The question is, is this being adopted in the enterprise and if so, how would that make an IP PBX or PBX administrator’s life easier?

To answer the first question, yes, it has been adopted thanks to Microsoft. Microsoft built OCS on the foundation of supporting ENUM, and all Microsoft Office communicator devices are numbered accordingly. Additionally, Cisco has also entered the ENUM world with their supported solution in Communications Manager 7.x solution. So it is being adopted quickly at least by the top two IP telephony competitors and most likely by other vendors as well.

Now the next question of how will this make your job easier as an administrator? At first glance it looks like more of a burden than help, especially since administrators will have to assign the full E.164 number routine for all lines associated to devices.

But, the savings will be from greater flexibility in deciding on a per-site behavior how many of those digits pressed would represent the local dial pattern.

For instance, in the above example I assigned the number +14043567893, but I only want or desire 4-digit dialing within the office. Well, I would simply translate the number, either in OCS or Communications Manager, to be able to dial just 7893 to reach that local line within the office itself.

So when you are trying to design complex number manipulations especially with a many international dial plans as well as the NANP; the implementation of the overall routing mechanisms between corporate sites around the world will be much easier and flexible.

Additionally, countries are now deploying ENUM DNS directories to be queried in order to find devices using the internet versus using the traditional SS7 telephony network! Remember that ENUM was originally developed to be deployed by DNS servers on the internet, but has also made call routing programming for a PBX in a multinational enterprise more flexible.

You need to get on the band wagon now and learn ENUM. The best way to do this is to start with RFC 3761, check out the online tutorials, and/or attend training courses which will teach you the ENUM fundamentals using either Microsoft OCS or Cisco’s Communications Manager 7.x.

Author: Joe Parlas

The International Telecommunication Union (ITU) is the responsible body for all telephony numbering around the world. The way the numbering plan laid out is:

• A telephone number can have a maximum of 15 digits
• The first part of the telephone number is the country code (one to three digits)
• The second part is the national destination code (NDC)
• The last part is the subscriber number (SN)
• The NDC and SN together are collectively called the national (significant) number

Now, each geographic area has responsibility for it’s own numbering plan. The United States and Canada share equally in the North America Numbering Plan (NANP) which entails a single-digit country code, followed by a 3-digit area code, a 3-digit prefix, and a 4-digit subscriber code. In other words, our numbering system is quite fixed. Other countries have variable length numbering plans, like England where the number grows based upon the density of a given city.

The E.164 has developed into something broader called ENUM (TElephone NUmber Mapping) which was the brain child of the IETF (internet engineering task force). Using the international E.164 number as a model, ENUM will assign a specific Uniform Resource Identifier (URI) to each and every networked device — including analog telephones and fax machines, smart phones, or computers. The reason for this is to make it easier to look up the numbers or devices using DNS servers on the internet.

The URI could be in a format of an email address (joe.parlas@cisco.com) or a number with an assigned domain name (+6197256999@cisco.com).  With URI all these devices will be able to contact each other directly using a single network address or phone number. ENUM also deals with storage of these numbers on the DNS (domain name server) so that voice over IP phones could look up a number over the internet and be connected to another voice over IP system.

RFC 3761 is defines the format of the number as:

The Application Unique String is a fully qualified E.164 number minus any non-digit characters except for the “+” character which appears at the beginning of the number. The “+” is kept to provide a well understood anchor for the AUS in order to distinguish it from other telephone numbers that are not part of the E.164 namespace.

For example, the E.164 number could start out as “+44-116-496-0348″. To ensure that no syntactic sugar is allowed into the AUS, all nondigits except for “+” are removed, yielding “+441164960348″.

So the full ENUM number must begin with a leading “+”. But the question remains, what does the “+” represent? Basically it represents your country’s access code to dial out to make international calls. For instance, if I were to dial an international number from my home in North America, I would begin by dialing “011” which is our code fore requesting international service.

In essence, a fully qualified ENUM number is one that could be dialed by any device, any place in the world, and the call would be properly set up. If you look closely at your cell phone when you dial from outside your home country you will notice that the cell provider has translated the number into a fully-qualified ENUM during the calling operation.

The beauty in this system is that I don’t have to worry about remembering international access codes for different countries, as long as the provider understands the leading “+” symbol.

Author: Joe Parlas

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