FIELD OF THE INVENTION

This invention relates to telephone systems of the kind permitting at least one external telephone line to be connected to a plurality of internal users.

BACKGROUND OF THE INVENTION

Most PABX exchanges require that a central telephone exchange be connected to an incoming telephone line and that each internal telephone extension unit within the system be separately connected to the PABX exchange. As a result, the installation of such PABX exchanges is a specialized and costly procedure.

WO 94/18780 in the name of the present Applicants discloses a telephone system comprising a plurality of telephone extension units each coupled, via an adaptor, to a common internal telephone line. The adaptor is constructed to allow each of the telephone units to undertake an intercom- type communication with other local telephone extension units or, by dialling a predetermined code, to connect to the external telephone line. Such a system offers all the advantages of a PABX exchange, without requiring separate connection of each telephone extension unit to a central control box. Using such a system, even domestic premises can enjoy all the advantages of a PABX exchange but at significantly reduced expense. This having been said, many domestic premises, in particular, do not require the advanced features of a PABX-type exchange: all that is actually required being the ability to make and receive external calls. On the other hand, in a conventional domestic setup wherein all telephone extension units are connected in parallel to the external line, there is no way of discriminating between each telephone extension unit. As a result, all telephone extension units ring in response to an incoming telephone call and if one member of the household, for example, answers the telephone there is no way in which he can transfer the call to another extension unit, short of verbally requesting that somebody else pick up a different extension unit. Likewise, if somebody answers the telephone and wishes to involve another member of his household, or office, in the conversation in order to establish a conference-type call, then this too is not possible if all the telephone units are connected to the line in a conventional manner. Whilst the above-mentioned international patent publication does address these shortcomings, it does so at the expense of providing an intercom facility for which many users have no need. Furthermore, the provision of an intercom facility requires discrimination between internal and external calls, thereby adding to the overall complexity and cost.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved telephone extension unit suitable for connection to a conventional telephone line and being adapted to provide enhanced features to a user. Within the context of the invention, the term "telephone extension unit" can refer to a telephone, a telephone answering machine, a facsimile machine, a cordless telephone or any other similar device.

According to a broad aspect of the invention, there is provided an improved telephone extension unit, comprising: a discrimination means for determining whether a telephone call were initiated locally or remotely and producing corresponding outgoing and incoming call discrimination signals, a call signal detector for detecting a call signal and producing a call detection signal, and an actuation means coupled to the discrimination means and to the call signal detector for operating in response to a predetermined combination of said discrimination and call detection signals.

Preferably, the telephone extension unit further includes a signalling means for transmitting signals to other telephone extension units connected thereto via a common telephone line.

In a preferred embodiment, a direct call selection is provided for allowing an incoming caller to be directed to a particular local extension unit.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how the same may be carried out in practice, some preferred embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

Fig. 1 is a flow diagram showing logically the essential inventive concept of the invention;

Fig. 2 is a block diagram showing functionally a telephone system incorporating enhanced telephone extension unit according to the invention; Fig. 3 is a block diagram showing the functional components associated with an enhanced telephone according to the invention;

Fig. 4 is a block diagram showing the principal components in an enhanced cordless telephone according to the invention;

Fig. 5 is a block diagram showing the principal components in an enhanced answerphone according to the invention;

Figs. 6a and 6b are state diagrams for explaining the logic associated with the enhanced telephone illustrated in Fig. 3;

Figs. 7a to 7c are state diagrams for explaining the logic associated with a base unit for the enhanced cordless telephone shown in Fig. 4; Fig. 7d is a state diagram for explaining the logic associated with a portable hand unit for the enhanced cordless telephone shown in Fig. 4;

Figs. 8a, 8b, 8c and 8d are state diagrams for explaining the logic associated with the enhanced answerphone shown in Fig. 5; and

Fig. 9 is a circuit diagram of a General Off Hook and Zero Nolt Pulse Detector.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Fig. 1 is a conventional flow diagram showing the principal logic associated with the invention. Thus, associated with any enhanced telephone extension unit for use with the invention is the ability to discriminate between whether a telephone call were initiated locally or remotely. A locally initiated telephone call denotes an outgoing call whilst a remotely initiated telephone call denotes an incoming call.

