US2005844A - Telephone system - Google Patents

Description

June 25, 1935. F. NEWFORTH, JR 2,005,844

v TELEPHONESYSTEM Filed April 17, 19:54

- ZINI/ENTORI ENEWFORTHgJR ATTORNEY Patented June 25, 1935 TELEPHONE SYSTEM Frank Newforth, Jr., TempleCity, Calif., .assignor to American Telephone and Telegraph Company, a corporation of New York Application April 17, 1934, Serial No; 721,041

Claims.

This invention relates to telephone systems and particularly to systems of the class using automatic switching apparatus for establishing connections.

The objects of the invention are to more accurately identify the condition of a subscribers line during the interval in which a' switch, such as a finder or a line switch, is in the act of seizing or extending the line; to avoid the necessity of rendering a line busy merely because the subscribers receiver is off the switchhook; to reduce the number of calls that fail because the called subscriber delays in hanging up. his receiver following a previous call; to enable all switches and apparatus to be released immediately by the calling subscriber; and to otherwise improve systems of this character.

It has been the practice heretofore in systems employing switches of the step-by-step type to release all switches except the final or connector switch when the calling subscriber hangs up his receiver and to hold the connector switch until the called party retires. It has also been proposed heretofore to place the release of all switches, including the connector switch, under the control of the calling subscriber and to provide special means to prevent the called line from seizing the central office equipment in case the called party delays hanging up his receiver.

According to the present invention advantages are secured over these prior systems by allowing the calling subscriber to release all of the switches immediately and permitting the called subscribers line to be seized by a finder switch in the central office in case he does not replace his receiver at once.

A feature of the invention is an arrangement in which the line of a subscriber, whose receiver is off the switchhook, as would be the case with a called party who has delayed replacing his receiver following conversation, is characterized in the multiple terminals of the connector switches as neither busy nor idle during the inter val that the line is being hunted by a finder switch. As soon as the finder reaches the terminals of the line, it is then identified as a busy line in the usual manner. Should, therefore, a connector switch seize the subscribers line during the time the receiver is oil? the hook, and before it has been seized by a finder switch, it will not appear as a busy line and, accordingly, no busy tone will be returned to the calling subscriber. Since the line does not appear to be idle, the connector switch will not apply ringing current thereto in the usual way but will merely wait on the terminals of the line. If the subscriber, whose line has been seized in this manner, hangs up his receiver before the calling party abandons the call, the connector will then proceed to apply ringing current and will thus call the subscriber back to his telephone.

Another feature of the invention is an arrangement in a system of the character above described in which all switches involved in an established .connection are released immediately that the calling subscriber replaces his receiver.

:These and other features of the invention will be more fully described in the following specification, taken in connection with the accompanying drawing.

The invention is illustrated in the'accompanying, drawing in which Figure 1 shows a subscribers station A, a line finder LF, a selector S in diagrammatical form, a connector switch C in detail another subscribers station B and its associated line circuit, an associated line finder LFI, and a selector SI, in diagrammatical form. Fig. 2 shows an alternative line circuit that may be used instead of the one shown within the broken lines in Fig. 1. I g

The subscribers stations A and B are provided with the usual subscribers set with a dial for controlling the establishment of desired connections. The line-finder switches LF and LFI are of the well-known Strowger type and may be similar to that disclosed in Patent 1,711,682 issued May '7, 1929 to H. Hovland, the brushes 8 and 9 of line finders LF and LFI respectively corre sponding to one of the two sets of brushes shown in the Hovland patent. The selector switches S and SI are also of the well-known Strow'ger type and reference may be had to pages 53 to 61 inclusive of the 2nd edition of Automatic Telephony by Smith and Campbell for a detailed description of the operation of the circuits as sociated with these switches. ,Only such portions of the circuits of the line finders and selectors are shown as are required'for a clear and complete description of this invention, the omitted portions of these circuits being represented by broken lines. p v

Referring to the drawing, a description will nowbe made of a calloriginating at subscribers station A, over line 5, through line finderLF, selector S, connector C and over line 4 to a called subscribers station B. When the subscriber A has been connected to the connector C through line finder LF and selector S in the usual manner, a circuit is completed through the subscribers loop from ground through lower winding of relay I, upper back contact, of relay 3, tip terminal and tip brush of selector S, tip brush and terminal of line finder 'LF tip conductor of line 5, through subset at station A, ring conductor of line 5, ring terminal and brush of line finder LF, ring brush and terminal of selectors, lower back contact of relay 3 and through the upper winding of relay I to battery. Relay I operates in this circuit and closes an obvious circuit for operating relay 2. Relay 2 operated connects ground to the sleeve terminal and brush of selector S for holding said selector in an operated position and.

for guarding the connector C from being seized by other hunting selectors.

