US2177069A

US2177069A - Telephone system

Info

Publication number: US2177069A
Application number: US188443A
Authority: US
Inventors: Kessler Frank
Original assignee: Associated Electric Laboratories Inc
Current assignee: Associated Electric Laboratories Inc
Priority date: 1938-02-03
Filing date: 1938-02-03
Publication date: 1939-10-24
Anticipated expiration: 1956-10-24
Also published as: USRE22813E

Description

Oct. 24, 1939. F. KESSLER 2,177,069

TELEPHONE SYSQPEM r1104 P. s, 1938 10 Sheets-Sheet 1 FIG. 1 1

WAY

FTUTOMATIC EXCHANGE l I FINDER swncnswncH I FINDER ECT I SWITCH SWITCH 182 as I AUTOWtTCI-W'? OMATIC SWITCHING EQUIPM INVENTOR. FRANK KESSLER ATTORNEY.

Och 24, 1939. F, ss 2,177,069

TELEPHONE SYSTEM Filld F010. 3, 1938 lo Sheets-Sheet 2 Have W C1236 RA 43 c1237 RA244 C1238 RA 45 INVENTOK FRANK KESSLER ATTORNEY.

0d. 24, 1939. F ss 2,177,069

TELEPHONE SYSTEM Filod Feb. 3, 1958 10 Sheets-Sheet 4 FRANK KESSL ER ATTORNEY.

0d.- 24, 1939. KESSLER 2,177,069

TELEPHONE SYSTEM 7 I Filld FQb. 3, 1938 10 Sheets-Sheet 5 7 HI TIT III :1: u C 2. m

(z o ru m INVENTOR. FRANK KESSLER A TTORNEY;

Oct. 24, 1939. KESSLER I 2,177,069

TELEPHONE SYSTEM Filed Feb. 3, 1958 10 Sheets-Sheet 7 [N6 RELAY m I g; a f I\ 2 as j - h INVENTOR.

d FRANK KESSLER BY E v ziag,

ATTORNEY.

Oct F. KESSLER I 2917479069 TELEPHONE SYSTEM F1104 Feb. 3, 1958 10 Sheets-Sheet 8 ALARM APPARATUS FIG. 8

BUSY 13 DIAL TONE APPARATUS meme APPARATUS FRANK KESSLER ATTORNEY;

BY r

Patented-Oct. 24, 1939 2, 77,0 9

UNITED STATES PATENT OFFICE TELEPHONE SYSTEM Frank Kessler, Villa Park, 111., assignor to Associated Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application February 3, 1938, Serial No. 188,443 38 Claims. 179-18) The present invention relates to telephone relay type which is fully directive in character.

systems, and more particularly to small auto- Another object of the invention is to provide matic telephone systems of the type adapted for in a telephone system including a plurality of installation in small towns or villages. finder switches, improved allotter or distributor An automatic telephone system of the charequipment associated with the finder switches for acter noted is generally known as a community assigning in a predetermined order idle ones of automatic exchange or C. A. X and usually has the finder switches to the use of calling lines.

a line capacity of one hundred lines or less. For A further object of the invention is to provide reasons of economy, the lines are usually of the allotter or distributor equipment associated with 10 multi-party type and code ringing is utilized for the finder switches of a telephone system which 10 selectively signaling the telephone stations on s Ope b e t ass an idle One Of t e finde the various subscriber lines. In order to proswitches to the use of the next calling line immevide toll service to the subscribers, provisions are diately after a previously assigned one of the also made for trunking calls to and from one or finder switches selects a calling line and to pre- 5 more distant exchanges. One improved all-relay vent the assignment of the previously assigned telephone exchange of t type is disclosed and finder switch as long as the selected calling line claimed in the copending application Serial No. is busy, and an improved arrangement respon- '86,046, (Norman H. Saunders), filed June 19, sive to a fault in one of the finder switches for 1936. causing operation of the allotter or distributor 'In brief, in the system as disclosed in the equipment to prevent the assignment of theme 30 above-mentioned Saunders application, the subfinder switch. scriber and trunk lines extend to the finder and Another object of theinvention is to provide connector switches of each of a, plurality of allin a telephone system, a numerical switch havrelay finder-connector links,vcommon equipment 118 access to a plurality of trunk nd s c ibe including a relay type-link distributor or allotter lines, and including improved PD 'QWS 0- 25 being provided for assigning idle ones 01' th links tively controlled in accordance with diilerent to successive calling lines in a predetermined relations between the line selecting digits for order. The finder switches of the various links causing the operation of the numerical switch are semi-directive in character; that is, it is to provi e trunk and u s r line c O necessary to hunt for the calling line in a pre- A further object of the invention is to provide an viously marked group of lines during the operain a numerical switch having access to a group tion of a link to seize the calling line. Although of lines including subscriber and trunk lines an this arrangement is entirely satisfactory from improved arrangement for causing operation 01 an operating standpoint, a substantial interval the switch to select a particular one of the of' time is consumed by the finder switch in subscriber lines or for causing operation of the 35 hunting the calling line in the previously marked switch to select a previously selected idle one of group of lines. Provisions are also made in the the trunk lines, and improved apparatus resystem of the Saunders application for testing a sponsive to the selection of the one trunk line selected line to determine the idle. or busyconfor immediately selecting anothenidle one of the 40 dition thereof, for applying busy tone current trunk lines for use. n to a calling line in the event the selected called The fea ur s of h Present nti n are line is bus and for applying coded ringing illustrated as being incorporated in a telephone current to a called multi-party subscriber line exchange having an ultimate capacity of one in the event the selected called lineis idle in hundred lines. The lines are arranged ina order to signal a particular telephone station plurality of groups of ten lines each of which 45 connected thereto. is individually divided into'two subgroups of It is an object of the present invention to profive lines each, certain of the lines being twovide, in a telephone system of the character way inter-ofllce trunk lines, others of the lines noted, an improved line finder switch of the being private exchange or P. B. X trunk lines,

all-relay type which requires a minimum numand the remainder of the lines being subscriber 50 her or relays both in the switch itself and in lines. The various lines individually terminate .the associated common equipment. in line circuits which are connected in the same It is another object of the invention to promanner regardless of whether a line is a trunk vide, in a telephone system of the character or a subscriber line. The telephone exchange 5 noted. an improved line finder switch of the allalso includesv a plurality of finder-connector and results in a considerable reduction in invention, the

links which individually have access to the lines, and allotter or distributor apparatus for assigning, in a predetermined order, idle ones of the links to the use of the calling lines.