Associated with each enhanced telephone extension unit according to the invention is a unique extension number which permits another telephone extension in the unit, even one which has not been enhanced according to the invention, to transfer a call thereto. This is desirable for several reasons. First, a local participant who initiated an outgoing call may, during the course of the conversation, wish to involve another local extension in a conference-type call. Alternatively, he may wish to transfer the call to another local participant after completing his part of the conversation. In the case of an incoming call, the same two considerations apply, albeit for slightly different reasons. Thus, upon receipt of an incoming call there is no direct way of identifying for which local extension unit the call is intended. Thus, it frequently happens that one local extension unit answers the call and then has an immediate need to transfer the call to another local extension unit prior to hanging up. Alternatively, as in the case of an outgoing call, he may wish to involve another local extension unit in a conference-type call.

In the case of an outgoing call, an enhanced telephone extension unit, upon detecting a call directed to its unique extension number, allows for operation of its ringer although the ringers of other local extension units will remain silent. The extension unit may then be connected to the line if desired. On the other hand, if the call is an incoming call, then such connection is permitted only in the case that the dialled extension number is not preceded by "#". If an unprefixed extension number is received, then the enhanced telephone extension unit corresponding to that number will take no action. By this means, it may be ensured that a remote extension unit (i.e. associated with the calling party) can transfer a call internally without the dialled extension code passing down the telephone line to the called party and activating an enhanced telephone unit associated with the called party and having the same extension code. On the other hand, as will

be clear from Fig. 1, providing that the telephone call were initiated locally (i.e. an outgoing call), a call is transferred upon receipt of the appropriate extension number, regardless of whether it is prefixed by "#" or not.

As thus stated, the inventive concept resides in the ability to discriminate between a locally and remotely initiated call and then to take appropriate action upon receipt of a call detect signal according to whether the call is an incoming call or an outgoing call.

In particular, the required discrimination is effected for an outgoing call by responding only to an extension number which is prefixed by a so-called "smart code", followed by a DTMF or pulse dialled extension number equal to the ID of the responding extension unit. Alternatively, when pulse dialling is used by the calling extension unit, the dialled number need not be prefixed by a "smart code". For an incoming call, an extension unit having an ID corresponding to a dialled number, responds only if the dialled number is not prefixed by a DTMF "#" signal. Thus, actuation will occur if the incoming number is pulse dialled or if it is tone dialled but not prefixed by a "smart code".

Fig. 2 is a block diagram showing a telephone system designated generally as 10 having a central office local line 11 coupled to a central office remote line 12 via a central office exchange 13. Connected to the central office local line is a standard telephone, an enhanced standard telephone 15, an enhanced cordless telephone 16 and an enhanced answer¬ phone 17. Likewise, connected to the central office remote line 12 is a standard telephone 18, an enhanced standard telephone 19, an enhanced cordless telephone 20 and an enhanced answerphone 21.

As will be shown with particular reference to Figs. 3 to 8 of the drawings, the implementation of the logic shown in Fig. 1 within the telephone system 10, allows for the provision of advanced features whilst requiring relatively little hardware modification to most telephone extension

units. Furthermore, completely compatibility with conventional telephone extension units, not having the advanced features of the invention, is assured.

Fig. 3 shows functionally the additional components associated with the enhanced Standard Telephone 15 shown in Fig. 2. Thus, such a telephone includes a Standard Telephone 25 having an Extension Off Hook Detector 26 for producing a signal when the telephone 15 is either off-hook or on-hook. The Standard Telephone 25 is coupled to a micro-controller 27 which is itself responsively coupled to the Extension Off Hook Detector 26. The Standard Telephone 25 is also connected, through the Extension Off Hook Detector 26 to the telephone line 11 coupled to a plurality of logic elements, to be described, all connected, via a common bus 29 to the micro¬ controller 27.

