Telecom/1996-04-telecom-walnutcreek.iso/reports/number.crisis.in.zone.1

Internet Message Format | 1993-11-25 | 28KB

Date: Fri, 19 Nov 93 18:18:17 EST
From: Carl Moore <[e-mail]>
Subject:  The Numbering Crisis in World Zone 1

(some corrections to the file installed by Carl Moore, November 1993).

JULY 1993

"The Numbering Crisis in World Zone 1" by Brian Hayes.  It comes under
"The Information Age" in the publication "The Sciences", November-December
1992.  (Brian Hayes is editor-at-large of American Scientist.)  Bracketed
remarks are mine! -- CGM

**Scarcity is no stranger in this land of plenty.  Form time to time it
seems we are running out of fuel, out of water, out of housing, out of
wilderness, out of ozone, out of places to put the rubbish, out of all
the stuff we need to make more rubbish.  But who could have guessed, as
the millennium trundles on to its close, that we would be running out of
numbers?  That was one resource every thought was infinite.

The numbers in short supply are telephone numbers.  In some parts of the
United States, they are already quite scarce, and they will have to be
carefully conserved over the next few years.  At first the idea of such
a shortage seems preposterous.  A standard North American telephone number
has ten digits:  three for the area code, three for the central-office
code and four for the local line number.  A ten-digit format allows for
ten billion distinguishable telephone numbers, from 000-000-0000 to 999-
999-9999.  [See next paragraph for flaw!]  Even if every person in North
America had a telephone at home and at work, as well as separate numbers
for a car phone, a fax machine, a modem and a beeper, there would still be
more than enough numbers to go around.

The flaw in this analysis is that not all ten-digit numbers are possible
telephone numbers.  Indeed, more than 90 percent of them are unacceptable
for one reason or another.  A telephone number is not just an arbitrary
sequence of digits, like the serial number on a ticket stub; it has a
surprising amount of structure in it.  As a matter of fact, the set of
all valid North American telephone numbers constitutes a formal language,
analogous to a computer programming language.  When you dial a telephone,
you are programming the largest machine on earth, the global telephone
network.

A look at the grammatical structure of telephone numbers reveals a lot
about the telephone system works and how it evolved.  And modifying that
grammar turns out to be the key to solving the numbering crisis.  The so-
lution is discussed in a document released earlier this year by Bellcore,
one of the surviving corporate fragments of the dismembered Bell System.
The document has an imposing title: "North American Numbering Plan Admin-
istrator's Proposal on the Future of Numbering in World Zone 1."

**When I was a boy, my grandmother's dialless telephone was an object of
mystery.  It was like a clock without hands or a ladder without rungs--
I couldn't fathom the use of it.  Then my grandmother demonstrated.  She
picked up the receiver and said, "Jenny, get me Mrs. Wilson, please.
Thank you, dear."

My grandmother's telephone was already quite an anachronism when I first
saw it in the 1950s.  Automatic switching gear--allowing the customer
to make a connection without the help of an operator--had been placed
in service as early as 1892.  The invention of the first telephone switch
comes with a story worth telling.  According to legend, Almon B. Strowger
was a Kansas City undertaker who found he was losing business to a rival.
Potential customers would telephone Strowger but "mistakenly" be connected
to his competitor.  Strowger noted that the competitor's wife was the
switchboard operator for the local telephone system.  His revenge was to
invent a device that would eventually displace operators almost everywhere.

Strowger's invention was a ten-position rotary selector switch with a pivot-
ing central arm that could rotate to connect with any of ten electrical con-
tacts.  The pivoting arm was moved by an arrangement of electromagnets,
springs and ratchets.  Each time the electromagnet received a pulse of cur-
rent, it advanced the arm by one position.  In the first network to try
Strowger's idea, the customer operated the switch by pressing a button.  If
you wanted to dial a 7, you pressed a button seven times, thereby sending
seven pulses of current to the electromagnet driving the selector arm.  The
push buttons were soon replaced by a rotary dial, which automated the count-
ing of pulses.

