Device for Establishing Conference Calls via at Least One Telephone Exchange Switching System

Telephone conferences in which several subscribers' telephones are connected via a common pair of wires or to a common connecting point by pairs of wires so that each telephone instrument may be in receipt of transmissions from all the others so as to form a multiparty teleconference connection are well known and many private telephone systems are arranged to be capable of adaptation so as to be able to set up and supervise such multiparty connections under control of the dialling or keysending of the subscribers or on the part of the operator either manually or through the automatic working of the private system in question.

However, through such conference arrangements relying on the control and supervisory arrangements of the private telephone system in question for the establishment and supervision of the teleconferencing connections their scope is commonly limited by the span of the private system so that such dial or key up conference connections can only be made to join subscribers on the same private exchange.

If arrangements are made to extend connections of the conference to subscribers on other exchanges then this is commonly performed through the intervention of the operator. Without the intervention of further distant operators such external connections have to be fanned out individually to each such external conferee from the conference bridge of the originating exchange. Many of these external conferees may be located at or close to the same distant exchange which will result in a multiplicity of paths being set up between the two exchange locations and carrying the same connection resulting in a high connecting charge for the conference, especially if the two exchange locations are far from each other and the connections are made over the public network. This will also result in excessive occupancy on exchange lines to the public network and/or excessive traffic on any privately and/or rented tie lines that are used in such multiple parallel paths.

The principle utility of multiparty conference connections is realised when they span conferee's widely separate locations. Restriction to the environs of the single exchange gives more of a convenience than a service since the accessible conferees are similarly located and least in need of this.

It is an object of the present invention to provide means whereby separate ancillary subscriber controlled conference equipments can be utilised in attachment with exchanges of any known type so as to be accessed through the exchange and controlled by the use of V.F. keypad telephones of the well known type, or dial telephones adapted to be able to send similar tones, so as to set multiparty telephone conference calls through the associated exchange and enable access to a wider network with full control over their collective holding and individual release from the common conference connection thus made and preferably with a separate talk path which can give individual secret access to each, all under the control of only two extra command signals beyond those necessary for the control of a normal two party telephone call.

The invention accordingly provides a device for use in establishing conference calls via at least one telephone exchange switching system, comprising a conference bridge for providing a two way speech path between any two or more ports thereof, first switching means for selectively connecting an inlet of said conference device to one of said conference ports or to any one of a plurality of outlets intended, in use, to be connected to corresponding lines of a telephone exchange switching system, second switching means for connecting any one or more of said outlets of the device to ports of said conference bridge, and control means responsive to respective incoming command signals received at said inlet for actuation of said first and second switching means, whereby a remote caller can firstly obtain a direct connection to a telephone exchange line connected at a selected outlet in order, by transmission of dialling or other call setting signals as required by said exchange, to establish a further switched connection to a called party, and then can establish a conference connection via an associated conference bridge between himself and that subscriber and any one or more similarly and successively connected called parties via further similar ports of said conference bridge.

Preferably the arrangement is such that the said command signals shall comprise not more than two more standard signal tones of a V.F. telephone keypad in addition to those corresponding to the diallable numbers. In this case the arrangement may conveniently be such that the said first switching means normally connects the said inlet of the device to said one port of the conference bridge, actuation of said first switching means to connect said inlet to a selected outlet being dependent upon the receipt by said control means of a first one of said additional two tone signals applied at said inlet, and actuation of said second switching means to connect a selected outlet to said conference bridge being dependent upon further actuation of said first switching means following the setting of a call from a said selected outlet by the transmission of call setting signals.

In order to enable the subscriber controlling the conference also to maintain individual control over the state of the lines of individual call parties in addition to the overall control provided by the supervisory equipment of the conference device the arrangement is preferably further such that with the said first switching means connecting said inlet to a selected outlet release of a call set from said selected outlet is dependent either upon clearing down of the line connected to said inlet or upon the receipt by said control means of the second one of said two additional signals. Thus a further control function is provided whilst still maintaining the requirement for only two additional V.F. signals as provided on the standard V.F. keypad.

It is a further, preferred object of the invention by means of this command simplicity and consequent ease of subscriber control and signalling to enable the subscriber controlled conference equipment to be used to access further similar equipments which may be remote whilst retaining the same full facilities and control to associate subscribers in the conference mode at any of the locations thus joined so that although there may be several accessed at each of the several subscriber controlled conference equipments there is not more than one switched or permanently tied transmission path between any of these equipments.

Accordingly in a further embodiment of the invention the arrangement is such that with said first switching means connecting said inlet to the said one port of the conference bridge, receipt by said control means of a predetermined signal other than the first one of said two additional signals is effective to inhibit further actuation of the said control means other than in response to receipt of unique diallable code signals replacing said first and second additional signals. In this manner ambiguity in signals transmitted to more than one device in accordance with the invention simultaneously may be avoided, since all devices other than that for which the said unique signals are intended may be rendered unresponsive. The fact that at the inlet to the conference bridge all V.F. signals other than the said first signal are redundant is inherent in the structure of the device, and advantage may be taken of this for utilising other coded signals to effect ancillary functions of the device whilst the first switching means is in this position. For example remote control of tape recorders, devices providing background music or prerecorded announcements, or the like, may all be operated by transmission of appropriate digitally coded signals. The device may further be adapted for conversion from the transmission of outwardly dialled signals suitable to any given exchange to signals to be received by a further conference device, in the same manner. Thus according to a further, preferred feature of the invention the said device may include a dial pulse generator for converting incoming V.F. tones received at said inlet into dial pulses for onward transmission as said call setting signals, the said control means being further arranged, when inhibited as specified above and when said first switching means connects said inlet to a selected outlet to inhibit operation of the V.F. to dial pulse converter upon receipt of the second one of said two additional signals so that received V.F. tones are transmitted onward as such and without mutilation by concurrent dial pulsing.

