Forrester Consulting has concluded after surveying high-level telecom network strategists at 11 large mostly incumbent telecom providers that ENUM, a long-emerging standard that facilitates voice-call routing across IP networks, is increasingly being seen as an essential routing function in the network.

The research also showed that the routing directory market in which ENUM plays a role will significantly increase over the next two years as more operators find the ENUM Routing Directory function to be an important component for enabling interoperability and monetizing communications products.

With 2011 as a target date for some service providers for having phased out their circuit-switched infrastructure, routing directories are being phased in to enable inter-operator interconnects between the PSTN and IP domains.

In the report, commissioned by Nominum, a provider of network naming and addressing solutions, Forrester said ENUM Routing Directories need to scale efficiently in order to sustain the load to be generated by next-generation services. The firm advised operators to maximize the horsepower of their networking functions such as routing directories to maintain predictable and scalable returns of NGN deployments.

For Nominum, the report validates the role of an ENUM-based routing directory function that enables the interworking of voice-over-IP and other emerging services.  It also confirms the widespread demand for a fully functional, secure, scalable and highly reliable application-level routing solution such as Nominum's Navitas, said Albert Gouyet, vice president of marketing for Nominum.

 Nominum's Navitas is an ENUM-based IP-Application Routing Directory (IPRD) for Next-Generation Networks. It enables real-time voice and multimedia communication over IP and serves as the main network database for holding E.164 numbers and Uniform Resource Identifier (URI) routing information for VoIP and next-generation value-added services. E.164 is the official number format defined by the IETF, whereas ENUM is a standard derived from the Internet Domain Name System (DNS.)

Two varieties of ENUM currently being considered and in some cases deployed are public and private ENUM. Public ENUM is public directory that relies on hierarchical management of telephone numbers based on country codes mapped as Top-Level Domains. Its content is publicly available and administered by an official administrative noncommercial authority. Carrier ENUM, on the other hand, is a directory that resides in telecom service provider networks, holds routing information relevant to the private domain of the service provider and is wholly managed by that service provider.

Forrester said that most telcos won't support the public ENUM model "because their business will depend on a publicly available service that may not offer the service-level agreements or quality of service sought by their customers." It added that carriers believe their customers will pay for value and that they stand to benefit from offering value-added services and packages that can enhance revenues.