A single switch of that kind could interconnect ten subscribers.  If you
were one of those subscribers, when you picked up your receiver, your line
would be connected to the central selector arm.  Dialing a one-digit number
would then ring one of the other nine telephones.  Adding a second stage of
switching could expand the service to a hundred subscribers.  Now the ori-
ginal switch, instead of being connected directly to ten subscriber lines,
would be linked to a bank of ten more identical switches.  Each subscriber
would be identified by a two-digit telephone number.  When you dialed the
first digit, say a 3, the first selector switch would connect your line to
the selector arm of the switch leading to lines 30 through 39.  Dialing a
second digit would move the selector arm of the second-stage switch to the
appropriate contact.

**It is easy to see how a Strowger switching network could be expanded to
handle 1,000 lines (with three banks of switches) or 10,000 lines (with
four banks).  In principle, such growth could be continued indefinitely,
but the quantity of switching gear would become impracticably large.  The
telephone company adopted a different plan.  It set up switching offices
that could each accommodate as many as 10,000 subscribers, then provided
trunk lines to connect the various offices.  At first, calls between cen-
tral offices were completed by operators, but soon that task too was put
in the hands of the customer.

Suppose you were a telephone subscriber when dialing between central offices
was introduced.  You were accustomed to ringing up your neighbors by dialing
a four-digit number.  Now you could reach towns and cities for miles around
by dialing seven digits.  The first three digits--actually two letters and
a number at the time--specified the central office, and the last four digits
were the line number within that office.  [Does not mention the use of 3
letters and 4 digits in some areas; does not mention 2 letters and 4 digits
in Cincinnati area, which added 1 after the letters in order to standardize
phone number length.]  But there was a price to pay: you would no longer be
able to call next door by dialing just four digits.  To reach local people
you would have to dial your own central-office code before dialing the four-
digit local number.  [Some places kept this, but this then caused restrictions
on available numbers.]

The extra dialing for local connections was a concern to telephone engineers,
who worried that customers would resent it.  Why couldn't you dial KLondike
5-2345 to reach your uncle across the river, but dial 5552 to reach your
sister across the street?  The question is a miniature version of a problem
that has plagued telephone switching for at least forty years.  In the first
place, KL5 is simply 555; the alphabetic encoding of numbers exists only on
the dial of the telephone.  Thus the first four digits of KL5-2345 are the
same as the local number 5552.  When you have dialed those four digits, what
should the switch do?  Should it connect you to your sister, or should it
wait to see if you dial more digits?

The Strowger step-by-step switch allows little flexibility in resolving
such ambiguities.  It is called a step-by-step switch, because once it
has made a selection, it cannot go back to revise the choice.  A Strowger
switch must determine on the basis of the first digit dialed whether to
set up a local call or to select a trunk line for a call to another ex-
change.  If the switch were to establish a tentative routing to your sister
as you dialed 5552, there would be no way to undo that connection if you
continued dialing.

Telephone switching gear has changed a great deal since Strowger's time.
Modern switches are fully electronic rather than electromechanical, and
they are capable of holding a series of digits in a buffer before determin-
ing what to do with them.  Nevertheless, the architecture of telephone num-
bers is still strongly influenced by decisions made to accommodate the pe-
culiarities of early step-by-step switches.  Moreover, in some rural tele-
phone office there may still be a Strowger switch clanking and clunking
away.

**Seven-digit dialing would seem, on first analysis, to give each telephone
direct access to ten million others.  Actually, the number of lines available
is only about half that.  The reason is that some numbers count for more than
others.

"Dial 0 for Operator" has been standard telephone practice almost from the
beginning of direct dialing.  As a consequence, you will never see a tele-
phone number such as 007-2345 or 099-6789, at least not in North America.
If you tried to dial such a number, you would be connected to an operator
before you could finish.  [Does not consider 0+ calling; does not consider
00 for long-distance operator.  But the numbers shown just above remain
unavailable.]  That special handling of 0 puts off-limits a million poten-
tial phone numbers in every calling area--all the numbers from 000-0000
through 099-9999.

