ENUM: Connecting Islands of VoIP

Canada to start trials of IP address lookup system this year How do you find an IP phone or other IP device on the Internet if all you know is a telephone number? A new standard called ENUM aims to provide a look-up mechanism to meet this need. It could well bring great benefits for business telecom users. If your organization uses IP Telephony, the IP-PBX will translate phone numbers into IP addresses on the corporate Wide Area Network. The call can be made end-to-end via IP, and ENUM is unnecessary. But suppose you’re calling a major supplier, which also uses IP Telephony. As things stand, there’s no way to find out the called party’s IP address except to route the call through the Public Switched Telephone Network (PSTN). The spread of IP Telephony is thus creating a VoIP archipelago: islands of Voice over IP whose only connecting fabric is the PSTN. And routing IP calls over the PSTN exacts a cost in terms of both carrier charges and a small degradation of call quality metrics. Some day in the future, your IP phone’s Uniform Resource Identifier (URI) or Web address, which identifies its Internet location, may be a standard part of your business card, better known than your phone number. But the world’s two billion telephone numbers represent an immense informational investment that will not be replaced any time soon. Besides, dialing an alphanumeric URI from a numbers-only keypad is cumbersome if not impossible. What’s needed is a way to link the address system of those two billion phones to that of the world’s 600 million PCs. The proposed solution is ENUM, which is not an acronym but the name of a standard being developed by the Internet Engineering Task Force (IETF RFC 2916). Development is coordinated by the ENUM Forum (www.enumf.org). ENUM (think Electronic NUMbering) will map all VoIP phone numbers to URIs. In the short run, it allows the phone directory system to embrace VoIP. Ultimately, it could port number lookup from the PSTN’s Signaling System 7 over to the Internet’s Domain Name Server system. What Is ENUM?"ENUM is not a directory, search service, or transport service," explains Ottawa-based consultant Tim Denton (www.tmdenton.com). "It is a partial mapping of telephone numbers to domain names, whose record defines a set of services. ENUM’s goal is that one party should be able to look up information in the DNS that another party has stored there." ENUM relates to more than IP phones. "It enables Internet-based users to select from a range of services available for communicating with another person when all that is known is the telephone number," Denton says. "The phone number becomes the only thing to remember." Sovereignty IssuesNational sovereignty complicates the picture. In most of the world, each country controls its own country code and therefore makes its own decisions on ENUM. Austria has already implemented it; Germany has completed trials and decided to roll it out this year. But the North American country code is shared by 19 countries, most of them small Caribbean nations. Ultimately, it is likely that each of the 19 will have the right to opt in. For now, Canada and the United States are working together on ENUM trials scheduled to begin later this year, on the basis of an agreement between the Canadian Internet Registration Authority (CIRA) and a U.S. ENUM authority, US ENUM LLC. ENUM development in Canada is coordinated through the CRTC by the Commission’s CISC ENUM Working Group (www.enumorg.ca). Enterprise BenefitsFor business users, ENUM promises to solve the challenge of bringing inter-enterprise calling into a VoIP framework. An IP-PBX, routing calls over a wide area network, can provide end-to-end IP transmission for all long-distance calls made within the enterprise—commonly estimated at 40% of the total for all businesses. ENUM will make it possible to take another slice of calls off the PSTN—those made to other enterprises using IP telephony. As IP technology gradually becomes generally adopted, this could affect another 40% of LD calls, bringing savings in carrier toll and access charges. Richard Shockey, co-chair of the IETF ENUM working group and senior manager for Neustar, which operates North America’s number portability database and its .US and .BIZ Top Level Domains, says organizations are showing interest in this potential. "Many companies are asking pointedly about the status of ENUM and probable next steps," he says. ENUM might be advantageous, for example, for a large company that is tightly integrated with an array of major suppliers. "Calls can go from one company to another, from Michigan to Ontario, with transparent IP-based communications, avoiding default PSTN routing and associated costs," he says. "This fosters tighter supplier relations." Since ENUM links a phone number to the entire range of a user’s IP devices, it can help businesses manage the proliferation of softphones, IP desk sets, and