US2300618A - Branch exchange - Google Patents

Description

FIG.

NOV. 3, 1942. J. DAHL 2,300,618

BRANCH EXCHANGE Filed Au 14, 1941 2 Sheets-Sheet 1 n. s. .4. o t/v4 ran: POSITION TERM/IVA TING mulwr' TERMINATING mumr lNl/ENTOR J F DAHL A TTORNEV NOV. 3, 1942. J F D BRANCH EXCHANGE Filed Aug.. 14, 1941 2 Sheets-Sheet 2 new a kSuEu $.35 km m ATTORNEY Patented Nov. 3, 1942 UNHTED STATS BRANCH EXCHANGE Jack F. Dalil, Millburn, N. 3., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y; a corporation of New York Application August 14, 1941, Serial No. 406,792

120mm. (Cl. 179-27) This invention relates to telephone systems and has for its object to facilitate the handling of call overloads directed to individual subscribers.

The telephone service of certain subscribers,

such as ball clubs, is normally handled by a brjanch exchange having a small number of. trunks. On occasions, however, for example when the weather is uncertain, the number of incoming inquiry calls will not only monopolize these trunks, preventing outgoing calls, but, where the branch exchange is connected with a crossbar central ofiice, the unsuccessful calls may employ so much of the terminating equipment that other subscribers may also be made inaccessible.

To obviate this difiiculty, in accordance with the present invention a group of terminating trunks appearing in jacks at a central office operators position, is added to the group of branch exchange trunks and these trunks are normally made busy. When a period of traffic congestion occurs, the operator may be informed by the office alarms or by inquiries from subscribers and will then remove the busy condition from the lines appearing at her position.

In order to permit calls to be originated at the branch exchange, one or more of the regular two-way trunks are provided with means whereby they may be made busy to terminatingv calls. This means is made dependent on the removal of the busy condition from the extra terminating lines. to the terminating equipment also appear in jacks at the central ofiice operators position topermit the operator to obtain the information necessary to reply to the inquiry calls and also to permit the completion of calls other than inquiry calls.

In the crossbar system connections to and from the subscribers line aremade over the primary and secondary line switches and the line hold magnet of the primary switch may be operated by either the originating or terminating control equipment. Therefore to mark a line busy-to terminatingcalls only, the circuit over which the terminating control equipment operates the line hold magnet must be opened and ground connected thereto while the circuit over which the originating control equipment operates the line hold magnet must be maintained and must not be grounded.

If the subscriber on a line so markedoriginatesa toll call, however, the'toll operator, be- Iore completing the desired connection makes a The trunks which are marked busy number checking connection with the calling line. In making such a connection, the marker applies alternating current to the circuit of the line hold magnet which is normally returned over the previous connetcion. to cause the operation of a signal at the toll operators. position. Therefore inorder to permit toll calls'to be made over the branchexchange trunks which are removed from terminating service, the operation of the make-busy means inserts in the hold magnet operating circuit, means, comprising a grounded autotransformer and a condenser, which is non-conducting to the direct current by which the hold magnet might be operated but does conduct the alternating current employed in number checking,

These features of the invention will be more apparent from a consideration of the following description in connection with the drawings in which:

Fig. 1 shows the operators position at the central ofiice, and

Fig. 2 shows the branch exchange and a part of the terminating control equipment.

A crossbar telephone system of the type with which the circuits of the present disclosure are adapted to function i disclosed in U. S. Patent 2,232,371 to J. W. Dehn et 2.1., February 18, 1941, while a system showing number checking applied to a slightly different crossbar telephone system may be found in U. S. Patent 2,105,921 to F. A. Korn, January 18, 1938.

At the branch exchange operators position appear jacks 2&0, 201 and 202 in which terminate two-way trunks connecting the branch exchange with the equipment at the central oilice. The trunk circuits 203, 29c and 205 represent the equipment at the branch exchange individualto each trunk and since they do not enter into the present invention they have been merely indicated. As many such trunk circuits are provided as desirable for normal service.

The auxiliary line circuits 2% and 281 are in-- serted at the central ofiice in the trunks terminating in jacks 260 and 2G! in order to give access from the DSA operator to the branch exchange. Only a limited number of the branch exchange trunks would be so modified.

At the DEA operators position appear jacks. I00, Hll, Hi2 to which are connected termina ing trunks 33, HM and H35. Asmany of these terminating trunks and jacks are provided. as seems desirable, perhaps two or three times the number of two-way trunks normally serving the branch exchange.

