A few days back I was having an IM chat with Aswath Rao, perhaps the most technically learned guy around in blogosphere on telephony, especially VoIP, and asked him to enlighten me about ENUM (or Telephone Number Mapping) for that seemed to be in everyone’s mind these days. He told me that he will send me a short note and he did oblige me.



Though many of us are aware of what the technical story behind ENUM is all about, it is very difficult to put it in simple words and uncomplicated language that non-geeks can understand. It was amazing how easily Aswath could manage it.



For the benefit of all I am reproducing the part of Aswath’s mail to me (hope he doesn’t mind me doing this) that deals with the technical aspect of ENUM in simple language:

The primary purpose of ENUM is to terminate calls from PSTN in VoIP. Currently this can be done only at the Class 5 switch that is serving the VoIP customer. I mean if I am a VoIP customer and you dial my PSTN number, PSTN will deliver it my class 5 switch, which will hand it to my SIP Proxy, which in turn will alert me. This may be inefficient, because I may be closer to you rather than my class 5 switch.



So the idea is to have a globally accessible database that maps PSTN numbers to VoIP reachable addresses so that any PSTN switch to look it up and route it accordingly. The mechanics of ENUM is simple: map the telephone number to a hierarchical domain name and then use DNS technology to do the mapping. Since tel nos are hierarchical this is easy. Each digit in the tel no from the left (country code first) becomes the top level domain. So 1234567890 will become 0.9.8.7.6.5.4.3.2.1. Of course this has to be placed under some other root in the domain name tree. There is a controversy here. Some place it under e164.org and others argue against it for political reasons.


Aswath also wrote about his views on the revenue opportunities ENUM databases might offer. However, I won’t discuss that here for he should be the one to post his opinions(that I would really love to read more often)in his blog than someone else.



The e164.org is a free service and they are the ones who took this up for what they claim in the ‘About’ section of their website:
We recognize a need to faciliate the adoption of Voice over IP, and thus we offer our service to the public at large by validating telephone numbers and allowing number owners to determine how Internet communication protocols should interoperate against their phone number.


In my opinion, the ones like e164.org are aggressively asking people to register do have plans apart from providing public service alone. Though not immediate, there are mid-term strategic commercial interests behind it.



The commercial viability may be diminished by the sprouting of many databases, still just consider when it gradually becomes a true VoIP directory, what the telemarketers can pay to get/use the databases most of which are going to be in the hands of private entrepreneurs. (Will there be anything like ‘Do Not Call’ lists then?) And that is just one way to make money out of many, many more.



The early birds as usual will be the biggest beneficiaries because they would be having the biggest dadabases and would be able to make money when it is there to be made. Anyway, it would not last forever. With multiple ENUM directories, the usefulness of the databases would be substantially diminished.



If there aren’t billions to be made (obviously there isn’t) there are certainly millions for the taking.



I will be discussing more on ENUM both from the technical and business angles in the coming days.



Thank you Aswath. You can read Aswath Rao’s blogs here