Asterisk - E164 and internal number ranges

[mike557]

The users on my Asterisk exchange have extension numbers, however they often forget the extension numbers and decide to use DDI (Direct Dialing In) numbers. The problem is the exchange uses my voip provider to provide the connection between the two extensions - which does incur a call charge

So what is the solution?

The simplest is to make the internal extension number the same as the DDI. This sounds good, but what about area codes and country codes? I could instruct the users to call each using the ddi number in local number format. This will work as Asterisk always checks internal numbers before using external numbers.

So now it appears as though the users have standard 'landlines' connected to the public network and they still have all the extra facilities that Asterisk can provide Smile

Another solution is to use the last 2 or 3 digits from the DDI number. This could work but if your DDI numbering plan is not sequential you could have problems.

So what about extensions that do not have a public DDI ?

I will need to choose extension numbers that do not map to 'real' public numbers. This will break up the numbering plan and may be very difficult to implement.

Other problems associated with using the DDI is the length of the number (probably 5 digits in length). Extension numbers need to be short preferably 2,3 or 4 digits depending upon the size of the organisation.

Why not use e164.org ?

e164 provides a free 'public' database containing PSTN (Public Switched Telephone Network) numbers that map to a sip uri. A sip uri is what is used to connect voip calls and looks something like SIP/16416418005558355@sip.tollfreegateway.com
This sip uri would connect you to the great 'TELL ME' service over in the USA.

By putting my DDI numbers into the e164 database and mapping to one of my DDI sip uri's it is possible to detect my own numbers and not incur any charges for the connection.

The more people that register their sip addresses with e164.org, the more free calls we can all make.

Wow that sounded complicated !!!

It does, but in fact once you get your head around the terms used things become very simple.

Asterisk allows us to specify ENUM as an outgoing trunk circuit. Whenever you make an outgoing call it checks e164.org (and other enum providers) to see if the number is in their database. If the number is found, Asterisk will attempt to connect directly with the sip uri given.

Now any user dialing a non extension telephone number is checked using enum and if it is our own ddi number the call is routed to the correct extension - excellent Smile

So what is the perfect numbering system?

It all depends upon the number of users your exchange is supporting (of course), also you must cater for expansion. Two digit numbers are easier to remember than 3 so keep things small. If you do run out of numbers, then it is not a difficult task to add a digit at the front of your current numbering system.

Should I use a digit to indicate an outgoing call e.g. 9 ?

I prefer to just dial and not have to worry about dialing a digit for an outside line. The other advantage is that when you receive a call from 'outside', you can use the callback service.

Another advantage is that the digit saved allows for more internal extension numbers or expansion / reserved level.