Technologies to work in tandem to aid IP telephony

By Carolyn Duffy Marsan
Network World, 05/07/01

Enum, an emerging technology that integrates the public switched telephone network and the Internet's domain name system, is getting a boost from another new Internet capability called SIP, for the Session Initiation Protocol. The Internet Engineering Task Force developed both communications protocols, which are being adopted hand-in-hand by vendors of IP telephony gear.

The newer of the two technologies, Enum lets users type a telephone number into a Web browser and find a corresponding URL, e-mail address or IP address. The IETF finalized the Enum specification six months ago, and most of the companies that are adopting Enum already support SIP.

SIP is a signaling protocol used to establish Internet telephone calls, multimedia conferences, chat sessions and other interactive communications. Completed more than two years ago, SIP is shipping in a slew of products including IP telephones, call management servers and carrier-class software.

Among the SIP vendors that have announced Enum support are Indigo Software, Pingtel and 3Com. These companies plan to use Enum to help initiate IP telephone calls by looking up the Internet resources available for a particular phone number. Enum can provide a single point of contact for a person's communications devices, including PCs, fax machines, handheld computers and cell phones.

Once the recipient's URL is found, SIP can handle the communications between the two parties over the Internet. Enum and SIP also can work together in unified messaging and instant messaging applications.

"Equipment suppliers and carriers are very, very positive about the use of Enum with SIP," says Richard Shockey, co-chairman of the IETF's Enum working group and an executive with NeuStar, which recently announced a test bed for companies developing Enum-enabled products. "Internet-enabled fax machines and SIP phones are how people will begin to deploy Enum."

"Most of the SIP vendors and SIP service providers are seriously looking at Enum," agrees Prabahla Laks, software development manager for Enum projects at VeriSign, which has attracted 400 companies to its 5-month-old Enum test bed. "Starting in 2002, we expect to see globally accepted Enum applications."

One Internet-based carrier that's interested in rolling out Enum and SIP together is Level 3 Communications. "There's a tremendous amount of interest in Enum, and that's going to continue to accelerate as SIP becomes more popular," says Jon Peterson, senior architect for Level 3. "You need to translate between SIP phones and PSTN endpoints, and Enum does that."

Peterson says Enum complements SIP by providing look-up features that will come in handy for such functions as 800 number translations and local number portability. For SIP carriers, Enum eliminates the need to support a special routing infrastructure that translates between IP addresses and telephone numbers.

"As Enum becomes a more prevalent technology, it's going to be integrated into the SIP proxies deployed on our network," he says. "We're going to require [Enum support] of our vendors in the 2001 timeframe."

Enum and SIP also will be deployed together by firms interested in combining voice and data traffic over Internet-based VPNs, industry experts predict.

"By the end of the year, Enum will be available in some of the SIP deployments," Peterson says. "I assume it's going to ramp up exponentially as soon as it becomes available across the [North American telephone numbering plan]."

Indeed, companies buying IP telephony systems may not even know they are using Enum and SIP together.

"Enterprises are interested in converged telephony solutions," says Dave Fraley, a principal analyst with Gartner. "Are they going to put in an Enum server? No. But would they buy an IP PBX that has Enum support? Yes. They're going to have to have Enum if they want to convert telephone numbers or extensions into IP addresses."