Jacks I and I01 connect with the auxiliary line circuits 206 and 201. The cord circuit I08 has been shown schematically only and may be any cord circuit standard for such a position.

Referring briefly to the control circuits, as set forth in the Dehn et al. patent above mentioned, the wanted line mirnber is registered in the marker which identifies the group of twenty numbers including the wanted number and from that identification selects a number group connector which connects the test terminals of the twenty lines corresponding to the twenty numbers to the marker, In the marker, a relay is connected to each of the twenty lines to test it and then a circuit is closed under the control of the units register to operate a relay associated with the wanted line if that line is idle. In the case of a group of trunks this circuit may be extended to operate the relay associated with thefirst idle trunk of the group.

For example, in testing the trunks serving the branch exchange under consideration the twenty block relay 208 is operated and connects the test leads 209 to 2I5 of trunks constituting the trunk group to the marker. One of these leads extends over the back contacts of relays 2I3 and 2I1 to the winding of relay 2 I 8 and battery. Therefore, if trunk circuit 203 is busy, relay 2I8 is operated. After an interval a circuit is closed from ground over back contacts of relay 2I9 through the units register 220 to the armature of relay 2I8. If trunk 203 is idle and relay 2I8 is not operated the circuit extends to the winding of relay 2I6 and battery. Relay 2H5 in operating disconnects the test relay and prepares the direct current operating circuit for the hold magnet.

If trunk'2fl3 is busy the circuit is extended as shown in detail in the above-identified Dehn et al. patent to operate the relay corresponding to the first idle trunk in the group.

When a number checking connection is made relays 2I1 and 2I9 are operated and alternating current from source 22I is connected over front contacts of relay 2I9, through the units register 220, condenser 222, front contact of relay 2 I1 and back contact of relay 2I6 to the test conductor of the trunk and thence to the sleeve conductor of the connection outgoing to the toll operators position.

Conductor 209'and the test conductors asso ciated with the other unmodified trunks extend directly to the test terminals and the hold magnets of the corresponding trunks.

Conductors 2I2 to 2I5 and the testconductors of the other terminating trunks extend to armatures on relay H2. With relay H2 normal, ground is connected over the back contacts of relay H2 to the test conductors to mark these terminating trunks busy. At times of traffic congestion, key I09 is operated, closing an obvious circuit for relay H2. Relay H2 operates to extend these conductors to trunk circuits I03, I94, I05, etc.

Conductors 2H) and 2I I are connected to armatures of relays H4 and H3, respectively. With these relays unoperated the conductors are connected over back contacts of these relays and conductors H8 and H1 to the auxiliary line circuits 201 and 206. When key I09 has been operated to make the terminating trunks available, keys H0 and III may be operated, closing circuits for relays II 3 and H4, respectively. With relay H3'operated, test conductor 2H is connected to the mid-point of retardation coil I I5. One

terminal of coil H5 is connected to ground thereby marking the test conductor busy to the direct current test circuit of the marker. The other terminal of coil H5 is connected through condenser IIS and the lower front contact of relay H3 to conductor H1 leading to auxiliary line circuit 206. Relay H4 functions in a similar manner to insert coil H9 and condenser I20 between conductors 2I0 and H8. It will be seen that coils H5 and H9 act as autotransformers to transmit the alternating current used in number checking to the originating side of the circuit while preventing the passage of the direct current used in operating the line hold magnet.

The operation of the terminating trunk circuit will now be considered.

Assuming that trunk circuit I03 is the first idle one of the group, the marker tests the circuit over conductor 2I5, front contact of relay H2, conductor I23, inner lower back contact of relay I24, winding of relay I22 to battery. Therefore the test relay such as relay 2I8 does not operate and when, subsequently, ground is connected to conductor 2I5, relay I22 operates, extending this ground over its lower front contact to conductor I2l, over which the line hold magnet is operated. With the'switches operated ground from the incoming trunk'circuit holds both the hold magnet and relay I22 operated. Relay I22 connects coil I25 across the tip and ring of jack I00 to provide cord circuit supervision.

When the incoming trunk applies ringing current to the tip and ring conductors I26 and I21, relay I28 operates in a circuit extending from conductor 126 through the upper winding of relay I23, condenser I29, outer upper back contact of relay I24 to conductor I21. Relay I20 locks in a circuit from battery through its lower winding, inner upper contact of relay I22, outer lower back contact of relay I24 to ground at the outer lower contact of relay I28. At its inner lower contact relay I28 closes a circuit for relay I30. Relay I30 in operating opens the talking circuit and connects resistance I33 in parallel with coil I3I and resistance I32 to prepare a tripping circuit for the ringing current. Relay I30 also closes a circuit from battery over its lower front contact, irmer upper back contact of relay I24 to lamp I34 and ground.