In accordance with one feature of the invention, each of the finder switches includes a plurality of group relays, a group of unit relays, and a subgroup relay, eachof the group relays being operative to select a corresponding group of lines, and each of the unit relays being operative to select-a corresponding line from each of the subgroups, depending upon the operated or non-operated condition of the subgroup relay. More specifically, each group of lines is divided into two subgroups respectively comprising odd and even numbered lines and the arrangement is that, when a call is initiated on an odd line, the corresponding group and unit relays operate, without operating the subgroup relay, in the finder switch of the assigned link to select the- On the other hand, when a call odd calling line. is initiated on an even line, the corresponding group and unit relays and the subgroup relay operate in the finder switch of the assigned link to select the even calling line. This arrangement reduces the number of unit relays required in each finder switch by approximately one-half the manufacturing cost of the finder switches.

In accordance with a further feature of the group relay and the unit relay in a finder switch of an assigned link are arranged to operate substantially simultaneously to select a line in one of the subgroups; and the group relay, the unit relay and thesubgroup relay in the finder switch of an assigned link are arranged to operate substantially simultaneously to select a line in the other of the subgroups. This is accomplished by providing common equipment for controlling the operation of a control relay provided in each of the finder switches. More particularly, the common equipment comprises a group of first auxiliary relays individually corresponding to a particular group of lines and to a particular group relay in each finder switch, a group of second auxiliary relays individually corresponding to a particular line in each subgroup of lines and to a particular unit relay in. each finder switch, and a third auxiliary relay corresponding to one of the subgroups in each group of lines and to the subgroup relay in each finder switch. With this arrangement and when a call is initiated on a particular line in one of the subgroups, the corresponding first and second auxiliary relays in the common equipment are operated and cause the corresponding group and unit relays in the finder switch of the assigned link to be conditioned to, be operated. Also, the second auxiliary relay in the common equipment causes theoperation of the control relay provided in the finder switch of the assigned link, which latter relay causes thepreviousiy conditioned group and unit relays in .the finder switch of the assigned link to operate substantially simultaneously, thereby to select the calling line. When a call is initiated on a line in the other of the subgroups, the corresponding first and second auxiliary relays and the third auxiliary relay in the common equipment are operated. The first and second auxiliary relays in the common equipment condition the corresponding group and unit relays in the finder switch of the msigned link to be operated, and

' the third auxiliary relay in the common equipment conditions the subgroup relay in the finder ment renders the finder switch fully directive and reduces the time required in extending a connection from a calling line to an idle link.

For the purpose of assigning, in a predetermined order, idleones of the finder switches to the use of calling lines, there is provided, in association with the severallinks, allotter or distributor equipment including a group of allotter relays individually corresponding to the links.

In accordance with a further feature of the invention, each of the allotter relaysis provided with operating and holding circuits for energizing the same, and circuits controlled by the operation of the allotter relay also being provided for assigning idle ones of the finder switches to the use of the lines having a calling condition thereon, and for preventing the assignment of the corresponding finder switch to the use of the lines having a calling condition thereon. More particularly, the arrangement is suchthat when one of the finder switches operates to select aline having a calling condition thereon, the operating circuit of the corresponding allotter relay is completed. Upon operating, the allotter relay completes its holding circuit, assigns an idle one of the finder switches to the use of the next line having a calling condition thereon, and prevents the assignment of the corresponding finder switch to the use of lines having a calling condition thereon. Idle ones of the finder switches are operated successively until the last finder switch in the group is taken for use by a calling line. At this time the holding circuits of all of the allotter relays are interrupted and those allotter relays corresponding to idle finder switches restore to recycle the idle finder switches for use by the lines'having a calling condition thereon.

In accordance with a still further feature of the invention, an arrangement is provided in association with each of the allotter relays for operating the same in response to the presence of a fault in the corresponding finder switch, in

pears in one of the finder switches, the fuse linkindividual thereto is operated or blown, causingv the. additional operating circuit of the corresponding allotter relay to be completed. Upon operating, the corresponding-allotter relay prevents the assignment of the finder switch having a fault therein to the use of one of the lines having a calling condition thereon.

In accordance with another feature of the invention, each numerical or connector switch of each link is provided with apparatus, including a group of impulse counting relays for causing operation of the numerical switch to provide trunk and subscriber line selection in an improved manner.- More particularly, the apparatus is responsive to a predetermined digit and a predetermined digit following the first-mentioned digit for causing the operation of the the links included in the switch to select a particular subscriber line, and is responsive to the first-mentioned digit and a different predetermined digit following the firstmentioned digit for causing the operation of the switch to select an idle one of a certain group of trunk lines. y

In accordance with a still further object of the invention, an improved arrangement is provided in conjunction with the last-mentioned group of trunk lines for assigning idle ones of the trunk lines to be selected by the numerical switches in a predetermined order. This arrangement is such that an idle one of the trunk lines is assigned for the use of the numerical switches immediately following the seizure of a previously selected one of the trunk lines by one of the numerical switches.

Further features of the invention pertain to a particular arrangement of the circuit elements whereby the above-outlined and additional op-- erating features are attained.

The novel features believed to be characteristic of the invention are set forth in the appended claims. The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the specification, taken in connection with the accompanying drawings, in which Figure 12 illustrates the general arrangement of a system embodying one form of the present invention; Fig. 9 fllustrates the mode of combining the remaining figures of the drawlugs to form a unified system; and Figs. 1 to 8, inclusive, 10 and 11, illustrate the details of a system having incorporated therein the features of the invention as briefly outlined above.

Referring now more particularly to Fig. 12 of the drawings the telephone system there illustrated comprises a small community automatic exchange I8, a second automatic exchange I85, and a third automatic exchange I88. The exchanges I85 and I86, respectively, are connected to the exchange I8 by first and second groups, respectively, of two-way-inter-ofllce trunk lines. One of the first group of inter-oflice trunk lines is indicated at 2i as terminating at a repeater I81; and one of the second group of inter-orifice trunk lines is indicated at 3| as terminating at a repeater I88, the repeaters I81 and I88 forming parts of the apparatus located at the exchange I8. Also extending to the exchange I8 are two groups of private branch exchange or P. B. X trunk lines, not shown, which are accessible to the finder and connector switches of the links included in the exchange I8. Also extending to the exchange I8 are a plurality of subscriber lines, two of which are indicated at 28 and 38. Each of the enumerated subscriber lines .is illustrated as being of the multi-party type having two or more telephone stations associated therewith. Thus, two telephone stations, IB and 2B are diagrammatically shown as being connected to the line 28, and two additional stations, ID and 21),

are diagrammatically shown as being connectedto the line 38. Each of the substations connected to the'various subscriber lines may comprise the usual hand set having embodied therein a conventional dial-controlled impulsing device. Each of the lines extending to the'Lchange I8 termi nates in a line circuit through which it is rendered accessible to the finder and connector switches of line 28 terminates at a line circuit 28', through which it is connected to the contact springs of a finder switch 288 and to the contact springs of the exchange. Thus, the I connector switch 588 which two switches are connected together by link lines to form a finderconnector link. Similarly, the line 38 terminates at a line circuit 38'; and the illustrated two-way trunk lines 2| and 3| interconnecting the exchange I8 and the exchanges I85 and I86, respectively, terminate at line circuits 2| and 3i, respectively.

