CHAPTER3

LOCALMANUAL SYSTEMS

3.1 THE MANUALSWITCHBOARD A. History On January 28, 1878, two years after Alexander Graham Bell was awarded a patent on his primitive telephone, the world's first commercial telephone exchange opened for business in New Haven, Connecticut. This enterprise was called the District Telephone Company of New Haven. It was a small beginning. There were only 21 subscribers, served by 8 lines with interconnecting service provided by the oper­ ation of two rotary switches. This was the first switchboard, a model of which is shown in Figure 3-1. As more and more subscribers were added, switchboard designs had to be altered to enable the interconnecting of the steadily increasing number of subscriber lines. As local central office areas began to be established, each devoted to the interconnecting of a group of subscriber lines terminated on its switchboard, further alterations were required. It soon became necessary to enable a subscriber whose line terminated in one central office to be connected to a sub­ scriber whose line terminated in another central office. With the ever increasing growth of subscribers, improvements in local central office switchboard designs were constantly made until they evolved into the manual switchboards de­ scribed in this chapter. B. Basic Switchboard Functions A telephone switchboard is defined as the unit of central office equipment which requires an operator to perform the switching function necessary to provide the requested telephone service. In a manual office operators are required to switch all calls from one subscriber to another subscriber whose line is terminated in the same central office. Operators are also required to terminate calls received from another central office to any of its subscribers. Further, operators must also be able to con­ nect any subscriber to a line terminated in another central office which will in turn connect him to one of the sub­ scribers in that office or to another switchboard elsewhere.

3.1

the the

middle middle

by by

to to

Since Since

while while

sub­

telephone telephone

"talking" "talking"

equipped equipped

same same

the the

operator operator

a a

to to

is is

connections connections

enable enable

local local

in in

the the

the the

offices offices

to to

answered answered

office. office.

and and

in in

the the

in in

designed designed

key key

Originating Originating

circuit. circuit.

above above

a a

in in

other other

are are

is is

connections connections

from from

order order

the the

still still

switchboard switchboard

and and

essentially essentially

another another

in in

switchboard switchboard

from from

area. area.

call call

of of

which which

Switchboard Switchboard

is is

are are

the the

in in

calls calls

end end

telephone telephone

SYSTEMS SYSTEMS

subscribers subscribers

to to

any any each each

subscribers subscribers

office office

switchboard switchboard

First First

each each

calls calls

circuits circuits

incoming incoming

3.2 3.2

to to

other other

of of

circuits circuits at at

requested requested

MANUAL MANUAL

to to

completion completion

subscribers subscribers

cord cord

terminating terminating

operator's operator's

the the

available available establish establish

Actually, Actually,

those those

central central

cord cord

plug plug

by by

Model Model

for for

LOCAL LOCAL

telephone telephone

a a

to to

and and

the the

are are

these these

established established

tool tool

operators operators

3 3 -

local local

made made

3-1 3-1

to to

these these

with with

of of

uses uses

by by

completed completed

local local

of of

establish establish

circuit. circuit.

the the calls calls CH. CH.

a a

basic basic

she she

forwarded forwarded

those those

and and

to to

in in

Figure Figure

Each Each

cord cord

number number

The The

or or

originating originating

Thus Thus

previously previously

are are

"bridge" "bridge"

a a

connection connection

completed completed

which which

the the

for for

line line

stage. stage.

is is

operator operator other other

and and

with with

and and office. office.

office office

calls calls operators operators Terminating Terminating

scribers scribers switch switch CH. 3 - LOCAL MANUALSYSTEMS

each subscriber's telephone line is terminated in a jack mounted in the upright portion of the switchboard (facing the operator), the operator can establish a talking path between any two such subscribers by inserting the cord circuit plugs into the two subscriber line jacks and thus establish a connecting "bridge" between the two lines. Before this can be accomplished however, the operator must be able to detect a subscriber's request for telephone service and then determine the nature of the call. If it is a call to another subscriber in the same central office, she locates the called subscriber's line jack, rings the sub­ scriber and waits until she detects an answer. When the conversation between the two subscribers has terminated which she detects by means of the lit cord circuit lamps, she removes both plugs from the subscriber's jacks. The cord circuit is now available for the subsequent connection of any other two subscriber lines. Each switchboard contains certain basic equipment necessary for the completion of subscribers calls. This is described in paragraph 3.2. Switchboards are usually referred to as local or toll, according to the type of traffic handled. The local switch­ board is designed for operators to switch calls between sub­ scribers in the same office, forward calls to another office or to complete incoming calls received from other offices. The toll switchboard is designed for switching calls between local offices and calls to and from other toll switchboards. In the more populated areas local and toll switchboards are generally separate units although they may be located in the same building. In smaller areas they may be separate lineups in the same operating room or even part of the same lineup. When part of the same lineup, the switchboard is sometimes arranged so that operators can switch both local and toll calls. This latter arrangement is called a combined local and toll board or a single channel switchboard. Toll Switchboards w~ll be discussed in a later chapter.