Thus the arrangement in accordance with the invention caters for a universal piece of conference equipment which can be connected in association with any exchange of commonly known type to provide this conference service for any subscriber accessible to the exchange either local or remote whilst allowing optimised trunking by requiring only a single switched transmission path between exchanges that are similarly equipped with such a conference attachment, irrespective of the number of conferees that are attached to the conference at each such exchange.

Further features, objects and advantages of the invention will become apparent from the following description taken in conjunction with the appended claims.

FIG. 1 shows a schematic block diagram of a subscriber controlled conference equipment in accordance with the invention and its connections to the exchange switching network,

FIG. 2 is a reduced symbolic diagram indicative of the arrangement of FIG. 1 to be subsequently used in the explanatory schematic block trunking diagram of FIG. 4,

FIG. 3 is an alternative symbolic diagram of FIG. 2,

FIG. 4 employs the reduced symbol of FIG. 2 to show a typical interconnection of several subscriber controlled conference equipments of the type indicated in FIG. 1 set up in tandem via successive telephone connections through the telephone network by V.F. keypad control signals from the originating telephone.

FIG. 5 shows the transmission plan of the conference interconnection established by the trunking interconnection of the several subscriber controlled conference equipments shown in FIG. 4.

FIGS. 6 and 7 comprise a more detailed circuit diagram of one embodiment of equipment as illustrated in FIG. 1, and

FIGS. 8 and 9 comprise a similar circuit diagram of a further embodiment of the invention.

Referring to FIG. 1, there is shown within the box 1 indicated in broken lines a general block schematic circuit arrangement of a subscriber controlled conference equipment in accordance with the invention, and also how this conference equipment is connected to the periphery of the exchange switch to which the conference equipment is associated, indicated by the box 2 shown in broken lines, by connections 4 and 5. The connection 4 represents the originating subscribers control port accessible to all telephone subscribers via the exchange 2 either directly from the local subscribers on that exchange or via the main switching network 6 which may be public or private or both if the subscribers are remote. This main switching network 6 is indicated on FIG. 1 by the chain lines confining this as an area of switching which need not be further specified. The connections 5 represent the outlet ports which access the wanted conferees directly via the local exchange 2 if they are located there or out via the normal external couplings 7 of the exchange 2 to the wanted subscribers via the main switching network 6 if they are remote. The conference equipment 1 is thus connected to the associated exchange 2 and thus to all subscribers via its switching actions and those it can evoke from the main switching network 6.

As shown in FIG. 1, the conference equipment includes in the box 1 an amplified conference bridge 10 providing a plurality of conference ports, a gain compensating amplifier 11 connected to the control port 4, a hybrid circuit 12 connected between the output of the amplifier 11 and a selector switch 8 and incorporating a pick-off point providing an output to a V.F. receiver 15, and a control circuit 16 which is responsive to outputs of the V.F. receiver 15 and controls actuation of the selector switch 8 and also of a further selector switch 9.

V.F. receiver 15 receives V.F. keypad control signals from the originating subscribers telephone via the gain compensated I/C port amplifier 11 and the hybrid pick-off circuit 12 and converts these signals to be suitable for use by the control circuit 16 which comprises the electronic logic functions necessary for the control of the conference from the originating subscribers keypad signals. The gain compensated I/C port amplifier 11 is provided to restore the transmission level at the input conference port 4, serving the originating subscriber, to a zero reference level. The operation of the amplifier 11 is described in more detail in my copending U.S.A. patent application No. 895,562 now abandoned and replaced by new Continuation-in-Part Application No. 91,687 filed Nov. 5, 1979, the disclosure of which is incorporated herein by reference, and thus will not be described in further detail here.

The selector switch 8 comprises a single inlet switch with single outlet paths connected on the one hand to contacts of the switch 9 and on the other directly to outlet ports 5. This switch under control of the circuit 16 in response to V.F. keypad signals from the originating telephone is able to access the lines serving all the oulet ports 5 from the amplified conference bridge 10 so as to be able to connect the speaking and dial paths circuitry which is associated with the orginating and controlling subscriber at the inlet conference port 4 out to any line of the exchange 2 in isolation. This enables the originating subscriber, after actuation of the switch 8, to dial through the conference equipment 1 and thus, by control of the switching functions of the exchange 2, to select a subscriber to be joined to the conference bridge 10. The switch 8 further provides a direct inlet to a port of the conference bridge 10 at the normal or "O" position so that the originating subscriber, having set up connections of conferees to the bridge 10 can then join himself to the corresponding inlet port of the conference bridge 10.