The following are the components which are added to the Standard Telephone 25, in addition to the micro-controller 27 in order to convert the Standard Telephone 25 to an Enhanced Telephone according to the invention. First, an Extension ID Set and Store means 29 is provided for allowing a unique extension number to be associated with the Enhanced Telephone 15. Typically, the Extension ID Set and Store means can be a DIL switch permitting each telephone extension unit within the system to be set to a different extension number, or address, by the user. Alternatively, the Extension ID Set and Store means 29 can be constituted by a non¬ volatile memory responsive to a program stored in the micro-controller 27 for allowing the desired extension code to be stored in the non-volatile memory thereof. Many conventional telephones allow storage and recall of the previously dialled number and it will be apparent to those skilled in the art that the Extension ID Set and Store means can be implemented in a similar manner.

Also provided is a Message Indicator and Message Signal Detector 30 which allows detection of a signal sent by a locally connected answerphone which is itself enhanced according to the invention as described below with reference to Fig. 5 of the drawings, for illuminating a Message Indicator Lamp so as to provide a visual indication to the user that a stored answerphone message awaits him.

A DTMF Transmitter 31 is provided as standard in the telephone 25 so as to permit DTMF dialling thereby. In order that the Enhanced Telephone 15 be suitable for use with DTMF exchanges a DTMF Receiver 32 is provided, and to allow each extension unit within the system 10 to detect an incoming call a Ring Detector 33 is provided. Each extension unit must also be able to identify the fact that another extension unit within the system 10 is off-hook and also to indicate to other local extension units an intention to transfer a call. To this end there is provided a General Off Hook and Zero Nolt Pulse Detector 34. A zero volt pulse is employed in order to distinguish between local and remote networks and is generated by a zero volt pulse generator 35 upon activation of a push button switch 36. Activation of the push button switch 36 appends the DTMF code "#" to the zero volt pulse, the combined signal being referred to throughout the specification as a "smart code".

All of the components described above are known, per se, from our International Publication No. WO 94/18780 which is incorporated herein by reference, thereby obviating any further requirement to describe the components in detail. Fig. 4 shows the enhancements which must be effected to a

Standard Cordless Telephone comprising a base unit 40 and a hand unit 41 for effecting R.F. communication therewith in conventional manner. Associated with base unit 40 is an Extension Off Hook Detector 42 which, together with the base unit 40, are connected to a micro-controller 43.

Connected to the micro-controller 43 is a bus 44 to which is connected a Cordless ID Set and Store means 45 for associating the unique extension number with the cordless telephone 16. Also associated with the base unit 40 is a DTMF Pulse Transmitter 46 and Ring Detector 47, all of these components being provided in existing base units and therefore not requiring further elaboration so far as the invention is concerned.

To the standard cordless base unit 40 and the above-mentioned standard components are added a Message Indicator and Message Signal Generator 48 for providing a visual indication to the base unit 40 in the event that a remote caller has left a message in the answerphone 17 (shown in Fig. 2). The Message Indicator and Message Signal Generator 48 further transmits a message signal to the portable hand unit 41 so that the presence of an awaiting answerphone message should be reflected in the hand unit 41. A General Off-Hook and Zero Nolt Pulse signal detector 49 provides an indication that another local extension unit is off-hook and also allows detection of a zero volt pulse consequent to another local extension sending a "smart code" down the line. A Zero Nolt Pulse Generator 50 which serves the same function as those described above with reference to Fig. 3 of the drawings, whilst a Push Button Signal Detect 51 is provided for detecting a push button signal transmitted to the base unit 40 by the hand unit 41.

Associated with the hand unit 41 are a Push Button switch 52, a Push Button Signal Generator 53 and a Message Indicator and Message Signal Detector 54. The Push Button Signal Generator 53 is responsively coupled to the Push Button 52 for generating a "smart code" which is transmitted, via R.F., to the base unit 40. The Message Indicator and Message Signal Detector 54 receives a message signal from the base unit 40 for illuminating a message indication lamp in the hand unit 41 so as to provide a visual indication that a message has been recorded in the local answerphone 17.