When the operator inserts the plug of a cord at her position in jack I00, to which lamp I34 is individual, battery on the sleeve of the cord extendsover the sleeve of jack I00 to the winding of relay I 24 and ground. Relay I24 operates, extinguishes lamp I34, disconnects relay I22 from conductor I23 andconnects direct ground thereto. At its outer upper front contact relay I24 closes one break in the talking circuit and completes the tripping bridge prepared by relay I30. It disconnects relay I28 from conductor I 21, closes a discharge circuit for condenser I29 and opens the locking circuit for relay I28 which now releases, opening the circuit of relay I30, but relay I30 is slow to release to maintain the tripping bridge for a sufiicient time to operate the ringing cut-off relay at'the incoming trunk. When relay I30 releases, the talking circuit is closed through from the incoming trunk to the operators cord. Coil I3I and resistance I32 remain connected across the incoming tip and ring conductors to operate the supervisory relay of the incoming trunk.

When the operator withdraws her cord, relay I24 releases, restoring trunk I03to normal and opening the connection between conductors I20 and I2! to permit the incoming trunk circuit to restore.

.The auxiliary line circuit 203 will now be described. If the trunk has not been made busy to terminating calls, the test circuit from the marker extends as above described to conductor Ill and over the inner upper back contact of relay 230 to the winding of relay MI and battery. When the marker connects ground to conductor III'I relay 2 3'I operates, extending ground over-its inner upper front contact to conductor 232 to operate the line hold magnet 243. After the switches have operated, ground from the incoming trunk serves to lock relay 23I. With relay 23! operated tip and ring conductors 233 and 234 are connected over the outer front contacts of relay 2-3'I and the outer back contacts of relay 230 to conductors 235 and 236 leading to the P. B. X. trunk circuit 2G5. Relay 23I also connects battery through resistance 239 to conductor 240 to mark the trunk .busy at the DSA operators position. At the end of the call the release of the switches releases relay 23I and restores the circuit to normal.

On a call originated at the branch exchange, a bridge is closed across conductors 235 and 2.36, completing a circuit from ground at the outer upper back contact of relay 23.1, outer upper back contact of relay 230, conductor 2 35, through the bridge in trunk circuit 285, conductor 236, lower back contact of relay 2'30, inner upper'back contact of relay 23I to the winding of relay 231 and battery. Relay 23! operates, connecting resistance 238 between conductors 233 and 234 to simulate the removal of the receiver and to start the functioning of the originating control circuits. At its lower contact, relay 23'! connects relay 23Ito conductor 232 so that relay 23I operates when the connection has been extended to the originating sender. Relay 231 looks to conductor 232 and connects conductors 233 and 234 to conductors 225 and 236 over back contacts of relay 239 to permit the branch exchange operator to dial into the sender. The ground which operates and locks relay 213] extends over the inner upper back contact of relay 230 to conductor II! to mark the trunk busy to terminatingcalls.

If the DSA operator wishes to call the branch exchange or to extend a connection thereto, she tests the sleeves of jacks I06 and I01 in the usual manner. Assuming that she finds no busy battery on jack I66, when she inserts the plug of her cord in that jack, battery from the sleeve of the cord completes a circuit over the sleeve of jack I06, conductor 2%, lower back contact of relay 23-I to the winding of relay 230 and ground. Relay 230 in operating disconnects relay 23I from conductor Ill and connects ground to that conductor to mark the trunk busy to terminating calls. Relay 23!) connects the tip and ring conductors 235 and 236 from the trunk circuit 205 to conductors 2M and 242 leading to jack III! to establish the talking circuit.

The above operations take place as above described when the two-way trunk is not marked busy to terminatingcalls. It will be apparent that even with relay II4 operated, calls originated at the branch exchange or the operators position proceed without interference. For terminating calls, the test circuit from the marker finds ground through coil I I5, while the operating circuit of relay 23I is opened by the insertion of condenser Isl-6. In the case of a toll call outgoing from the branch exchange, relay 2'3I is held operground. Current induced in the upper winding flows through condenser H6, lower front contact of relay M3, conductor I I1, inner upper back con-' tact of relay 23B, inner upper front contact of relay 23I to conductor 232 and thence over the out- I o going connection back to the marker as described in the previously mentioned Korn patent.

