New directions for ENUM

Most voice-over-IP calls today fall into one of two groups. Some calls are carried in an IP format end-to-end between customers of the same VoIP service provider. Other calls begin in IP but connect to the traditional public switched network at the other end.

Sooner or later, though, we're almost certain to see heavier use of a third option — connecting calls end-to-end using IP, even when the end users get their VoIP service from different providers. A key enabler underlying that capability is electronic numbering (ENUM), a database that associates a traditional telephone number with the VoIP end point assigned to that number. Without ENUM, VoIP providers must complete calls to other VoIP providers through the public network at significantly greater cost.

In North America, ENUM originally was implemented through third-party providers, sometimes referred to as “federations” in ENUM jargon. But today there is a wider range of options, including ENUM databases operated by individual service providers or by enterprises. Increasingly, ENUM also is being used to enable a broader range of applications, including providing a more economical alternative to traditional local number portability (LNP) solutions. These new ENUM initiatives show strong potential, assuming the industry can come to grips with the inevitable interoperability and interconnection issues.

Ultimately, ENUM could even hasten the obsolescence of the public network, said Hunter Newby, chief strategy officer for TelX, which provides interconnection services to carriers and to ENUM providers. Although TelX does not offer ENUM services itself, Newby has become somewhat of an ENUM expert through his interest in interconnection. “Couple private IP networks with the routing intelligence of ENUM, and it becomes [a public network] displacement,” Newby said.

At last count, there were at least half a dozen third-party providers of ENUM services. Previously, there were more, but consolidation already is occurring. However, despite consolidation, no two providers seem to offer exactly the same thing.

Stealth Communications, for example, operates an ENUM database that is projected to provide 1.74 billion minutes of VoIP interconnectivity in 2006. Service provider members — including AT&T, iBasis and others — pay monthly interconnection fees depending on the size and number of connections to the database. “Any number in the database can be reached for free by other members,” said Stealth CEO Shrihari Pandit, who added that such an arrangement is known as multi-lateral peering. ENUM services supplement Stealth's core business, which is providing IP-to-TDM interconnection services via a private IP network. Service providers using Stealth's ENUM offering report savings of 10% to 30% in comparison with connecting calls through the public network, Pandit said.

Some other operators of ENUM databases, including NeuStar, offer service provider members the ability to determine the other service providers with which they will exchange ENUM information. That approach “allows groups of carriers to design virtual peering requirements among themselves,” said NeuStar chief technology officer Mark Foster, who also touts NeuStar's location within Internet exchange points operated by Equinix, Telehouse and others.

“We're globally positioned at physical data centers, where 80% of the world's Internet traffic is exchanged,” Foster said. “We're implemented where we can provide the lowest latency, and many of these relationships are exclusive.”

Service provider customers can pay for NeuStar's ENUM services on a per-transaction or bundled basis, Foster said. He declined to reveal any customers by name but said NeuStar provides resolution for more than 1.3 billion phone numbers.

XConnect, a U.K.-based ENUM service provider that expanded its North American operations through its acquisition of IPeerX in September, offers service providers the ability to pay on a per-transaction basis or to exchange traffic with one another on a no-charge, or “bill-and-keep” basis. “This year we're beginning to see a growing number of service providers choosing the bill-and-keep model,” said Eli Katz, XConnect CEO and founder. The company makes its money by providing what Katz calls a “safe and secure managed environment,” which includes services such as registration, signaling management, security and commercial and contractual components.

In addition to offering ENUM services on an outsourced basis, XConnect and some other third-party ENUM companies offer service provider a totally different option. Service providers can subscribe to a service that provides them with ENUM information that they can use to operate their own ENUM databases. “The benefit of pushing out data is that the query will have the lowest latency and the least reliance on third-party infrastructure,” Katz said. He added that XConnect pushes data per the data owner's policy, sharing it only with approved parties.

Telcordia also offers service providers a choice of outsourced ENUM services or a subscription information service. Its hook is that it already administers the local exchange routing guide (LERG) database, a vestige from the monopoly era originally designed to keep track of the local switch on which a traditional telephone number resides based on the local exchange prefix. Telcordia now offers service providers that get numbers from the North American Numbering Plan the ability to share information about numbers that have been converted to VoIP with other VoIP providers.

“We're extending the LERG to include routing information for VoIP-to-VoIP calls,” said Gary Richenaker, chief information services architect for Telcordia. “All the routing is centrally managed.”

Like some of the other third-party ENUM providers, Telcordia offers service providers a level of control over the information they share with other service providers. “In an IP environment, they'll have edge servers or resolvers, and there would be a feed from our registry to one of those edge devices,” Richenaker said. “We would give them a view of information that other carriers wanted them to see. Everyone gets their own view of everybody else's information.”

Other third-party ENUM providers include VeriSign and Global Crossing, which offers a service to its wholesale connectivity customers.