Fig. 5 shows functionally the enhanced answerphone 17 shown in Fig. 2 and itself comprising a standard answerphone 55 associated with which is an Extension Off-Hook Detector 56, both being responsively coupled to a micro-controller 57. A DTMF Transceiver 58 allows trans- mission and reception of DTMF tone signals and a Ring Detector 59 allows detection of a ring signal consequent to an incoming call. All of these components are fitted as standard in existing answerphones. To the above- mentioned components are added a General Off-Hook and Zero Nolt Pulse Signal Detector 60. A Zero Nolt Pulse Generator 61 allows detection of a zero volt pulse transmitted by another local extension consequent to the push button associated with the other local extension being depressed. Since there is no requirement for calls to be transferred manually from the answerphone 17 to other local extension units, no push button switch is provided in the enhanced answerphone 17. On the other hand, since there must be associated with the answerphone 17 a unique extension number, there must be provided an Answerphone ID Set/Store Means 62 connected, together with the other components to a bus 63 fed to the micro-controller 57.

Figs. 6a and 6b are state diagrams showing the principal logic steps associated with the enhanced telephone 15 shown functionally in Fig. 3.

The initial condition is that the local extension is On-Hook and this is denoted in the Figure at step 65, also labelled START. In this state, the local extension unit can detect four different states: RING DETECT 66, EXTENSION OFF HOOK 67, GENERAL ON HOOK 68 and GENERAL OFF HOOK 69. The logic associated with each of these states will now be described.

At step 66 a RING DETECT signal is detected, thus denoting an incoming call. The micro-controller 27 is awakened at step 70 thus initiating a routine labelled INCOMING CALL. Three possible states can now

be detected: GENERAL OFF HOOK 71, EXTENSION OFF HOOK 72 and RING STOPS 73. At step 73 the RING DETECT signal stops, denoting that the remote caller hung up without the call being answered. In this case, at step 74, the micro-controller is switched off and control branches to START. At step 71, a GENERAL OFF HOOK condition is detected, denoting that another local extension answered the call. In this case, all remaining local extension units go into STANDBY mode permitting the call to be transferred thereto by the particular extension unit which answered the call or by another local extension unit to which the call was transferred previously. When in STANDBY mode, two conditions can occur: GENERAL ON HOOK condition or the local extension's user ID number can be detected. At step 75 a GENERAL ON HOOK condition is detected, denoting that all local extension units are closed and thus indicating that the extension unit which answered the incoming call has hung up. In this case, at step 76 the micro-controller is switched off and control again branches to START.

Otherwise, if in STANDBY mode at step 77 the local extension unit detects its own ID number, then at step 78 its internal ringer is sounded so as to provide an audible indication that a call has been directed to the current extension unit. This puts the extension unit into CALL TRANSFER mode allowing four possible states: GENERAL ON HOOK 79, SMART CODE 80, USER ID NUMBER 81 and EXTENSION OFF HOOK 82. Each of these four states will now be described.

At step 79, a GENERAL ON HOOK condition is detected, indicating that the local extension unit which originally attempted to transfer the call to the current extension unit has had second thoughts and closed before receiving a reply and, further, that no other local extensions are off hook. In this case, at step 83 the ringer is deactivated and, at step 84, control branches to START. At step 80 a SMART CODE is detected. This indicates that the local extension unit which answered the incoming call and attempted

to transfer the call to the current extension unit now has second thoughts and wishes to abort the transfer, and possibly transfer the call to another local extension unit instead. In either case, this is achieved by depressing the push button switch 36 and, then, dialling the number of the local extension unit to which the call is to be transferred. In the event that it is desired to cancel a pending call transfer, this is achieved by depressing the push button switch 36 and dialling the same ID number which was previously dialled in order to effect the attempted call transfer.

In either case, depressing the push button switch 36 generates a SMART CODE, upon detection of which at step 80, the ringer is deactuated at step 85 and, at step 86, control branches to STANDBY. The same applies if, during the CALL TRANSFER routine, the ID number of the current extension unit is detected at step 81. Here again, the extension unit which attempted to transfer the call to the current extension unit has had second thoughts and decided to abort the CALL TRANSFER. Thus, steps 85 and 86 are performed as described above.