The switch 9 comprises a number of individual parallel switched paths which when set by the control circuit 16 can join the outlet ports 5 individually through to the amplified ports of the amplified conference bridge 10. Conversely the release of these paths by the control circuit can cause the conference lines to be isolated from the conference bridge 10 for reasons described below. The actuation of the switches 8 and 9 is determined by the control circuit 16 in a manner to be described below.

The operation of the control circuit 16 of FIG. 1 will now be described in further detail with reference to FIGS. 6 and 7 which illustrate the circuitry interconnecting the V.F. receiver 15, the dial pulse chip 14, the selector switch 8 and the selector switch 9 of FIG. 1.

The circuit diagrams of FIGS. 6 and 7 are drawn to read onto each other as a single diagram, if they are laid side by side, with FIG. 6 to the left. Together they show by way of example how a sequential stepping form of the switch 8 of FIG. 1 and the switch 9 of FIG. 1 can be provided through the use of a commonly available British Post Office relay of the reverse acting and so-called industrial type with only four change over contacts, so as to interact under control of a V.F. receiver and a memory toggle relay to make connections to the conference bridge 10. In the drawing, the respective contacts of each relay indicated by reference letters (for example A) are indicated by corresponding letters and numerals (A1, A2, etc.) and the contact positions shown correspond to those with the relay idle. The relays A to N and CHA with AL to NL and CH together comprise a sequential counter providing a sequential form of the selector switch 8 of FIG. 1. This counter is set to have relays CH and CHA operated when contacts RT are closed by the ringing tone detector of the circuit 21 in known manner when the circuit is seized and current is allowed to flow. The contact CHA1 is short circuited by break contacts A2 to N2 of the relays A to N in chain connection, causing relays CH and CHA to be operated when the earth is connected by contacts RT. Operation of relay CHA closes contact CHA1, providing a holding path for itself and relay CH, and closes contact CHA2 and CHA4 thus connecting the inlet port 4 to amplifier 25. Amplifier 25 in combination with amplifiers A to N form the conference bridge 10 indicated in FIG. 1, and thus upon initial seizure of the circuit 1, the inlet port is connected directly to an inlet of the conference bridge, corresponding to setting of switch 8 of FIG. 1 to the normal or "O" position.

The switch 9 of FIG. 1 is provided by the relays AH, BH . . . MH, NH, and the corresponding changeover contacts AH2, AH3 . . . NH2, NH3, which provide for connection of amplifiers A to N to the respective outlet ports 5.

The control circuit 16 is provided by relays CS, SS, and SD in conjunction with transistor T1 and diodes D7-D16, connected to the outlets of the V.F. receiver 15 indicated diagrammatically as a series of switches.

The operation of the circuit 1 in response to command signals transmitted from a V.F. sender and received by the V.F. receiver 15 will now be described. Assuming that an incoming caller, who is to act as conference chairman, has succeeded in obtaining a connection to the inlet port 4 and, through response of the relays CH and CHA has been connected to the conference bridge 10 with the switch 8 in the normal position, he must now proceed to connect himself directly to an outlet port 5 in order to dial a switched connection to a conferee. This is achieved by transmission of a V.F. signal by means of his "#" or gate button, which causes the V.F. receiver 15 to respond and to actuate relay SS. The closure of contact SS3 thus operates the relay A via contacts CH3 and AL1 and contact A1 prepares a path for relay AL to operate in series with relay A. When the earth is removed by the reopening of contact SS3 then relay AL operates in series with the relay A and contact AL1 releases the relays CH and CHA, contact AL2 and contact CH3 preparing a path for the relay B of the next stage of the counter. Release of the contacts CHA2 and CHA4 disconnects the originating subscriber or chairman from amplifier 25 and connects him instead via the dial pulse contact DP1, contact CS1 and contacts AL3 and AL4 to a corresponding outlet port 5. DON1 dial off normal contacts of the dial pulse chip 14 and the line circuit and ring detect function 21 serving the incoming port 4 and thus the chairman or originating subscribers line, provides a pick-up loop and dialling path shown as the speak and call setting bus 20 whereby the originating subscriber or chairman can establish telephone connections to any conference port that is accessed by this path under control of his V.F. keypad and the V.F. receiver 15 through the dial pulse chip 14 and out to whichever of the conference ports 5 is connected by the setting of the relay counter 8 relays AL to NL at contacts AL3, AL4 to NL3, NL4 connecting their associated conference ports through to the speak and dial call setting bus 20, where the chairman or originating subscriber is connected to set the connections and speak, as described for the relay counter 8 of FIG. 1 in the previous text. Thus the stepping of the switch 8 from the normal or "O" position to the next sequential position has the effect of separating the chairman or originating subscriber from the conference bridge to connect him to a port 5 and to subtend a pickup loop to the port 5 to seize an exchange line of the exchange 2 and receive dial tone which will be heard by the chairman connected there by contacts CHA4 and CHA2, as described.

The chairman now has the opportunity to dial out switching signals to the seized exchange line. In the illustrated embodiment it has been assumed that this requires dial pulse signals which are generated by the dial pulse chip 14 to actuate relays DP and DON and thus dial pulse contacts DP1 and DON1 in known manner, in response to signals on the digital outputs from V.F. receiver 15. However, if the exchange is a V.F. tone operated exchange, then the dial pulse chip 14 may be dispensed with, the originating V.F. tones generated at the chairman's telephone instrument being transmitted through the circuit 1 to effect direct control of switching, or possibly serving to actuate a V.F. repeater.