The connector C is now ready for the reception of the dialing impulseswhich when dialed, by the calling subscriber, cause the line relay I to alternately release and reoperate each time the subscribers loop is opened and closed at the dial. The release of relay I in response to the first impulse closes a circuit from ground atthe lower back contact of relay I, upper front contactof relay 2, normally closed contact of vertical off-normay springs VON, and through windings of relay 6. and vertical magnet I to battery- Relay 6 and the Vertical magnet will operate in this circuit,

and the vertical magnetadvances the brushes of this connector Cone step. Relay 2 due to its slow-to-release characteristics holds during the receipt of the remaining impulses of the impulse train.

As soon as the shaft of connector C is moved off-normal the vertical off-normal springs VON are actuated to open the aforementioned operating circuit for relay 6 and magnet I and to close an independent operatingcircuit for said relay and magnet through the front contact of relay 6. The reoperation of relay I releases, magnet I, but relay 6 due to its slow-to-release characteristics remains operated until all of the impulsesof the impulse train are received. Each successive release and reoperation of relay I causes the operation and release of magnet 1, thereby advancing thebrushes of the connector C step-by-step to the level through which the call may be extended toward the called station.

When all of the impulses, corresponding to the digit dialed, have been received, relay 6 and vertical stepping magnet I release. Relay 6 released closes a circuit for energizing rotary magnet I and relay II when relay I releases forthefirst impulse of the next series of dialing impulses. This circuit may be traced from ground at lower back contact of relay I, upper front contact of relay2, lower closed contacts of vertical off-normal springs VON, back contact of relay 6, right outer back contact of relay I2, thence in parallel; one path extending through the winding of relay II to battery; and the other extending through lower next to inner 'back contact of,relay I3 and'through rotary stepping magnet II] to battery. Relay II in operating closes a circuit; at itsright front contact, for maintaining an operating'circuit for itself and magnet I0 independently of the right outer back contact of relay I2. Relay II also connects the test relay I2 to the sleeve conductor I'I to prepare the connector for a busy test when the terminals of the called subscribers line have beenseized. The rotary magnet I0 operated rotates the shaft and brushes of connector 0 to thefirst set of terminals in the selected level. 'The reoperation of relay I releases magnet I0, but relay II is slow-to-release and is designed to remain operated until all of the impulses of the impulse .train are received.

Each successive release and reoperation of relay I causes the operation and release of magnet I0,

thereby advancing the brushes of the connector I C step-by-step to the terminals associated with the called subscribers line.

When-all of the impulses corresponding to the mentioned busy test of the called subscribers line. I on the sleeve terminal of this line. This results If the line is busy, a ground will be found in an operating circuit for test relay I2 from said ground, sleeve brush of connector C, sleeve conductor I'I, left front contact of relay II, lower next to outer back contact of relay I3 and through windingof relay I2 to battery. Relay I2 operated prepares a locking circuit for itself which is effective when relay II releases. This circuit is traceable from ground at lower outer front contact of relay 2, left front contact-of relay I2, left inner back contact of relay II, lower next to outer back contact of relay I3 and through the winding of relay I2 to battery. Relay I2 also opensthe operating circuit for the rotary magnet I0 and applies a busy tone from source I8 through the right inner front contact of relay I2 over the ring conductor to condenser 2|, and thence to the calling subscribers station.

