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Re: [isn-discuss] Testing ISNs with FreePBX

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  • From: John Todd <>
  • To:
  • Subject: Re: [isn-discuss] Testing ISNs with FreePBX
  • Date: Fri, 30 Oct 2009 01:48:06 -0400

On Oct 29, 2009, at 7:52 PM, James Cloos wrote:

"John" == John Todd

John> I can completely understand the desire to have "0" as the main
John> number of an organization, though maybe it shouldn't be the "main
John> number", but should be "human operator". This still makes for
John> very difficult dialplan interpretation for those who are not using
John> a fully SIP-compliant system (a "dial-as-you-go" interface like an
John> older ESS, which still runs the majority of the phones in the world.)

That is one of the bugs with choosing endian-little rather than big- endian
strings for the ISN format.

I know that the idea was to emulate the format of email addresses (perhaps
indirectly, via the format of sip: urls?), but one can argue that that is
also a bug for email addresses. And it never felt quite right to me.

Emulating for big-endian format of most other urls would make for (or would
have made for) easier dialplans and also provide the conceptual advantage,
when phoning an organization, of thinking "this org" and then "this person"
or "this role".

The ENUM lookup would be the same as now, only the advertising and dialing
order(s) of the number would be (or would have been) different.

That is not to say that there would be no bugs with choosing the big- endian
order. (Although I cannot think of any off-the-cuff. :)

I understand the shortcomings of the chosen method, but the hope is that eventually we'll all be dialing SIP URIs some day. So, it's easier to explain and have people remember "An ISN is like an email address - username, then a separator, then a domain - except you can do it all from a standard 12-digit phone keypad." The intent is to create a transition between E.164 and SIP URIs, so there is a structure that is similar to URI format rather than E.164 big-endian format.

There were other reasons, too, but it's 1:45 AM and I'm too tired to dredge them out of my memory. :-)


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