IP Communications

ENUM (TElephone NUmber Mapping or “Electronic Numbering”), developed by Cisco Engineer, Patrik Faltstrom and the Internet Engineering Task Force’s (IETF’s) Telephone Number Mapping working group, is a Domain Name System (DNS)-based service that maps a standard telephone number to a list of contact URLs. It thus builds a bridge between the Public Switched Telephone Network (PSTN) and the Internet.

 

For example, a caller dials a person’s telephone number, the caller’s VoIP service provider converts the telephone number into an ENUM domain name and launches a query to the DNS, which responds with the Internet address of the user. The VoIP switch routes the call to the Internet, and the VoIP service provider completes the call to the user. Therefore, the user dials something like +1 202-555-1212, which resolves to 2.1.2.1.5.5.5.2.0.2.1.e164.arpa = zippy@tmcnet.com (or whatever).

 

Thus, the ENUM protocol, which is based on (and acts as an overlay to) DNS, makes it possible to convert world standard e.164 telephone numbers into Internet domain names (representing an e.164 telephone number as an Internet address using the e164.arpa domain in the Internet’s Domain Name System) and then to associate them with services for communication through the associated URI. A URI is a sequence of characters that make it possible to identify resources such as a document, image, file, database, e-mail address or other resource or service presenting a common format. The most well-known form of URI is the “Uniform Resource Locator” (URL), many of which are used to locate resources using World Wide Web.

 

This original ENUM standard that dictates that the domain names are in e164.arpa, is called “Public ENUM” or the e164.arpa ENUM. Public ENUM is subject to various regulatory controls. This has turned out to be not so popular, as opposed to “Private ENUM” which is an ENUM implementation in a domain other than e164.arpa. A network element, such a VoIP switch, can still query it with a telephone number using an ENUM-like domain name, and receive a response of the address of another switch or user to whom a phone call can be sent.

 

NeuStar, for example, some years ago set up a private ENUM implementation for the U.S. wireless industry for routing MMS (Multimedia Messaging Service) messages. When number portability appeared in 2003, the wireless industry needed a way to route their MMS message traffic for ported numbers. In NeuStar’s implementation, when a user sends an MMS message from one carrier to another, NeuStar’s ENUM database is queried to find the correct MMS controller and carrier to send that message to.

 

NeuStar’s next devised their SIP-IX service offering (derived from NeuStar’s commercial private ENUM infrastructure), which enables service providers take advantage of the direct network-to-network interworking capabilities of SIP (Session Initiation Protocol (News - Alert)) and future IMS-based applications that will work between and among federated communities. Existing IP network peering facilities can be used to originate, terminate and share calls or sessions for mobile, fixed and broadband communications. SIP-IX enables this direct network-to-network peering between carriers for voice, video and content services using SIP-based technologies such as IMS and ENUM.

 

Hence, private ENUM generally involves the creation of a closed user group in a restricted domain to avoid many limitations of public ENUM (i.e., ENUM in the e164.arpa domain)

 

Georges Smine (News - Alert), director of product marketing at Nominum, says, “Public ENUM is dead — or best case in a deep coma. In contrast, Private ENUM is no longer a technology issue, but a practical business reality for carriers trying to deliver voice over IP or trying to do ‘spot’ or perhaps ‘tactical’ implementations of IMS. Carriers must efficiently route their voice calls over a pure IP network to increase margins and deliver valuable incremental services among other things. This means they must take advantage of the optimized routing information that can only be delivered with commercial, carrier-scale, highly reliable ENUM server technologies. Nominum has focused on delivering such a solution for this urgent need. The Navitas IP routing directory is optimized for easy deployment into any voice infrastructure with soft switches or session border controllers with flexible integration using ENUM interfaces. This allows ENUM technology to serve its defined purpose as a standards-based interface for multiple infrastructure components.”

 

“So, we’re definitely seeing more traction for Private ENUM than Public ENUM,” says Smine. “In the long run, Public ENUM may become a small part of the ENUM implementations, but nowhere as dominant as the other category. There is no incentive from the carrier’s side, nor is there a overwhelming benefit to consumers and corporations. Carriers want a light ENUM implementation they can control as an ‘in-network’ database that handles requests from their existing calling elements, such as switches, session border controllers, and so forth. The need for a low-cost software approach that’s easy to deploy trumps all the difficult and lengthy processes to implement a so-called Public ENUM implementation. That’s why Nominum focused with its Navitas product line on the Private ENUM scenario where carriers can achieve tenfold the performance and efficiency at a fraction of the cost of traditional SCPs [Service Control Points].”

