GB1602473A - Telephone systems providing conference facilities - Google Patents

Description

(54) IMPROVEMENTS IN TELEPHONE SYSTEMS PROVIDING CONFERENCE FACILITIES (71) I, BLOOMFIELD JAMES WARMAN, a British Subject, of 67, King Harold's Way, Bexley Heath, Kent, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to improvements in telephone systems providing conference facilities.

It is well known that simultaneous common telephone communication can be provided between a number of separate locations by connecting the telephone instruments in these several locations in parallel so as to allow the electrical speech signals from any one of the telephones to be received by the other telephones.

Such multi-party connections have become known as conference connections and that point at which the common speaking connection is made whilst holding separate the several sets of supervisory conditions of the several lines, has become known as the "conference bridge" so as to distinguish it from the "supervisory bridges" used to join speech and hold separate the supervisory conditions of the more usual two party telephone connection.

It is quite usual for such multi-party conference connections to employ the standard switched lines and telephone instruments that have been made generally available for the more normal two party telephone connections. Such lines and telephone instruments have however been designed so that their electrical sound sensitivity and balance between the sending and receiving levels and the efficiency of acoustic transduction in these two paths are appropriate only for two party connections.

When such telephone instruments are connected in common so as to become part of a multi-party telephone conference connection by normal telephone lines then the receiving level to each of the telephones is reduced by a degree corresponding to the number of extra telephones that are connected, resulting in a corresponding reduction in the hearing level of each of the telephones thus connected.

For this reason it is common practice to restrict the number of telephones that can be connected to such a common conference connection to be not more than 4 or 5 and to permit such connections only where relatively favourable levels of electrical speech signalling can be expected. Conference connections involving larger number of parties can be achieved by introducing amplification into the conference bridge.

Such amplified conference bridges are, however, relatively difficult to design so as to give good dependable operation in practice, and even with amplification the connection of a substantial number of parties into a conference bridge tends to reduce clarity owing to the fact that even if only one party to the conference is speaking at any given time, the background noise from the listening parties will be present on the line and this will accumulate to give a reduced signal to noise ratio which becomes worse as a factor of the number of parties on the conference connection.

Further factors which tend to reduce the number of parties which can in practice be tolerated on a conference call are the problems of imposing discipline upon the parties to the call so that the discussion is not rendered unintelligible by a multiplicity of parties speaking simultaneously, and that of voice recognition such that a listener can identify respective speakers and thus gain a mental orientation of their locations which is necessary for the logical conduct of a conference discussion.

Accordingly, an object of the invention is to provide telephone apparatus enabling the establishment of a multi-party conference call connection whilst retaining acceptable clarity of speech transmission.

A preferred object of the invention is also to provide means facilitating the conduct of a conference via such a conference connection.

In accordance with the present invention there is provided a telephone system adapted to enable a multiparty telephone conference connection to be established, wherein the arrangement is such that a plurality of telephone lines may effectively be connected in parallel, each line so connected being provided with individual amplifying means for compensating transmission loss, and each said amplifying means being associated with a direction detecting switching means responsive to speech transmission in at least one direction and arranged to increase the gain of the amplifying means in the direction of speech to which it responds, and/or to attenuate signal transmission in the other direction, each switching means being biased into a condition in which transmission by the associated amplifying means of speech from the connected telephone line in the speaking direction is inhibited and speech is transmitted to said line in the listening direction, said switching means being responsive to speech signals transmitted from said line in the speaking direction in order to enable said amplifying means to transmit in the speaking direction.

In a system in accordance with the invention, the provision of individual amplifying means for each telephone line, to provide a corresponding conference port of which the direction of amplification is switchable in response to speech transmission from the respective telephone line has the advantage that the amplifying means associated with each individual speaker can be controlled to provide compensation of transmission loss in the transmission direction only when the corresponding party is speaking. Thus, when the party-is not speaking the presence on the conference bridge of amplified background noise transmitted from that party's telephone instrument can be avoided, with a consequent improvement in the signal to noise ratio of the overall conference connection.

Advantageously, each direction detecting switching means is inhibited from responding to speech signals whilst signals are being transmitted by said amplifying means to said line in the listening direction. This has the advantage that whilst one party to the conference call is speaking, the other parties are effectively prevented from interrupting him by transmitting speech signals onto the conference bridge, and thus the parties to the conference are subjected to a discipline which prevents the conference call being rendered unintelligible to a listener by simultaneous speech from more than one party.