As many as ten telephone stations may be connected to each multi-party subscriber line, these telephone stations being arranged in two groups comprising five telephone stations each. The signals or ringers of one of the groups of telephone stations are connected between one side of the subscriber line and ground, while the ringers of the other group of telephone stations are connected between the other side of the subscriber line and ground, thereby providing an arrangement utilizing divided ringing.

As indicated above, the exchange I8 is designed to serve a relatively small number of lines comprising two groups of inter-ofiice trunk lines, two

. groups of P. B. X trunk lines, and a plurality of subscriber lines, these lines being arranged in ten groups of ten lines each. Accordingly, all of the trunk and subscriber lines are arranged to be served by any one of a plurality of finder-connector links included in the exchange I8. Obviously, the number of links required for satisfactory service will depend upon the volume of telephone traflic, but, taking into account the character of the exchange, ten links are considered adequate for reasonably good service. In order to assign the links to successive calling lines in a predetermined order, so that a link is always available for the use of a calling line, excepting, of course, those instances when all of the links are simultaneously busy, there is provided in association therewith common equipment indicated at I which includes a link distributor or allotter. The several links also have associated therewith common, ringing tone and timing apparatus which is diagrammatically shown at 888.

The operation of the system to extend a call initiated at any one of the telephone stations to another of the telephone stations is described briefly below, neglecting the details of the circuit arrangement. In extending a.- call initiated at one of the telephone stations to one of the telephone stations connectedto a subscriber line included in the second, third, fourth, fifth, sixth or seventh group of ten lines, a corresponding tens digit, a corresponding units digit and a corresponding code ringing digit are dialed, in the order named, at the telephone station when the call is initiated. For'example, when a subscriber at the telephone station IB connected to the line 28 initiates a call, by lifting his receiver from its switch hook, which is to be extended to the telephone station ID connected to the subscriber line 38, or the tenth line in the third group of ten lines, the line circuit 28' operates to cause the finderconnector link previously assigned by the link distributor or allotter in the common equipment GM to the calling line, to be set into operation to seize the calling line. Assuming that the link 388 is assigned by the link distributor to set up the connection, the finder switch 288 of the link operates to select the calling line and to connect it through to the conductors of the link line incoming to the connector switch 588 of the link. When the calling line 28 is seized and extended by way of the finder switch 288 to the associated switch 588, it is marked as busy in all of the other connector switches of the links, and the control equipment of the seized link is automatically conditioned to respond to the impulses of the first digit transmitted from the impulsing device provided at the calling telephone station IB. Since the subscriber lines are of the multi-party type, provisions are made for selectively signaling the desired called telephone station on any selected subscriber line. With the arrangement to be described more in detail hereafter, coded ringing is paratus included in the link circuit functions to test this line for the purpose of determining the busy or idle condition thereof. If the called line is busy, busy tone current is applied tothe link line and returned over the loop to the calling telephone station to indicate to the party at the calling telephone station that the desired connection cannot immediately be completed.

On the other hand, if the called line is idle at the time it is selected, the code selecting or ringing digit which is dialed at the calling telephone station, causes a selected coded ringing current to be applied to the side of the line to which the ringer of the telephone station ID is connected, the code of the selected ringing current corresponding to the called telephone station vID. While each of the ringers of the telephone stations included in the group of telephone stations with the telephone station ID are operated, the character of the code ring indicates that the telephone station ID is the telephone station being called. During the ringing operation, ringback tone current is applied to the loop extending to the calling telephone station to indicate to the party at this station that the desired called telephone station is being signaled.

Finally, a connection between the calling and called telephone stations is completed when the I call is answered at the called telephone station tioned to operate ID. As pointed out with particularity hereinafter, the arrangement of the link circuit apparatus is such that a link utilized in setting up a desired connection is released only when the connection is cleared out at the calling telephone station.

In extending a call initiated at one of the telephone stations to one of the telephone stations connected to a subscriber line included in the first, eighth, ninthor tenth group of ten lines, a predetermined prefix digit, a corresponding tens digit, a corresponding units digit, and a correspnding code ringing digit are dialed, in the order named, at the telephone station initiating the 'call. For example, when a subscriber at the telephone station IB initiates a call, by lifting his receiver from its switch hook, which is to be extended to a telephone station connected to a particular subscriber line included in the first group of ten lines, the line circuit 20 operates and causes the finder-switch of a previously assigned finder-connector link to be operated to seize the calling line, as previously, explained. When the predetermined prefix digit is dialed at the calling telephone station IB, the seized link is condiits connector switch to select the first, eighth, ninth or tenth groups of ten lines. Thereafter the connector switch responds -'group of ten lines,

dialing of the units digit, corresponding to the particular subscriber line to which the called telephone station is connected, to select the called subscriber line from the selected group of ten lines. The operation of the system to test the selected line for the purpose of determining the busy or idle condition thereof and to apply busy tone current to the link line in the event that the selectedline is busy is the same as that previously described. Also, the system operates, as described above, to cause a selected coded ringing current, corresponding to the called telephone station, to be applied to the side of the line to which the ringer of the called telephone station is connected upon dialing the code selecting digit at the calling telephone station IB. A connection between the calling telephone station I B and the called telephone station connected to. the particular line in the first group of ten lines is completed when the call is answered at the called telephone station.

The switching apparatus located in the exchange Ill may also be utilized in setting up a connection between two telephone stations connected to the same subscriber line, the sole function of the apparatus in this regard being that of selecting and applying ringing current to the calling line of the proper code to signal a party at the called telephone station. Carrying out .this function necessitates the seizure of the calling line by an idle link, in the manner described above. Thereafter, and following the dialing of the digits of the directory number of the called telephone station at the calling telephone station, the calling party replaces his receiver upon its switch hook. When the calling party hangs up, the finder switch of the operated link is released and ringing current of the selected code corre telephone station. Finally, the-line circuit of the line in use is released when the connection is cleared out at the calling and called telephone stations.

