I think of Unified Communications (UC) as expansive as well as contractive. It wasn’t that long ago when electronic communication was limited to telephone calls. In the 1980’s we added email to that very short list. Since then we’ve expanded to video, instant message, SMS text, social media, and Twitter. For the millennial generation, land-line telephones have become passé and cell phones are used for nearly anything except voice communication.
As we continue to add new ways to communicate the addresses for all those forms becomes very important. Imagine what it would be like if my VoIP address was firstname.lastname@example.org, my video address was email@example.com, and firstname.lastname@example.org was used for instant message. Remembering all those addresses and how they are applied would create a condition where people stopped using one or more forms of communication. Instead, UC allows me to contract that list to one address for voice, video, and instant messages – SIP:email@example.com. In the IP world, SIP:firstname.lastname@example.org is known as a Uniform Resource Identifier (URI). “SIP” indicates the protocol for this form of communication, “aprokop” is the subscriber name, and “mycompany.com” is the domain of the subscriber. Note that mycompany.com can be used for multiple services. For example, web, email, and communications could all be member services of mycompany.com. The protocol designation in the URI is used to determine which service should be invoked.
This leaves us with a big problem to solve. How do I pick up an old-fashioned, analog telephone at home and call my SIP telephone at work? Touchtones are not easily translated into alphanumeric values. Additionally, resources like the White Pages have yet to understand anything but numbers to identity a telephone user. However, as I transform my enterprise with UC I don’t want to prohibit calls from the public switched telephone network (PSTN) to the SIP world.
Enter E.164 Number Mapping, or ENUM for short. ENUN is used to translate E.164 numbers (the standard format for telephone numbers) to something more Internet friendly. This allows a UC user the ability to employ a user-friendly, character-based name that maps to an IP address that maps to a number that can dialed from any telephone in the world. ENUM is a standard and is managed by the Internet Engineering Task Force (IETF) – the same people who manage SIP all the web protocols.
As with every other Internet address translation, ENUM utilizes the Directory Name System (DNS) to perform the mapping between telephone numbers and IP addresses. Specifically, it uses the public e164.arpa domain for ENUM services. While the actual mapping of telephone numbers to IP addresses is a bit technical, the only thing that you need to understand is that in order for a number to be available for translation it needs to be registered with the e164.arpa domain. Once registered, the DNS lookup process will return an IP address for the telephone number query.
Of course, some enterprises might not want their internal IP addresses available to anyone who asks. This is where private ENUM comes in. Private ENUM acts exactly like public ENUM with the exception that the e164.arpa domain is not used for the telephone number to IP address mapping. Instead, an enterprise will create its own domain that restricts access to only authorized users. An authorized user may be an individual or a trusted organization such as a PSTN carrier. Over time the privacy issues that arise from public ENUM may be resolved and private ENUM no longer required, but until then enterprises may wish to maintain their own ENUM system.
There is Still Work to be Done
It’s important to note that both public and private ENUM are still works in progress, but a great deal of thought an effort is going into solving the PSTN to IP communications problem. ENUM is a start and may or may not be the road to the finish line. Stay tuned as this technology evolves and finds its way into your daily communications life.