FUNDAMENTAL CONSIDERATIONS OF AUTOMATIC SYSTEMS
=Definition.= The term automatic, as applied to telephone systems, has
come to refer to those systems in which machines at the central office,
under the guidance of the subscribers, do the work that is done by
operators in manual systems. In all automatic telephone systems, the
work of connecting and disconnecting the lines, of ringing the called
subscriber, even though he must be selected from among those on a party
line, of refusing to connect with a line that is already in use, and
informing the calling subscriber that such line is busy, of making
connections to trunk lines and through them to lines in other offices
and doing the same sort of things there, of counting and recording the
successful calls made by a subscriber, rejecting the unsuccessful, and
nearly all the thousand and one other acts necessary in telephone
service, are performed without the presence of any guiding intelligence
at the central office.
The fundamental object of the automatic system is to do away with the
central-office operator. In order that each subscriber may control the
making of his own connections there is added to his station equipment a
call transmitting device by the manipulation of which he causes the
central-office mechanisms to establish the connections he desires.
We think that the automatic system is one of the most astonishing
developments of human ingenuity. The workers in this development are
worthy of particular notice. From occupying a position in popular regard
in common with long-haired men and short-haired women they have recently
appeared as sane, reasonable men with the courage of their convictions
and, better yet, with the ability to make their convictions come true.
The scoffers have remained to pray.
=Arguments Against Automatic Idea.= Naturally there has been a bitter
fight against the automatic. Those who have opposed it have contended:
First: that it is too complicated and, therefore, could be neither
reliable or economical.
Second: that it is too expensive, and that the necessary first cost
could not be justified.
Third: that it is too inflexible and could not adapt itself to special
kinds of service.
Fourth: that it is all wrong from the subscribers' point of view as the
public will not tolerate "doing its own operating."
_Complexity._ This first objection as to complexity, and consequent
alleged unreliability and lack of economy should be carefully analyzed.
It too often happens that a new invention is cast into outer darkness by
those whose opinions carry weight by such words as "it cannot work; it
is too complicated." Fortunately for the world, the patience and
fortitude which men must possess before they can produce meritorious,
though intricate inventions, are usually sufficient to prevent their
being crushed by any such offhand condemnation, and the test of time and
service is allowed to become the real criterion.
It would be difficult to find an art that has gone forward as rapidly as
telephony. Within its short life of a little over thirty years it has
grown from the phase of trifling with a mere toy to an affair of
momentous importance to civilization. There has been a tendency,
particularly marked during recent years, toward greater complexity; and
probably every complicated new system or piece of apparatus has been
roundly condemned, by those versed in the art as it was, as being unable
to survive on account of its complication.
To illustrate: A prominent telephone man, in arguing against the
nickel-in-the-slot method of charging for telephone service once said,
partly in jest, "The Lord never intended telephone service to be given
in that way." This, while a little off the point, is akin to the
sweeping aside of new telephone systems on the sole ground that they are
complicated. These are not real reasons, but rather convenient ways of
disposing of vexing problems with a minimum amount of labor. Important
questions lying at the very root of the development of a great industry
may not be put aside permanently in this offhand way. The Lord has
never, so far as we know, indicated just what his intentions were in the
matter of nickel service; and no one has ever shown yet just what
degree of complexity will prevent a telephone system from working.
It is safe to say that, if other things are equal, the simpler a machine
is, the better; but simplicity, though desirable, is not all-important.
Complexity is warranted if it can show enough advantages.
If one takes a narrow view of the development of things mechanical and
electrical, he will say that the trend is toward simplicity. The
mechanic in designing a machine to perform certain functions tries to
make it as simple as possible. He designs and re-designs, making one
part do the work of two and contriving schemes for reducing the
complexity of action and form of each remaining part. His whole trend is
away from complication, and this is as it should be. Other things being
equal, the simpler the better. A broad view, however, will show that the
arts are becoming more and more complicated. Take the implements of the
art of writing: The typewriter is vastly more complicated than the pen,
whether of steel or quill, yet most of the writing of today is done on
the typewriter, and is done better and more economically. The art of
printing affords even more striking examples.