As heretofore pointed out, the inter-office trunk lines are arranged in two groups. More specifically, the first group is included in the second and the second group is included in the third. group of ten lines. In the operation of the link to select one of the first group of inter-office trunk lines including the line 2| interconnecting the exchange 10 and the exchange y one predetermined digit -or comprising a predetermined number of impulses is dialed at the calling telephone station. The connector switch of the seized link responds to the impulses of this one digit to select a previously assigned'idleone of the first group of trunk lines, More specifically, these inter-ofiice trunk lines have associated therewith apparatus for setting up idle ones of the lines for selection by the connector switches, which apparatus functionsto assign an idle line for use immediately ductors are provided in character and after a. previously assigned line is takenior use. Hence, at the conclusion of the predetermined trunk selecting digit dialed at a calling telephone station, the connector switch oi! the seized link immediately operates to select the previously assigned idle trunk line. When the trunk line is selected, the calling line is switched through by way of the selected trunk line and its associated repeater circuit to the terminating apparatus located in the exchange I85. In this connection, it is pointed out that two sets of link line conthe link circuit of each link, one set of which is devoid of all voice frequency coupling elements such, for example, as condensers or repeating coils, and is utilized in extending a connection by way of one or the trunk lines. Following the extension of the connection to the trunk line terminating apparatus located in the exchange I85, the connection may further be extended to a desired called telephone station such, for example, as the telephone station A, by dialing the connection is released following the establishment of a connection to the telephone station A depends upon the nature of the repeater circuit associated with the trunk line which is used in setting up the connection.

Since the trunk lines interconnecting the exchanges I and I85 are of the'two-way type, it will be understood that any one of these lines of the switching apparatus included in the exchange I I! may be utilized in the completion of calls originating or extended by way of the exchange I85, and which are to be extended to one of the subscriber lines terminating at the exchange Ill. The mode of operation of the equipment in the exchange I0 following the extension or a call thereto by way of one of the lines in the first group of trunk lines is substantially similar to that set forth with reference to the connection established between the telephone stations IB and ID.

In the operation of the link to select one of the second group of inter-oflice trunk lines including the line 3i interconnecting the exchange I0 and the exchange I86, only one different predetermined digit X comprising a predetermined different number of impulses is dialed at the calling telephone station, The operation and arrangement of this apparatus for selecting an idle one of the trunk lines in the second group of inter-ofiice trunk lines are otherwise the same as that of the apparatus for selecting an idle one of the trunk lines in the first group of inter-oflice trunk lines, as described above.

As heretofore pointed out, the P. B. X-trunk lines are arranged in two groups. The first group is included in the ninth group of ten lines, and the second group is included in the tenth group of ten lines. To select .an idle one of the first group of P. B. X trunk lines, the number P, X, Y, R is dialed at the calling telephone station, the digits P, X and Y being different in the digit R being any desired ringing digit. More specifically, the number 8911 is dialed at the calling telephone station. When the prefix digit 8 is dialed, the seized link is conditioned to operate its connector switch to select the first, eighth, ninth'or tenth group of ten lines. Thereafter the connector switch responds to the tens digit 9 to select the ninth group of ten lines. Thereafter the connector switch responds to the units digit 1 to select a previously regular directory number corresponding to the line to which the telephone station A is connected. The manner in which the assigned idle one of the first group of P. B. X trunk lines. More specifically, the first group of P. B. X trunk lines have associated therewith apparatus for setting up idle ones of the lines to be selected, which functions to assign an idle trunk line for use immediately after a previously assigned trunk line is taken for use. Dialing of the ringing digit 1 causes coded ringing current corresponding to the code ringing digit 1 to be applied to the selected P. B. X trunk line in order to signal the operator at the private branch exchange connected thereto. A connection between the calling telephone station and the operator's station at the private branch exchange is completed when the call is answered at the operators station.

As indicated above, only a portion of the lines of the ninth group are P. B. X trunk lines, the remaining lines of this group being subscriber lines. The connector switch arrangement is such that when the digits P, X, and X or Z are dialed into one of the connector switches one of the subscriberfs lines of the ninth line group is selected. For example, if the number 899 or the number 896 is dialed at a calling telephone station the connector switch of the assigned link responds by selecting the particular subscriber line of the ninth line group corresponding to the

units digit

9 or 6.

In order to select an idle one of the second group of P. B. X trunk lines the number 8011 is dialed at the calling telephone station. The operation and arrangement of this apparatus for selecting an idle one of the second group of P. B. X trunk lines are otherwise the same as that of the apparatus for selecting an idle one of the first group of P. B. X trunk lines described above.

Considering now in greater detail the appara tus embodied in the exchange I II and involved in the above-described sequence of operations, and

referring to'Figs. 1 to 8, inclusive, 10 and 11 of the drawings, there are illustrated the elements of the line circuits 2|, 3|, and terminating the lines 2|, 20, 3| and 30, respectively, the elements of the finder-connector link 300, and the elements of the distributor and common equipment 89L lustrated those portions of the ringing, tone and timing apparatus understanding of the operation of the system. The line circuits individually terminating the subscriber and trunk lines are of more or less conventional arrangement. the line circuit 20' terminating the subscriber line 20, comprises a line relay RI25, a cut-off relay RIM, and a line lock-out relay RI I5 connected and arranged to operate in the usual manner. The corresponding relays of the line circuit 30' terminating the subscriber line 30 are indicated at Rl55, RIM, and RI45, respectively.

The line circuits individually terminating the respective trunk lines are identical in character and circuit arrangement. More particularly, the line circuit 2| terminating the inter-oifice trunk line 2| comprises a line relay RI III, a cut-oif relay Rl05, and a line l0ck-out relay RIM. The corresponding relays of the line circuit 3| terminating the inter-oflice trunk line 3| are indicated at RIM], Rl and RI30.

Each of the finder switches is of the fully directive all relay type, group and unit relays being provided for performing the line selecting functions. The lines terminating at each finder switch are arranged in groups of ten lines and the lines of each group terminate at the contact More particularly,-

There are also diagrammatically il- 890 which are essential to an springs of one group R000 and one subgroup or gang relay. More partieularly, the finder switch 200 comprises ten group or gang relays corresponding to and including the two relays R210 and R000 individually having contact springs for terminating the conductors of ten lines. While the group relays may he of any'desired commercial type having the required number of contact springs, preferably these relays are of the improved form disclosed and claimed in the copendlng application Serial No. 109,813, Herbert F. Obergfell, filed November 9, 1936. The lines of each group are divided into two equal mibgroups respectively comprising the odd numbered lines and the even numbered lines, and, through the provision of a subgroup relay in each finder switch, a group of five unit relays is sufilcient to permit the selection of any desired one of a selected group of ten lines. Thus, the finder switch 200 comprises a subgroup relay R225, and five unit relays R200, R200, R2 I0, R2" and R220, each of which unit relays is operative to select either of two lines in a selected group of ten lines depending upon the operated or noncperated condition of the subgroup relay R220. The finder switch 200 also includes a pair of switching or control relays R200 and R200 which are arranged to be controlled by way of the common equipment I illustrated in Fig. 6, and are operative to initiate the operation of the finder switch to seize a calling line.