It should be noted at this stage that any transmission of digital signals by the chairman is effective to actuate relay SD via the corresponding digital output of V.F. receiver 15. Relay SD then holds via contacts SS2 and SD1 which provide a path to earth. This relay serves to provide a memory function to indicate that dialled digits have been transmitted during a call setting operation, for the purpose of initiating later control functions described below.

If the chairman has been unsuccessful in setting a call from the selected outlet port 5 and wishes to open the circuit of the pick up and dial loop subtended to the exchange line to cancel the call then he can do this by causing the operation of the relay CS which breaks the loop to the conference port at CS1 and this releases any connection that has been made to the exchange from the conference port outlet that has been coupled. The operation of the CS relay has been shown to be directly from the V.F. receiver 15 at the * or star output, and is thus effected by the chairman depressing the star button on his telephone instrument. Operation of relay CS also opens contact CS2 to release relay SD and thus to cancel the memory function provided thereby.

Assuming that the chairman connected to the outlet port 5 via relay contacts AL3, AL4 now wishes to actuate the selector switch to transfer from that port to the next available port provided in the sequence of the switch 8, then he operates the switch 8 by further actuation of his "gate" button which operates relay SS as described above. Simultaneously with stepping of the switch 8, the switch 9 must be actuated in dependence upon whether a called party at the outlet port 5 is to be connected to the conference bridge. For this purpose it is assumed that any connection of an exchange line to the port 5 following the transmission of dialled digits, and which has not been cancelled is a successful connection and is to be retained. As described above, this condition is indicated by actuation of the relay SD. The circuit action is as follows.

If the SD relay is operated at the time of operation of the SS relay then its locking path via SD1 is disconnected by the contact SS2 so that it would release rapidly, after the fashion of the miniature reverse acting type of industrial B.P.O. 4 changeover relay employed here, except for the conduction path provided through the transistor T1, which is rendered conductive by the base current provided by the conduction path through the contact SS1 and the contact SD2 to relay AH via the operated contact A3 of relay A. The relay AH operates via this path offered to the base of the transistor T1, the majority of the relay operating current flowing to earth via the low value resistor R1 which shunts the transistor base. On operation, the relay AH provides a holding path to earth via contacts AH1, A4 and RT thus shunting the base current path of the transistor T1 so that it is no longer held conducting and the relay SD releases due to the continued removal of its holding path by contact SS2. Contacts AH2, AH3 prepare a path from amplifier A to the respective outlet port 5. When the relay SD releases then earth is presented to relay B via the contact SS3 operated and the contact SD3 released, to operate relay B before release of the relay SS at the end of the "gate" button pressure. Operation of relay B prepares the path of relay BL for actuation when relay SS releases. Operation of relay BL operates contact BL1 to release relays A and AL, and contacts BL3, BL4 connect the chairman to the next outlet port 5 served by the switch 8. Release of relay AL completes the path from the respective port 5 to the amplifier A via contact AL3, AL4. Contact AL2 prepares a path for the next step of the counter sequence under similar control by SS3. Stepping of switch 8 and operation of switch 9 is thus completed.

If the relay SD was not operated and locked then the contact SD2 would not have been closed to provide a path for the operation of the relay AH of the switch 9 and so this relay would not have been given the opportunity of operating by the SS1 and SD2 contact path and since relay SD is already released when the relay SS operates, the SS3 and SD3 contact path will provide an immediate stepping earth for the next relay in the sequence of switch 8, as has already been described. This latter stepping action of the speak and dial switch counter 5 can be invoked merely by repeated operations of the "gate" button to operate relay SS and to step the relay counter which is the equivalent of the sequential form of the speak and dial switch 8 of FIG. 1, stepping it round to access its outlets to the conference ports 5 by contacts AL3, AL4 to NL3, NL4 so as to step over them, without keying call setting digits to them and thus without operating the SD relay and thus without causing their connection to the conference. This stepping action can be used to step over unwanted conference port outlets as the chairman sets the switch 8 back to the zero position where he is connected by the relay contacts CHA2 and CHA4 to the conference amplifier 25, and can thus join in conference with the conferees connected at conference ports 5 by the actions previously described. At any time during the conference the chairman can again invoke the sequential stepping action described for the relay counter to access free ports 5 for further call setting or to gain a secret confidential talk path to those conference ports on which a connection has been made and thereby also re-establishing the ability to cancel the connection by operating the relay CS to open the holding loop now again provided for the line, as in its original connection. Operation of relay CS also releases the appropriate relay AH to NH, whose holding action has been made dependent upon the contact CS3 by the operation of the contact A4 to N4 removing the direct holding earth of contact RT. If the chairman or originating subscriber wishes to use the conference port thus cleared, for a new call, then he can do so because by this action he will again set the relay SD which will ensure the reconnection of the conference port to the conference with the new connection by operation of the appropriate relay AH to NH when he steps away, as he did before. Alternatively he can use the free conference port to make an enquiry type call and cancel it when complete, thus releasing it and restoring the SD relay, so that this now vacant outlet is not connected to the conference when he steps the relay counter away from this outlet to access another outlet or to sequentially step his way back to re-access the conference bridge by again operating the CH and CHA relays in the normal position of the counter chain.

