What’s Enum all About?

Jim Lynch, MD of SIP trunking specialist Voiceflex, says that Enum can be thought of as DNS for telephone numbers and sees the largest uptake likely to be the service providers who can use Enum to save money by directly routing calls via IP to users.

“For the uninitiated, DNS lets your PC work out how to get to www.cbmagazine.co.uk on the internet. For example, your browser would lookup www.cbmagazine.co.uk and DNS would return, which is the IP for the server the website is sitting on. So Enum does something very similar.

Give Enum a telephone number and it will provide you with an address, such as an IP address, to send the call to. In theory this would allow your PBX to send calls directly to a 3rd parties PBX without even previously having connected to them, using SIP.

Unfortunately, Enum is actually quite difficult to understand and there are a number of reasons you need to think through your use of Enum.

Enum is actually a means of mapping a telephone number (E.164 to be precise, +44 etc) to the internet addressing system. Ok, so I’ve probably lost you at this point, so here’s an example:

I want to call +442074401800

My PBX requests Enum details for +442074401800

Enum returns a series of complicated addresses for all the methods that this number can be contacted by. Methods could be SIP, email, IM or even PSTN.

In this example, I want to make a voice call. So I the PBX selects the SIP address: sip: 442074401800@sip.voiceflex.com

The PBX can now make the call via SIP directly to the Voiceflex SIP Proxy.

Enum has more uses than just for voice. If I wanted to send an email, but I only have the persons’ phone number then I could type the number into Outlook and Enum could be used to look up the email address for me. Confusing, well just think that a telephone number will know all the ways you can be contacted. The client (voice, email, Instant Messenger) decides which connection method to use.

What’s been described so far is probably misleading to what Enum is really going to be used for in the next few years. The largest uptake is likely to be the service providers, who can use Enum to save money by directly routing calls via IP to users. Although, the speed of this uptake isn’t clear. There have been numerous successful test runs of Enum, some with tens of thousands of numbers and users.

The overall Enum space and strategy is far from clear, even with the recent UK announcements. Public v Private, underlying systems, architecture and ownership of the data are big issues which need to be worked through. Then we get to the business model, which is probably the biggest issue. Will this information be free? Or will there be a subscription costs or transaction fees? Whatever happens, the first signs of the death of SS7 are on the horizon and the start of real convergence.

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