The common equipment "I shown in Fig. 6

includes a plurality of first auxiliary relays which are arranged to be energized over start circuits controlled by the line circuitsassociated with the I respective lines terminating at the exchange l0.

These relays are selectively operative in response to the selective completion of the start circuits and individually function to condition for operation a particular grouprelay embodied in the finder switch of an assigned link. hlore particularly, ten first auxiliary relays including the three relays R000, R0l0 and R020 are provided, which individually correspond to the gang relays embodied in the finder switch of each link. A group of five second auxiliary relays R000, R000, R000,

R000 are similarly provided which individually correspond to the unit relays embodied in the finder switch of each um: and are operativeto condition the corresponding unit relays 'in the finder switch of an link for op-.

eration. 'Ilie energization of the subgroup relay in the finder switch of an-assigned link is dependent upon the operated or non-operated condition of a third ahxiliaryrelay R000 provided in the common equipment, this latter relay also beingarranged to. be energi'ledover those of thestartcircults which are adapted to be coinpleted in the line circuits terminating the lines included in predetermined ones of .the line subgroups. the arrangement or the appar'atus is such that when a calling condition is created on .one of the hues terminating at the exchange, start circuits are completed by the line relay associated with the calling linefor causing the operation of the-one of the first auxiliary relays R000, R0l0, etc., which corresponds to the group or lines including the calling line and for energizing the one of thesecond auxiliary e ays R000, R000, etc., which is operative to select the particular calling line. If the calling line is in of its particular group the third 0118111017 completed start circuits, but if the calling line is in the other subgroup the third auxiliary relay mflisenergildmdoperlteltoouidiflonthc device operative in response relay R000 is not energized over the subgroup relay embodied in the finder switch of the selected link for operation. In order to give the finder switch of any assigned link ample time to seize the calling line to which it is assigned and to connect the line through to the connector switch, of the link before the common equipment 09| is reconditioned to respond to another call, a relay R000 is provided, which relay is operative immediately a link starts to seize a calling line and functions to open the operating circuits for all of the'auxillary relays in the common equipment 001.

The link allotter or distributor 000 is illustrated in Figs. 2 and 6 as comprising a group of ten allotter relays R200, R010, R000, etc., which individually correspond to the ten links corresponding to and including the link 000, two control relays R000 -and R010, a busy meter relay M000 and an overflow meter relay M000. Each of the allottcr relays corresponds to the allotter relay R200 and is operative to assign an idle one of the links to the use of the next calling line immediately after a previously assigned link seizes a calling line and to prevent the assignment of the corresponding link to the use of a calling line. The allotter relays are operated successively to assign the links to the use of calling lines; and after the tenth allotter relay of the group operates, the control relays R000 and- R010 are operated to recycle the allotter relays in order to provide for the reassignment of idle ones of the links and to operate the busy meter relay M000 if all of the links are busy at this time. If all of the links are busy, 2. call initiated at one of the telephone stations is not completed and the overfiowmeter relay M000 is caused to operate.

Alarm apparatus 000 associated withv a pinrality of fault detectors. individual to the links is provided in the exchange for the purpose of signaling a supervisory operator in one of the distant exchanges any one of the links. The alarm apparatus 000 comprises a start relay R000 operative in response to an urgent fault in the link, a start relay R000 operative in response to a non-urgent fault in the link, a local alarm or buzzer I, and a plurality of control relays R000, R000, R010 and R010. Each of the fault detectors comprises a device operative in response to the presence of a fault in the finder switch of the link, a device operative in response to the failure of the ring pick-up relay to operate in order to apply ringing current to a selected line, a device operative in response to the presence of a hot coil in certain of the relays associated with the link, and a to an undercharged condition of certain of the batteries associated with the link. Thefirst above operate to cause the operation of the start relay R000, while the last two devices mentioned above operate to'cause the operation of the start relay R000. The first-mentioned device includes a fuse link and is operative to cause operation of the allotter relay corresponding to the finder switch having a fault therein, thereby to prevent the allotter 000 from assigning the finder switch to the use of calling lines, in addition to causing in the event a fault appears in two devices mentioned operation of the start relay R000. Each of the start relays R000 and R000 is operative to initiate the operation ofthe alarm apparatus000 apply a characteristic tone current to the line I I for the purpose of informing a supervisory operator as to the nature of the fault.

The link circuit proper is illustrated in Figs. 3, 4, 7 and 8 of the drawings. The link line conductors CHM and Cl263 are arranged to be included in the operating circuit of the line relay R3l0. The line relay R3! 0 is of the usual impulse responsive type and in combination with the two additional relays R305 and R3l5 forms an impulse correcting network for repeating impulses transmitted thereto from a calling telephone station over an impulsing circuit to the slow-torelease control relay R800 and the impulse counting relays illustrated in Figs. 8 and .7, respectively. The link hold relay is indicated at R320. The relay R350 is the usual switching through relay which is energized only when the link is utilized in extending a connection by way of one of the inter-oflice trunk lines to one of the distant exchanges I or I86; The called party answer relay is indicated at R365, this relay being arranged to operate in the usual manner when a call is answered at a called substation, and functions to control the operation of a slave relay R330 which performs the battery reversing operation. For the purpose of preventing the link from being permanently tied up through seizure by a defective line or a line having a calling condition present thereon for an unreasonable time interval, there is provided a link release relay R300 and timing apparatus diagrammatically illustrated at 310. This timing apparatus may be of any desired construction which includes means'for applying ground pulses to the conductor C|213 at spaced intervals, which normally retains ground on the conductor C1212, and which removes ground potential from the conductor Cl212 at intervals spaced from the intervals during which ground potential is applied to C1213. If desired, this apparatus may comprise a commutator driven by a synchronous motor through a gear reduction box and including commutator segments suitably arranged to control the application of ground potential to the two leads Cl!" and Cl213 in the manner described.

The counting relay network illustrated in Figs. 7 and 8 includes ten impulse counting relays R to R180, inclusive, which relays. are seouentially operative in response to the impulses of each of a plurality of series of impulses transmitted to the connector switch 600 and function to control the selection of a desired called line and to control the selection of the code of the ringin current to be projected over the called line. Each of the counting relays is arranged to be locked energized in series with a corresponding one of the three control relays R8l0, R820 and R830 and to be deenergized in response to the operation of its succeeding counting relay in the manner described in detail hereinafter.