The cable industry, meanwhile, appears poised to create its own ENUM federation. CableLabs, the cable industry's research arm, recently issued a request for proposal for a registry service to enable VoIP calling among cable companies.

Perhaps it's no surprise that service providers are taking an interest in operating their own ENUM databases. Many service providers are renowned for wanting to control the infrastructure underlying their service offerings. Even when they start with an outsourced approach, often they later opt to build their own infrastructure. As Richenaker put it: “Service providers want to tend, care and feed ENUM information themselves.”

In the case of ENUM, there may be other factors motivating service providers to implement their own databases beyond the desire to simply have more control. Albert Gouyet, vice president of marketing for Nominum, a company that provides purpose-built devices on which service provider or third-party ENUM databases can reside, suggests three additional factors:

• reducing costs by avoiding public network phone number inquiries,

• improving call quality by minimizing the complexity and latency of the call and

• enabling future IP-based services.

“In that context, you can't transit the [public network],” he said. “Presence, video and conferencing all need to stay over IP end-to-end.”

Nominum also has seen strong interest from service providers wanting to use ENUM to reduce their LNP costs. Initially service providers outsourced that functionality to NeuStar. But by facilitating the look-up of information associated with individual phone numbers, ENUM is well-suited to handling that functionality — and by getting a copy of the LNP database from NeuStar, service providers can avoid the per-transaction charges they previously paid to NeuStar. Noting that the LNP database contains 170 million records, Gouyet said, “Service providers can put that into our database and can make it available inside the carrier environment.”

Not all service providers are rushing to do their own ENUM implementations, said Lynda Starr, a senior analyst with Frost & Sullivan who specializes in IP communications. “Some say it's not worth doing yet because VoIP traffic is still small.” Eventually, however, Starr estimates that service providers could save about 20% of the cost of a call by implementing ENUM — even more if they exchange traffic with one another as peers.

Service providers aren't the only ones taking an interest in operating their own ENUM databases. Some enterprises also are exploring that option. “Enterprises will drive ENUM because they have the most to gain,” said TelX's Newby, who predicts that enterprise IT managers will administer phone numbers for employees and trading partners in much the same way that they manage e-mail connectivity today. “Operating a telephone system in the IP world is no more difficult than e-mail, and it works better,” Newby said. “You can have stereo sound and things you can't do in the current world, and you never have to call a PBX administrator again.”

Richenaker also is bullish on enterprise ENUM, noting that enterprises are more willing to do IP interconnection because of the call volumes and cost benefits involved — although here, too, Starr provided a counterpoint. “We're hearing mixed things from enterprises,” she said. “They might not want to be a telco.”

Despite the industrywide increase in the quantity and variety of ENUM initiatives, all ENUM implementations to date have a significant limitation. Each is essentially an isolated island. Service providers using a third-party ENUM supplier can only reach other service providers that use that supplier — and even that is not always true. And carrier-implemented databases also can provide routing information only for a limited amount of numbers.

Newby believes service providers eventually may connect to multiple third-party suppliers and apply least-cost routing algorithms to find VoIP number information in the most economical manner. Alternatively, some suggest, individual ENUM federations — such as Stealth or XConnect — may find it in their best interest to peer with each other. Still others envision a federation of federations that would direct service providers to the right database.

Another possibility is that service providers may subscribe to multiple ENUM data suppliers and load all of that information onto their own databases. As Richenaker said, “It's not so much a technical issue but a commercial one.”

But making interconnectivity solutions even more challenging is the eventual need to encompass international VoIP-to-VoIP calling. Other parts of the world have been slower to adopt ENUM, and the International Telecommunications Union to date has focused on what it calls “public ENUM.” That approach leaves the responsibility for sharing VoIP number information in the hands of end users, an approach that many North American observers say is doomed to failure here. An ITU committee plans to begin looking at service provider-based ENUM in 2007, but based on that organization's track record and the need to consider a broad range of international interests, it is unlikely that the organization will take any specific action in that area any time soon.

Ultimately, service providers may find it in their own interest to share information about their VoIP numbers with other service providers. NeuStar's Foster likens the situation today to that of the U.S. wireless industry when it initially implemented short message service (SMS) only within service provider islands. Eighteen months after service providers made the decision to implement SMS interoperability, their overall message volume increased thirty-fold, he said.

Meanwhile, some industry stakeholders already are considering the next evolutionary step beyond ENUM. Newby predicts that VoIP providers eventually will move more toward a service record (SRV) approach, an alternative to ENUM that is based on e-mail addresses rather than phone numbers. Noting that universities already use SRV to call each other, Newby believes IT managers will drive the migration. “As you move away from the PBX and move more toward an Asterisk server model of an IP PBX, those systems are built to work with domain name addresses and e-mails moreso than the [public network],” he said.

But not everyone agrees. “What we've found is that phone numbers remain the only universal and most compact form of end-user addressing that exists,” Foster said. “It doesn't matter how big the keyboard is; it's hard to beat the ten-digit phone number.”