Thus it will be seen that the interaction between the relay counter and the line connecting relays in conjunction with the relay SD providing memory of the dialling history of the connections to the conference ports, is able to meet all the requirements of the switches 8 and 9 of FIG. 1 and the toggle memory in the control providing the single bit dialling history of the call to a conference outlet, upon which the control decision to connect the connection to the conference bus is based.

If desired, the relay counter circuit may be replaced by a relay access switch which is code marked to adopt its setting in response to digital outputs of the V.F. receiver so that a given conference port required can be accessed directly without the need for the sequence stepping actions described with reference to FIGS. 6 and 7. The "gate" signal would, however, still be necessary to prefix these digital setting signals, to avoid their being mistaken for call setting digits.

From the above description, it will be appreciated that the device in accordance with this embodiment of the invention provides the facility for any subscriber who is equipped with a telephone terminal equipped to send V.F. tones providing the standard minimum of 12 encoded signals, that is 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, * (star) and # (gate), to set up a local, star radiated conference connection using the switching functions of a conventional exchange as represented by the box 2.

However, as mentioned above, the utility of a conference connection is substantially increased when it spans a greater distance, and in order to provide for longer distance conference connections with enhanced economy the possibility exists, as described in my copending U.S.A. patent application No. 895562 of connecting a plurality of conference circuits as shown in the box 1 of FIG. 1 in tandem, so that groups of conferees served by each conference circuit 1 are linked by single tie lines spanning remote locations and thus reducing the call charges that would otherwise be incurred. The trunking pattern involved in such a connection is illustrated in FIG. 4.

FIG. 4 shows a parallel, series trunked conference of circuits 1 of FIG. 1 connected in chain and star form to associate subscribers in different locations to the conference with a minimum of inter-connecting switching paths between the separate locations `A`, `B`, `C` and `D`.

The trunking pattern depicted draws on four conferees at location `A` using a further outgoing port from location `A` to join to location `D` via the main switching network 17 which can of course be either public of private or both where five further conferees are connected and the option exists to bring on further conferees by contacting a further conference equipment which could of course be local as well as remote.

A further outgoing port from location `A` joins to location `B` via the main switching network 17 where five more conferees are drawn onto the connection with a further outgoing port extending to location `C` where five more conferees are shown to be connected with a further port giving the option of further connections via the main switching network as required.

Thus the arrangement shown in FIG. 4 offers the prospect of nineteen conferees at four remote locations with only three main switching transmission paths joining the four locations where the conference equipment 1 as depicted in FIG. 1 is located by association with the existing telephone switching equipment there. The three main switching transmission paths between the four locations are those provided for use on normal telephone calls between these locations and are thus now shared with the needs of this new conference service.

FIG. 5 shows the transmission plan provided for conferees connected to the conference trunked in accordance with FIG. 4 and how each conferee is subject to only the normal telephonic loss since in each case the transmission path provided between interconnected conference circuits and involving tandem connected lines of two local exchanges 2 and one trunk 17 is compensated to zero loss by the amplifier 11 at the input port 4 of the interconnected conference circuit 1. The manner in which this is achieved is, as already mentioned above, described in my copending patent application Ser. No. 895562.

In order for a subscriber to set up a connection as illustrated in FIGS. 4 and 5, it is necessary for him, after having gained access to an outlet port 5 of the conference equipment 1 of FIG. 1 to connect that port via the local exchange 2 to the inlet port 4 of a further, remote conference equipment 1 associated with the desired, distant exchange.

It will be appreciated that when a subscriber who is already connected to one conference equipment 1 and wishes to access a second, tandem connected conference equipment 1 and to forward command signals to the second equipment to set up a conference there in the manner already described, the difficulty will exist that although the second conference equipment will recognise command signals as appertaining to itself, the same control circuits in the first conference equipment will also respond unless previously disabled.

In order to overcome this problem, each conference equipment 1 to be used in the configuration of FIGS. 4 and 5 incorporates a logic circuit which responds to the "star" signal when switch 8 is in the normal or "O" position and changes the structure of the coding field connecting the V.F. receiver to the relays CS and SS so that the latter are subsequently only operated upon receipt of unique dialled digits following the operation of the "gate" button. A further logic circuit which responds to the "star" signal when switch 8 is then subsequently connected to an outlet 5 may be made effective to disable the dial pulse chip 14 and arrange for the onward transmission of the V.F. tones in place of dial pulse signals. In this way, following the transmission of dial pulse signals to gain access to a second or subsequent conference equipment 1 via the exchange network as shown in FIG. 4, the chairman's act of transmitting the "star" signal to said equipment 1 to change its coding field is simultaneously effective in the preceding equipment 1 to replace the dial pulses with V.F. tones to which the later equipment will respond.