In telephony, while every effort has been made to simplify the component
parts of the system, the system itself has ever developed from the
simple toward the complex. The adoption of the multiple switchboard, of
automatic ringing, of selective ringing on party lines, of
measured-service appliances, and of automatic systems have all
constituted steps in this direction. The adoption of more complicated
devices and systems in telephony has nearly always followed a demand for
the performance by the machinery of the system of additional or
different functions. As in animal and plant life, so in mechanics--the
higher the organism functionally the more complex it becomes physically.
Greater intricacy in apparatus and in methods is warranted when it is
found desirable to make the machine perform added functions. Once the
functions are determined upon, then the whole trend of the development
of the machine for carrying them out should be toward simplicity. When
the machine has reached its highest stage of development some one
proposes that it be required to do something that has hitherto been done
manually, or by a separate machine, or not at all. With this added
function a vast added complication may come, after which, if it develops
that the new function may with economy be performed by the machine, the
process of simplification again begins, the whole design finally taking
on an indefinable elegance which appears only when each part is so made
as to be best adapted in composition, form, and strength to the work it
is to perform.
Achievements in the past teach us that a machine may be made to do
almost anything automatically if only the time, patience, skill, and
money be brought to bear. This is also true of a telephone system. The
primal question to decide is, what functions the system is to perform
within itself, automatically, and what is to be done manually or with
manual aid. Sometimes great complications are brought into the system in
an attempt to do something which may very easily and cheaply be done by
hand. Cases might be pointed out in which fortunes and life-works have
been wasted in perfecting machines for which there was no real economic
need. It is needless to cite cases where the reverse is true. The matter
of wisely choosing the functions of the system is of fundamental
importance. In choosing these the question of complication is only one
of many factors to be considered.
One of the strongest arguments against intricacy in telephone apparatus
is its greater initial cost, its greater cost of maintenance, and its
liability to get out of order. Greater complexity of apparatus usually
means greater first cost, but it does not necessarily mean greater cost
of up-keep or lessened reliability. A dollar watch is more simple than
an expensive one. The one, however, does its work passably and is thrown
away in a year or so; the other does its work marvelously well and may
last generations, being handed down from father to son. Merely reducing
the number of parts in a machine does not necessarily mean greater
reliability. Frequently the attempt to make one part do several diverse
things results in such a sacrifice in the simplicity of action of that
part as to cause undue strain, or wear, or unreliable action. Better
results may be attained by adding parts, so that each may have a
comparatively simple thing to do.
[Illustration: WESTERN ELECTRIC COMPANY TYPICAL CHARGING OUTFIT AT
DAWSON, GEORGIA]
The stage of development of an art is a factor in determining the degree
of complexity that may be allowed in the machinery of that art. A
linotype machine, if constructed by miracle several hundred years ago,
would have been of no value to the printer's art then. The skill was not
available to operate and maintain it, nor was the need of the public
sufficiently developed to make it of use. Similarly the automatic
telephone exchange would have been of little value thirty years ago. The
knowledge of telephone men was not sufficiently developed to maintain
it, telephone users were not sufficiently numerous to warrant it, and
the public was not sufficiently trained to use it. Industries, like
human beings, must learn to creep before they can walk.
Another factor which must be considered in determining the allowable
degree of complexity in a telephone system is the character of the labor
available to care for and manage it. Usually the conditions which make
for unskilled labor also lend themselves to the use of comparatively
simple systems. Thus, in a small village remote from large cities the
complexity inherent in a common-battery multiple switchboard would be
objectionable. The village would probably not afford a man adequately
skilled to care for it, and the size of the exchange would not warrant
the expense of keeping such a man. Fortunately no such switchboard is
needed. A far simpler device, the plain magneto switchboard--so simple
that the girl who manipulates it may also often care for its
troubles--is admirably adapted to the purpose. So it is with the
automatic telephone system; even its most enthusiastic advocate would be
foolish indeed to contend that for all places and purposes it was
superior to the manual.