The ringing tone and timing equipment diagrammatically illustrated at 800 comprises ringing apparatus 850 and a code interrupter I000. This apparatus is arranged in. a conventional manner, the ringing apparatus 850 including a rin in generator from which ringing currentis derived, and the code interrupter apparatus 000 being connected alternately to impress pulsating battery potential and ground potential on each of the five interrupter leads Cl334 to Cl338, inclusive, for coded'intervals which are different .for each of the leads and comprise combinations of short and long pulsating battery impulses.

The switching relay R4|0 functions to connect the link line conductors C|36l and Cl363, incoming to the link circuit, by way of voice frequency coupling apparatus to the link line conductors C I28! and CI290, outgoing from the link circuit, to cause operation of a ring pick-up relay R430 and to initiate the operation of the code interrupter apparatus I000. The switching relay R4l0 is controlled by the control relays R8l0, R820 and R830, which latter relays are controlled by the counting relays R100, R1l0, etc., in their response to the impulses of a code selecting digit dialed at a calling telephone station. The counting relays also select one of the interrupter leads to apply coded ringing current to one side of the selected line, and control the operation of a generator reversing relay R440 which functions to select the side of the selected line to which the coded ringing current is to be applied. In order to terminate the ringing operation when a call is answered at a called telephone station there is provided a ring cut-off relay R450 which is operative to terminate a ringing operation by causing the deenergization,

of the ring pick-up relay R430.

The reverting call relay R400 cooperates 'with certain of the other relays to hold the connector switch 500 of the link 300 operated during the period when ringing current is being applied to a calling line on a reverting call. Also, the reverting call relay R400 operates when a predetermined prefix digit is dialed at a calling telephone station to control the operation of the prefix digid relay R340, which latter relay controls the prefix digit slave relay R460. These latter two relays function to condition the connector switch 500 to select a line in the first, eighth, ninth or tenth groups of ten lines, as previously explained. The busy relay R420 is provided for the purpose of causing busy tone current derived from the busy and dial tone apparatus 040 to be applied to a calling subscriber line when a selected called line is found busy.

In order to rearrange the circuit connections so that the counting relays are rendered effective to perform different duties during the successive series of impulses transmitted thereto, two transfer relays R410 and R480 are provided, in addition to the prefix digit relay R340 and the prefix digit slave relay R460. More particularly, the relays R340 and R460 are arranged to operate at the end of a first series of impulses corresponding to a predetermined prefix digit to connect the counting relays so that predetermined ones of the group relays in the connector switch of the link may be selected for energization; the relay R410 is arranged to operate at the end of the second series of impulses corresponding to a tens digit to condition the counting relays to select one of the unit relays in the connector switch of the,link for energization and to condition the subgroup relay in the connector switch for em ergization; and the relay R480 is operative at the end of the third series of impulses corresponding to a units digit to condition the counting relays to select the particular code of the ringing current to be applied to the selected called subscriber line.

The connector'switch 500 of the link 300, including the apparatus for preassigning idle ones of the interoflice and P. B. X trunk lines to be selected, is illustrated in Figs. 5 and 11. The connector switch per se is similar to the finder switch in that ten group or gang relays each terminating the conductors of ten lines, five unit one of the lines returns busy tone over relays, and a subgroup relay are provided for performing the line selecting functions. Specifically, the connector switch illustrated comprises ten gang relays corresponding to and including the two relays R510 and.R580 illustrated, five unit relays R520, R530, R540, R550 and R580, and a subgroup relay R500. Here again, the lines terminating at. the contact springs'oi each group relay are divided into two subgroups and each unit relay is operative to select either of two lines, individually included indifferent subgroups, depending upon the operated or non operated condition of the subgroup relay R500. Preferably, each of. the group relays R510, R580, etc., like each of the group relays of the finder switch 200, is of the form disclosed and claimed in the copending application, Serial No. 109,813, Herbert F. Obergiell, filed November 9, 1936.

The apparatus for preassigning idle ones of the inter-oflice'trunk lines in the ten lines is common to all of the links and includes a group of trunk select relays RI I 00\, RI I I0 and RI I20, which individually correspond to the first, second and third inter oflice trunk lines terminating at the contact springs of .the second group relay R510, and a group of control relays RI I80, RI I82 and RI I84, which individually correspond' to the inter-office trunks numbered from one to three in the second group of ten lines. As pointed out in greater detail hereinafter,'the two groups of relays cooperate in a manner such that an idle inter-ofllce trunk line in the second ten line group is preselected and ready for the use of any one of the links so long as any of the trunk lines in this group is idle, and when all of the trunk circuit apparatus of a link attempting to select the loop extending to the calling subscriber.

The arrangement and operation of the apparatus for preassigning idle ones of the interoflice trunk lines in the third group of ten lines are substantially the same as that of the apparatus for preassigning idle ones of the interofiice trunk lines in the second group of ten lines, as described above. This apparatus comprises a corresponding group of trunk selecting relays RII30 and RII40, and a corresponding group of control relays RI I88 and RI I88.

The arrangement and operation of-the apparatus for preassigning idle ones of the P. B. X

trunk lines in the tenth group of ten lines are similar to that of the apparatus for preassigning idle inter-oillce trunk lines described above.

This apparatuscomprises a group of trunk selecting relays RII50, RI I and RI I80 and a group of control relays RII80 and RII88 corresponding to the relays RI I50 and RI I 80. Also, apparatus (not shown) substantially the same as that described for preassigning idle ones of the P. .B. X trunk lines: in the tenth group of ten lines is provided for preassigning idle ones of the P. B. x trunklines in'the ninth group of ten lines.

Operation of the finder switch to extend a call initiated at. a telephone station connected to an odd-numbered line to an idle link A call is initiated at a telephone station connected to an odd numbered line by removing the receiver of the telephone instrument from its associated switch hook, thereby completing a circuit between the telephone station and the line relay individual to the odd numbered line. For example, a call initiated at the telephone A, the call is extended second group of lines become busy the link.

. cuit of the. assigned link 300.

2| is connected to the link 800, the line relay station A is-extended to the finder switch, I82 in the automatic exchange I and from the latter to the selector switch I83 therein. Upon dialing the proper digit at the telephone station from the selector switch I83 through the two-way repeater181 to the odd numbered inter-ofllce trunk line 2I, whereupon the ,line relay RI I0 individual to the line 2| is operated. The operating circuit of the line relay RII'0 extends from ground at RIIO by way of the upper winding of RIIO, RAI08, the conductor CI200 of the line 2I, the-repeater I81, the selector switch I83, the finder switch I82, the telephone instrument at the telephone station A, the finder switch I82, the selector switch I83, the repeater I81, the conductor CI20I of the line 2I,.RAI01 and the lower winding of 'RI I0 to battery. Assuming that the link illustrated is the link assigned use of the calling line, the line relay RIIO, upon operating, completes at RAII2 an operating circuit for the auxiliary group relay R800, this circuit extending from ground at RAII2 by way of RAI02, CI2I2, the winding of R800, RA809, RA882, RA621, etc., RA8I1, RA801 and the resistor 883 to battery. The line relay RI I0 also completes at RAII3 an operating circuit for the auxiliary unit relay R835, this circuit extending from ground at RA83I by way of CI2I8, RAII3, RAI03, CI2I4, RA805, CI288, the windby the allotter to the ing of R835, RA539, RAGBI, RA658,RA853,RA848,

RA643, RA838 and the resistor 884 to battery.

