THE AUTOMANUAL SYSTEM
Two systems of telephony are now in common use in this country--the
manual system and the automatic. With the growth of the automatic, and
the gradually ripening conviction, which is now fully matured in the
minds of most telephone engineers, that automatic switching is
practical, there has been a growing tendency toward doing automatically
many of the things that had previously been done manually. One of the
results of this tendency has been the production of the _automanual_
system, the invention of Edward E. Clement, an engineer and patent
attorney, of Washington, D. C. In connection with Mr. Clement's name, as
inventor, must be mentioned that of Charles H. North, whose excellent
work as a designer and manufacturer has contributed much toward the
present excellence of this highly interesting system.
=Characteristics of System.= The name "automanual" is coined from the
two words, automatic and manual, and is intended to suggest the idea
that the system partakes in part of the features of the automatic system
and in part of those of the manual system.
We regret that neither space nor the professional relation which we have
had with the development of this system will permit us to make public an
extended and detailed description of its apparatus and circuits. Only
the general features of the system may, therefore, be dealt with.
[Illustration: POWER APPARATUS FOR COMMON-BATTERY MANUAL OFFICE OF
MEDIUM SIZE]
The underlying idea of the automanual system is to relieve the
subscriber of all work in connection with the building up of his
connection, except the asking for it; to complicate the subscriber's
station equipment in no way, it being left the same as in the
common-battery manual system; to do away with manual apparatus, such as
jacks, cords and plugs, at the central office, and to substitute for it
automatic switching apparatus which will be guided in its movements,
not by the subscriber, but by a very much smaller number of operators
than would be necessary to manipulate a manual switchboard.
=General Features of Operation.= A broad view of the operation of the
system is this. The subscriber desiring to make a call takes down his
receiver, and this causes a lamp to light in front of an operator. The
operator presses a button and is in telephonic communication with the
subscriber. Receiving the number desired, the operator sets it up on a
keyboard in just about the same way that a typist will set up the
letters of a short word on a typewriting machine. The setting up of the
number on the keyboard being accomplished, the proper condition of
control of the associated automatic apparatus at the central office is
established and the operator has no further connection with the call.
The automatic switching apparatus guided by the conditions set up on the
operator's keyboard proceeds to make the proper selection of trunks and
to establish the proper connections through them to build up a talking
circuit between the calling subscriber and the called and to ring the
called subscriber's bell, or, if his line is found busy, the apparatus
refuses to connect with it and sends a busy signal back to the calling
subscriber. The operator performs no work in disconnecting the
subscribers, that being automatically taken care of when they hang up
their receivers at the close of the conversation.
From the foregoing it will be seen that there is this fundamental
difference between the automatic and the automanual--the automatic
system dispenses entirely with the central-office operator for all
ordinary switching functions; the automanual employs operators but
attempts to so facilitate their work that they may handle very many more
calls than would be possible in a manual system, and at the same time
secures the advantages of secrecy which the automatic system secures to
its subscribers.
=Subscriber's Apparatus.= One of the main points in the controversy
concerning automatic _versus_ manual systems is whether or not it is
desirable to have the subscriber ask for his connection or to have him
make certain simple movements with his fingers which will lead to his
securing it. The developers of the automanual system have taken the
position that the most desirable way, so far as the subscriber is
concerned, is to let him ask for it. It is probable that this point
will not be a deciding one in the choice of future systems, since it
already seems to be proven that the subscribers in automatic systems are
willing to go through the necessary movements to mechanically set up the
call. The advantage which the automanual system shares with the manual,
however, in the greater simplicity of its subscriber's station
apparatus, cannot be gainsaid.
[Illustration: Fig. 405. Operators' Key Tables]
[Illustration: Fig. 406. Top View of Key Table]
=Operator's Equipment.= The general form of the operator's equipment is
shown in Fig. 405. A closer view of the top of one of the key tables is
shown in Fig. 406. As will be seen, the equipment on each operator's
position consists of three separate sets of push-button keys closely
resembling in external appearance the keys of a typewriter or adding
machine. Immediately above each set of keys are the signal lamps
belonging to that set.
