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Stephen Sprunk

On 02-Apr-12 21:29, wrote:
On Apr 2, 8:05 pm, Stephen Sprunk wrote:
Note that our current ten-digit scheme allows for nearly 6.4 billion
phone numbers, which would be plenty for the 400 million people living
within the NANP if they weren't assigned so inefficiently.

It amazes me that dedicated outward trunks of a PBX get dialable
numbers even though no on ever calls them.

PBX trunks aren't numbered. However, key systems ("KTS"), which many
people mistakenly call PBXes, use normal POTS lines, not trunk circuits.
Some telcos had the ability to give multiple POTS lines the same
number, but others apparently did not--and I'm not sure how recently
that came about.

They should get specially
identified numbers (eg in the 1nn-xxxx series) so they don't waste
addressable numbers.

YXX exchanges are reserved for internal network purposes (eg. billing);
they _can't_ be assigned to customer circuits, even though it's now
possible to dial them in areas with 10-digit local calling.

I'm not sure what, if anything, YXX area codes are used for; they're not
dialable by _anyone_ on a land line.

Note that the lack of YXX exchanges is key to the planned scheme to
extend phone numbers: ABC-DEF-GHIJ will become ABC-1DEF-GHIJK (except in
Canada, where it will become ABC-0DEF-GHIJK). Once the transition is
over, and everyone is dialing 12 digits all the time, the fourth digit
will change from Y to X.

Actually, inward trunks to a PBX really need only one addressable
number, all the hunt lines could be a special series, too.

Heck, I think even in panel days a hunt group didn't need to be
consecutively numbered lines, only step demanded that.

The practice had ossified by the time it was no longer a technical
requirement. Even today, hunt groups up to 10 lines usually have a
pilot number ending in 0, and hunt groups up to 100 lines usually have a
pilot number ending in 00.

PBXes don't need (telco) hunt groups, though; trunk circuits can accept
dozens of calls to the same number. (Telco) hunt groups are only used
for KTSes.

S

--
Stephen Sprunk "God does not play dice." --Albert Einstein
CCIE #3723 "God is an inveterate gambler, and He throws the
K5SSS dice at every possible opportunity." --Stephen Hawking