Another number you will never see for a North American telephone is 123-4567,
in which the leading digit is 1.  It turns out that various dialing codes be-
ginning with 1 are reserved for internal uses within the telephone system,
such as selecting trunk lines between switching centers.  There go another
million numbers.

The special functions of 0 and 1 forbid their use as the first digit of a
central-office code, but traditionally 0 and 1 have been avoided as the
second digit as well.  At the outset that restriction had nothing to do
with the operation of the switching network; instead it was a matter of
mapping letters to numbers.  Central-office codes were introduced with
names rather than numbers because the telephone company company thought
BUtterfield 8 would be more memorable than 288.  On the telephone dial,
0 and 1 are not assigned any alphabetic equivalents, and so they could
not appear as the second letter of a central-office name.  That subtle
constraint, imposed to help avoid confusion between O and 0 and between
I and 1, has had remarkably far-reaching consequences for the telephone
system.  Named exchanges are gone, but their influence on the format of
telephone numbers remains.

For a long time 0 and 1 were avoided even as the third digit of central-
office codes.  There was no compelling reason for the practice, although
again it helped avoid mistaking 0 for O or 1 for I.

In any case, for some decades most North American telephone numbers followed
a pattern that can be expressed as NNN-XXXX, where N represents any of the
eight digits from 2 through 9 and X is any decimal digit at all, from 0
through 9.  The maximum capacity of this numbering system is equal to
8 x 8 x 8 x 10 x 10 x 10 x 10, or 5,120,000.  In practice, it is an upper
limit that can be approached but not reached.  A few lines in each central
office are needed for testing and similar purposes, and a few exchange codes,
such as 555, have traditionally been reserved.  Moreover, telephone companies
try never to fill a central office completely, since that would leave no flex-
ibility when customers move or request a change in service.

**By 1950 seven-digit dialing had spread to much of the U.S. (though not
to my grandmother's house).  A telephone connected to the network had
the theoretical potential of reaching five million other telephones.
At the time there were fewer than fifty million telephones in the
nation.  [from CGM: what about Canada and the Caribbean?]  Thus all
that was needed, in order to allow a subscriber to reach out and touch
everybody, was a factor-of-10 increase in the numbering capacity.  One
extra digit would do it.  The planners of the telephone system decided
to be conservative.  They came up with a scheme that would increase the
capacity almost 150 times.  A spokesman for one of the local Bell operating
companies recently noted that under the plan the supply of numbers was ex-
pected to last for 300 years.  It held out for almost fifty.

The idea, now familiar to all telephone users, was to divide the continent
into area codes, know officially as numbering-plan area, or NPA, codes.
In the original proposal, published in 1947, there were eighty-six assigned
codes, with another fifty or so held in reserve for growth.  Each state had
at least one code to itself; the more populous states had multiple codes.
The largest cities were assigned codes such as 212, 312 and 213, which were
the quickest to dial on a rotary-dial telephone.  Every code had three digits.

To deflect resistance to the further lengthening of telephone numbers, the
Bell System was careful to design the NPA codes so that extra digits would
be needed only for dialing long distance; local calls could still be placed
with seven digits, as in the past.  [This article never deals specifically
with long distance within an area code.]  Accordingly, the format of the NPA
codes had to satisfy one fundamental requirement: the switching equipment
had to be able to distinguish an NPA code from a central-office code.  The
key to making the distinction turned out to be the middle digit of the code.
As noted above, the second digit of a central-office code had always been
confined to the range 2 through 9; the corresponding digit of an NPA code
is invariably either 0 or 1.  [The "is" is to become "was" at the start
of 1995.]  Thus the middle digit alone distinguishes the two kinds of
code.  The complete pattern of an NPA code is NZX, where N again designates
2 through 9, Z is 0 or 1, and X is 0 through 9.  The pattern for an entire
telephone number is [was!] NZX-NNN-XXXX.

