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## RE: New module Algorithm::Interval2Prefix

From:
Orton, Yves
Date:
December 5, 2003 07:06
Subject:
RE: New module Algorithm::Interval2Prefix
Message ID:
```
> Lars> I totally agree that when generating prefixes from number
> Lars> intervals, this depends squarely on the involved numbers being
> Lars> the same number of digits.  But telephone numbers *will* be the
> Lars> same length in the same prefix-area[2].
>
> Lars> [2] Since this is the only way the telephony switch can know
> Lars> when the number you are dialling is 'complete'.
>
> That's not true in Japan, where the area codes are variable length.
> The local numbers are fixed, so they can make that decision (when the
> complete number is dialed) after they have parsed the area code.
>
> The way I beleive it works (I lived in Japan from 1988 to 1994, but I
> beleive this is still true today), is that the length of the area code
> depends on the 2nd digit.
>
> All area codes start with 0, so if you start dialing any other
> numberm, it is assumed to be local, and thus fixed length.  If you
> start with a 0, then the 2nd digit is examined, and that determines
> the length of the area code.
>
> For example, is the 2nd digit is a 7, those area codes are all 4
> digits (07??).
>
> I am basing these statements on memory, so don't quote me as
> authoritative.  Just something I noticed while living there.  If
> someone living in Japan today, with more knowledge of Japanese
> telophony could confirm or deny this, that would be great (my wife,
> who's Japanese, had absolutely no clue, but then she's not a geek, and
> doesn't understand why I find this even remotely interesting).

I'd be pretty suprised if this is how it works. Variable length prefixes are
the norm outside of North America and the Carribean. Its pretty simple,
prefixes are the length they are. There arent deterministic lengths. There
may have been some attempt by the Japanese regulator/ PTT to do such a
system, but it would effectively be by convention and not a widespread
technical implementation.

A telphony switch can tell the call is complete when it terminates at a
switch that does not route any further. We sometimes get CDR data that
contains duplicated B'numbers due to accidental use of an autodialler that
are twice the normal length doesnt confuse anything.

Yves

```