Preferably the arrangement is further such that transmission of signals by said amplifying means in the listening direction is inhibited while said switching means is responsive to signals in the speaking direction.

Advantageously, each said amplifying means includes a self-adjusting amplifier, arranged to provide an output signal of substantially constant level in response to input signals of varying level. Such an arrangement enables the compensation of different signal levels from different lines connected to the conference bridge towards a good level, without exceeding the maximum level permitted to be applied to the conference lines. Such an arrangement is particularly advantageous if the conference bridge spans different localities by the utilisation of the public exchange network in respect of which the levels of transmitted signals are strictly controlled.Furthermore, the fact that the signals from the respective conference lines are compensated towards a common level ensures that a listener will be spared the strain of constantly readapting himself to a wide range of different received listening levels, which may occur not only due to the condition of the conferees' lines but also to their habit of speaking either loudly or softly.

Although it might be assumed that the arrangement according to the invention in which separate amplification is provided for each conference line may prove more bulky and expensive than the provision of a common conference bridge amplifier, the requirements of a conference port amplifier are much less stringent than those for a line amplifier, since the need to pass dialling and ringing signals may be avoided, and suitable electronic amplifiers for such a purpose are now readily and cheaply available. In fact, it is now the line terminating coupling transformers that represent the prime cost, especially if these are of the balanced winding type to provide good return loss in a hybrid formulation.

However, in accordance with a further, preferred feature of the invention, more economic use may be made of a plurality of amplified conference ports made available in a telephone switching system by the inclusion of switching means for selectively connecting said amplifying means to any one of a plurality of conference busses, whereby from a common pool of said amplifying means, a plurality of conference connections may be simultaneously and selectively established via the respective conference busses.

Such an arrangement enables a given number of amplified conference ports to be utilised, either for one conference call involving a large number of individual ports, or alternatively a plurality of simultaneous conference connections each involving a lesser number of conference ports.

In accordance with a particularly advantageous embodiment of the invention, there is associated with each amplifying means a means for generating a burst of a uniquely identifiable tone, and a bistable device arranged to be set upon response of the respective switching means and to be reset upon response of another switching means, the arrangement being such that upon setting of the bistable device it initiates actuation of the associated tone generation means. Such an arrangement has the advantage that as a speaking party is interrupted by a further party during the course of the conference call, the new speaking party is introduced by a distinct indentifying tone burst or "pip" which will indicate to listeners not only that the previous speaker has been interrupted, but also the identity of the new speaker, in terms of the identifiable characteristics of the tone, e.g. its pitch.During the course of the conference call, each different tone burst will become identified by a listener with a corresponding party of the conference connection, thus facilitating the logical conduct of the conference call.

It is possible that in some circumstance a conference call may be set up by interconnecting in tandem a plurality of conference bridges set up at different locations, and in this case it is advantageous if the above mentioned tone burst identifying the speaker of a conference bridge is supplemented by a further tone burst which identifies the particular conference bridge onto which he is connected.

The invention is illustrated by way of example in the accompanying drawings, in which: Fig. 1 is an explanatory block schematic diagram showing an amplified conference bridge formed from a number of amplified conference ports in accordance with the invention each joining one of the several conference lines to a common connecting bus, Fig. 2 is a block schematic circuit diagram of an individual conference port amplifier of Fig. 1, Fig. 2A is a circuit diagram of a switching means allowing selective connection of the amplifier of Fig. 2 to any one of a plurality of conference buses.

Fig. 3 is a block schematic diagram of a device for providing audible identification of individual conference bridges established by means of the switching device of Fig. 2A, and Fig. 4 is a block schematic diagram illustrating the interconnection of three conference bridges of the kind shown in Fig. 1.

Referring to Fig. 1, the conference ports P I to PN are shown connecting conference lines LI to LN to a common conference connecting bus 1, the arrangement being such that the single conference port circuit set to a speaking mode can pass speech signals to all the remaining ports which are set in a listen mode and effectively connected in parallel, the attenuation of the speech signal at each conference line due to this parallel connection being compensated by the amplifying means provided in the individual conference port circuits, either in the speech path of the speaking port, or the listening path of the listening port, or compositely in both.