These remarks are far from being intended as a plea for complex
telephone apparatus and systems; every device, every machine, and every
system should be of the simplest possible nature consistent with the
functions it has to perform. They are rather a protest against the
broadcast condemnation of complex apparatus and systems just because
they are complicated, and without regard to other factors. Such
condemnation is detrimental to the progress of telephony. Where would
the printing art be today if the linotype, the cylinder press, and other
modern printing machinery of marvelous intricacy had been put aside on
account of the fact that they were more complicated than the printing
machinery of our forefathers?
That the automatic telephone system is complex, exceedingly complex,
cannot be denied, but experience has amply proven that its complexity
does not prevent it from giving reliable service, nor from being
maintained at a reasonable cost.
_Expense._ The second argument against the automatic--that it is too
expensive--is one that must be analyzed before it means anything. It is
true that for small and medium-sized exchanges the total first cost of
the central office and subscribers' station equipment, is greater than
that for manual exchanges of corresponding sizes. The prices at which
various sizes of automatic exchange equipments may be purchased vary,
however, almost in direct proportion to the number of lines, whereas in
manual equipment the price per line increases very rapidly as the number
of lines increases. From this it follows that for very large exchanges
the cost of automatic apparatus becomes as low, and may be even lower
than for manual. Roughly speaking the cost of telephones and
central-office equipment for small exchanges is about twice as great for
automatic as for manual, and for very large exchanges, of about 10,000
lines, the cost of the two for switchboards and telephones is about
equal.
For all except the largest exchanges, therefore, the greater first cost
of automatic apparatus must be put down as one of the factors to be
weighed in making the choice between automatic and manual, this factor
being less and less objectionable as the size of the equipment increases
and finally disappearing altogether for very large equipments. Greater
first cost is, of course, warranted if the fixed charges on the greater
investment are more than offset by the economy resulting. The automatic
screw machine, for instance, costs many times more than the hand screw
machine, but it has largely displaced the hand machine nevertheless.
_Flexibility._ The third argument against the automatic telephone
system--its flexibility--is one that only time and experience has been
able to answer. Enough time has elapsed and enough experience has been
gained, however, to disprove the validity of this argument. In fact, the
great flexibility of the automatic system has been one of its surprising
developments. No sooner has the statement been made that the automatic
system could not do a certain thing than forthwith it has done it. It
was once quite clear that the automatic system was not practicable for
party-line selective ringing; yet today many automatic systems are
working successfully with this feature; the selection between the
parties on a line being accomplished with just as great certainty as in
manual systems. Again it has seemed quite obvious that the automatic
system could not hope to cope with the reverting call problem, _i. e._,
enabling a subscriber on a party line to call back to reach another
subscriber on the same line; yet today the automatic system may do this
in a way that is perhaps even more satisfactory than the way in which it
is done in multiple manual switchboards. It is true that the automatic
system has not done away with the toll operator and it probably never
will be advantageous to require it to do so for the simple reason that
the work of the toll operator in recording the connections and in
bringing together the subscribers is a matter that requires not only
accuracy but judgment, and the latter, of course, no machine can supply.
It is probable also that the private branch-exchange operator will
survive in automatic systems. This is not because the automatic system
cannot readily perform the switching duties, but the private
branch-exchange operator has other duties than the mere building up and
taking down of connections. She is, as it were, a door-keeper guarding
the telephone door of a business establishment; like the toll operator
she must be possessed of judgment and of courtesy in large degree,
neither of which can be supplied by machinery.
In respect to toll service and private branch-exchange service where, as
just stated, operators are required on account of the nature of the
service, the automatic system has again shown its adaptability and
flexibility. It has shown its capability of working in harmony with
manual switchboards, of whatever nature, and there is a growing tendency
to apply automatic devices and automatic principles of operation to
manual switchboards, whether toll or private branch or other kinds, even
though the services of an operator are required, the idea being to do by
machinery that portion of the work which a machine is able to do better
or more economically than a human being.
_Attitude of Public._ The attitude of the public toward the automatic is
one that is still open to discussion; at least there is still much
discussion on it. A few years ago it did seem reasonable to suppose that
the general telephone user would prefer to get his connection by merely
asking for it rather than to make it himself by "spelling" it out on the
dial of his telephone instrument. We have studied this point carefully
in a good many different communities and it is our opinion that the
public finds no fault with being required to make its own connections.