Since the CALL TRANSFER routine is responsive not only to the detection of a SMART CODE, but also simply to the user ID of the current extension unit, this permits calls to be transferred to the local extension unit even by conventional telephone extension units which themselves have no facility to transmit a SMART CODE. Such telephones cannot, of course, receive transferred calls but they can themselves transfer calls to other local extension units.

If at step 82 an EXTENSION OFF HOOK condition is detected, this means that the local extension unit to which the call was transferred has answered and, in this case, at step 87 the ringer stops and control branches to a CALL ACCEPTED subroutine. In this condition, detection at step 88 of an EXTENSION ON HOOK signal denotes that the local extension unit to which the call was transferred has now hung up and, at step 89, control

branches to STANDBY which allows for detection of a GENERAL ON- HOOK condition or for a extension unit ID to be detected. The CALL ACCEPTED routine also allows for the call to be transferred to another extension unit, either for the purpose of redirecting the call or for the purpose of invoking a conference-type call. In this case, the push button switch 36 must be depressed giving rise to a PUSH BUTTON DEPRESSED state at step 90, upon detection of which a SMART CODE is sent at step 91. This loop repeats indefinitely until an EXTENSION ON HOOK state is detected at step 88. In the INCOMING CALL routine, an EXTENSION OFF HOOK state may be detected at step 72 denoting that a current extension unit answered the incoming call. In this case, control branches to the CALL ACCEPTED routine.

At step 68 a GENERAL ON HOOK condition is detected, denoting that no incoming calls are on the line, since no RING DETECT signal was detected and all local extension units are closed. In this state, a message indication signal can be transmitted by the answerphone 17, either in order to indicate to all local extension units that a message has been recorded in the answerphone or, when all such messages have been listened to and erased from the answerphone's message buffer, to extinguish the message indicator on all of the local extension units. Thus, if at step 92 no MESSAGE SIGNAL is detected, control branches to START. If at step 93 a MESSAGE "ON" signal is detected, then at step 94 the message indication lamp in the local extension unit is switched on and at step 95 control again branches to START. If at step 96 a MESSAGE OFF signal is detected, then at step 97 the message indication lamp is switched off and at step 95 control branches again to START.

The START routine also allows, at step 69, for the detection of GENERAL OFF HOOK signal denoting that another local extension unit has

been lifted with the intention of dialling an outgoing call. It will be appreciated that we are concerned here with initiation of an outgoing call by another local extension unit and not by receipt of an incoming call by another local extension unit, such discrimination being possible because an incoming call must be preceded by a RING DETECT signal as at step 66. Thus, in the absence of a RING DETECT signal, a GENERAL OFF HOOK condition can only mean that a local extension unit wishes to initiate an outgoing call. In this case, at step 98 the micro-controller is awakened and an OUTGOING CALL routine is initiated as shown in Fig. 6b. This routine allows for two initial states: detection of a SMART CODE followed by the ID of the local extension at step 99 or detection of a GENERAL ON HOOK condition at step 100. The latter condition simply denotes that the local extension which contemplated making an outgoing call has had second thoughts and hung up. In this case, at step 101, control branches to START. If at step 99 a SMART CODE and the ID of the local extension unit are detected this denotes that the local extension unit which initiated the outgoing call wishes now to transfer the call to the current local extension unit, either for the purpose of redirecting the call or in order to initiate a conference-type call. In this case, at step 102 the ringer is activated and an EXTERNAL CALL TRANSFER routine is initiated. This allows for one of four possible states: a GENERAL ON HOOK condition at step 103, a SMART CODE at step 104, a DIALLED EXTENSION number having a different ID to that of the current extension unit at step 105 and, at step 106, an EXTENSION OFF HOOK condition. When, at step 103, a GENERAL ON HOOK condition is detected, this means that all local extension units are hung up, implying that the local extension unit which initiated the outgoing call has had second thoughts about transferring the call to the current local extension unit and has simply

hung up. In this case, at step 107 the ringer of the local extension unit is stopped and, at step 108, control branches to START.