Referring now to Fig. 2, which illustrates in more detail the circuit arrangement of each conference port P1 to PN, each port comprises a telephone line 34 connected via a line transformer T1 to lead 35, and a lead 25 connected to the common. conference bus, the lead 35 and the lead 25 being interconnected by separate speech and listen paths indicated at 32 and 30 respectively. Mutual separation of the speech and listen paths 32 and 30 is provided by means of switchable amplifiers 21 and 22, and gain adjustment is achieved by amplification circuits enclosed within the broken lines 5 and 6 respectively.

The circuit 5 includes an amplifier 7 which is connected to provide a compressor function in conjunction with an operational amplifier 8 and a reference element 9, the arrangement being such that signals of different levels received from the conference line 34 are compensated to provide a single transmission level at the output of amplifier 7. The circuit 6 includes an amplifier 10 which serves to provide a convenient means of gain adjustment to suit different situations, and also serves as a buffer for isolating from speech signals applied at lead 35 an amplifier 11 connected to the listen path 30 for the purpose to be described below.

Each of the amplifiers 21, 22, 7 and 10 comprises a so-called attenuator chip, which is an amplifier with an approximate gain of4 and which can be regulated to give an attenuation of approximately 90 d.b. incremented by the gradual variation of an applied voltage on a control lead which varies between approximately 3 volts and 6 volts. Such chips are marketed by the Motorola Corporation under the code MC3340P.

The amplifiers 21 and 22 are controlled via leads 26 and 27 connected to outputs of tandem connected monostable devices 13 and 14, the latter being connected in antiphase so that when the listen path 30 is opened via amplifier 22 the speech path is closed via amplifier 21, and vice versa. The monostables 13 and 14 are normally biased into the condition such that the amplifier 21 is blocked and the amplifier 22 is open, unless the monostables are switched into the opposite state by way of an output signal provided on lead 38 from a speech detector 40. The speech detector 40 is arranged to be actuated by a signal from the speech path 32 transmitted via lead 29, amplifier 12 and lead 39, and to be inhibited by a signal from the listen path 30 transmitted via lead 28, amplifier 11, gate 46 and lead 41.

In addition to the outputs from monostables 13 and 14 provided on leads 26 and 27, further outputs are provided at leads 37 and 42, the latter being connected to a common lead 43 for the purpose to be described below. Lead 37 is connected to one input of a bistable device 19, of which an output is connected to a timing circuit 20 arranged to provide an electrical signal of predetermined duration on an output lead 44 upon change of state of the bistable 19 in response to the signal provided on lead 37. The signal provided on lead 44 is arranged to inhibit the gate 46 via a lead 41, and also to inhibit a further gate 18 provided at the second input to the bistable device 19. The lead 44 is also connected to an oscillator 17 which is arranged to provide a tone signal at the output thereof, in response to the signal provided on lead 44.

The output of the tone generator 17 is connected to a lead 36 which is connected in common with corresponding leads of the other conference ports of the conference bridge, and is also connected via an amplifier 16 and the gate 18 to the second input of bistable 19. In addition, the output of tone generator 17 is connected via an amplifier 15 on the one hand to the listen path 30 of the conference port, and on the other hand directly to the lead 25 of the conference port via an amplifier 45.

The operation of the conference amplifier described above will now be described as follows. In the idle condition the conference port is biased into a state such that the listen path 30 is open and the speech path 32 is closed. Incoming signals are transmitted to the conference line 34 via lead 25, amplifier 22, listen path 30, amplifier 10, lead 35 and the line transformer T1. Assuming that the listener at line 34 wishes to speak to the other parties connected to the conference bridge as shown in Fig. 1, he must first gain control of the conference bridge by switching his conference port to a speaking condition. This is effected by transmitting speech signals so that an output appears from the amplifier 7, and is transmitted via lead 29, amplifier 12 and lead 39 to the speech detector 40.If another party is already speaking, then speech signals will be already transmitted via amplifier 22, speech path 30, lead 28, amplifier 11 and gate 46 to the inhibit input of the speech detector 40 and the latter will be unable to respond. However, assuming that no other party on the conference bridge is speaking, the speech detector 40 will respond to the input on lead 39, and will cause switching of the monostables 13 and 14 so that the amplifier 21 is opened and the amplifier 22 is blocked.Security against two such conference ports simultaneously being switched to the speaking condition is effected due to the connection of the monostables 14 via leads 42 and common connection 43 to a common one-only allotting circuit of known type which is arranged to control the monostable 14 in such a manner that the monostable 14 of only one conference port can be caused to change state at any given time. The operation of such a one-only allotting circuit is well known in the telephone art and will not therefore be described further.