3.2 SWITCHBOARDEQUIPMENT Figure 3-2 shows the front equipment and keyshelf of a typical local manual switchboard. In the figure, the keys, lamps and plugs for 17 cord circuits are shown mounted on the keyshelf. The relays and equipment associated with these keys, lamps, and plugs are not shown in the figure, but are mounted on a relay rack behind the keyshelf. The figure shows

3.3

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one one

various various

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jacks jacks

multipl~ multipl~

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apparatus apparatus

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position position

lamps. lamps.

SWERING SWERING

is is

equipment equipment

are are

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the the

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of of

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brackets brackets

MULTIPLE MULTIPLE

JACKS JACKS

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other other

jack jack

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unit. unit.

SUBSCRIBER SUBSCRIBER

line line

contains contains

Switchboard Switchboard

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front front

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multiple multiple

and and

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upper upper

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positions positions mounting mounting

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consists consists

switchboard switchboard

Manual Manual

shelf shelf

cable. cable.

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the the

for for

such such

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the the

as as

subscriber subscriber

SYSTEMS SYSTEMS

the the

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Typical Typical

and and

section. section.

only only

equipment equipment

three three

the the

a a

cord cord

3.4 3.4

known known

are are

above, above,

necessary necessary

of of

MANUAL MANUAL

jacks jacks

the the

cables, cables,

switchboard switchboard

is is

shows shows

front front

Usually Usually

lamps lamps

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for for

position, position,

portion, portion,

the the

LOCAL LOCAL

Units Units

switchboard switchboard

and and

of of

operator. operator.

described described

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each each

multiple multiple

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Lower Lower

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CH. CH.

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illustration illustration

jacks jacks

lamps lamps

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3-2 3-2

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by by

into into

of of

operator). operator).

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in in

portion portion

three three

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unit unit

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and and

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all all

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shown. shown.

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lower lower

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required required

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and and

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supporting supporting

(for (for

consists consists

for for

combined combined

A. A.

jacks jacks are are

the the

subscriber subscriber Above Above of

then

is

to

located

starts

then

for

to

jack

line

the

and

in

oper­

oper­

somewhere

for

cord

assigned

of

the cord

in

and

busy

shown

share

number

with

jack

567

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up,

answer

of

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whose

use

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are is

one

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operator

multiple

3-3

the

to

109

the

request

by

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assigned

along of

when

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multiple

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each

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in to

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each

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parallel

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in

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are in

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proportionate

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in

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into

the

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plugging

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for

one

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appear

positions.

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(whose

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SYSTEMS

that

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subscriber

subscriber

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whose

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side.

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LOCAL

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------/1/1------CH. 3 - LOCAL MANUALSYSTEMS

3.3 SWITCHBOARDCIRCUITS A. Subscriber Line Circuit The evolution of the subscribers line circuit is illustrated in Figure 3-4. One of the circuits used in the early manual switchboards was the cut-off jack line circuit, Figure 3-4{a). When the subscriber removed his handset a circuit across the T and R leads was closed and the lamp lit.· When the operator plugged into the jack with the answering cord, the plug physically opened the lamp circuit and at the same time connected the subscriber to the operator. The dif­ ficulty here was that different subscribers required different sizes of lamps depending upon the resistance of the subscribers loop due to varying lengths of line. Also, the jack cut-off springs were hard to adjust. An improvement was the line relay circuit, shown in Figure 3-4{b). The lamp was now replaced with a high resistance relay which operated regardless of the amount of loop resistance. The lamp circuit, controlled by the line relay, was office contained and in addition, all lamps were now of the same size. There was still one difficulty, which was, the jack itself. The jack was rather large and required the plug on the cord to physically break the circuit by the action of the plug in the jack. This was overcome by use of the line circuit with line and cut-off relays, shown in Figure 3-4{c). Figure 3-4{c) shows that when the operator plugs into the jack of this circuit, the sleeve of the plug puts battery on the sleeve of the jack. This causes the cut-off relay to operate, releasing the line relay and extinguishing the lamp. There are fewer parts to this jack and it is smaller; since there is no required physical movement in the jack, the jacks can be located closer together, thus allowing more jacks to be placed in any switchboard position. There is another advantage to this circuit. When the operator plugs into this circuit she places battery on the sleeve of the jack. In a multiple switchboard this means that there is battery on the sleeve of every multiple of this jack. This allows other operators to test for a "busy" condition of a subscriber line. If a subscriber line is "busy," the operator will hear a click in her headset when she touches the tip of a cord circuit to the sleeve of the jack. B. Cord Circuit The cord circuit permits the operator to talk to subscribers, interconnect lines and trunks, ring the sub­ scriber's telephone, supervise the connection and perform a number of other duties. It also provides talking battery for the subscribers.

3.7

and and

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SYSTEMS SYSTEMS

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MANUAL MANUAL

Cut-Off Cut-Off

Line Line

Cut-Off Cut-Off

Cut-Off Cut-Off Line Line

LOCAL LOCAL

3-4(b) 3-4(b)

3 3 -

3-4(a) 3-4(a)

3-4(c) 3-4(c)

CH. CH.