If the called subscribers line is idle the sleeve terminal of the line will be ungrounded and, therefore, relay I2 will not operate. However, a circuit is completed as follows for the operation of relays I3 and I4, after the release of relay II. Battery through the cut-off relay I4 of the called line, back contact of. relay I6, sleeve terminal and brush of connector C, sleeve conductor I1, left outer back contact of relay II, lower winding of relay I3, left back contact of relay I2 to ground at the lower outer front contact of relay 2. The operation of relay I 4 opens the connection to battery and ground for the ring and tip conductors of line 4 respectively; and relay I 3'is sufliciently energized to close its upper inner front contacts,

thus closing'a circuit from battery through its upper winding to ground at the lower inner front contact of relay 2. The energization of the upper Winding of relay I3 causes the complete operation of this. relay, which thereby connects an obvious ground to the sleeve conductor I! to maintain the operation of. thecut-ofi relay I4 and to guard the sleeve from seizure by other connector switches. Relay I3 also applies ringing current to the'called subscribers line in a circuit traced from ground through ringing source I9, upper next to inner front contact of relay 13, lower winding and back contact of ringing trip relay 20, lower outer front contact of relay I3, ring brush and terminalfof connector C, ring conductor of subscribers line 4, through the'bell at substation B and back over the tip conductor of subscribers line 4, tip terminal and brush of connector C, upper outer front contact of relay I3 to ground at the upper outer back contactof relay 20.

When the called subscriber. removes thereceiver in response to the ringing signal, relay 20 is sufliciently energized to close its upper inner front contact, thus closing a circuit from battery through its upper winding to ground at the lower inner front contact of relay 2. The energization of the upper winding of relay 20 causes thecomplete operation of this relay and thereby opens the aforementioned ringing circuit. 'I'he operation ofrelay 20 also establishes a connection through its upper outer front contact and its lower front contact to battery and ground respectively for the tip and ring conductors through the windings of relay 3. Relay 3 operates through the called subscribers loopand reverses, at its lower and upper armatures and contacts, the connection from battery and ground through the windings of relay I to the calling line. Talking battery for the calling subscriber is supplied from battery and ground, through thewinding of relay I and talking battery for the called subscriber is supplied from battery and ground through the windings of relay 3. The talking circuit is-completed through condensers 2I.- Condenser 22, which is used to divert a small part of the ringing current to the calling subscriber, as an indication that the called subscriber is, being signalled, is short circuited uponthe operation of relay 20.

When the connection is released by the calling subscriber hanging up his receiver, relay I releases, thereby causing the release of relay 2. Relay 2 causes the release of all operated relays and causes the operation of the release magnet 23. This circuit may be traced from ground at the back contact of relay I, back contact of re lay 2, upper back'contact of. relay I3, through upper closed contacts of vertical off-normal springs VON and thence through the winding of release magnet 23 to battery. When relay 2 releases the ground is removed from the sleeve conductor of selector S thereby restoring the selector and line finder LP to normal. The operation of the release magnet 23 restores the connector C to normal thereby opening the circuit for the release magnet at the vertical off-normal contacts VON. When relay I3 released ground was removed from the sleeve conductor I'I, thereby releasing cut-ofi relay I4 which connects the line relay I 5 and auxiliary line relay I6 to the tip and ring conductors of the called subscribers line.

Let it be assumed that the subscriber at station B is tardy in replacing his receiver on the receiver-hook, and that a second call is extended to the terminals of line 4 by a connector such as C. When the cut-off relay I4 releases as aforementioned, a circuit is closed to operate relays I 5 and I6 which is traceable from ground through the left winding of relay I5, through winding of relay I6, right back contact of relay I4, tip conductor of line 4, through subset at station B, ring conductor of line 4, left back contact of relay I4 and'through the'right winding of relay I5 to battery; Relay I5 operatedconnects ground to the start lead 26 causing the line finder LFI to operate and hunt for the subscribers line 4 in the usual manner; and closes a circuit for operating the cut-off relay I4 when said line is found. Relay I6 in operating opens the sleeve circuit associated with the connector switch bank so that, until the line finder LFI finds the line, the line is neither identified'as a busy nor as an idle line in the connector switch bank due to the absence of ground and battery on said sleeve conductor. Accordingly aswitch, such as connector C, seizing the line during this interval will not reject it as a busy line and, on the other hand, will not attempt to apply ringing as it would to an idle line. The application of ringing current to the line by a connector during this period would cause premature tripping of the ringing relay thereby resulting in a failure to complete the call. Should the subscriber replace the receiver on the receiver hook before the aforementioned line finder LFI found the line, relays I5 and-I6 would-release. Relay I5 released opens the start lead 26 to the line finder LFI thereby restoring the line finderin the usual manner. Relay I6 released closes the sleeve circuit, associated with the connector switch bank, so that the connector 0, if not released by the new calling subscriber abandoning the call, will identify the line asidle and proceed to apply ringing current in-an aforementioned manner.