What is claimed is: p p

1. In a telephone system, a group of trunks serving a single subscriber, 'said'gr'oup of trunks lb comprising aplurality of subgroups, each subgroup terminating at a different ofiice and means for normally marking one of said subgroups busy.

2. In a telephone system, a group of trunks serving a single subscriber, said group of trunks 20 comprising a subgroup of trunks appearing-at said subscribers branch exchange and 'a supplementary subgroup, an operators position at the central office, said supplementary subgroup of trunks appearing at said operators position,

ated over conductor 232. When the marker con- 7 means for normally marking said supplementary subgroup busy and means for removing said busy condition to permit incoming calls to be answered by said operator. I

3. In a telephone system, a group of trunks serving a single subscriber, said group of trunks comprising a subgroup of two-way trunks appearing at said subscribers branch exchange and a supplementary subgroup of terminating trunks appearing before an operator at the central office.

4. In a telephone system, a group of trunks serving a single subscriber, said group of trunks comprising a subgroup of two-way trunks appearing at said subscribers branch exchange and a supplementary subgroupof terminating trunk-s appearing before an operator at the central ofilce, means for normally marking said supplementary subgroup busy and means for removing said busy condition to permit incoming calls to be answered by said operator.

5. In a telephone system, a group of trunks serving a single subscriber, said group of trunks comprising a subgroup of two-way trunks appearing at said subscribers branch exchange and a supplementary subgroup of terminating trunks appearing before an operator at the central office, means for marking certain of said two way trunks busy to terminating calls and means to permit said operator to extend a call received over one of said supplementary trunks to one of said busy marked two-way trunks.

6, In a telephone system, a group of trunks serving a single subscriber, said group of trunks comprising a subgroup of two-way trunks appearing at said subscribers branch exchange and a supplementary subgroup of terminating trunks appearing before an operator at the central oilice, means for marking certain of said two-way trunks busy to terminating calls, operator controlled means for determining whether one of said two-way trunks is in use, and means to permit said operator to extend a call received over one of said supplementary trunks to said one of said busy marked two-way trunks.

'7. In a telephone system, a group of trunks serving a single subscriber, said group of trunks comprising a subgroup of two-way trunks apway trunks busyto terminating calls, said marl:- ing means being-efiectiveonly if the busy condition has been removed fromsaid supplementary trunks, and means to permit said operator to extendacall received over one ofsaid supplementary trunks to oneof said busy marked two.- way trunks. V v

8. In a telephone system, a subscriber's that;

test terminal for'said line, a switch for extending connections to and from said line, a magnet for operating said switch; aterminating,marker-for controlling said switch, means to connect said marker with said test terminal, direct current means in saidmarker to operate said magnet over said test terminal completing a connection to said line, alternating current means in said marker for number checking a connection from said ,line, and means associated with said test terminal to render said directcurrent means ineffective without disabling said alternating cur rent means.

9. In a-telephone system, a subscribers line, a test terminal for said line, a switchfor extending connections to and from said line, a magnet for operating saidswitch and connected with" 10. In a telephone system, a subscribers line,

a test terminal for said line, a switch for extending connections to and from said line, a magnet for operating said switch and connected wan said terminal, aterminating marker for controlling said switch, means to connect said marker with said test terminal, direct current means in said marker to operate said magnet over said test terminal in completing a connection to said line, alternating current means in said marker for number checking a connection from said line, and means to open the connection between said test terminal and said magnet and to insert therein agrounded autotransformer.

"IL-In a telephone system, a branch exchange trunk, a test terminal for said trunk, a switch for extending connections to and from said trunk, amagnet for operating said switch, a terminating marker for controlling said switch, means to connect said marker with said test terminal, direct current means in said marker to operate said magnet over said test terminal in completing a connection to said trunk, alternating current means in said marker for number checking a connection from said trunk, and means to adapt said trunk to make outgoing calls only, comprising means to open the connection between said test terminal and said magnet and insert therein a grounded circuit element conducting only alternating current.

12. In a telephone system, subscribers lines, test terminals for said lines, switches for extending connections to and from said lines, magnets for operating said switches, a terminating marker for controlling said switches, means to connect said marker with any one of said test terminals, direct current means in said marker to operate one of said magnets over said test terminal in completing a connection to the associated line, alternating current means in said marker for number checking a connection from said line,

and means associated with certain of said test terminals to render said direct current means ineiiective without disabling said alternating current means to permit the associated line to make outgoing calls only.

JACK F. DAHL.

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