 

“As for ENUM, in general,” says Smine. “It’s certainly viable as a technology, as it enables signaling and peering across all NGNs — meaning all IP network. However, as a concept, it’s viable for solutions such as number portability, or federated peering such as the GSMA project.”

 

Tekelec’s advanced signaling solutions are the result of the company’s considerable expertise in core multimedia session control and network intelligence. They enable the interworking of different network applications, technologies and protocols, providing a smooth transition to next-gen networks.

 

Tekelec recently led a workshop at the Number Portability conference in Budapestm, led by Robby Benedyk, Tekelec’s senior product manager, and Amrit Wadhwa, product marketing manager. They discussed the technical challenges of using ENUM to facilitate number portability, explaining the knowledge they’ve gained over the past ten years of working with more than 70 operators in more than 25 countries to deploy number portability solutions.

 

“Many changes have been taking place in the marketplace for ENUM over the last year,” said Benedyk. “Operators such as BT (News - Alert) Group, KPN Telecom and Deutsche Telecom AG have started migrating to VoIP networks. U.S. cable operators have made VoIP services a core component of their growth strategy and have actively deployed VoIP throughout their territories. VoIP currently is deployed in 90 percent of the cable footprint.”

 

“Thirteen countries have trialed ENUM, including the U.S., Japan, Germany, Austria, Poland and the U.K.,” says Benedyk. “The focus of the trials to date has been on VoIP and MMS delivery. Tekelec’s experience shows that when VoIP service penetration surpasses 10 percent, operators push toward ENUM utilization. The overall market appears to be headed for the magic 10 percent mark by 2009. Operators of all types are investigating, trialing or deploying ENUM now, in preparation for the implementation of new networks and services such as VoIP, MMS and IP Multimedia Subsystem (News - Alert) [IMS].”

 

“The Telecommunications Industry Association [TIA] forecasts that the number of residential VoIP customers (excluding PC-to-PC services) will grow by a compound annual growth rate (CAGR) of 43.9 percent from 2005 through 2009. As VoIP subscriber penetration approaches 10 percent, the current approach of routing every VoIP call over the TDM domain will become increasingly inefficient and costly. It’s worth noting that some cable operators have already reached 30 percent VoIP penetration,” adds Benedyk.

 

With the advent of multimedia services, a more efficient and cost effective solution is needed. ENUM has long been mentioned in this regard and appears to be heading towards widespread deployment over the next few years. ENUM solves many routing issues, simplifies network operations, slashes costs and enables end-to-end IP services, including VoIP, MMS and multimedia services.

 

“Tekelec’s ENUM-based solution enables providers to operate more efficient networks and is based on a heritage of field-proven, reliable, operator-grade telecom equipment and high-capacity database systems,” says Benedyk. “Combining the ENUM solution with an NP database provides a logical solution for operators as they search for an efficient way to route calls over VoIP networks. Tekelec’s ENUM trial experience, IMS deployments, CableLabs participation, and joint solutions with companies such as Verisign provide evidence of our expertise with ENUM solutions.”

 

However, the PSTN numbers themselves are generally tight controlled by national governments and telcos. In this month’s “The Next Wave Redux” column, industry legend Brough Turner says, “Frenum.org has a better answer — ISN [ITAD Subscriber Numbers]. This is a free numbering system, delivered via DNS and compatible with SIP. You obtain an ITAD [Internet Telephony (News - Alert) Administrative Domain] number from IANA [the Internet Assigned Numbers Authority]. Then you concatenate local extension numbers with your ITAD, separating the two with an asterisk. For example, subscriber 21234 in ITAD 270 would have ISN: 21234*270. ITADs were defined in RFC 3219, Telephony Routing over IP [TRIP], and ISN trials began in 2006, sponsored by MIT, Internet2, Packet Clearing House and Tello. While ISNs remain in ‘trial,’ more than 200 organizations are participating and what started with just a few U.S.-based Intenet2 institutions is now global and has significant commercial participation.”

 

So perhaps ENUM will finally take off as predicted, but it looks like it may face stiff competition from competing technologies.

 

 

Companies mentioned in this article:

 

NeuStar

www.neustar.com

 

Nominum

www.nominum.com

 

Tekelec

www.tekelec.com