To our minds it is proven beyond question that either the method
employed in the automatic or that in the manual system is satisfactory
to the public as long as good service results, and it is beyond question
that the public may get this with either.
_Subscriber's Station Equipment._ The added complexity of the mechanism
at the subscriber's station is in our opinion the most valid objection
that can be urged against the automatic system as it exists today. This
objection has, however, been much reduced by the greater simplicity and
greater excellence of material and workmanship that is employed in the
controlling devices in modern automatic systems. However, the automatic
system must always suffer in comparison with the manual in respect of
simplicity of the subscriber's equipment. The simplest conceivable thing
to meet all of the requirements of telephone service at a subscriber's
station is the modern common-battery manual telephone. The automatic
telephone differs from this only in the addition of the mechanism for
enabling the subscriber to control the central-office apparatus in the
making of calls. From the standpoint of maintenance, simplicity at the
subscriber's station is, of course, to be striven for since the proper
care of complex devices scattered all over a community is a much more
serious matter than where the devices are centered at one point, as in
the central office. Nevertheless, as pointed out, complexity is not
fatal, and it is possible, as has been proven, to so design and
construct the required apparatus in connection with the subscribers'
telephones as to make them subject to an amount of trouble that is not
serious.
=Comparative Costs.= A comparison of the total costs of owning,
operating, and maintaining manual and automatic systems usually results
in favor of the automatic, except in small exchanges. This seems to be
the consensus of opinion among those who have studied the matter deeply.
Although the automatic usually requires a larger investment, and
consequently a larger annual charge for interest and depreciation,
assuming the same rates for each case, and although the automatic
requires a somewhat higher degree of skill to maintain it and to keep it
working properly than the manual, the elimination of operators or the
reduction in their number and the consequent saving of salaries and
contributory expenses together with other items of saving that will be
mentioned serves to throw the balance in favor of the automatic.
The ease with which the automatic system lends itself to inter-office
trunking makes feasible a greater subdivision of exchange districts into
office districts and particularly makes it economical, where such would
not be warranted in manual working. All this tends toward a reduction in
average length of subscribers' lines and it seems probable that this
possibility will be worked upon in the future, more than it has been in
the past, to effect a considerable saving in the cost of the wire plant,
which is the part of a telephone plant that shows least and costs most.
=Automatic vs. Manual.= Taking it all in all the question of automatic
versus manual may not and can not be disposed of by a consideration of
any single one of the alleged features of superiority or inferiority of
either. Each must be looked at as a practical way of giving telephone
service, and a decision can be reached only by a careful weighing of all
the factors which contribute to economy, reliability, and general
desirability from the standpoint of the public. Public sentiment must
neither be overlooked nor taken lightly, since, in the final analysis,
it is the public that must be satisfied.
=Methods of Operation.= In all of the automatic telephone systems that
have achieved any success whatever, the selection of the desired
subscriber's line by the calling subscriber is accomplished by means of
step-by-step mechanism at the central office, controlled by impulses
sent or caused to be sent by the acts of the subscriber.
_Strowger System._ In the so-called Strowger system, manufactured by the
Automatic Electric Company of Chicago, the subscriber, in calling,
manipulates a dial by which the central-office switching mechanism is
made to build up the connection he wants. The dial is moved as many
times as there are digits in the called subscriber's number and each
movement sends a series of impulses to the central office corresponding
in number respectively to the digits in the called subscriber's number.
During each pause, except the last one, between these series of
impulses, the central-office mechanism operates to shift the control of
the calling subscriber's line from one set of switching apparatus at the
central office to another.
