over IP (VoIP) technology. A media gateway links the IP network to the PSTN and translates between VoIP and TDM. A convergence server tracks the presence of each handset, so that it can direct incoming calls to the proper access link. It also manages the handoffs between cellular and Wi-Fi access as handsets move between coverage areas.

Some FMC solutions combine the convergence server and the media gateway in a single device at the edge of the cellular network. But this yields only access convergence, i.e. dual-mode access to the cellular network. A more flexible approach—exemplified by the Voice Call Continuity (VCC) function in the IP Multimedia Subsystem (IMS)—keeps the convergence server and media gateway functions separate. The convergence server never “touches” actual bearer traffic. Instead, it uses standard signaling protocols to control media gateways and other network elements. By separating transport from control, the VCC model enables true multimedia service convergence: a consistent user experience across diverse access types, diverse media, and diverse service provider networks.

Enterprise-Hosted FMC
A number of FMC equipment vendors offer enterprise-hosted solutions. “Why depend on a service provider when you can implement FMC yourself?” they ask. And they have a point. Enterprise-hosted solutions offer the basic benefits of FMC: dual-mode convenience, expanded wireless coverage, and increased use of low-cost VoIP. And through integration with the company’s IP PBX, they can also make PBX features available to mobile handsets. Most importantly, enterprise-hosted servers give companies direct control over their communication services, and they do not require enterprises to share sensitive directory information with outside parties.
In an enterprise-hosted solution, the convergence server maintains presence information about the company’s own dual-mode handsets and, whenever possible, uses VoIP/Wi-Fi connections to avoid cellular, PSTN and cross-network charges. For example, when the convergence server detects that both ends of a call are company handsets within Wi-Fi reach of the corporate IP network, it steers the call over the corporate network end-to-end, avoiding cellular and PSTN charges altogether (Figure 2). Where both parties are roaming beyond the corporate network but are available through Wi-Fi access, the media must still traverse the enterprise network, which may not be the optimal route.

However, an enterprise-hosted convergence server cannot track the whereabouts of other companies’ handsets or consumers’ handsets, which precludes certain optimizations. If, for example, an employee at corporate headquarters calls a non-employee, only one leg of the call travels over the corporate IP network. Lacking presence information about the called phone number, the convergence server must rely on the PSTN to complete the connection (Figure 3). The enterprise incurs PSTN charges even if the called party is standing in the next office.

Provider-Hosted FMC
Provider-hosted FMC solutions deliver the same basic benefits as enterprise-hosted solutions, including optimized call routes between handsets belonging to the same enterprise. But a provider-hosted solution can go further. From its vantage point in the provider network, the convergence server can gather presence information across multiple enterprises and consumer populations, so it can also optimize calls between handsets belonging to different enterprises or user groups.

For example, an employee of company A places a call to an employee of company B, and both companies subscribe to FMC service from the same provider. The provider-hosted convergence server knows if both employees are within Wi-Fi range of their corporate IP networks, and it knows if the two companies have agreed to form a “calling community.” If they have, the convergence server can direct inter-company calls over the service provider’s managed IP network and create cost-saving VoIP connections end-to-end (Figure 4).

Similar optimizations can be applied to enterprise-to-consumer calls and consumer-to-consumer calls, as long as both ends of the call “belong” to the same service provider. Like enterprise networks, each service provider network comprises a separate FMC island. But unlike enterprises, which can depend on service providers for inter-enterprise routing, there is no “super-provider” to furnish inter-provider route optimization.

In addition to route optimization, provider-hosted FMC gives handsets easy access to new network-based services. As service providers adopt the IMS architecture for their next-generation networks, more and more advanced multimedia services will originate within the provider infrastructure or from network-attached third-party sources. Because it sits within the IMS infrastructure, a provider-hosted convergence server can “see” and invoke network-based services that are not visible to enterprise-hosted servers.
Still, some enterprises may not be comfortable with provider-hosted FMC. They may, for example, feel that a self-managed service will be more responsive to change requests and repair orders. Or they may have concerns about privacy: Will a provider-hosted service allow sensitive information to leak across company boundaries?

Federated FMC
A new FMC solution model has emerged that satisfies enterprise requirements for privacy and control while also supporting more extensive call optimization and access to new network-based services. This “federated” approach relies on convergence servers hosted both by enterprises in partnership with the service provider. Each enterprise-hosted server maintains presence and other information about its company’s own handsets and employees. The provider-hosted convergence server tracks handset presence for other subscribers—consumers, for example—and acts as a trusted agent for the enterprise-hosted servers.

When an employee of company A calls an employee of company B, the provider-hosted convergence server relays just enough information between the companies’ enterprise-hosted convergence servers to allow optimal call routing between the handsets. Since the provider-hosted server can “see” into public Wi-Fi hotspots and other consumer locations, it can also optimize call routing to and from non-enterprise locations (Figure 5). With the federated model, FMC benefits are no longer restricted to calls placed to or from company premises.

Because it includes a provider-hosted convergence server, federated hosting supports the global route optimizations and greater cost savings of provider-hosted solutions. It also gives enterprise users access to new network-based services as they are deployed, without requiring changes to the enterprise network. Moreover, because handset presence, authentication information, and other critical data are stored on enterprise-hosted servers, the federated approach gives companies all the privacy and control of enterprise-hosted FMC. Each enterprise maintains its own convergence server, while strict, jointly-enforced policies prevent unwanted data leakage between companies.

Enterprise-hosted FMC and provider-hosted FMC both offer attractive benefits to enterprise subscribers. But both also have certain advantages that the other lacks. Enterprise-hosted FMC gives companies more direct control over their services and user data. Provider–hosted FMC offers more optimization opportunities and easier access to new network-based services. With FMC based on federated hosting, enterprises can enjoy the best of both worlds: direct control, privacy, maximum cost savings, and access to advanced network-based services.

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