When at step 104 a SMART CODE is detected, this again implies that the local extension unit which attempted to transfer the call has had second thoughts and decided not to transfer the call after all. The logic now follows steps 80 and 85 of the INTERNAL CALL TRANSFER routine described above and at step 109 the ringer is deactivated, whilst at step 110 control branches to the OUTGOING CALL routine. Likewise, when at step 105 another local extension unit is dialled, either in pulse mode or DTMF, the current local extension unit detects an extension number having a different ID to its own ID, and this indicates that the transferring extension has decided, for whatever reason, to transfer the call to a different local extension unit. In this case, also, at step 109 the ringer stops and at step 110 control branches to the OUTGOING CALL routine. When at step 106 an EXTENSION OFF HOOK state is detected, this indicates that the current local extension unit has accepted the call transfer and at step 111 the ringer is deactivated. There now ensues an EXTERNAL CALL CONNECTED routine allowing two states: a PUSH BUTTON SIGNAL DETECTION state at step 112 and an EXTENSION ON HOOK state at step 113. On detecting that the push button is depressed at step 112, a SMART CODE is transmitted at step 114. This allows for the external call to be transferred to yet another local extension unit, again either for the purpose of redirecting the call or for the purpose of involving further local extension units in a conference-type call. Thereafter, at step 114A control branches to the EXTERNAL CALL CONNECTED routine. Otherwise, detection of an EXTENSION ON HOOK state at step 113 indicates that the current local extension unit has hung up and, in this case, control branches, at step 115, to the OUTGOING CALL routine.

As was stated above, the START routine also contemplates, at step 67, an EXTENSION OFF HOOK state indicating that the current extension unit initiated an outgoing call. In this case, at step 116 the micro-controller is awakened and, at step 117, control branches to the EXTERNAL CALL CONNECTED routine described above.

Figs. 7a to 7c are state diagrams showing the principal logic steps associated with the base unit 40 of the enhanced cordless telephone 16 shown functionally in Fig. 4. Fig. 7d is the corresponding state diagram associated with the portable hand held unit 41. The initial condition is that the local extension is On-Hook and this is denoted in Fig. 7a and 7b at step 120, also labelled START. In this state, the local extension unit can detect five different states: RING DETECT 121, EXTENSION OFF HOOK 122, PUSH-BUTTON SIGNAL DETECT 123, GENERAL ON HOOK 124 and GENERAL OFF HOOK 125. The logic associated with each of these states will now be described.

At step 121 a RING DETECT signal is detected, thus denoting an incoming call. The micro-controller 43 is awakened at step 126, and at step 128, the base unit 40 transmits an R.F. ring signal to the hand unit 41 in order to initiate connection of the hand unit 41 to the line, thus initiating a routine labelled INCOMING CALL. Three possible states can now be detected: RING STOPS 127, GENERAL OFF HOOK 129 and HAND UNIT EXTENSION OFF-HOOK 132. At step 127 the RING DETECT signal stops, denoting that the remote caller hung up without the call being answered. In this case, at step 130, the micro-controller is switched off and control branches to START at step 131.

At step 132, the hand unit 41 is lifted, so producing a HAND UNIT EXTENSION OFF HOOK condition causing the hand unit 41 to be connected to the line at step 133. At step 134, the ringer in the hand unit 41 is switched off and a HAND UNIT CONNECTED routine is initiated, as shown in

Fig. 7c to which reference is now made. There are two initial states: HAND UNIT CLOSED 135 and PUSH BUTTON SIGNAL DETECTED 136. When, at step 135 a HAND UNIT CLOSED condition is detected, this means that the hand unit 41 has been replaced, in which case at step 137 control branches to the HAND UNIT STANDBY routine shown in Fig. 7a, allowing the base unit 40 again to transfer an incoming call to the hand unit 41.