In case a four-digit number is being selected first, the movement of
the dial by the calling subscriber will correspond to the thousands
digit of the number being called, and the resulting movement of the
central-office apparatus will continue the calling subscriber's line
through a trunk to a piece of apparatus capable of further extending his
line toward the line terminals of the thousand subscribers whose numbers
begin with the digit chosen. The next movement of the dial corresponding
to the hundreds digit of the called number will operate this piece of
apparatus to again extend the calling subscriber's line through another
trunk to apparatus representing the particular hundred in which the
called subscriber's number is. The third movement of the dial
corresponding to the tens digit will pick out the group of ten
containing the called subscriber's line, and the fourth movement
corresponding to the units digit will pick out and connect with the
particular line called.
_Lorimer System._ In the Lorimer automatic system invented by the
Lorimer Brothers, and now being manufactured by the Canadian Machine
Telephone Company of Toronto, Canada, the subscriber sets up the number
he desires complete by moving four levers on his telephone so that the
desired number appears visibly before him. He then turns a handle and
the central-office apparatus, under the control of the electrical
conditions thus set up by the subscriber, establishes the connection. In
this system, unlike the Strowger system, the controlling impulses are
not caused by the movement of the subscriber's apparatus in returning to
its normal position after being set by the subscriber. Instead, the
conditions established at the subscriber's station by the subscriber in
setting up the desired number, merely determine the point in the series
of impulses corresponding to each digit at which the stepping impulses
local to the central office shall cease, and in this way the proper
number of impulses in the series corresponding to each digit is
determined.
_Magnet- vs. Power-Driven Switches._ These two systems differ radically
in another respect. In the Strowger system it is the electrical impulses
initiated at the subscriber's apparatus that actually cause the movement
of the switching parts at the central office, these impulses energizing
electromagnets which move the central-office switching devices a step at
a time the desired number of steps. In the Lorimer system the switches
are all power-driven and the impulses under the control of the
subscriber's instrument merely serve to control the application of this
power to the various switching mechanisms. These details will be more
fully dealt with in subsequent chapters.
_Multiple vs. Trunking._ It has been shown in the preceding portion of
this work that the tendency in manual switchboard practice has been away
from trunking between the various sections or positions of a board, and
toward the multiple idea of operating, wherein each operator is able to
complete the connection with any line in the same office without
resorting to trunks or to the aid of other operators. Strangely enough
the reverse has been true in the development of the automatic system. As
long as the inventors tried to follow the most successful practice in
manual working, failure resulted. The automatic systems of today are
essentially trunking systems and while they all involve multiple
connections in greater or less degree, all of them depend fundamentally
upon the extending of the calling line by separate lengths until it
finally reaches and connects with the called line.
_Grouping of Subscribers._ In this connection we wish to point out here
two very essential features without which, so far as we are aware, no
automatic telephone system has been able to operate successfully. The
first of these is the division of the total number of lines in any
office of the exchange into comparatively small groups and the
employment of correspondingly small switch units for each group. Many of
the early automatic systems that were proposed involved the idea of
having each switch capable in itself of making connection with any line
in the entire office. As long as the number of lines was small--one
hundred or thereabouts--this might be all right, but where the lines
number in the thousands, it is readily seen that the switches would be
of prohibitive size and cost.
_Trunking between Groups._ This feature made necessary the employment of
trunk connections between groups. By means of these the lines are
extended a step at a time, first entering a large group of groups,
containing the desired subscriber; then entering the smaller group
containing that subscriber; and lastly entering into connection with the
line itself. The carrying out of this idea was greatly complicated by
the necessity of providing for many simultaneous connections through the
switchboard. It was comparatively easy to accomplish the extension of
one line through a series of links or trunks to another line, but it
was not so easy to do this and still leave it possible for any other
line to pick out and connect with any other idle line without
interference with the first connection. A number of parallel paths must
be provided for each possible connection. Groups of trunks are,
therefore, provided instead of single trunks between common points to be
connected. The subscriber who operates his instrument in making a call
knows nothing of this and it is, of course, impossible for him to give
any thought to the matter as to which one of the possible paths he shall
choose. It was by a realization of these facts that the failures of the
past were turned into the successes of the present. The subscriber by
setting his signal transmitter was made to govern the action of the
central-office apparatus in the selection of the proper _group_ of
trunks. The group being selected, the central-office apparatus was made
to act at once _automatically_ to pick out and connect with _the first
idle trunk of such group_. Thus, we may say _that the subscriber by the
act performed on his signal transmitter, voluntarily chooses the group
of trunks, and immediately thereafter the central-office apparatus
without the volition of the subscriber picks out the first idle one of
this group of trunks so chosen_. This fundamental idea, so far as we are
aware, underlies all of the successful automatic telephone-exchange
systems. It provides for the possibility of many simultaneous
connections through the switchboard, and it provides against the
simultaneous appropriation of the same path by two or more calling
subscribers and thus assures against interference in the choice of the
paths.