In one example of the above arrangement, which permits the unique addressing of conference equipments at each of five separate locations, the unique digital signals which follow the "gate" signal are as follows:

In order to set up a connection as illustrated in FIG. 4, for example, the chairman, after having set up a local conference at location A will then return switch 8 to the home or `O` position and press his "star" button to convert to the above coding, by then pressing the "gate" and digit 1 buttons he may step the switch 8 on to a free outlet 5, as before, and transmit dial pulses to set a connection for example to the conference device at location B. Having gained a connection, he will then, whilst remaining on the relevant outlet port 5, again press his "star" button. In view of the changed coding at location A this will not be seen as a cancel signal there and will be transmitted onward to location B, where, since the switch 8 is in the home position the signal will be seen as an instruction to change the command coding to that indicated above. Simultaneously the signal will be effective at location A to inhibit dial pulse transmission so that the chairman is able, by transmission of the now V.F. coded " gate" plus "digit 3" and "gate" plus "digit 4" signals to actuate the conference equipment at location B to set up a local conference connection there, in precisely the same manner as already described above. He may also establish a further connection to conference equipment at location `C` likewise, with the exception that since he has already changed the coding at location B, there is no need to return to the home position at location B for this purpose.

The inhibition of dial pulses is cancelled by the action of SD relay when the circuit 1 is stepped away from this outlet accessing a subequent circuit 1 so as to permit further call setting at other selected outlets 5. If the control connection of switch 8 is subsequently re-established then the "star" button signal must be re-transmitted even though the distant circuit 1 is already set to this mode of command in order that dial pulses will be inhibited at the nearer circuits 1 to avoid mutilation of the V.F. control signal forward by dial pulses.

The gate signal, which in this mode of command precedes the digital address and control signal also inhibits the dial pulse chip 14 of all circuits 1 in the connection--which inhibition being removed by all circuits 1--whether responsive or not at the end of the command signalling sequence that the gate button has indicated.

A second pressure of the gate button before completion of the command signalling sequence serves to cancel the command sequence and similarly to clear the dial pulse chip inhibition.

More than one simultaneous conference may be allowed for by providing one or more of the conference equipments 1 as shown in box 1 of FIG. 1, connected to the exchange line circuits of a hunting group accessing this service via the input ports of the conference equipment at 4 in FIG. 1 and addressed by calling to this exchange line number or numbers. Each such conference equipment will cater for a conference connection at that location thus if there are three such circuits then three simultaneous conferences can proceed at any time.

In the conference equipments described above, each conference circuit 1 incorporates its own unique arrangement of conference amplifiers A-N and corresponding outlet ports 5. Thus although the number of ports 5 must be adequate to allow of the maximum convenient number of conferees as desired, in many cases the conference capacity will be under used and exchange lines connected to outlet ports will be idle but blocked to other conference connections.

In accordance with a further embodiment of the invention illustrated in FIGS. 8 and 9, a conference circuit is provided which is adapted to be connected in common with other similar conference circuits so that the associated outlet ports to exchange lines form a common pool with graded access from which conference ports may be seized as necessary, the arrangement being such that those seized by one conference equipment are marked busy to the others.

FIGS. 8 and 9 are drawn to run onto each other and form a single circuit diagram when they are laid adjacently with FIG. 8 to the left. The circuit is similar to that of FIGS. 6 and 7 like parts being indicated with like references, and these will not be described in detail.

The circuit differs from FIGS. 6 and 7 in that FIG. 9 illustrates the relays HA to HN of relay counters of three conference equipments each of which is operable by means of a respective control circuit as illustrated in FIG. 8 and connected thereto as illustrated in the case of conference equipment 1 by means of the connections at the left-hand edge of FIG. 9. The access circuitry associated with relays HA and HN of conference equipment 1 is shown in full it being understood that the same circuitry is repeated in the case of the intermediate relays HB to HM in the counter chain, as indicated by the broken lines interconnecting the two parts to the circuit enclosed in dashed and dotted lines. The interconnections with conference equipments 2 and 3 are likewise shown, the remainder of the circuits of the latter equipments being identical with that of conference equipment 1.

Referring now to the drawing, the switch 8 of FIG. 1 for each separate conference equipment is formed of a relay counter including relays A to N and CH and AL to NL and CHA where CHA and CH provide the Zero or Home outlet of the sequence switch, to which outlet it is set by the operation of CH and CHA relays when the conference circuit is seized through the A4 to N4 series chain of break contacts, after the same fashion as the circuit of FIGS. 6 and 7.

The relay counter steps in an identical fashion to that described for FIGS. 6 and 7 through the application of a stepping earth at the contact SS4 when the relay SS is operated by the "gate" output of the V.F. receiver 15. The contacts A2, A3 to N2, N3 of the counter provide a changeover of any connection made to the conference lines by the contacts HA3, HA4 to HN3, HN4 between the conference port amplifiers A to N and the call setting bus 20 to which the chairman or originating subscriber is connected when the relay counter is off normal and the contacts CHA2 and CHA4 are released. This makes his connection from the line circuit and ring detect circuit 21 terminating his incoming line through to the conferee on the speak and dial call setting bus 20 via the quenched dial pulse contact DP1 with the contact DON1 to provide a clean dial pulse loop, all under control of the dial pulse chip 14 marked by the V.F. receiver 15 joined to the chairman's or originating subscriber's V.F. keypad at the line circuit and ring detector 21 by the hybrid transformer 12 giving rejection of noise passed back from the conference connection.

With the relay counter set to zero through the relays CH and CHA being operated then contacts CHA2 and CHA3 connect the chairman at the line inlet 4 to the conference bus 20 via his conference port amplifier 25. The relays HA to HN may be operated successively by the action of the contact SS4 as it steps the relay counter to the next setting and in this process applies the line test function, which gives the appropriate relay HA to HN the opportunity of operating and connecting to the line, if it is free, on each setting of the relay counter, as will be described below.