The NZX pattern yields 8 x 2 x 10 three-digit codes, for a total of 160.
But as with the central-office codes, a few of the NPA codes were set aside
for other purposes.  Certain codes of the form N11 codes were reserved for
reaching the telephone company itself (411 for directory assistance, 611 for
repair, 811 for the business office); later 911 was added for emergency
services.  The numbers of the N00 series were designated service access codes
instead of NPA codes; among various services offered, toll-free 800 has
proved the most popular.  Codes of the form N10 were given to the Telex
network.  Excluding all those twenty-four reserved codes left 136 combinations
for ordinary geographic NPA codes.  With 5.1 million numbers for each area
code, the maximum capacity of the system was just under 700 million numbers.

**Direct distance dialing with ten-digit numbers first went into service
in 1951, in Englewood, New Jersey.  If you were designing the switch for
the central office in Englewood, how would you handle the challenge of the
new extended numbers?  Here is an informal description of one straightforward
algorithm:

If the first digit is 0, connect to the operator.

If the first digit is 1, signal an error.

Otherwise, since the first digit is in the range 2 through 9, examine the
second digit.  If it is anything other than 0 or 1, the dialed number must
be a local one, and so it can be handled by the established seven-digit
protocol.

If the second digit is 0, examine the third digit.  If the third digit is
also 0 (so that the first three digits form the pattern N00), connect to
the appropriate special service.  Otherwise (the pattern being N01 or N0N),
connect over the long-distance network to the appropriate NPA.

If the second digit is 1, examine the third digit.  If the third digit is 0
or 1, connect to the indicated N11 or N10 service.  Otherwise (the pattern
being N1N), connect over the long-distance network to the appropriate NPA.

[END OF ALGORITHM]

An algorithm like this one worked in Englewood, but a problem showed up when
telephone engineers elsewhere tried to implement it.  The algorithm will not
work on a step-by-step switch.  As I noted above, such a switch must commit
itself to the routing of a call when the first digit is dialed, but the algo-
rithm offered here cannot know whether a number is local or long distance
until the second digit has been examined.  Deferring the decision was not a
problem in Englewood, because the central office there has a switch capable
of storing the first few dialed digits in a buffer, but many other switching
offices still relied on step-by-step equipment.

A couple of solutions to the step-by-step problem were tried.  The scheme
that caught on was to ask the customer to dial yet another digit for long-
distance service, namely a 1 before the area code, a practice that came to
be known as 1+ dialing.  (The plus sign is not dialed, of course; it is
meant to suggest that the 1 is only a prefix code.)  Since 1 could not be
the initial digit of any valid NPA code or central-office code, the new
marker was unambiguous.

There is something ironic about the introduction of 1+ dialing.  The planners
of the telephone network had taken pains to design area codes that could be
distinguished automatically from central-office codes, but 1+ dialing made
the internal distinction redundant.  If the 1+ prefix had been part of the
plan from the outset, there would have been no need to restrict NPA codes to
the NZX format, and the codes could have been supplied more liberally.  For
a time, a faction within the Bell System hoped and expected that 1+ dialing
would eventually disappear.  In their view the NPA coding was an elegant and
parsimonious scheme that cleverly exploited all the peculiarities of the
existing switching network to extract the maximum information from the mini-
mum number of digits.  In contrast, 1+ dialing was a crude and wasteful patch
that should be dispensed with as soon as the last step-by-step switching
plant was scrapped.  But the patch is still with us, and it has patches of
its own now.

**Number shortages are nothing new in the larger metropolitan areas.  New
York, Los Angeles and Chicago have been struggling for years to eke out the
supply.  One of the first steps taken when area code starts to fill up is to
expand the list of central-office codes to include numbers of the format NNX,
rather than just the ones that conform to the template NNN.  In other words,
exchanges ending in 0 and 1 are allowed.  The change is painless, since the
third digit of a central-office code carries no special significance anyway.
It increases the number of available codes from 512 to 640, a gain of 25
percent.

