ENUM: INSIDE THE WORKING GROUP

ENUM is the new IETF protocol designed to function like a directory services feature linking PSTN phone numbers to Internet telephony oriented services. We interview Rich Shockey who was co-chair of the ENUM working group.

E164 refers to the international telephone number protocol established by the International Telecommunication Union. E164 resolution means the use of the ENUM protocol (RFC2916) to connect any number in the globally switched telephone network to whatever Internet services have been provisioned for it. Such services may range from a personal web page look up to the ability to retrieve voice mail from anywhere in the world with a local phone call. ENUM makes it possible for the first time to connect a voice over IP service to any POTS phone whose number has been ENUM provisioned.

Currently one SIP provisioned phone can find another only if the owners of each number are aware of the other's existence. Before the web to FTP a file from a directory you had to know it existed or you had to browse directories and stumble by chance on anything interesting. The web became a means of finding and indexing such files and eventually of stitching them together so they could be intelligently located with great ease. ENUM will offer a way for a VOIP service like SIP to transparently find every PSTN phone on the globe whose owner has ENUM provisioned it through national registries to be set up late next year, When a PSTN phone is ENUM provisioned much of its use will begin to flow over the Internet. If ENUM services become as popular as expected, they will be a means by which huge amounts of PSTN traffic will be sucked out of the PSTN and onto the Internet. ENUM has sometimes been referred to as the service control point for the deconstruction of the PSTN by the Internet.

ENUM in a single sentence has been defined as "telephone number in URL out using NAPTR". An ENUM specific domain (in other words the ENUM expression of a telephone number under a single unique administrative DNS domain) must list any and all services available for that domain. The new ENUM GTLD is e164.arpa. It was added to the Root late last month.

ENUM itself is a simple protocol taking only five pages to describe. Shockey reports that the central development issue revolved around a debate of whether or not to use NAPTR records for service discovery. "NAPTR stands for the Naming Authority Pointer Resource record. It is RFC 2915 written by Mike Meeling of Network Solutions and Ron Daniel of Data Fusion. Debate about what resource records had to be returned for ENUM service resolution was extremely contentious."

Shockey describes RFC 2915 as "a profoundly elegant and powerful document for service resolution within a domain. For example it has an ability to list "n" number of services for a domain through the use of regular expressions and a variety of other features and functions. The importance of the use of NAPTR records in this environment cannot be stressed highly enough." Shockey states that the advantage in the use of NAPTR was having a single resolution methodology for resources associated with a telephone number. "If we did not use NAPTR for a resolution we would have issued a sort of directive to the Internet community saying that it was OK to resolve a telephone number to any resource record." (Tony Rutkowski in a short article of his own in Communications Week International also lauds the importance of NAPTR as the glueballs holding ENUM together.)

It seems to the Editor that the intent of use of NAPTR for resource records may be to ensure that the customer has in effect only a single key chain for use in tying together all advanced services to which he subscribes in what is regarded as the most important enabling technology of convergence between telephony and computers as represented by the Internet.

Shockey acknowledges that since ENUM becomes a single point of control and also a single point of failure, the way in which services are provisioned will be absolutely critical. The consumer must be given absolute and total control over his ENUM services which may become the single tool set by which he controls his business and personal communications.

Under this ENUM business model there will be only a single ENUM provisioning authority for each nation state. The IETF and ITU have agreed not to break the e164 mould which means that each national telephone numbering authority will be asked to decide who will provision ENUM services within its borders.

In the US it is likely that an early decision of the new administration will be to choose whether the Department of Commerce or the FCC will issue a solicitation for a national ENUM administrator. Some think that giving the task to the FCC would be both Bell head friendly and ensure a slower role out than an assignment to the Net head friendly Department of Commerce. In any case it is assumed that a successful bidder will have to provide assurances that customer control over the selection of ENUM services and over the privacy issues involved in having what may become a single identifier for all one's telecommunications activity will have to be very carefully respected. It will also be critical to guarantee that when a business or individual changes phone numbers, that all ENUM services attached to an old number are severed from that number immediately on customer disconnect and attached to the new phone number as soon as it becomes live. Critical issues with ENUM are thought to be far more political in nature than technical.

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