If the contacts HA3, HA4 to HN3, HN4 operate to couple the conference line then it gives dial tone to the dialling and talk loop of the speak and dial call setting bus 20 as in the previously described embodiment. If the relay HA to HN does not operate to couple the conference line, because it is already engaged in use by another conference circuit, then the contacts AL2, AL3 to NL2, NL3 of the switch counter for that conference port will be operated and connecting busy tone to the speak and dial call setting bus 20 which will be heard by the chairman or originating subscriber via the unoperated condition of the contacts HA3, HA4 to HN3, HN4 to indicate that this step of the relay counter has failed to seize a free conference line. Thus if the chairman steps the relay counter through its cycle by repeated applications of the "gate" signal then he will hear dial tone from those conference lines that are available for him to set a conference connection and busy tone from those that are not. If insufficient lines are available for the conference he needs, then he can release the connection and try again later. If there are only just sufficient available then he can dial a holding digit to simulate a connection to the line, which will cause it to be held to the conference bus 30 against seizure by another conference equipment, by retaining the operation of the relay HA to HN when the switch counter 5 is stepped to release the contacts A2, A3 to N2, N3 appropriate to that conference line. If necessary the chairman knowing that he will need to make several outgoing calls from the exchange hosting the conference equipment, can alternatively key digits which will secure the outgoing exchange lines necessary for his conference connection against seizure by other telephoning parties so that he knows these outgoing lines are seized and held available for his use when he comes to set the conference connections to them. This he can do at any time, through being able to return the relay counter to any line during the seizure of the conference equipment, so as to speak and/or rearrange the connection he has set there. As in FIGS. 6 and 7 the discrimination on whether to set the connection to the conference bus 30 via the conference port amplifiers A to N, when the chairman chooses to decouple from it by stepping the relay counter away to another setting, is based on the dialling history of the connection, as indicated by the condition of relay SD. This is released when the relay counter is stepped to the port, unless there is a conference line already coupled to that outlet through the relay HA to HN there being already operated to provide this coupling. In this case the high speed relay SDX and its slave SDXS both operating and locking together through the diode D6 to contact SS2, will not operate because the path of operation of relay SDX is via the make before break or so-called K action contacts HA2 to HN2 and the diodes D3 and D1 to the contact SS4, which in the action of stepping of the relay counter, is applying an earth in response to the "gate" signal from the V.F. receiver to operate the relay A to N of the stage of the counter that is being set to access the conference port 5 associated with this step of the counter and the relay HA to HN, which may or may not already be coupling the conference line there through its associated contacts HA3, HA4 and HN3, HN4. Thus if relays SDX and SDXS operate and lock during the stepping of the relay counter it will mean that the relay HA to HN corresponding to that step was not previously operated and that a line was not already coupled and that if the relay SD were operated then it will be released by the operation of contact SS1 when relay SS operates to step the relay counter because of contact SDXS2 severing the operate path to the relay SD that the operation of contact SS otherwise offers, in this same action. If the slave combination SDX and SDXS did not operate with relay SS and the stepping of the counter from the earth at contact SS4, then when contact SS1 operates to offer the opportunity for relay SD to release due to the operation of contact SDXS2, if this contact is not operated to break the connection indicating that there is a connection to the conference line through the relay HA to HN being operated to access it, then the relay SD is operated by the operation of contact SS1, irrespective of whether it was operated prior to the stepping action. Thus when the switch 8 of FIG. 1 steps to an outlet 5 which is already coupled to the conference equipment then the assumption is that a satisfactory call exists on this line and should be recorded as such by the operation of the relay SD. If it is not satisfactory then the chairman or originating subscriber, with the perogative of control gained by this coupling action, can apply a cancel signal, indicated for simplicity in FIGS. 7 and 8 as a "star" signal from the V.F. receiver 8 to operate the relay CS. This opens the holding loop subtended to the coupled line via the speak and dial call setting bus 20 at contact CS1 to release the connection and also clears the record of this connection by releasing the relay SD from the locking path of contact SD1 and the contact CS2. The relay SD is set as a record of attempted call setting to a conference port by recognising the sending of dialled digits to the line. This is indicated, so as to operate relay SD, by passing the digital markings from the V.F. receiver 15 which control the dialling of the dial pulse chip 14 to the line, as an earth marking via the decoupling diodes D7 to D16, to operate the relay SD, so that it holds at contact SD1 in memory of this dialling action. The operation of relay SD is followed by the operation of relay HH when relay SS is released to provide the path at contact SS3 and the stepping action of the relay counter is completed. The action of the relay HH is important, since its task is to pass the condition discriminated by the operation of the relay SD as to whether the common conference line, coupled by the operation of the relay AH to NH, should be connected to the conference bridge by retaining the operation of the relay AH to NH, when the relay counter is stepped. This can be because an uncancelled dialled connection has been made to the line during this coupling, which state it so construes requires the maintenance of the coupling. Or there already was a connection to this line by the relay HA to HN when the relay counter accessed it, which means the connection should be similarly maintained, unless the connection is cancelled. The relay SD is thus in the position of possibly operating in response to a marking feed when the relay SS operates, which must not be effective until the relay SS operates for the next time, and it is the relay HH which provides the necessary discrimination which allows this conflict of timing to be spanned.