Alternatively, at step 136 a push-button signal is detected by the PUSH-BUTTON SIGNAL DETECTOR 51 in the base unit 40, consequent to the push-button 52 in the hand unit 41 having been depressed. This is done when the hand unit 41 wishes to transfer the call to another local extension unit or, alternatively, to involve another local extension unit in a conference- type call. Thus, at step 138, the base unit 40 sends a SMART CODE to the line and awaits receipt from the hand unit 41 of the extension's user ID number to which a call transfer is to be initiated. At step 139 a HAND UNIT OPEN state is detected, signifying that the hand unit 41 is still connected to the line, in which case at step 140 control reverts to the HAND UNIT CONNECT routine, thereby repeating the above cycle and allowing the still- connected hand unit 41 to transfer the call to another local extension unit. Alternatively, at step 141 a HAND UNIT CLOSED state is detected, in which case at step 142 control reverts to the HAND UNIT STANDBY routine shown in Fig. 7a.

Thus, referring again to Fig. 7a of the drawings, it will be noted that, upon detection of an INCOMING CALL, when at step 129 a GENERAL OFF HOOK state is detected, then at step 143 the base unit DTMF is awakened and again the HAND UNIT STANDBY routine is initiated which will now be described in detail. At entry to the HAND UNIT STANDBY routine there are four possible states: GENERAL ON HOOK 144, "#" followed by the base unit's extension ID 145, SMART CODE followed by the base unit's extension ID 146 and an unprefixed extension ID 147.

When at step 144 a GENERAL ON HOOK condition is detected, this means that the telephone extension unit which answered the incoming call is disconnected from the line and, in this case, at step 148 control branches to START. When at step 145, a "#" followed by the hand unit's ID is detected, this is due to the remote caller having sent a SMART CODE followed by the same extension ID in respect of what to him is a local extension unit in order to transfer the call thereto. Obviously, such action by the calling party must not be reflected in the system 10 belonging to the called party. Such interference is, of course, avoided because the SMART CODE is not itself transmitted down the line and, consequently, all that is received at the local end is the SMART CODE stripped of the zero volt pulse. Therefore, upon receipt of the "#" unprefixed by the zero volt pulse, no action is taken and at step 149 control reverts to the HAND UNIT STANDBY routine, thereby repeating the cycle. When at step 146 a SMART CODE followed by the hand unit's ID is detected and also when at step 147 an unprefixed ID is detected, then a ring signal is sent to the hand unit at step 150 so as to alert the hand unit 41 that a call awaits it.

There are now three possible states: a GENERAL ON HOOK at step 151, a HAND UNIT EXTENSION UNIT OFF HOOK at step 152 and either an unprefixed extension ID number or an ID number prefixed by a SMART CODE at step 153. When a GENERAL ON HOOK state is detected at step 151, this indicates that the hand unit 41 has not responded to the ring signal sent at step 150 and, in this case, after the extension unit which intended to transfer the call has hung up, the ring signal is stopped at step 154 and control branches to START at step 155. Otherwise, when at step 152 a HAND UNIT EXTENSION OFF HOOK signal is detected, this means that the hand unit 41 has responded and, in this case, at step 156 the ring signal is stopped and the base unit 40 R.F. connects the hand unit 41 to the line. Thereafter, at step 157 control branches to the HAND UNIT ON LINE routine shown in

Fig. 7c to which reference is now made. Associated with the HAND UNIT ON LINE routine there are two initial states: PUSH-BUTTON SIGNAL DETECTED 158 and HAND UNIT CLOSED 159. When at step 158 a PUSH-BUTTON SIGNAL is detected, this implies that the Push-Button 52 in the hand unit 41 has been depressed for the purpose of transferring the call to another local extension unit. In this case, the base unit 40 transmits a SMART CODE to the line at step 160. The hand unit 41 can now remain open, i.e. connected to the line, either if it wished to remain connected in a conference-type call or if it wished to remain on the line until the transfer is successfully effected. In this case, at step 161 a HAND UNIT OPEN state is detected and at step 162 control reverts to the HAND UNIT ON LINE routine so as to allow the complete cycle to be repeated for as long as the hand unit 41 is connected to the line. Otherwise, if the hand unit 41 hangs up, then at step 163 a HAND UNIT CLOSED state is detected and at step 164 control reverts to the HAND UNIT STANDBY routine described above with reference to Fig. 7a so as to allow another local extension unit connected to the line to transfer the call to the hand unit 41. When at step 159 a HAND UNIT CLOSED state is detected, this is because the hand unit 41 has hung up and, in this case, at step 159A control again reverts to the GENERAL OFF-HOOK condition associated with the HAND UNIT STANDBY routine shown in Fig. 7a of the drawings. If now a GENERAL OFF-HOOK condition is detected, control reverts to START.