The next recourse is to allow central-office codes of the form NXX, where
both the second and the third digits can be any number, including 0 or 1.
That easing of the rules creates 160 more codes, bringing the total to 800,
but it also has a grave consequence.  It eliminates the structural distinc-
tion between central-office codes and NPA codes.  Once a network has intro-
duced NXX office codes, some kind of extra signal, such as 1+ dialing, is all
but mandatory to distinguish local from long-distance calls.  There is no go-
ing back to the original plan of eliminating ambiguity by examining the sec-
ond digit of the dialed sequence.  Los Angeles was the first city to adopt
NXX central-office codes, in 1973, New York held out until 1980, and Chicago
followed in 1983.  By now about twenty areas have converted to NXX.

NXX exchanges yield eight million subscriber numbers for each area code.
When that supply proves insufficient, the only option is to split the area
and introduce a new NPA code.  That process began soon after direct distance
dialing was launched, and by the late 1980s it had become apparent that all
136 of the available NPA codes would soon be allocated.  Growth in demand
was not abating.  Where could more numbers be found?  A stopgap was to recover
some of the N10 codes that had been assigned to the Telex network.  They all
were returned except 610, which is still used by the Canadian Telex system,
and 710, whose function is now listed as Government Special Services.  NPA
codes 310, 410, and 510 are already in service, and they will soon be joined
by 210 and 810.  At that point World Zone 1 will have only one NPA code left:
910.  [ 810 is announced, not yet in use, in Michigan; and at the beginning
of this year, you saw the notes for 610 in Pa. and 910 in NC. ]

**The United Nations agency that regulates internal telecommunications div-
ides the world into nine zones.  World Zone 1 includes the U.S. and Canada
and about a dozen Caribbean nations.  There are eight other world zones: 2
is Africa; 3 and 4 cover Europe; 5 is Central and South America; 6 is the
Pacific; 7 is the territory of the former U.S.S.R.; 8 is Asia; and 9 is the
Middle East.

Within Zone 1 the administration of numbering has been delegated to Bellcore,
which was therefore expected to find a solution to the NPA code shortage.
The heart of Bellcore's plan is to relax the syntactic constraints on the
form of an NPA code.  Specifically, area codes, like the newest central-
office codes, are to have the format NXX: the middle digit can be any number,
not just 0 or 1.  That change yields a fivefold increase in the number of
possible codes, from 160 to 800.  Of the 640 new codes, Bellcore proposes
that 300 be held for use as ordinary geographic codes.  Thus the capacity of
the system would triple.  With an eventual total of 442 area codes, each
using NXX office codes, there would be room for 3.5 billion telephone numbers.

Another ninety of the new codes are earmarked for nongeographic services, such
as the existing N00 series of service access codes.  That large allocation re-
flects the tremendous success of 800 service (AT&T recently reported that 40
percent of its long-distance calls go to 800 numbers) and the more recent pop-
ularity of 900 service.  Perhaps even more important is the advent of "person-
al communications numbers," or numbers associated with a person rather than
a telephone.  AT&T recently introduced service of that kind--a number that
follows you wherever you go--keyed to the 700 service access code.  Such
applications can have a double impact on the demand for telephone numbers.
The way the telephone system now works, when you call an 800 number, that
number is looked up in a data base, which records the "real" telephone number
with which each 800 number is associated; then your call is passed along to
the second number.  Thus for every 800 number there is at least one ordinary
number needed as well.  Unless that assignment changes, filling up ninety
service area codes will also fill up another ninety ordinary NPA codes.

After these allocations for geographic and nongeographic codes, 250 numbers
remain.  Bellcore recommends that 170 of them be set aside for events and
needs that simply cannot be foreseen.  The last eighty codes would be held
in reserve, to be applied when even the expanded supply of numbers is finally
exhausted.  At that point there will be no choice but to add more digits to
phone numbers.