Figure Figure

-Figure -Figure Figure Figure

by by

of of

coil, coil,

in in

lighted lighted

con­

into into

call call

the the

the the

wishes wishes

a a

ringer ringer

n1eans n1eans

circuit circuit

is is

flows flows

is is

closing closing

connected. connected.

the the

inserting inserting

by by

the the

may may

which which

receiver receiver is is

that that

with with

the the

the the

signaling signaling

conductors conductors

of of

by by

connection connection

current current

repeating repeating

with with

central central

illustrated illustrated

induces induces

the the

station station

merely merely

current current

alternating alternating

coil, coil,

party party

is is

hook, hook,

circuit circuit

the the

call call

by by

across across

and and

subscriber subscriber

heavy heavy

operator operator through through

same same

subscriber's subscriber's

for for

each each

of of

condition condition

This This

the the

induces induces

the the

function function

two two

cord cord

the the

the the

the the

telephone telephone

at at

line line

removing removing

on on

a a

receiver. receiver.

calling calling

subscriber's subscriber's

associated associated

a a

such such

or or

closed closed

bridged bridged

circuits circuits

at at

induction induction

the the

the the

is is

operator operator

is is

by by

coil. coil.

calling calling

circuit circuit

in in

action action

is is

the the

is is

the the

SYSTEMS SYSTEMS

jack jack

windings windings

to to

answers answers

It It

the the

ringing ringing

the the

shows shows

circuit circuit

over over

is is

of of

the the

as as

same same

and and

of of

set set

the the

telephone telephone

which which

operator operator

receiver receiver

ringing ringing

far far

MANUAL MANUAL

subscriber's subscriber's

the the

line line

calls calls

associated associated

talks talks

figure figure

terminating terminating

the the

learns learns

operator operator

so so

the the

of of

circuit circuit

the the

answering answering

the the accomplished accomplished

transformer transformer

the the

telephone telephone

its its

She She

through through

ringer ringer

operator's operator's

in in

capacitor. capacitor.

LOCAL LOCAL

is is

concerned concerned

The The

This This

secondary secondary

of of

telephone telephone

the the

the the

call call

a a

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calling calling

when when

the the

and and

is is

the the

close close

the the

3 3 -

through through

1 1

which which

stations stations

open open

the the

subscriber subscriber

operator operator

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windings windings

into into

which which

of of

with with

as as to to

3-5. 3-5.

circuit circuit

to to

open open

means means

hook. hook.

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CH. CH.

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the the

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Figure Figure

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of of

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the the

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back back

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from from

in in subscriber subscriber

plug plug the the

office. office.

current current

capacitor capacitor

exception exception

in in

the the

normally normally

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1 1 .~''lating .~''lating CH. 3 - LOCAL MANUALSYSTEMS

Not only does the operator's voice current flow from the central office cord circuit to the subscriber's receiver, but there is direct current furnished by the central office battery through two of the four windings of the repeating coil of the cord circuit, over the line and through the subscriber's transmitter. This permits

t~e subscriber to talk by virtue of the transmitter carbon resistance varying the strength of the current, which, by means of the repeating coil windings at the central office, induces an alternating voice current across to the opposite side of the cord circuit.

c. Trunk Circuits

A 11 trunkn is a telephone line which connects one central office with another central office. In the case of a local manual system, when a subscriber calls a subscriber whose line terminates in another central office, the local switchboard operator connects him to a trunk line which routes his call to that office. The operator accomplishes this by inserting the cord circuit plug into one of the outgoing trunk jacks (O,G.T.) mentioned previously. The trunk jack is part of the trunk relay circuit. The number

3.11

the the

func­

more more

the the

a a

These These

only only

intra­ line line

the the

of of

"A" "A"

the the

of of

to to

same same

incoming incoming

trunk trunk

the the

This This

also also

function function

and and

put put

sub­

are are

of of

of of

type type

is is

upon upon

and and

the the

enable enable

the the

the the

to to

these these

are are

usually usually

operator. operator.

"A" "A"

in in more more

requires requires

establish establish

switching switching

chapter. chapter.

line line

of of

offices. offices.

board board

and and

function function

subscribers. subscribers.

types types

composed composed

operator operator

also also

nature nature

switchboards. switchboards.

of of

as as

subscriber subscriber

depend depend

to to

appearance, appearance,

section. section.

each each

were were

sections, sections,

multiple multiple

to to

its its

is is

"B" "B"

one one this this

Some Some

jack jack

and and

in in

switchboard switchboard

of of

the the

circuits circuits trunk trunk

circuits, circuits,

type type

impossible impossible

in in

the the

distant distant

established, established,

trunk trunk

for for

in in

calls calls

lineups lineups

circuits circuits

line line

switching switching

features. features.

different different

"B" "B"

building. building.

However, However,

on on

in in

required required

switchboard switchboard

SYSTEMS SYSTEMS

line line

perform perform

reach reach

trunk trunk

switchboards switchboards

operators operators

are are

"B" "B"

manual manual

other. other. from from

varying varying

of of

containing containing

its its

the the

to to

the the

switchboard switchboard

with with

became became

jacks jacks

"B" "B"

by by

switchboard switchboard

the the

switchboards switchboards

Trunk Trunk

basic basic

the the

later later

jacks jacks

particular particular

signalling, signalling,

of of

of of it it

possible possible 3.12 3.12

each each

or or

MANUAL MANUAL

of of

local. local.

lines. lines.

