The Promise of ENUM

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The Promise of ENUM

By Micah Singer, CEO, VoIP Logic  |  November 02, 2016

Ten years ago the promise of ENUM – Electronic Numbers meant to replace PSTN telephone numbers as a mechanism for routing telephone calls to the right place – was all the rage. The idea then was that cost, quality, and network utilization could be refined by moving calls from origination to destination in their native VoIP format. 

While the promised efficiencies of ENUM have not materialized in the format envisioned, some recent events (notably, Level 3’s application to discontinue use of PSTN in Portland in favor of IP-based cloud services) have me thinking that it is time again to consider what carriers and service providers can do to embrace the promised advantages of ENUM in 2016 and beyond.

Unlike a decade ago, today, many telephones are connected directly to the internet.  The numbers are staggering with an estimated total, when factoring in residential and business lines globally, somewhere in the neighborhood of 400 million to 600 million. In addition, the very concept of a telephone line as a useful measure of subscribers to the technology is starting to fade with the emergence of app-based communications which supplant telephone numbers with presence technology.  From widely available consumer mobile applications like WhatsApp, Skype (News - Alert), Viber, and Google Chat to corporate unified communications solutions that allow end-to-end VoIP/SIP calling intra-company, the percent of calls that are efficiently routed is much higher today than when ENUM technology was at its peak adoption.

However, even with statistically significant VoIP penetration among business and residential voice users, the dream of service provider-agnostic efficient routing as the standard is still a dream. Nevertheless, the technology in subscribers’ hands (quite literally in their hands – often from mobile devices) points toward an all-IP future for voice. The shape that this future takes, however, depends on decisions that carriers and service providers will make. Here are some of the developments that we will see and others that we would like to see as we move toward an all-IP world of voice communications.


The basic concept behind ENUM was that carriers and service providers would create federations where networks would peer and information would be shared to identify the most efficient call paths. In this scenario, if a user of Service Provider A called a number homed to Service Provider B, the call packets would be routed directly across their interconnection, foregoing a circuitous route through multiple networks, devices and, most likely, involving media conversion and reconversions.

Many carriers have attempted to create federations of telephone routing information to, essentially, mirror the function of the SMS/800 database used to route toll-free phone calls. What was, and is still, lacking is a central, impartial authority – assigned maybe by the FCC (News - Alert) – responsible for managing the database and trusted by the industry to perform this function. SMS/800 – now rebranded Somos Inc. – was the trusted provider of this bureaucratic function. Admittedly, the task is more daunting on the internet because of the complexity of IP voice but, until there is a universally trusted purveyor of the shared data required to find users on the IP voice network irrespective of carrier, widespread efficient routing is unlikely to take root on VoIP.

Universal Standards

Telephone numbers, like VoIP identifiers, also started in chaos but, eventually in the 1950s, they were standardized to the current fixed format of seven digits preceded by an area code. This standardization happened at a different pace around the world, but eventually was completed and allowed for widespread uniformity in the switching layer used for call routing.

SIP User IDs are the closest comparison we have to telephone numbers.   These, too, take a standard format. The remaining challenge would be to bring presence technology – primarily XMPP and XMPP variants – into alignment to extend IP voice routing to the whole constellation of devices receiving and sending IP telephony calls.

Importance of Quality of Service

Quality of service was historically an underappreciated component of ENUM.  Carriers and service providers were, from the start, more focused on cost savings from IP to IP interconnections. Now, with an increased value placed on using higher definition codecs like G.722 that result in richer voice quality, QoS has the potential to be a point of differentiation. There is no question that more direct call routing without media conversion has the potential to allow more consumptive codecs to be negotiated between endpoints and, therefore, holds the promise for improved MoS scores. Bottom line: Centralized routing technology across the IP voice universe will make call quality better.


The Level 3 filing to end PSTN is an early indicator that the telephone numbering and routing system is entering its final chapter. In spite of this natural evolution toward IP voice, the value of that evolution as an improvement will be determined by how – and whether – carriers and service providers, working together in ways envisioned above, can forge a more efficient system for call routing. With the few ingredients mentioned in this article, however, the promise of ENUM – efficient, carrier-agnostic routing, improved call quality – may finally be realized in the age of VoIP.

Micah Singer (News - Alert) is CEO with VoIP Logic (

Edited by Stefania Viscusi