The operator's keys are arranged in strips of ten, placed _across_
rather than _lengthwise_ on the key shelf. One of these strips is shown
in Fig. 407. There are as many strips of keys in each set as there are
digits in the subscribers' numbers, _i. e._, three in a system having a
capacity of less than one thousand; four in a system of less than ten
thousand; and so on. In addition to the number keys of each set is a
partial row of keys, including what is called a _starting key_ and also
keys for making the party-line selection.
[Illustration: Fig. 407. Strip of Selecting Keys]
[Illustration: Fig. 408. Wiring of Key Shelf]
The simplicity of the operator's key equipment is one of its attractive
features. Fig. 408 shows one of the key shelves opened so as to expose
to view all of the apparatus and wiring that is placed before the
operator. The reason for providing more than one key set on each
operator's position is, that after a call has been set up on one key
set, a few seconds is required before the automatic apparatus controlled
by the key set can do its work and release the key set ready for another
call. The provision of more than one key set makes it possible for the
operator to start setting up another call on another key set without
waiting for the first to be released by the automatic apparatus.
[Illustration: Fig. 409. Switch Room of Automanual Central Office]
=Automatic Switching Equipment.= A general view of the arrangement of
automatic switches in an exchange established by the North Electric
Company at Ashtabula, Ohio, is shown in Fig. 409. The desk in the
foreground is that of the wire chief. This automatic apparatus consists
largely of relays and automatic selecting switches. The switches are of
the step-by-step type, having vertical and rotary movements, and an idea
of one of them, minus its contact banks, is given in Fig. 410. The
control of the automatic switches by the operator's key sets is through
the medium of a power-driven, impulse-sending machine. From this machine
impulses are taken corresponding to the numbers of the keys depressed.
[Illustration: Fig. 410. Selecting Switch]
=Automatic Distribution of Calls.= A feature of great interest in this
system is the manner in which the incoming calls are distributed among
the operators. From each key set an operator's trunk is extended to what
is called a secondary selector switch, through which it may be connected
to a primary selector trunk and calling line. When a subscriber calls by
taking down his receiver, his line relay pulls up and causes a primary
selector switch to connect his line with an idle local trunk or link
circuit, at the same time starting up a secondary selector switch which
immediately connects the primary trunk and the calling line to an
operator's idle key set. If an operator is at the time engaged in
setting up a call on a key set, or if that key set is still acting to
control the sending of impulses to the automatic switches, it may be
said to be busy, and it is not selected by this preliminary selecting
apparatus in response to an incoming call. As soon, however, as the
necessary impulses have been taken from the key set by the automatic
apparatus, that key set is released and is again ready to receive a
call. In this way the calls come before each operator only as that
operator is able and ready to receive them.
=Setting up a Connection.= As soon as the key-set lamp lights, in
response to such an incoming call, the operator presses a listening
button, receives the number from the subscriber, and depresses the
corresponding number buttons on that key set, thereby determining the
numbers in each of the series of impulses to be sent to the selector and
the connector switches to make the desired connection. The operator
repeats this number to the calling subscriber as she sets it up, and
then presses the starting button, whereupon her work is done so far as
that call is concerned. If, upon repeating the call to the subscriber,
the operator finds that she is in error, she may change the number set
up at any time before she has pressed the starting button.
=Building up a Connection.= The keys so set up determine the number of
impulses that will be transmitted by the impulse-sending machine to the
selector and the connector switches. These switches, impelled by these
impulses, establish the connection if the line called for is not already
connected to. If a party-line station is called for, the proper station
on it will be selectively rung as determined by the party-line key
depressed by the operator. If the line is found busy, the connector
switch refuses to make the connection and places a busy-back signal on
the calling line.
=Speed in Handling Calls.= This necessarily brief outline gives an idea
only of the more striking features of the automanual system. A study of
the rapidity with which calls may be handled in actual practice shows
remarkable results as compared with manual methods of operating. The
operators set up the number keys corresponding to a called number with
the same rapidity that the keys of a typewriter are pressed in spelling
a word. In fact, even greater speed is possible, since it is noticed
that the operators frequently will depress all of the keys of a number
at once, as by a single striking movement of the fingers. The rapidity
with which this is done defies accurate timing by a stop watch in the
hands of an expert. It is practically true, therefore, that the time
consumed by the operator in handling any one call is that which is taken
in getting the number from the subscriber and in repeating it back to
him.
