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Industry Imperatives
April 2003


ENUM -- It's All In The Numbers

BY MAX SCHROEDER & RICHARD SHOCKEY

Today�s telephony market has some shining stars with Voice over Internet Protocol (VoIP) being one of the brightest. In a Telecommunications Industry Association (TIA) benchmarking report released in March (www.tiaonline.org/marketdev/benchmarking.cfm), the migration to VoIP by the reseller community is well documented. The convergence of voice and data has even resulted in the emergence of a new class of reseller, the Voice VAR. Many Voice VARs have migrated from the traditional interconnect business by incorporating customized software applications into their offerings. While maintaining a strong focus on the sale of voice products (more than 50 percent of revenue) they incorporated data as a supplemental business focus. Many of these resellers prefer to �fly below the radar� to keep competitors from realizing the potential of this market.

Standards bodies and equipment suppliers have made significant improvements to the quality of VoIP. It is clear now that voice communications made over the Internet sound as good if not better than a traditional circuit switched call.

There are 400 million telephone numbers and over 130 million Internet customers in the United States. This alone is creating an unstoppable trend towards convergence of which VoIP is now in the center. Customer focus on the convergence of voice and data is a key to the growth of VoIP. TIA calculates a total voice/data market size of $296.8 billion for 2001. This represents a rise of 12 percent from 2000. The move to VoIP is driven by both the desire of IT departments to merge voice and data, and by financial managers to take advantage of the lower phone charges. For multi-site companies, the migration to VoIP allows for multiple locations to connect via IP thus dramatically lowering phone charges.

One of the most vexing problems of VoIP is inter-domain call routing based on a telephone number. This is an issue that has plagued both H.323 and SIP for some time. As it stands now, most VoIP is used intra-domain or for calling within an enterprise to various remote locations. Vendors have all developed proprietary routing tables in their gateways or proxies that translate the dial string to a host name or URL necessary to set up a call.

This is where ENUM enters the picture. ENUM was developed by the Internet Engineering Task Force as a solution to the question of how VoIP systems can find each other on the Internet using only a telephone number, and how telephones, which have an input mechanism limited to 12 keys on a keypad, can be used to access new and innovative Internet services. ENUM at its most basic is the convergence of PSTN and IP networks.

ENUM has a number of meanings but the most basic is that it is a protocol (RFC 2916) that resolves a complete international telephone number (i.e., +1 202 123 1234) to a series of URLs using a Domain Name System (DNS)-based architecture. In other words, your personal phone number can also become your personal VoIP phone address. ENUM preserves the convenience, simplicity, and investment that consumers and businesses have made in telephone numbers.

How does it actually work? Once a telephone number is entered into a VoIP terminal or other Internet enabled device, it is translated into an Internet address using the following steps:

1. The number is first stored as +1-202-555-1234. �1� is the country code for the United States, Canada, and the seventeen other countries that make up the North American Numbering Plan (NANP). The �+� indicates that the number is a complete, international E.164 telephone number. E.164 is the name of the international telephone numbering plan administered by the.

2. All characters are removed except for the digits. Example: 12025551234

3. The order of the digits is reversed. Example: 43215552021. The telephone number is reversed because DNS reads addresses from right to left, from the most significant to the least significant character. Dots are placed between each digit. Example: 4.3.2.1.5.5.5.2.0.2.1. This is very important since, in DNS terms, each digit becomes a �zone.� This means that authority can be delegated to any point within the number.

4. The domain �e164.arpa� is appended to the end of the numbers in order to create a Fully Qualified Domain Name. For example: 4.3.2.1.5.5.5.2.0.2.1.e164.arpa

5. The Domain name is queried for the Resource Records that define URLs necessary to access services such as SIP- or H.323-based VoIP.

Once the authoritative name server for that domain name is found, ENUM retrieves relevant records and will use that data to actually complete the call or service. So 12025551234 would ultimately return back SIP:my.name@bigcompany.com, for instance.

VoIP is generally considered the most important application for ENUM. The workings of ENUM are designed to be invisible to both the end user and the subscriber. The IP network will be accessible either by the use of a Internet enabled telephone, or a standard phone that has access to an IP enabled PBX or even a classic carrier class 5 switch that has IP enabling software added to it.

It is a core principle in the design of the system that ENUM will not change the existing right-to-use rules and principles for telephone numbers. ENUM is not intended to change how telephone numbers are administered, but instead facilitate a wide range of applications using phone numbers as subscriber names. ENUM also will not interfere with existing PSTN functions and technology, such as circuit switching, SS7 (ISUP or TCAP), or Intelligent Networking.

Through the use of ENUM additional applications can be linked to telephone numbers, such as Internet fax or Internet enabled voice mail. More importantly, ENUM can be used to facilitate interoperability of services between the PSTN and the Internet, such that SMS messages on wireless phones could be linked to desktop Instant Messaging and vice versa.

What is now important for the industry to consider is that there will be a variety of policies and procedures necessary to make sure that the ENUM system here in the United States and around the world maintains the security and integrity of phone numbers.

No one has to use ENUM. It is not a requirement for Internet telephony or any other service; rather, ENUM is a technology that consumers or enterprises may choose to use in order to facilitate communications over IP networks.

There will have to be a process by which a user can register a telephone number in the ENUM system and be assured that the information being stored is accurate and complete. The process of ENUM registration may be part of a traditional sale of a PBX system or hosted IP telephony service from a carrier. That company would inform you that it would, on your behalf and with your consent, register your telephone number within the ENUM system. First, the service provider or reseller, will need to authenticate that you actually have the right to the telephone number you are trying to register, in order to prevent others from hijacking your number. Second, that reseller or service provider will create NAPTR records for your number in an appropriate and secure DNS server. Finally, it will need to inform the appropriate national ENUM registry of where those servers are located.

ENUM trials and discussions are now going on around the world as governments have recognized that ENUM can play an important role in the convergence of the PSTN and the Internet and become a platform for the development of new and innovative services.

Here in the United States, the U.S. ENUM Forum has been established by a variety of companies in the telecommunications and Internet related industries to discuss and make recommendations on how ENUM should deploy. And the U.S. government has issued a clear statement of direction that it believes the United States should participate in ENUM and it is actively soliciting comments and input from industry and interested parties.

Max Schroeder is Chairman of TIA�s VAR Working Group and Vice President, Channel Operations, Telephony@Work, Inc.

Richard Shockey is Senior Manager, Strategic Technology Initiatives, NeuStar Inc.


TIA is a leading trade association serving the communications and information technology industry, with proven strengths in market development, trade shows, domestic and international advocacy, standards development, and enabling e-business. Through its worldwide activities, the association facilitates business development opportunities and a competitive market environment. Visit them online at www.tiaonline.org.

[ Return To The April 2003 Table Of Contents ]



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