The relay HH cannot operate to follow the operation of relay SD, until relay SS is released, which indicates that the previous stepping procedure of the relay counter is now complete. Likewise the relay HH held by the operation of contact SS3 through its own locking contact HH2 is held, independently of relay SD during the operation of relay SS in stepping the relay counter when relay SD may or may not release and may operate when relay SS operates, depending upon the conditions on the conference ports between which the speak relay counter is stepping. The condition is thus that if the relay HH is operated, indicating that relay SD was operated, then the stepping of the relay counter to access the next conference line in sequence should not release the relay HA to HN, of the previously accessed conference line, if it were operated. The holding path of relays HA to HN is normally via the make before break changeover contacts HA1, HA2 to HN1, HN2 from the resistor R1 and diode D2 and the contacts AL1 to NL1 released, to the common earth line of the earth contact RT1. When the relay counter is accessing a conference port then the contacts AL1 to NL1 associated with that conference port outlet 5 will be operated and the normal holding path for the relays HA to HN will be disconnected so that the continued operation of the relay HA to HN in question will be provided only via the diode D4 to the common earth line provided by the back contact of the changeover contact SS4.

Thus, when the relay SS operates to the "gate" signal to step the relay counter by applying earth at the make action of the changeover contact SS4, its break contact is disconnecting the hold path of the relay HA to HN so that the one accessed by the relay counter is caused to release unless the relay HH is operated to provide an alternative hold path through the contact HH1 masking the break action of the changeover contact SS4, so that the relay HA to HN in question does not release but is held throughout the stepping action of the relay counter which is until relay SS is released which at contact SS3 has been holding relay HH, if operated, via its holding contact HH2.

Once the stepping action of the relay counter is completed, as is indicated by the release of the relay SS then the next relay AL to NL will be operated and the previous one released so that the relay HA to HN, whose release has been restrained by the operated condition of the relay HH, during the operation of the relay SS now has a holding path provided by the normal condition of the contact AL1 to NL1 for that access stage. The relay HA to HN of the newly accessed stage will, if operated through having successfully coupled to the conference line, because it was free and available, as will be described presently, be holding upon the earth provided via the back contact of changeover contact SS4 and the diode D4 and prepared for a similar further step to that just now described.

The contacts A2, A3 to N2, N3 of the relay counter of the stage just released, will now be connecting the centre pole of the contacts HA3, HA4 to HN3, HN4 to the conference bus 30 so that if these contacts are operated, the conference line will be extended there and if not then the busy tone at contacts AL2, AL3 to NL2, NL3 will be disconnected from connection to the conference bus there, by the released condition of these contacts.

Thus, the conference line was connected to the conference when the chairman set the relay counter to a new setting, if there was a memory of uncancelled dialling to the connection since its seizure, or there was already a connection to the line when it was seized, which has not been subsequently cancelled, all as was shown and described for the arrangement of FIGS. 6 and 7.

The difference in the functions provided by these two arrangements lies in the testing and seizing of the conference line, which for the arrangement of FIGS. 8 and 9 can be in common pool to be shared by several such conference equipments, as will now be explained.

When the relay counter is stepped to a new setting by the application of the earth from the contact SS4, then this stepping earth from contact SS4 is also fed not only to operate the appropriate relays A to N by the chain of sequence contacts CH1 and AL4 to NL4 but also via diode D3 to the appropriate relay HA to HL, where it provides a path for the operation of that relay from the resistor R1 via the similarly designated contacts HA1 of all the conference equipments able to access that conference line, in an exclusive one-only chain connection of the make before break changeover contacts HA1 of all the conference equipments able to access that conference line, such that only one of the relays HA to HN of the several conference equipments can operate and maintain its operation since by doing so the relay HA of the circuit most towards the resistor R1, at the head of the chain, will disconnect the path of any other, which is making a similar simultaneous test and attempt to seize the line. It will be seen that each conference circuit has been provided with a resistor R1 but only that at the head of the testing chain is used. The return feed for this exclusive "one-only" path is returned in a parallel common to all the circuits via the diodes D5, which provide the operate path for the relay HA to HN in question, which, when operated, provides its own path independent of the make contact SS4 and initially via the diode D2 because the contact AL1 to HL1 is not yet operated to disconnect this path. When contacts AL1 to HL1 operate then hold is via diode D4 when contact SS4 releases to put the earth behind the common rail connecting to the diodes D4 and the contacts AL1 to NL1 have opened in completion of the relay counters stepping action to remove the holding earth via diode D2. This same contact AL1 to NL1 releases the two relays of the previous stage of the relay counter in the normal action of its working.

Thus when the relay counter operates the relay A to N in the first stage of its normal two stage action, the application of earth from the contact SS4 is also connected to apply the appropriate relay HA to HN in a testing mode to try the free and available condition of the conference line thus accessed and if it is free to operate and seize and hold it against other seizure, so as to provide the access for the relay counter which is connecting to the chairman from that line via the speak and dial call setting bus 20 as has already been explained.

It will be apparent to those skilled in the art that although the above described embodiments of the invention are constructed using electromechanical relay switching circuits, the same functions could be achieved through the application of electronic data processing and logic technology, without departing from the scope of the invention as defined in the appended claims. 9n