"A" "A"

circuits circuits

of of

manner, manner,

used used

and and

it it

the the

terminating terminating

subscriber subscriber

lineups lineups

of of

different different

line line

arriving arriving

these these

perform perform

Although Although

subscriber subscriber

or or

the the

offices offices

within within

with with

required required

parts parts

types types

board. board.

trunk trunk multiple multiple

LOCAL LOCAL

or or

capacity, capacity,

connections connections

are are

types types

to to

at at

trunks. trunks.

the the

type type

to to

made made

relay relay

the the

described described

switchboards switchboards

which which

have have

two two

calls calls

the the

similar similar

"A" "A"

3 3 -

and and

jacks jacks

section section

installed, installed,

number number

are are

of of

to to

a a

are are

which which

which which

central central

problem problem

are are

of of

all all

cabled cabled

jacks jacks

trunk trunk

the the

CH. CH.

elements elements

into into

In In

subscriber subscriber

incoming incoming

incoming incoming

subscriber subscriber

different different

use use

were were incoming incoming

elements elements

different different

great great

communicate communicate

SWITCHBOARDS SWITCHBOARDS

stationed stationed

of of

of of

over over

this this

connections. connections.

These These in in

about about

line line

a a

complete complete

facilities, facilities, office office The The

The The

Switchboard Switchboard

The The

Switchboard Switchboard

trunks trunks

multiple multiple to to

The The

circuits. circuits.

elements elements

two two

basic basic

circuits circuits

to to

of of

basic basic

subscribers subscribers

divided divided

LOCAL LOCAL

called called

types types

"B" "B"

"A" "A"

solve solve

trunk trunk

circuits circuits

continuation continuation

two two

completing completing

These These

B. B.

characteristics characteristics

tions. tions.

switchboards switchboards desired desired

cord cord

three three circuits circuits

located located

A. A. "A" "A"

These These

telephones telephones

switchboards switchboards

brought brought

enough enough

was was To To 3.4 3.4

scriber scriber service service

office office are are

connected. connected.

office office

type type operators operators

used used distant distant and and

the the

it it

"B" "B"

and and

rack rack

local local

relays relays

circuits circuits

high high

specifi­

the the

calls calls

are are

the the

relay relay

incoming incoming

terminate terminate

generally generally

trunk trunk

in in

calls calls

keyshelf keyshelf

Since Since

circuit circuit

on on

48 48

to to

Accordingly, Accordingly,

the the

signals signals

will will

to to

complete complete

Switchboard Switchboard

board board of of

handle handle

trunk trunk

30 30

comparatively comparatively

jacks. jacks.

Lamp Lamp

located located

"B" "B"

"B" "B"

trunks trunks

is is

SYSTEMS SYSTEMS

for for

The The

a a

subscribers subscribers

lamps lamps

board board

are are

48 48

operator. operator.

practicable practicable

to to

operators operators

of of

and and

trunk trunk

to to

it it

cords. cords.

"B" "B"

one one

multiple multiple

MANUAL MANUAL

3.13 3.13

typical typical

and and

a a

30 30

View View

a a

arranged arranged

per per

keys keys

for for

at at

ended ended

makes makes

equipment equipment

cord cord

LOCAL LOCAL

are are

from from

switchboard. switchboard.

completion completion

Front Front

shows shows

calls calls

plug plug

3 3 -

cords, cords,

trunks trunks

subscriber subscriber

each each

the the

traffic traffic

that that

of of

for for

3-6 3-6

feature feature

3-6 3-6

control control

CH. CH.

in in the the

the the

with with

single single

to to

found found

keyshelves keyshelves

This This

enough enough

number number

Figure Figure

Only Only

Incoming Incoming

on on

Figure Figure

directed directed

field. field.

located located

position position

been been

jack jack

trunks. trunks.

and and

are are

bays. bays.

trunks trunks furnish furnish

average average

directly directly

position position has has

cally cally

associated associated office. office.

L•:.MP L•:.MP

SIGNAL SIGNAL

I----t---AUXILIARY I----t---AUXILIARY

Call Call

Trunking Trunking

OFFICE OFFICE

KILDARE KILDARE

Manual Manual

SYSTEMS SYSTEMS

3.14 3.14

KEY KEY

(Straightforward (Straightforward

Completing Completing

Method) Method)

MANUAL MANUAL

LISTENING LISTENING

3-7 3-7

LOCAL LOCAL

-

3 3

Figure Figure

OFFICE OFFICE

MERRIMAC MERRIMAC

BOARD BOARD

CH. CH.