,If on the other hand the line finder LFI finds the line and extends said line to selector SI before the subscriber at station B replaces the receiver on the receiver hook, cut-off relay I4 will be operated in a circuit from ground on sleeve brush and terminal of line finder bank front contactof .relay I5 and through winding of relay I4 to battery. Relay I4 in operating releases relays I5 and I6 as aforementioned; relay I6 released, connects ground at the line finder sleevecon ductor to the sleeve'conductor associated with the. connector switch bank so that the connector C,.if not releasedby the new calling subscriber abandoning the call, and provided the slow-torelease relay II has not released to disconnect the test relay I2 from the sleeve conductor I1, will identify the line as busy and proceed to apply busy. tone to the calling line in an aforementioned manner. In case, however, the test relay I2 is already disconnected from the sleeve conductor IT by the release of relay II, the connector cannot function to identify the line until the receiver at the called station is replaced on the receiver hook, at which time the line relay (not shown) of selector SI will release, thereby releasing line finder LFI which causes the release of cut-off relay I4 in the usual manner. The removal of ground from the line finder sleeve, associated with the line, removes the aforementioned busy condition for the connector C and the latter (if the call has not been abandoned) idem-- tifies the line as idle and proceeds to apply ring-- ing current as aforementioned.

Let it be assumed now that the subscriber at station B originates a call to a station (not shown) which is completed throughline finder LFI selector SI and other switches (not shown). The removal of the receiver from the hook at station B causes relays I5 and I6 to operate and function as aforementioned. Let it be assumed further that while the line finder LFI is hunting for the terminals 24 of the subscribers line a subscriber at station A has initiated a call for station B and that the associated connector C has seized the terminals of this line. The sleeve conductor associated with the connector switch bank is open at this time so that the connector C cannot identify the line as busy or idle. However, when the line finder LFI finds the line and thereby causes the'operation of cut-off relay I4, relays I5 and I6 release as aforementioned. Relay 6] released connects ground to the sleeve conductor, associated with the connector switch bank, so that-the connector may now identify the line as busy, provided the test relay I2 is associated with the sleeve conductor II at this time. The connector, identifying the line as busy, applies the usual busy indication to the calling subscriber. However, if the test relay I2 has been disconnected from the sleeve conductor I'I, before relay I6 releases, the presence of ground potential on the sleeve conductor will finding the line, is effected by connecting the front contacts of relay l6to ground at terminals 21 so that the operation of relay I B connects ground to the sleeve circuit, associated with the connector switch bank, instead of opening said sleeve circuit as -aforementioned. A connector seizing'the line at this time identifies the line as busy and proceeds to transmit the usual busy indication to the calling subscriber, provided the line is a direct subscribers line and the connector, like the connector 0, is notlarrangedior private branch exchange trunk hunting. However, the line may be one ofra group of private branch exchange lines, and thelconnector may be arranged to hunt, in which case, finding the line busy, it steps to the next line in the group.

Fig. 2 shows an alternate line circuit arrangement, which provides all of the features of the line circuit just described, with the exception of the meansprovided in Fig. 1 for connecting ground to the connector bank sleeve conductor at terminals 21, during the line finder hunting period. By superimposing Fig. 2 onto Fig. 1 it is obvious that the circuit arrangements'of both figures are similar and that the only difference resides in a .means for combining the functions of relays I5 and [6, said means being relay 25.

Although the invention has been disclosed in connection with direct subscribers lines, it should be understood that it is applicable to other types of lines such as private branch exchange trunks.

What is claimed isi v 1. The combination in a telephone system of a conversational circuit, a terminal for said circuit arranged to assume one electrical condition when the circuit is idle and another electrical condition when the circuit is busy, means effective if said circuit is in a calling condition to remove the idle condition from said terminal so, that the terminal presents neither the idle nor the busy condition, switching means for extending said circuit, and means effective in response to the extension of said circuit for placing the busy condition on said terminal.