wireless smartphones, PDAs and laptops. Shockey also believes ENUM will help large enterprises integrate IP-PBXs from different manufacturers, by permitting all-IP calling from one PBX to another and unifying complex enterprise-wide dial plan management. Of course, other measures are needed to achieve that goal, he says, such as providing a way to cross firewall boundaries within a heterogeneous network. Termination ChargesBut there’s a law in the world of standards: just because something is logical and feasible and widely beneficial does not mean that it will be done. Vested interests of major stakeholders come into play. And deployment of ENUM could be damaging to the bottom line of some telecom carriers. PSTN call completion is based on reciprocal compensation. When a call initiated on one carrier is terminated on another, the terminating carrier receives a payment. Administration of reciprocal compensation is a large part of the cost of making a call. In the United States, these termination charges average a cent a minute, which adds up to $20 billion a year for the national phone system. Some small independent telcos receive as much as 40% of their revenue from access charges. VoIP service providers such as Vonage or Primus, on the other hand, pay out as much as a quarter or a fifth of their income in termination charges. The Internet, by contrast, works on peering: the service provider terminating the transmission receives no payment. Public and Carrier ENUMThese tensions among stakeholders are reflected in the two different forms of ENUM under development.Public ENUM is a service to which individuals and organizations can subscribe, regardless of their carrier. Fully deployed, it could become a universal URI look-up system of the type just described. Carrier or private ENUM (IETF RFC 3261) uses the same URI look-up mechanism, but only for the subscribers of the carrier—or of a group of carriers. The customer does not need to subscribe and need not be aware of the service, which is controlled by and internal to the carrier.Shockey thinks cable and wireless operators are possible users of carrier ENUM. "They may have a common interest in banding together to privately exchange data, providing continent-wide calling within their networks." This form of peering is far more economical than reciprocal compensation used in the PSTN. "It’s not just about cost avoidance. It’s about new services that require IP end-to-end integrity, and the fact that the existing SS7 signaling network is not designed for IP applications," Shockey says. Private ENUM is among the services provided by XConnect, an interconnection service for VoIP providers launched in March (see page 23). "Public and private ENUM are not rivals; they do different things," Shockey adds. "Public ENUM is oriented to consumers and enterprises; private ENUM concerns how service providers optimize their networks and operations." Will ENUM Succeed?Whenever a major new standard is in development, there’s a tendency for private, proprietary implementations to run far ahead of the open standard. In ENUM’s case, private ENUM is likely to proceed more quickly, since the carriers need it for routing private information and can implement it on their own. Public ENUM must travel a difficult road: in addition to formidable practical challenges, it must secure cooperation from carriers who could well lose—at least in the short run—from its implementation. Moreover, public ENUM depends on user registration, and it may be that few non-specialist users take this step. The impact of conflicting carrier interests is greatest in the United States, where service providers are divided between predominantly local carriers (who could lose from ENUM) and interexchange carriers (who stand to gain). In Canada, there is no such dichotomy. Bell Canada is playing a prominent role in ENUM development; other telcos and cablecos are taking part. As for this year’s trial, Denton says, "There’s a common will to try things out."Questions before the Canadian ENUM Working Group include: Choice of a Canadian ENUM provider. Relationship of public to private ENUM. Whether there will be a Canadian registry. Whether the registry should be farmed out to carriers. Whether carriers should be able to make ENUM entries on their subscribers’ behalf. How ENUM will be paid for. How to protect privacy of user information.Even enthusiastic ENUM proponents such as Shockey and Denton do not project the success of public ENUM as a sure thing. But it does address a need that will grow in urgency for telecom users in the coming years. The beginning of North American trials is encouraging. The growth in interest reported by Shockey among large U.S.-based corporations is also good news. Here’s an issue where Canada’s leading business users could gain by making their voices heard.

ENUM: Connecting Islands of VoIP

News | March 29, 2005

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