"A" "A"

CALLING CALLING

ME·?-66441 ME·?-66441

SUBSCRIBER SUBSCRIBER ~ ~ CH. 3 - LOCALMANUAL SYSTEMS

3.5 METHODOF OPERATION There are two general methods by which telephone calls may be completed in a central office containing "A" and "B" switchboards. One, the earlier method, uses "call circuit" trunks and the other or newer method, uses "straight­ forward" trunks. A. Call Circuit Trunk When a call circuit trunk is used, the number called is passed by the "A" operator to the "B" operator over a separate circuit, known as a call circuit. The trunk to be used for the connection is assigned by the "B" operator. The "A" operator then plugs the calling cord into the out­ going trunk and the "B" operator plugs the cord on the other end of the assigned trunk into the desired subscribers multiple jack. B. Straightforward Trunk When a straightforward trunk is used, the number called is passed by the "A" operator to the "B" operator over the trunk to be used for the connection. In this case the trunk used is selected by the "A" operator. The call circuit is, therefore, not required. It should be noted from the above comparison that the straightforward method entirely 'eliminates the call circuit. This has several advantages, among which are: elimination of interference between "A" operators, who use the same call circuit (each call circuit is multipled to a large number of "A" positions); the clearing of the keyshelf of the large number of call circuit key buttons (in large central office districts the number of buttons required is above one hundred); and the service rendered to subscribers is somewhat improved. Straightforward trunks are divided into three classes, knows as: 1. Key listening 2. Automatic Listening 3. Jack listening

1. Key Listening Straightforward Trunks - This class of straightforward trunks 1s so called because each trunk has a key associated with it at the "B" board which must be operated before the "B" operator can be connected to it to receive the number of the line being called. 3.15

is is

a a

to to

the the

oper­

the the

at at

the the

cord cord

idle idle

the the

she she

key key

switch­

call call

lo­

plug. plug.

of of

straight­

tone tone

that that

receive receive

trunk trunk

lamp, lamp,

the the

the the

while while

of of

associated associated

at at

the the

"A" "A"

an an

operator operator

one one

telephone telephone

the the

is is

signifying signifying

cord cord

the the

to to

"A" "A"

the the

and and

hear hear

she she

below below

that that

signal. signal.

the the

in in

associated associated

outgoing outgoing

the the

which which

of of "A" "A"

operator operator When When

The The

straight­

of of

connected connected

only only

After After

so so

the the

keyshel£ keyshel£

can can

straightforward straightforward

sleeves sleeves

party, party,

to to

cord cord

the the

ready ready

lighted lighted

room. room.

operator operator

the the

idle idle

"B" "B"

with with

Indicator Indicator

listening listening

given given

momentary momentary

at at

a a lamp lamp

the the

signals signals

selected selected

operation operation order, order,

the the

assignment assignment

the the

handles handles

been been

is is

is is

an an

answering answering

flashing flashing

operator's operator's

"B" "B"

in in

the the

jack. jack.

it, it,

subscriber subscriber

key key

be be

trunk trunk

operates operates

in in

trunks. trunks.

an an

to to

the the

using using

a a

(Call (Call

calling calling

and and

tone tone

has has

an an

listening listening

trunk trunk

operation operation sends sends

for for

switchboard switchboard

of of

the the

"B" "B"

listening listening

necessary. necessary.

in in

Having Having

the the

to to

trunk trunk

terminal terminal

she she

a a

are are

into into

and and

will will

switchboard switchboard

tells tells

the the

cord cord

key key

set set

key key

SYSTEMS SYSTEMS

the the

to to

associated associated

if if

established, established,

called called

"A" "A"

CITS CITS

way way

also also

operator operator

The The

key key

description description

the the

located located

circuit circuit

supervisory supervisory

of of

lamp lamp

"A" "A"

into into

this this

a a

when when

plug plug

it it

cord cord

answering answering

the the

be be

subscriber's subscriber's

then then

the the

the the

the the

trunk trunk

plugging plugging

mainly mainly

"B" "B"

key key

in in

jacks. jacks.

switchboard switchboard

momentary momentary

to to

of of

all all

the the

of of

usual usual

MANUAL MANUAL

3.16 3.16

the the

operator operator

relays relays

and and

the the

in in

call call

extinguished. extinguished.

types types

operated, operated,

the the

trunk trunk

trunk. trunk.

listening listening

"B" "B"

telephone telephone

for for

meantime, meantime,

general general

to to

B" B" addition, addition,

this this

rack rack

is is

tip tip

the the

understanding understanding

which which

11

indicating indicating

lamp lamp

key, key,

plugged plugged for for

calling calling

The The correct correct

differ differ

cord cord

key key

LOCAL LOCAL

In In

the the

of of

the the

the the

the the

in in

in in

operator operator

however, however,

opera.tor opera.tor

The The

that that

assignment assignment

is is

the the

when when

as as

multiple multiple

the the

and and the the

switchboard switchboard

can can

answers, answers,

trunk trunk

thus thus

to to

relay relay trunk trunk

In In

at at

received received

answered answered

3 3 -

subscriber's subscriber's

basic basic

several several

on on

this this

connection connection

"A" "A"

"A" "A"

which which

to to

a a

a a

• •

cord cord

"B" "B"

tests tests

and and

is is

the the

knows knows

lamp lamp

the the

connection connection

trunk trunk

office office

an an

operator's operator's

has has

CH. CH.