_Outline of Action._ In order to illustrate this point we may briefly
outline the action of the Strowger automatic system in the making of a
connection. Assume that the calling subscriber desires a connection with
a subscriber whose line bears the number 9,567. The subscriber in making
the call will, by the first movement of his dial, transmit nine impulses
over his line. This will cause the selective apparatus at the central
office, that is at the time associated with the calling subscriber's
line, to move its selecting fingers opposite a group of terminals
representing the ends of a group of trunk lines leading to apparatus
employed in connecting with the ninth thousand of the subscribers'
lines.
While the calling subscriber is getting ready to transmit the next
digit, the automatic apparatus, without his volition, starts to pick out
the first idle one of the group of trunks so chosen. Having found this
it connects with it and the calling subscriber's line is thus extended
to another selective apparatus capable of performing the same sort of
function in choosing the proper hundreds group.
In the next movement of his dial the calling subscriber will send five
impulses. This will cause the last chosen selective switch to move its
selective fingers opposite a group of terminals representing the ends of
a group of trunks each leading to a switch that is capable of making
connection with any one of the lines in the fifth hundred of the ninth
thousand. Again during the pause by the subscriber, the switch that
chose this group of trunks will start automatically to pick out and
connect with the first idle one of them, and will thus extend the line
to a selective switch that is capable of reaching the desired line,
since it has access to all of the lines in the chosen hundred. The third
movement of the dial sends six impulses and this causes this last chosen
switch to move opposite the sixth group of ten terminals, so that there
has now been chosen the nine hundred and fifty-sixth group of ten lines.
The final movement of the dial sends seven impulses and the last
mentioned switch connects with the seventh line terminal in the group of
ten previously chosen and the connection is complete, assuming that the
called line was not already engaged. If it had been found busy, the
final switch would have been prevented from connecting with it by the
electrical condition of certain of its contacts and the busy signal
would have been transmitted back to the calling subscriber.
_Fundamental Idea._ This idea of subdividing the subscribers' lines in
an automatic exchange, of providing different groups of trunks so
arranged as to afford by combination a number of possible parallel paths
between any two lines, of having the calling subscriber select, by the
manipulation of his instrument, the proper group of trunks any one of
which might be used to establish the connection he desires, and of
having the central-office apparatus act automatically to choose and
connect with an idle one in this chosen group, should be firmly grasped.
It appears, as we have said, in every successful automatic system
capable of serving more than one small group of lines, and until it was
evolved automatic telephony was not a success.
_Testing._ As each trunk is chosen and connected with, conditions are
established, by means not unlike the busy test in multiple manual
switchboards, which will guard that trunk and its associated apparatus
against appropriation by any other line or apparatus as long as it is
held in use. Likewise, as soon as any subscriber's line is put into use,
either by virtue of a call being originated on it, or by virtue of its
being connected with as a called line, conditions are automatically
established which guard it against being connected with any other line
as long as it is busy. These guarding conditions of both trunks and
lines, as in the manual board, are established by making certain
contacts, associated with the trunks or lines, assume a certain
electrical condition when busy that is different from their electrical
condition when idle; but unlike the manual switchboard this different
electrical condition does not act to cause a click in any one's ear, but
rather to energize or de-energize certain electromagnets which will
establish or fail to establish the connection according to whether it is
proper or improper to do so.
_Local and Inter-Office Trunks._ The groups of trunks that are used in
building up connections between subscribers' lines may be local to the
central office, or they may extend between different offices. The action
of the two kinds of trunks, local or inter-office, is broadly the same.