You will probably be aware that we have been talking rather a lot about ENUM recently, and that following the recent result of the vote at our EGM, Nominet intends to bid to become the Tier one registry for ENUM in the UK.

But what is ENUM exactly? How will it work? Who will use it? If these are questions you’ve been pondering recently, please read on!

What is ENUM?

ENUM is a protocol that maps traditional telephone numbers onto Internet domain names (ENUM domains). The usual Internet application addresses for email, web sites and also VoIP (Voice over Internet Protocol) telephones typically consist of letters, numbers and various special characters. ENUM links these addresses with a simple telephone number, thus solving the problem of dialling this address on a traditional telephone with a number keypad. This is a precondition that enables a simple addressing of VoIP telephones from the conventional telephone network. Vice versa, if you make an Internet call, the end device (e.g. PC telephone software or IP telephone) checks whether there is an ENUM domain corresponding to the number called. If this is the case, the call is forwarded to the address that has been configured by the called partner, which in turn can address a PC, a notebook or an IP telephone. As a result the entire connection is established via the Internet, and there are neither call charges nor the need to transcode the communication several times. If no ENUM domain is found for the called number, the connection is established via the conventional telephone network.

The first ENUM commercial registry service in the world was launched in Austria in February 2004 and the technology has already become routine there, as it is offered by several service providers. Internet Privatstiftung Austria (IPA), the Austrian organisation which operates that registry is also a partner in the consortium that is providing the commercial registry of ENUM in Ireland.

The UK ENUM group has been conducting trials of the system in the UK, and will be calling for bids to run the Tier one registry for ENUM before the end of the year.

Nominet intends to bid to run the registry, and has been involved with the work of the UK ENUM group since it was formed in 2001.

What are the benefits of ENUM?

The first main use of ENUM will be to link different VoIP servers so that telephones within businesses that use VoIP technology to connect users within an internal network can use the same technology to connect users to external customers via the Internet.

At present it is easy to connect from one employee within a company to another in the same company using a VoIP server. That still works if an employee is a home worker who connects over the Internet - the VoIP server recognises the numbers within its system and connects the call as if the home worker were in the office.

However, if someone within Company A wishes to connect to someone in Company B using their VoIP server currently, they need to connect to a telephone network provider who makes the connection to the other company. Obviously this costs money, as the calls are charged for by the telephone company.

The advantage of ENUM is that it will enable Company A’s VoIP server to connect with Company B’s VoIP server via the Internet without having to connect to the telephone network for the call.

This is done by translating the telephone number into a domain name:-

01865 332211 becomes 1.1.2.2.3.3.5.6.8.1.4.4.e164.arpa where ‘44′ is the UK’s international dialling code, ‘e164′ is the name of the telephone numbering system and ‘.arpa’ is the Internet infrastructure equivalent of .uk or .com. A computer can understand and connect to this address in a fraction of a second which makes ENUM a quick, stable and cheap link between the telecommunications system and the Internet.

Further information

There is a brief overview of ENUM on our web site, and there have been interesting articles on this technology published in the Times Online and Guardian Unlimited. Jay Daley, our Director of IT recently posted his thoughts on the longevity of ENUM and the growing importance of VoIP technology on our Technical Blog.

This entry was posted in January, 2007.
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