TABLE XI
Total Time Consumed by Operator in Handling Calls on Automanual System
+-----------------------------------------------------------------+
| First 100 Calls |
+-----------------------------------------------------------------+
|Longest Individual Period 12.40 seconds |
|Average five longest Individual Periods 7.44 seconds |
|Average ten longest Individual Periods 6.34 seconds |
|Shortest Individual Period 1.60 seconds |
|Average five shortest Individual Periods 1.92 seconds |
|Average ten shortest Individual Periods 1.96 seconds |
|Average Entire 100 Calls 3.396 seconds |
|Hourly Rate at which calls were being handled 1060 |
+-----------------------------------------------------------------+
+-----------------------------------------------------------------+
| Second 100 Calls |
+-----------------------------------------------------------------+
|Longest Individual Period 7.60 seconds |
|Average five longest Individual Periods 5.52 seconds |
|Average ten longest Individual Periods 5.34 seconds |
|Shortest Individual Period 2.00 seconds |
|Average five shortest Individual Periods 2.04 seconds |
|Average ten shortest Individual Periods 2.18 seconds |
|Average Entire 100 Calls 3.374 seconds |
|Hourly Rate at which calls were being handled 1067 |
+-----------------------------------------------------------------+
+-----------------------------------------------------------------+
| Third 100 Calls |
+-----------------------------------------------------------------+
|Longest Individual Period 5.40 seconds |
|Average five longest Individual Periods 5.32 seconds |
|Average ten longest Individual Periods 4.44 seconds |
|Shortest Individual Period 1.60 seconds |
|Average five shortest Individual Periods 1.65 seconds |
|Average ten shortest Individual Periods 1.80 seconds |
|Average Entire 100 Calls 3.160 seconds |
|Hourly Rate at which calls were being handled 1139 |
+-----------------------------------------------------------------+
Owing to the difficulty of securing accurate traffic data by means of a
stop watch, an automatic, electrical timing device, capable of
registering seconds and hundredths of a second, has been used in
studying the performance of this system in regular operation at
Ashtabula Harbor. The operators were not informed that the records were
being taken, and the data tabulated represents the work of two operators
in handling regular subscribers' calls. The figures in Table XI are
given by C. H. North as representing the total time consumed by the
operator from the time her line lamp was lighted until her work in
connection with the call was finished, and it included, therefore, the
pressing of the listening button, the receiving of the number from the
subscriber, repeating it back to him, setting up the connection on the
keys, and pressing the starting key.
It will be seen that the average time for each 100 calls is quite
uniform and is slightly over three seconds. The considerable variation
in the individual calls, ranging from a maximum of 12.40 seconds down to
a minimum of 1.60 seconds, is due almost entirely to the difference
between the subscribers in the speed with which they can give their
numbers. These figures indicate that, in each of the tests, calls were
being handled at the rate of more than one thousand per hour by each
operator.
The test of the subscriber's waiting time, _i. e._, the time that he
waited for the operator to answer, for one hundred calls made without
the knowledge of the operator, showed the results as given in Table XII,
in which a split second stop watch was used in making the observations.
TABLE XII
Subscribers' Waiting Time
+----------------------------------------------------------+
|Number of Calls Tested 100 |
|Longest Individual Period 5.20 seconds |
|Average 5 Longest Individual Periods 4.64 seconds |
|Average 10 Longest Individual Periods 3.80 seconds |
|Shortest Individual Period 1.00 seconds |
|Average 5 Shortest Individual Periods 1.28 seconds |
|Average 10 Shortest Individual Periods 1.34 seconds |
|Average Entire 100 Calls 2.07 seconds |
+----------------------------------------------------------+
The length of time which the subscriber has to wait before receiving an
answer from the operator is, of course, one of the factors that enters
into the giving of good telephone service, and the times shown by this
test are considerably shorter than ordinarily maintained in manual
practice. The waiting time of the subscriber is not, of course, a part
of the time that is consumed by the operator, and the real economy so
far as the operator's time is concerned is shown in the tests recorded
in Table XI.