2. The combination in a telephone system 01' a telephone line, a terminal forsaid line arranged to assume one electrical condition when the line is idle and another electrical condition when theline is busy, means effective if the subscribers receiver is off the hook to remove the idle condition from said terminal so that the terminal presents neither the idle nor the busy condition, switching means for-extending said line, means effective in'response to theextension of said line for placing the busy condition on said terminal, and means responsive to the replacementof the subscribers receiver for -removing the busy condition and replacing the idlecondition on said terminal.

3. In a telephone system, aline finder switch, 7

a connector switch, a subscribers line, having a terminal in'said finder switch: and a terminal in said connector switch, means for placing an idle test potential on said connector terminal, means responsive to the removal of the subscribers receiver for starting said finder switch to find the line and for removing said idle potential from the connector terminal so that the line appears neither busy nor idle to the connector switch, and means responsive to the finder finding-said line for applying a busy potential to said connector terminal. a 4. In a telephone system, a subscribers line h vms t st ternnnal, a.. ir. u t f appl in a idle potential to said terminal, means fiective if the subscribers receiver is off the switchh'ook a busy potential to said terminal.

5. In a telephone system, a line having a tee terminal, a circuit for applying an idle potential to said terminal, means effective if the line is in a calling condition'for opening said circuit to remove said idlepotential from the test terminal, such that theline appears neither idle nor busy, means for seizing said line, means responsive to the seizureof said line for closing said circuit and for applying a -busy potential to 'said'terminal, and means for releasing said seizing means and for removingthe busy'potential from said terminal. v 1

6. Ina telephone system, a line finder switch and a connector switch,-a-subscribers line appearing in terminals in said'line-finder and in terminals in said connector, means for applying battery potential to the test terminal in the connector to identify the line as idle, means responsive to the removal of the subscribers receiver for removing said potential from the connector test terminal and for starting said finder to find the line, means controlled by said finder on seizing the line for applying a busy'ground potential to said connector test terminal, means controlled by the subscriber for releasing said finder to restore said idle battery potential to said connector test terminal, and means responsive to the seizure of said line by said connector for applying a busy ground potential to said test terminal.

7. In a telephone system,'a finder switch and a connector switch, a subscribers line appearing in terminals in said finder and in said connector, means for applyin'g an idle test potential to the test terminal of said line in the connector switch, means responsive to the removal 'of the subscribers receiver for removing said idle potential and for startingsaid finder to seize the line, means for operating-said connector switch to seize the'terminals of said line, means responsive to the subsequent seizure of said line by the finder for applying a busy potential to the test terminal in said connector switch, means controlled by the subscriber for releasing said finder to remove the busy potential'from said test terminal and for reapplying the idle potential thereto, and means in the connector switch responsive to the reapplication of said idle potential for signaling line bythe non-numerical switch for placing a busy condition on said test terminal, said testing means in, the connector being effective neither to send the busy; tone nor to apply ringing current in case the connectorseizes said line between the time said-:idle lpotential is removed and :theitime afiel- M;

said busy potenital is applied to said test terminal.

9. In a telephone system, lines, automatic switches including a connector switch for establishing .a connection between a calling line and a called line, said called line having terminals in said connector switch, means for applying an idle potential to the test terminal in said connector switch, means controlled by the calling party for efiecting the immediate release of all of said switches, means controlled by the called party in case he delays the release of his line for withholding the application of said idle potential to said test terminals, means for seizing said called line, and means responsive to the seizure of said line for applying a busy potential to said test terminal.

10. In a telephone system, subscribers lines, automatic switches including a connector switch for establishing a connection between a calling line and a called line, said called line having terminals in said connector switch, means for applying an idle potential to the test terminal in said connector switch, means controlled by the calling party for effecting the immediate release of all of said switches, means controlled by the called subscribers switchhook in case he delays the replacement of his receiver, whereby said called line will appear neither busy nor idle to a second connector switch subsequently seizing said called line, a non-numerical switch for seizing said called line in response to the closed condition thereof, means controlled by said non-numerical switch for placing a busy potential on the terminals of said line, means responsive to the replacement of, said called subscribers receiver for releasing the non-numerical switch and for re' placing said busy potential by an idle potential on the test terminals of said called line, and means responsive to the replacement of said idle test potential for causing said second connector switch to signal the called subscriber.

FRANK NEWFORTH, JR.

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