Upon operating, the relay R800 completes at RA808 an obvious holding circuit for itself and prepares at RA808 gang relay R210 in RA242 the operating circuit of the gang relay R210 and completes at RA248 the operating circuit of the unit relay R200, the operating circuit of the gang relay R210 extending from ground at RA805 by way of CI235, RA242, CI22I and the winding of R210 to battery, and the operating circuit of the unit relay R200 extending from ground at RA838 by way of CI238, RA248, CI250 and the winding of R200 to battery. The relay R240 also completes at RA25I a circuit for energizing the relay R880, this circuit extending from ground at R880 by way of the winding of R880, CI245, RA25I, CI258, the link conductorCl283 of the link 300, RA355, RA335 and the upper winding of the line relay R3I0 to battery. Upon operating, the relay R880 interrupts at RA882 a point in the operating circuits of the auxiliary group relays R800, R8I0, etc., and interrupts at RA88I a point in the operating circuits of the auxiliary unit relays R835, R840, etc., thereby busying the allotter 800 so that it is non-responsive to other calls.

The gang relay R210 operates to close its contact springs connected to the lines numbered from 20 to 29 and the unit relay R200 operates to connect the calling line 2-I to the link cir- When the line R3") is operated, this circuit extending from ground at RAM 2 by way of the link conductor CI282, RA352,'the link conductor CI26I, RA226, CI253, RA202, the contact springs of the gang relay R210, the conductor C|200 of the line 2|, the repeater I81, the selector switch I83, the finder switch I82, the telephone instrument at the telephone station A, the finder switch I62, the selector switch I83, the repeater I81, the conductor C.|20| of the line 2|, the contact springs of the gang relay R210, RA203, CI255, RA221, the link conductor CI263, RA355, RA335 and the upper winding of R3I0 to battery.

Upon operating, the line relay R3I0 completes at RA3|| a circuit for operating the link impulsing relay R305, this circuit extending from ground at RA323 by way of RA3II, and the winding of R305 to battery; interrupts at RA3I2 a point in the circuit extending from battery by way of the upper winding of R3I0, RA335, the resistor 3|0' and RA3|2 to the link control conductor C|264; and prepares at RA3I2 a point in the circuit for applying ground to the control conductor C 264.

Upon operating, the link impulsing relay R305 completes at RA309 an obvious circuit for operating the hold relay R320, which is of the slow- -to-release type, and an obvious circuit for applying ground to the control conductor CI264, thereby to mark the link 300 as busy in the allotter. When the control conductor CI264 is grounded, the lock-out relay RIM and the cut-off relay Rl05, individual to the line 2|, are operated, the circuit for energizing these relays extending from the grounded control conductor CI264 by way of RA228, CI251,'RA204, the contact springs of the gang relay R210, the control conductor CI202 of the line 2 I, the winding of R|05 and the winding of RI to battery. Upon operating, the cut-off relay RI interrupts at RAI06 and RA|01 the operating circuit of the line relay RI I0. The line relay RI I0 then restores and interrupts at RAI I2 the holding circuit of the relay R600 and interrupts at RAI I3 the holding circuit of the relay R635, and the latter relays restore. The lockout relay R|00 operates and interrupts at RAI02 a further point in the holding circuit of the relay R600 and interrupts at RAI03 a further point in the holding circuit of the relay R635. The presence of ground potential on the control conductor CI202 of the calling line serves to busy this line in the other automatic switches having access thereto.

Upon operating, the hold relay R320 completes at RA322 a holding circuit for itself, this circuit extending from ground at RA322 by way of RA3| 6 and the winding of R320 to battery; applies at RA323 multiple ground to the control conductor CI2-64 in order to retain the cut-off relay RI 05 and the lock-out relay R|00 individual to theline 2| operated during impulsing periods; and completes at RA32| holding circuits for the operated gang relay R210 and 'the operated finder unit relay R200. The holding circuit of the operated gang relay R210 extends from ground at RA304 by way of 'RA32I, CI25I, the contact springs of R210 and the winding of R210 to battery, while the holding circuit of the operated unit relay R200 extends from ground at RA304 by way of RA32I, CIL5I, RA20I and the winding of R200 to battery.

The hold relay R320 also completes at RA325 a circuit for operating the start relay of the dial ,and busy tone apparatus 840,- thls circuit extending from ground at RA325 by way of (H302,

RA4I9', the start lead C|3I4 and they winding of the start relay, not shown, in the dial and busy tone apparatus 840 to battery. The dial and busy tone apparatus 840 then operates to apply dial tone to the link 300, this circuit extending from pulsating battery in the dial and busy tone apparatus 840 by way of the dial tone conductor CI346, RA414, RA462, RA424, RA4I4, the link conductor C|29|, the condenser C|29I and RA355 to the link conductor CI263, through the telephone instrument at the telephone station A connected to the link conductors CI263 and C|26| by way of the finder switch 200, the line 2|, the repeater I81, the selector switch I83 and the finder switch I82, and from the link conductor C|26I by way of RA352, the link conductor CI282 and RA4I2 to ground. The party initiating the call at the telephone station A then receives dial tone indicating that a link has been seized and that he may operate the dialing mechanism associated with the telephone instrument to extend the call from the link to the called line.

In a similar manner, when calls are initiated at telephone stations connected to the odd-numbered lines 23, 25, 21 and 29, respectively, the relay R600 and one of the relays R640, R645, R650 and R655, respectively, are operated in the auxiliary or common equipment. The relay R600 operates the gang relay R210, and the relays R640, R645, R650 and R655 operate the unit relays R205, R2I0, R2|5 and R220, respectively, in the finder switch 200 to connect the lines 23, 25, 21 and 29, respectively, to the link 300.

Similarly, when calls are initiated at telephone stations connected to the odd-numbered lines 3|, 33, 35, 31 and 39, respectively, the relay operates the gang relay R260 and the relays R635,

R640, R645, R650 and R655 operate the unit -relays R200, R205,'R2|0, R2|5 and R220, re-

spectively, in the finder switch 200, to connect the lines 3|, 33, 35, 31 and 39, respectively, to the link 300.