Upon change of state of the monostables i4 and 13, the monostable 13 provides an output on lead 37 which triggers the bistable 19, causing the latter to provide at the output thereof a signal actuating the timing circuit 20. Consequently, the oscillator 17 is actuated for a predetermined period to provide a brief tone signal at its output which is transmitted via amplifiers 15, lead 31 and amplifier 45 to the output lead 25 of the conference port connected to the common conference bus. Thus, as the speaker initially starts to speak a distinct burst of tone will appear on the conference bridge to announce the fact that the previous speaker has been interrupted and a new party is commencing to speak.Each individual conference port is arranged to provide a tone signal of corresponding pitch, so that the parties to the conference call may identify the location of the speaker in accordance with the pitch of the introductory tone signal. The tone signal is also returned to the speaker via lead 31 and listen path 30, to indicate to him that he has been successful in seizing the conference bridge for speech. Although the burst of tone appears on the listen channel 30, it is prevented from inhibiting the speech detector 40 and thus interfering with the switching of the monostables 13 and 14 due to the fact that the gate 46 is blocked for the duration of the tone signal by the output from the timer circuit 20 provided on lead 41.Likewise, resetting of the bistable 19 by the output from the tone generator 17 is prevented by the gate 18 which is inhibited by the output from timer circuit 20.

The bistable 19 now remains in its set state so that despite pauses in speech by the speaking party and consequent changes in state of the monostables 13 and 14, no further tone signals are generated. Should the speaker be interrupted by another party during a pause in his speech, then switching of the other party's conference port takes place precisely as described above, and the bistable 19 of the interrupted speaker's conference port is reset by the introductory tone signal applied to the common lead 36, so that the latter conference port is returned to its idle state.

The fact that each conference port as described above includes its own self-contained amplification and is simply connected to a common conference bus enables a conference bridge of any desired number of ports to be built up simply by connection of the ports in parallel, and conveniently, a plurality of such conference ports may be arranged in a common pool from which ports may be selectively connected by way of a suitable switching system to any one of a plurality of different conference busses, thus allowing for a plurality of simultaneous conference connections with an economy of conference ports.Fig. 2A illustrates a suitable switching arrangement which enables the conference port of Fig. 2 to be selectively connected to any one of the different conference busses ACI, BCl, CCI and DCI in association with other, identically arranged conference ports of the common pool. Similar switching of the common leads 36 to a common bus is likewise necessary, the common busses AC2, BC2, CC2 and DC2, and associated switches A2, B2, C2 and D2 being provided for this purpose, it being understood that the latter switches are linked to the corresponding switches Al, B1, Cl and D I providing connection to the conference busses. It will be appreciated that the common one-only allotting leads 42 will require switching in a similar manner, although the one-only allotting arrangement is optional and may be dispensed with if desired.

Patent Specification No. 41713/77 (Serial No. 1 602474) describes a telephone exchange switching system which provides a facility for the interconnection of conference bridges established at different locations, so that a single conference connection can be established in which a plurality of local conference connections are linked by tielines to provide a multilocational conference bridge, Such an arrangement is shown diagrammatically in Fig. 4, in which a plurality of conference ports of the kind described above with reference to Fig. 2 are connected in parallel at each of a plurality of locations indicated at A, B and C respectively. The ports P1 to PN at each of these locations correspond to the ports P 1 to PN forming a conference bridge as shown in Fig. 1.However, in order to enable the serial connection of the conference bridges at different locations, each bridge additionally comprises conference ports PX and PY which do not serve speaking parties of the conference but are merely linked together in tandem for example via a telephone exchange switching system indicated by the dotted lines extending between the telephone lines LX and LY.

The ports PX and PY operate in precisely the same manner as described above with reference to Fig. 2 in providing communication between the respective conference bridges.