are are

steady steady

a a

on on

the the

manner manner

The The

Straightforward) Straightforward)

called. called.

assignment assignment

restores restores

with with

listening listening

signals; signals;

herein. herein.

oper,ation oper,ation the the

to to

touching touching

plugged plugged

by by

the the

the the

"B" "B"

calling calling

call call

the the

over over

switchboard. switchboard.

waiting waiting

for for

trunks, trunks,

trunks trunks

cord, cord, number. number.

the the

connected connected

In In

the the

When When

same same

subscriber subscriber

furnish furnish

passed passed

by by

A A

There There

terminates terminates The The

then then

to to

lamp lamp

and and

on on

way way

indicates indicates

is is

the the

the the

is is

operator operator

number number

located located

switchboard, switchboard,

trunk. trunk. "B" "B"

outgoing outgoing

operator operator

the the

disconnect disconnect

the the

changes changes

connected. connected.

This This

call call

"B" "B"

key. key.

"A" "A" the the

signals signals

set set trunk trunk

a a

are are

called called

board, board,

trunk trunk

in in the the

that that

trunk trunk

cated, cated,

desired desired

connected connected

the the

atore atore into into

Associated Associated leaves leaves

"A" "A"

their their

calling calling

number number

forward forward should should

considered considered

waiting waiting

forward forward

usual usual

waits waits Temporarily Temporarily CH. 3 - LOCALMANUAL SYSTEMS

After the "B" operator learns the number of the called subscriber, she tests the called line in the usual way by touching the tip of the plug to the sleeve of the called line multiple jack. If the line is idle, she inserts the plug in the multiple jack and the ringing starts automatically. If the line is busy, she inserts the plug in the busy back jack which returns a busy tone to the calling subscriber and flashes the supervisory lamp at the "A" switchboard. Insertion of the plug into any working jack extinguishes the flashing assignment lamp and disconnects the "B" operator from the trunk. The operator is now ready to take up a call on another trunk. Although both subscribers control supervisory signals (the lighting of the lamps) at the "A" switchboard, neither subscriber has any control over the disconnect signal associated with the trunk at the "B" sw1tchboard. Tfiis signal is entirely controlled by the "A" operator. The "A" operator disconnects from the trunk by removing the calling cord from the trunk jack. This causes the disconnect lamp to light. The "B" operator removes the trunk cord, extinguishing the disconnect lamp. Should the "B" operator fail to remove the cord before the trunk is selected for another call, the assignment lamp will relight together with the disconnect lamp, but ringing current will not be placed on the trunk. In such a case the operator must remove the cord, and extinguish the disconnect lamp. If this is not done, her telephone set will not be connected to the trunk when the key is depressed. Several assignment lamps may be lighted simultaneously, each indicating a call waiting on the associated trunk; however, only one trunk can be connected to the operator's set at a time. In order to facilitate handling calls when traffic is heavy, the equipment may be arranged to permit the operator to overlap her calls, that is, operate a second key to disconnect her set from a trunk to which she is con­ nected and cause her set to be connected to the second trunk while she is completing the connection for the first trunk. It is necessary for the operator to remember the number wanted on the first trunk until she completes that connection.

3.17

at at

to to

a a

and and

sub­

the the

says, says,

the the

into into

plug plug

as as

idle idle

"B" "B"

an an

a a

removes removes

a a

to to

the the

lamp lamp

test test

of of

the the

This This

lamp lamp

switch­

the the

switch­ to to

operator operator

receive receive

is is

-

Merrimack Merrimack

lights lights

trunk trunk

trunk. trunk.

steadily steadily

and and

the the

for for

automatic automatic cord cord

same same

over over

lamps, lamps,

being being

that that

that that

to to

lamp lamp

signals signals

"A" "A"

(When (When

"B" "B"

type type

which which

6644, 6644, "A" "A"

set set

the the disconnect disconnect

plug plug

·This ·This

the the

the the

An An

at at

operator operator

answering answering

signal signal

This This

so so

cord cord a a

the the

on on

inserts inserts

is is

the the

the the

selects selects

tests tests

Trunks Trunks

tone tone

lights lights

on on

light light

used used

party party

ready ready

guard guard

lamp. lamp.

is is

cord cord because because

"A" "A"

signal signal

assume assume

the the

and and

at at

at at

supervisory supervisory

jack. jack. calling calling

trunk, trunk,

of of

is is

trunk trunk

offic~. offic~.

the the

plug plug

3-7). 3-7).

Merrimack Merrimack number number

operator operator

the the

a a

operator's operator's

cord cord

with with

of of

circuit, circuit,

auxiliary auxiliary

call, call,

steady steady

trunk trunk

signal signal

guard guard

waiting waiting

idle idle

spot spot

operator operator

called called

subscriber subscriber

associated associated

operat1on. operat1on. of of

to to

calling calling

cord cord

The The

"B" "B"

switchboard switchboard

momentary momentary

a a

a a

generally generally

of of

the the

light. light.