Operation of the finder switch to extend a call initiated at a telephone station connected to an even-numbered line to an idle link A call is initiated at a telephone station connected to an even-numbered line by removing the receiver of the telephone instrument from its associated switch hook, thereby completing a circuit between the telephone station and the line relay individual to the even-numbered line. For example, when a call is initiated at the telephone station IB connected to the line 20, the line relay RI25, individual to the line 20, is operated, the operating circuit of the line relay RI25 extending from ground at R|25 by way of the upper winding of RI 25, RA|2I, the conductor C|203 of the line 20, the telephone instrument at the telephone station IB, the conductor CI204 of the line 20, RA|22 and the lower winding of R|25 to battery. Upon operating, the line relay RI 25 completes at RA|21 an operating circuit for the relay R600 in the common equipment, this circuit extending from ground at RA|21 by way Upon operating, the relay R600 completes at RA606 an obvious holding circuit for itself, and completes at RA60I the series operating circuit of the relays R630 and R655, this circuit extending from ground at R630 by way of the upper winding of R630, CI2I1, RAI28, RAII6, CI2I6, RA60I, C1265, the winding of R655, RA659', RA66I, RA656, RA653, RA646, RA643, RA638 and the resistor 664 to battery. Also, the relay R600 prepares at RA606 the circuit for energizing the gang relay R210.

7 Although the relays R630 and R655 are energized in series, the relay R655 does not operate at this time due to the relatively high resistance of the upper winding of the relay R630 connected in series therewith. However, the relay R630 operates and prepares at RA63Iv a circuit for energizing the group unit.or subgroup relay R225 in the iinder switch 200, and connects its relatively low resistance lower winding in parallel with its upper winding to cause the relay R655 to be operated in series with the relay R630.

I Upon operating, the relay R655 completes at RA659 an obvious holding circuit for itself, completes at RA651 a circuit for energizing the control-relays R230 and R240 in parallel and pre-' pares at RA656 a circuit for energizing the unit relay R220 in the finder switch 200. The operatrelays;

ing circuit of the relays R230 and R240 extends from ground at RA651 by way of CI241, RA262,

CI249' and the winding of R230 and R240 in parallel to battery.

Upon operating,the relay R240 completes at RA242 the operating at RA250 the operating circuit of the group unit relay R225, and completes at RA249 the operating circuit of the unit relay R220; the operating circuit of the gang relay R210 extending from ground at RA606 by way of CI235, RA242, CHM and the winding of R210 to battery; the operating circuit of the group unit relay R225 extending from ground at RA63I by way of CI244, RA'250,'CI255 and the winding of R225 to battery; and the operating circuit 01' the unit relay R220 extending from ground at RA656 by way 0! C I343, RA249, CI254 and the winding of R220to battery. The relay R240 also completes at RA25I a circuit for energizing R560, this circuit extending from ground at R660, byway of the winding of R660, CI245, RA25I, CI256, the link conductor CI263 of .the link 300, RA355,

'RA335, and the upper winding of the line relay R3I0 to battery. Upon operating, the relay R660 interrupts at RA662 a point in the operating circuits of R600, R6I0, etc., and interrupts at RA66I a point in the series operating circuit of R630 and one of the relays R635, R640, etc., thereby to busy the allotter 600 to other calls.

The gang relay R210 operates to close its contact springs to connect the. lines between'20 and 29 through to the armature springs. of the unit the groupunit relay R225 operates to disconnect its armatures RA226, RA221, RA226, RA229, from the conductor CI253, CI255, CI251, CI 259, respectively, and to connect these armatures .to the conductors CI254, C I256, CI256 and CI260, respectively; and the unit relay R220 operates to connect the line 20 to the link circuit of the link 300. when the line 20' is connected through. to the link circuit, the line relay' R3I0 is operated, this circuit extending from ground ,at RA4I2 by way of the link conductor CI202,

RA352, the link conductor CI26I, RA226, CI254, RA222', the contact springs of the gang relay R210, the conductor CI203 of the line 20, the

telephone instrument at the telephone station IB, the conductor CI204 of the line 20, the concircuit of the gang relay 'The party initiating the call tact springs of the gang relay R210, RA223', CI256, RA221, the link conductor CI263, RA355, RA335 and the upper winding of R3I0 to battery.

Upon operating, the line relay R3I0 completes at RA3I I the above-traced circuit for operating the link impulsing relay R305, interrupts at RA3I2 a point in the priming circuit for R3l0, and prepares at RA3I2 a point in the path for applying ground to the control conductor CI264.

Upon operating, the link impulsing relay R305 completes at RA303 an obvious circuit for energizing the hold .relay R320 and for applying ground to the control conductor CI 264, thereby to mark the link 300 as busy in the allotter and to mark the calling line as'busy. when the control conductor CI264 is grounded, the lock-out relay RI I5 and the cut-oil. relay RI20, individual to the circuit of the relay R600 and interrupts at RAI28' the series holding circuit of the relays R630 and R655, causing the latter relays to restore. The lock-out relay RII5 operates and interrupts at RAI I1 a further point in the holding circuit of the relay R600 and interrupts at RAI I8 a further point inthe series holding circuit of the relays R630 and R655.

Upon operating, the hold relay R320 completes at RA322 a holding circuit for itself, completes at RA323 a path for applying multiple ground to the control conductor CI 264 in order to retain the cut-ofl relay RI20 and the lock-out relay RI l5, individual to the line 20, operated during impulsing periods, and completes at RA32I holding circuits for the operated gang relay R210, the operv ated group unit relay R225 and the operated unit relay R220 in the finder switch 200. The holding circuitof the operated gang relay R210 extends from ground at RA304 by way of RA32I, C I25I, the contact springs of R210 and the winding of R210 to battery. The holding circuit 'of the operated group unit relay R225 extends from thegrounded conductor CI25I by way 'of RA229' and the winding of R225 to battery, while the holding circuit of the operatedunit relay R220 extends from the grounded conductor CI25I by way of RA22I and thewinding of R220 to battery.

The hold relay R320 also completes at RA325 a circuit for energizing the start relay, not shown, of the. dial and busy tone apparatus 040, thereby to initiate the operation of this apparatus to return dial toneto the telephone instrument at the telephone station IB as previously explained. at the telephone station IB upon receiving dial tone is informed that a link has been seized andthat he may operate the dialing mechanism associated with the telephone instrument to extend the call from the link to the called line.

In a similar manner, when calls are initiated at telephone stations connected to the even-numbered iries 22, 24, 26 and 26, respectively, relay R600, the relay R630 and one of the relays R635, R640, R645 and R650, respectively, are operated in the common equipment. The relay R600, causes the operation or the, gang relay R210; the relay R630 'causes the operation of the