However, since these ports do not serve speaking parties the tone pulse generators thereof are redundant, and are disabled. This disablement can either be in the form of a permanent wiring change so that such a modified conference port must be selected for joining between conference bridges, or may be effected by the control equipment setting up the tandem conference connection.

When a plurality of conference bridges at different locations are interconnected as shown in Fig. 4, it is desirable for the introductory tone pulses generated to announce each speaker who is a party to the conference not only to indicate the location of the speaker within his individual conference bridge, but also to provide identification of the relevant conference bridge at which the speaker is connected. For this purpose, each conference bridge may be provided with an additional tonal generator as illustrated in Fig. 3, which shows a plurality of tone generators AB, BP, CP, DP, each connectable via a corresponding bus AC2, BC2, CC2 or DC2 of Fig. 2A to the common leads 36 of the conference ports selected to provide a corresponding conference bridge.

Each of said tone generators comprises a tone detector I responsive to the tone pulses applied to common lead 36 by the respective conference ports, a timer 2 actuated by the tone detector 1, and an oscillator 3 activated by the timer 2 which feeds a unique conference bridge identifying tone back to the common lead 36 for the duration of the period set by timer 2. The timing of the action of the detector 1 and timer 2 is such that the tone generator 3 supplements any initial burst of tone from an individual conference port with the bridge identifying tone in order to provide a composite audible address for the relevant speaker.

It will be appreciated that the circuit of Fig. 3 will not be required on purely local conference bridge connections, and that on multilocational conference bridge connections the period of the tonal signal provided by the tone generating circuit of Fig. 3 must be lengthened to allow for the switching time of the tandem connected conference ports of the multilocational connection. However, it will be appreciated that these requirements can be taken account of by a suitable common control equipment responsible for setting up the conference call.

WHAT I CLAIM IS: 1. A telephone system adapted to enable a multiparty telephone conference connection to be established, wherein the arrangement is such that a plurality of telephone lines may effectively be connected in parallel, each line so connected being provided with individual amplifying means for compensating transmission loss, and each said amplifying means being associated with a direction detecting switching means responsive to speech transmission in at least one direction and arranged to increase the gain of the amplifying means in the direction of speech to which it responds, and/or to attenuate signal transmission in the other direction, each said switching means being biased into a condition in which transmission by the associated amplifying means of speech from the connected telephone line in the speaking direction is inhibited and speech is transmitted to said line in the listening direction, and said switching means being

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. conference ports. Fig. 2A illustrates a suitable switching arrangement which enables the conference port of Fig. 2 to be selectively connected to any one of the different conference busses ACI, BCl, CCI and DCI in association with other, identically arranged conference ports of the common pool. Similar switching of the common leads 36 to a common bus is likewise necessary, the common busses AC2, BC2, CC2 and DC2, and associated switches A2, B2, C2 and D2 being provided for this purpose, it being understood that the latter switches are linked to the corresponding switches Al, B1, Cl and D I providing connection to the conference busses.It will be appreciated that the common one-only allotting leads 42 will require switching in a similar manner, although the one-only allotting arrangement is optional and may be dispensed with if desired. Patent Specification No. 41713/77 (Serial No. 1 602474) describes a telephone exchange switching system which provides a facility for the interconnection of conference bridges established at different locations, so that a single conference connection can be established in which a plurality of local conference connections are linked by tielines to provide a multilocational conference bridge, Such an arrangement is shown diagrammatically in Fig. 4, in which a plurality of conference ports of the kind described above with reference to Fig. 2 are connected in parallel at each of a plurality of locations indicated at A, B and C respectively. The ports P1 to PN at each of these locations correspond to the ports P 1 to PN forming a conference bridge as shown in Fig. 1.However, in order to enable the serial connection of the conference bridges at different locations, each bridge additionally comprises conference ports PX and PY which do not serve speaking parties of the conference but are merely linked together in tandem for example via a telephone exchange switching system indicated by the dotted lines extending between the telephone lines LX and LY. The ports PX and PY operate in precisely the same manner as described above with reference to Fig. 2 in providing communication between the respective conference bridges. However, since these ports do not serve speaking parties the tone pulse generators thereof are redundant, and are disabled. This disablement can either be in the form of a permanent wiring change so that such a modified conference port must be selected for joining between conference bridges, or may be effected by the control equipment setting up the tandem conference connection. When a plurality of conference bridges at different locations are interconnected as shown in Fig. 4, it is desirable for the introductory tone pulses generated to announce each speaker who is a party to the conference not only to indicate the location of the speaker within his individual conference bridge, but also to provide identification of the relevant conference bridge at which the speaker is connected. For this purpose, each conference bridge may be provided with an additional tonal generator as illustrated in Fig. 3, which shows a plurality of tone generators AB, BP, CP, DP, each connectable via a corresponding bus AC2, BC2, CC2 or DC2 of Fig. 2A to the common leads 36 of the conference ports selected to provide a corresponding conference bridge. Each of said tone generators comprises a tone detector I responsive to the tone pulses applied to common lead 36 by the respective conference ports, a timer 2 actuated by the tone detector 1, and an oscillator 3 activated by the timer 2 which feeds a unique conference bridge identifying tone back to the common lead 36 for the duration of the period set by timer 2. The timing of the action of the detector 1 and timer 2 is such that the tone generator 3 supplements any initial burst of tone from an individual conference port with the bridge identifying tone in order to provide a composite audible address for the relevant speaker. It will be appreciated that the circuit of Fig. 3 will not be required on purely local conference bridge connections, and that on multilocational conference bridge connections the period of the tonal signal provided by the tone generating circuit of Fig. 3 must be lengthened to allow for the switching time of the tandem connected conference ports of the multilocational connection. However, it will be appreciated that these requirements can be taken account of by a suitable common control equipment responsible for setting up the conference call. WHAT I CLAIM IS:

1. A telephone system adapted to enable a multiparty telephone conference connection to be established, wherein the arrangement is such that a plurality of telephone lines may effectively be connected in parallel, each line so connected being provided with individual amplifying means for compensating transmission loss, and each said amplifying means being associated with a direction detecting switching means responsive to speech transmission in at least one direction and arranged to increase the gain of the amplifying means in the direction of speech to which it responds, and/or to attenuate signal transmission in the other direction, each said switching means being biased into a condition in which transmission by the associated amplifying means of speech from the connected telephone line in the speaking direction is inhibited and speech is transmitted to said line in the listening direction, and said switching means being

responsive to speech signals transmitted from said line in the speaking direction in order to enable said amplifying means to transmit in the speaking direction.

2. A system as claimed in Claim 1, wherein the arrangement is further such that each said switching means is inhibited from responding to speech signals whilst signals are being transmitted by said amplifying means to said line in the listening direction.

3. A system as claimed in Claim I or 2, in which the arrangement is such that transmission of signals by said amplifying means in the listening direction is inhibited whilst said switching means is reponsive to signals in the speaking direction.

4. A system as claimed in Claim 3, in which the said amplifying means includes a self-adjusting amplifier, arranged to provide an output signal of substantially constant level in response to input signals of varying level.

5. A system as claimed in any one of Claims 1--4, in which each of said switching means is connected to a one-only allotting circuit, whereby of the respective switching means only one can respond at any given time.

6. A system as claimed in Claim 5, in which there is associated with each amplifying means a means for generating a burst of a uniquely identifiable tone, and a bistable device arranged to be set upon response of the respective switching means and to be reset upon response of another switching means, the arrangement being such that upon setting of the bistable device it initiates actuation of the associated tone generation means.

7. A system as claimed in any one of Claims 1 to 6, including switching means for selectively connecting said amplifying means to any one of a plurality of conference busses, whereby from a common pool of said amplifying means, a plurality of conference connections may be simultaneously and selectively established via the respective conference busses.

8. A system as claimed in any one of Claims 1-7, including a common means for generating a uniquely identifiable burst of tone, each said common means being responsive to a burst of tone from an individual tone generating means associated with an amplifying means of the system, whereby the burst of tone identifying the individual amplifying means is accompanied by a further burst of tone identifying the telephone system.

9. A system as claimed in Claim 8 when appended to Claim 7, wherein a separate common tone generating means is connected to each of said conference buses.

10. A telephone system adapted to enable a multiparty telephone conference connection to be established, substantially as described herein with reference to the accompanying drawings.