(O.G.T.) (O.G.T.)

11 11

an an

so so

auxiliary auxiliary

Merrimack Merrimack SYSTEMS SYSTEMS

the the

whose whose

switchboard switchboard

the the

the the

Kildare Kildare

the the

(Figure (Figure

cord cord

operator operator

call call

terminates terminates

the the

switchboard switchboard

the the

panel panel

trunk. trunk.

"A" "A"

to to

~s ~s

plug plug

number number

a a

a a

into into

calling calling

both both

of of

to to

Straightforward Straightforward

most most

and and

The The

a a

type type

that that

"B" "B"

of of

calling calling

to to

"B" "B"

"A" "A"

trunk trunk

used used

calling calling

of of

into into

call call

the the lights, lights,

the the

3.18 3.18

auxiliary auxiliary

the the as as

Associated Associated

the the

MANUAL MANUAL

trunk trunk the the

the the

connected connected

and and

a a

office, office,

changes changes

the the

L~sten1ng

selected selected trunk trunk

tip tip

line line

The The

this this

the the

to to

to to

an an

the the

are are

the the

means means

key key

is is

cord cord

lamp lamp

at at

plugged plugged acts acts

switchboard. switchboard.

of of

as as

(O.G.T.) (O.G.T.)

of of

the the

by by

the the

gives gives

LOCAL LOCAL lamp lamp

This This

arranged arranged

"Key "Key

plug. plug.

Listening Listening

5-5000". 5-5000".

indicate indicate

that that

indicating indicating

is is

inserts inserts

switchboard switchboard

outgoing outgoing

trunk trunk

causing causing

lamps lamps

- Having Having

This This

using using

"A" "A"

lamp lamp

so so

3 3 -

to to

trunk trunk

and and

for for

trunk. trunk. which which

line line

originate originate

Merrimack Merrimack

"A" "A"

the the

trunk trunk

Please." Please."

the the

connected connected

cord cord

then then

and and

listening listening

connected. connected.

example example

knows knows

are are

7-6644, 7-6644,

CH. CH.

answering answering

to to

the the

a a

jack, jack,

automatically automatically of of

touching touching

visually visually

the the

called. called.

trunk trunk

lamp lamp

signal, signal,

sometimes sometimes

cord cord

operation operation

-

is is

an an

jack.) jack.)

above above

straightforward straightforward

Automatic Automatic

the the

signal signal

over over

a a

is is

stra~ghtforward stra~ghtforward

by by

"Kildare "Kildare

the the

in in

rim rim

waiting. waiting.

you," you,"

Merrimack Merrimack

As As

the the When When

and and

When When

indicating indicating

2. 2.

The The

"Number "Number

extinguishing extinguishing

she she

in in

trunk trunk

of of outgoing outgoing

of of

guard guard

trunk trunk

operator operator

O.G.T. O.G.T.

Merrimack Merrimack

is is

subscriber subscriber

handset handset

operator operator

sent sent

number number

circuits circuits

made made

the the

a a

a a

(O.G.T.) (O.G.T.)

the the

the the

trunk trunk

idle idle

"A" "A"

is is

sleev·e sleev·e

idle idle

called, called,

"Thank "Thank

jack, jack,

says, says,

the the

MErrimack MErrimack

on on

operates operates

plug plug

the the his his

scriber scriber

flashing flashing

"A" "A"

are are

which which automatically automatically

as as

The The

is is

board, board,

signal signal

listening listening

described described

board board

call call

straightforward straightforward class class operator operator CH. 3 - LOCALMANUAL SYSTEMS

Current from the calling cord at the Merrimack "A" switchboard operates relays in the Kildare incoming trunk circuit which causes the associated guard and disconnect lamp and the auxiliary signal lamp to light at the Kildare "B" switchboard •. If no other calls are waiting to be answered at the Kildare "B 11 switchboard, the control relays in the associated "B" switchboard position operate, causing the guard and disconnect lamp to flash and automatically connect the "B" operator's telephone circuit to the trunk, at the same time sending out two momentary "order" or "Zip" tones which are heard by the "B" operator, the Merrimack "A" operator, and the calling subscriber. The Merrimack "A" operator hearing the order tones knows that the Kildare "B" operator is connected and says "5000" and then releases the listening key. The Kildare "Bu operator picks up the trunk cord plug associated with the flashing guard and disconnect lamp and tests line 5000 in the multiple by touching the tip of the trunk cord plug to the sleeve of the jack. I£ the line is found idle, she inserts the plug into the jack. This causes trunk relays to operate which extinguish the guard and disconnect lamp and auxiliary signal lamp, connect ringing current to the called line, and disconnect the operator's telephone set from the trunk. The calling subscriber hears ringing induction, as an indication that the called party's bell is being rung. When the Kildare-5 subscriber "5000" answers, relays in the incoming trunk circuit operate disconnecting the ringing current and extinguishing the calling cord supervisory lamp at the Merrimack nA" switchboard. While the subscribers converse, battery is being furnished by the "A" and "B" board cord circuits. When they have finished and replaced their handsets the answering and calling cord supervisory lamps on the Merrimack "A" switchboard light up. The Merrimack "A" operator then removes the answering and calling cord plugs from the jacks, again lighting the trunk guard and disconnect lamp at the Kildare "B" board. The Kildare "B" operator removes the associated trunk cord plug from the multiple jack extinguishing the guard and dis­ connect lamp and equipment is again normal. There are some Special Features associated with these trunks. For instance, several guard lamps may be lighted at the same time, each indicating a call waiting on the associ­ ated trunk, but only one trunk can be connected to the operator's set at a time. Each trunk on which a call is waiting will be connected in rotation, the lowest number cord first, then the next higher, etc. 3.19