**The adoption of NXX-format area codes will eliminate all distinctions be-
tween an area code and a central-office prefix.  How will switches tell them
apart?  One possibility is to continue requiring a 1+ prefix on any ten-
digit call but to forbid 1+ on all seven-digit calls.  The Bellcore plan
recommends a different approach: it would require a ten-digit number for
every call, including local calls.  Then the switch could always treat the
first three digits dialed as an area code, the next three digits as a central-
office code and the final four digits as a customer line.  The 1+ prefix
could be dropped, since there would be no need to alert the switch that ten
digits are coming.  [This Bellcore approach shows up in the Orange Card in-
structions and also in the instructions for the airplane phone.]

The Bellcore plan is a thoughtful and circumspect document, which carefully
acknowledges all the hazards and limitations of technological forecasting.
It was prepared with the advice of some forty "experts and futurists," and
it doubtless also draws on quantitative analyses of population growth and of
trends in the telecommunications industry.  Still, I cannot help wondering
if it might not represent another major miscalculation.

The planners of the 1940s underestimated the demand for telephone numbers
because they could not foresee the variety of ways those numbers would be
used.  At that time a telephone was a black box permanently wired to the
wall, and nothing other than a telephone was ever plugged in to the Bell
network.  No one anticipated the proliferation of modems and fax machines
--or of telephones that don't plug in at all.  The Bell System engineers
never dreamed that people would chat on the phone while strolling through
the supermarket or tanning on the beach or plowing a cornfield.  They never
guessed that paging devices (each with its own phone number) would be carried
not only by doctors on call but also by plumbers and professors and street-
corner cocaine dealers.

The mistake that now seems hard to avoid is assuming that the demand for
telephone services, and particularly for numbers, will continue to grow in
the same way.  I have no doubt that communications traffic of all kinds will
increase dramatically.  But it seems possible that some substantial fraction
of the traffic will be diverted from the telephone system into other channels.
The coming decades will sure bring communications devices just as unexpected
as the fax machine, the cellular telephone, and the beeper, but it should not
be taken for granted that those devices all will have telephone numbers.

**The telephone system is a circuit-switched network.  For most of the history
of the system, when you placed a call, you were renting a pair of copper wires
that ran continuously from you telephone to the other party's phone.  You had
exclusive use of those wires during the call; when you hung up, they were
rented to someone else.  Today the transaction is more complicated (your call
may well share a fiber-optic cable or a satellite with hundreds of other
calls), but conceptually the system still works the same way.  When you dial
the phone, you get a private connection to one other party.

There is an alternative network architecture called packet switching, in
which all stations are always connected to the network, but they receive
only the messages addressed to them.  It is as if your telephone were
always tuned in to thousands of conversations going by on the wire, but
you heard only the occasional word intended for you.  Most computer net-
works employ packet switching, because it is more efficient than circuit
switching when traffic is heavy.  It seems reasonable that the existing
packet-switched networks will grow, and new ones may be created; they
could well absorb traffic that would otherwise go to the telephone system,
and thereby reduce the demand for telephone numbers.

As the architecture of communications networks changes, so will the user
interface.  Telephone numbers may eventually become obscure internal codes
that the general public has no need to know.  Already many telephones come
with speed-dialing buttons so that you record frequently called numbers
(and thereafter forget them).  There are also pocket-size dialers you hold
up to the mouthpiece of a telephone.  If you wish, the telephone company
will store your list of favorite numbers, so that you can dial them with a
one- or two-digit code.  Such strategies for insulating the customer from
the number itself will become more prevalent as numbers grow longer and
harder to remember. I can imagine a kind of user interface that might ul-
timately evolve.  In a couple of decades, perhaps, the telephone will have
no dial at all.  You will simply pick up the receiver and say, "Jenny, get
me Mrs. Wilson, please.  Thank you, dear."