of of

by by

the the

and and

sig­

by by

and and

be be the the

"B" "B"

a a

key key

oper­

from from

signal signal

before before

over over

signals signals

trunk trunk

class class "B" "B"

usual usual

trunk. trunk. operator operator

in in

sub­

before before

the the

release release

position position will will

causes causes

trunk trunk

"A" "A"

learning learning

waiting waiting

key," key,"

cord cord

the the

connected connected

The The

~p ~p

the the

at at

"B" "B"

the the guard guard

This This

is is

connected, connected,

sequence sequence

waiting waiting

it it

is is

release release

cord cord

the the

the the

-

be be

first first

connected connected

each each

disconnect disconnect

in in

the the control control

is is

trunk trunk so so

the the

from from

After After

the the

a a

by by

is is the the

that that

the the still still

trunk trunk

call call

call. call.

the the disconnects disconnects

is is

release release

jack, jack,

extinguishing extinguishing

from from

any any

supervisory supervisory

will will

the the

as as

call call

a a

set set

a a

it it

call call

is is

regular regular

of of

Trunks Trunks

on on

however, however,

calls, calls,

the the

but but a a

jack. jack.

removes removes

has has

trunk, trunk,

in in

the the

because because

for for

her her

trunk trunk

calls, calls,

remove remove

cord, cord, trunk trunk

call, call,

light light

which which

trunk trunk

"master "master

which which

SYSTEMS SYSTEMS

control control

of of with with

as as

the the

to to set set

controlled controlled

led led

trunk trunk

operator operator

the the

which which

her her

the the to to

the the

on on

to to

to to

the the

a a

operation operation

handling handling

disconnects disconnects

ca ca

on on

as as

operator operator

release release

"B" "B"

3.20 3.20

connection connection

condition, condition,

fail fail

listening listening

another another

called called

from from

subscriber subscriber

MANUAL MANUAL

so so

Strai,htford Strai,htford

not not

The The

trunk trunk

trunk trunk a a

key. key.

into into

trunk trunk

disposes disposes

"B" "B"

the the

sequence sequence

may may

the the

soon soon overlap overlap

removes removes

entirely entirely

1s 1s

this this

trunk trunk

a a

or or

for for

associated associated

operator's operator's

the the

cord cord

subscribers subscribers

any any

rerung. rerung.

to to

as as

is is

operator operator

LOCAL LOCAL

the the and and

into into

connected connected

and and

11 11

case case

plugs plugs

facilitate facilitate

button, button,

operator operator

neither neither

to to

from from

be be

next next

"B

a a

release release trunk trunk

is is

Under Under

a a

3 3 -

"A" "A"

with with

both both

regular regular

Listening Listening

to to

jack jack

signal signal

flash flash

the the

whether whether keyshelf. keyshelf.

operator operator

trunk trunk

set set

the the not not

the the

set set

selected selected

calling calling

signal signal

the the

in in

completing completing

the the

CH. CH.

lighted lighted

such such

wanted, wanted,

of of

operator operator

lamp. lamp.

with with

board, board,

Jack Jack

the the to to

to to

is is

"B" "B"

the the

her. her.

jack. jack.

operator operator is is

will will

order order

the the

in in

will will

This This

3. 3.

operator operator

it it

the the

on on

Should Should

When When

"A" "A"

trunk trunk

Although Although

In In

The The

11 11

"A" "A"

she she

associated associated

listening listening

number number

remain remain

lamp lamp

trunk trunk

disconnect disconnect

"B

telephone telephone

the the

the the

operating operating

an an

provided provided

the the

the the way. way.

connects connects plugging plugging

straightforward straightforward

scriber scriber

regardless regardless the the

connected connected

multiple multiple the the

disconnect disconnect

lamp lamp

removing removing

nal. nal.

the the ator. ator.

board. board.

at at

to to

operator operator by by the the

If If

will will

connect connect

is is while while

her her

permits permits mounted mounted CH. 3 - LOCAL MANUALSYSTEMS

3.6 LOCAL MANUALSWITCHBOARDS TODAY The conversion of local offices from manual to various electromechanical (Step-by-step, Crossbar #5, etc.) offices and eventually to electronic (No. 1 ESS, etc.) offices did not entirely eliminate the need for Local Manual Switchboards. Such a switchboard is still required to handle the originating and terminating traffic which the automatic equipment is unable to complete, or in certain areas where the installation of automatic equipment is as yet not economical.

3.21