Referring again to Fig. 7a, when, during the HAND UNIT STANDBY routine, the extension ID number, either alone or prefixed by a SMART CODE is detected at step 153, this is because the local extension unit which originally wished to transfer the call to the hand unit 41 has now had second thoughts and retransmitted the same ID number in order to cancel the transfer or, alternatively, has simply pressed his Push-Button switch prior to dialling the extension ID of another local extension unit. In either case,

since there is now no desire to transfer the call to the hand unit 41, at step 165 the ring signal is stopped and at step 166 control reverts to the HAND UNIT STANDBY routine which has now been described in its entirety.

When the hand unit 41 itself wishes to initiate a call, lifting the handset generates an EXTENSION OFF HOOK state at step 122 and at step 167 the hand unit 41 is connected to the line whereupon control reverts, at step

168, to the HAND UNIT ON LINE routine described above with reference to

Fig. 7c of the drawings.

The PUSH-BUTTON SIGNAL DETECT state 123 arises when the hand unit 41 depresses its Push-Button 52, so sending an R.F. Push-Button signal to the base unit 40. The base unit 40 responds at step 169 by allowing the hand unit 41 to communicate therewith in conventional R.F. INTERCOM MODE.

Referring now to Fig. 7b of the drawings the remaining initial states of the START routine will be described. When at step 124 a GENERAL ON HOOK state is detected, this denotes that no incoming calls are on the line, since no RING DETECT signal was detected and all local extension units are closed. In this state, a message indication signal can be transmitted by the answerphone 17, either in order to indicate to all local extension units that a message has been recorded in the answerphone or, when all such messages have been listened to and erased from the answerphone's message buffer, to extinguish the message indicator on all of the local extension units. Thus, if at step 170 no MESSAGE SIGNAL is detected, control branches at step 171 to START. If at step 172 a MESSAGE "ON" signal is detected, then at step 173 the message indication lamp in the base unit is switched on and at step 174 a MESSAGE INDICATION "ON" signal is sent to the hand unit 41 so as to illuminate the message indication lamp in the hand unit. Thereafter, at step 175 control reverts to START. If at step 176 a MESSAGE "OFF" signal is detected, then at step 177 the message indication lamp is

switched off in the base unit and at step 178 a MESSAGE INDICATION "OFF" signal is sent to the hand unit 41 so as to extinguish the message indication lamp therein. Thereafter, control again branches to START at step 175.

The START routine also allows, at step 125, for the detection of a GENERAL OFF HOOK state denoting that another local extension unit has been lifted with the intention of dialling an outgoing call. It will again be appreciated that we are concerned here with the initiation of an outgoing call by another local extension unit, and not by receipt of an incoming call by another local extension unit, such discrimination being possible because an incoming call must be preceded by a RING DETECT state as at step 121. Thus, in the absence of a RING DETECT signal, a GENERAL OFF HOOK condition can only mean that a local extension unit wishes to initiate an outgoing call. In this case, at step 179 the micro-controller is awakened and an OUTGOING CALL routine is initiated. This routine allows for three initial states: detection of a SMART CODE followed by the ID of the base unit at step 180, detection of a pulse-dialled ID of the base unit at step 181 and a GENERAL ON HOOK state at step 182. The latter condition simply denotes that the local extension which contemplated making an outgoing call has had second thoughts and hung up. In this case, at step 183, control branches to START. If, at step 180, a SMART CODE and the ID of the base unit are detected, this denotes that the local extension unit which initiated the outgoing call wishes now to transfer the call to the cordless telephone 16 shown in Fig. 2. This may be either for the purpose of redirecting the call or in order to initiate a conference-type call. The same applies at step 181 when a pulse-dialled ID of the base unit 40 is detected. In either case, at step 184 a ring signal is sent by the base unit 40 to the hand unit 41 and a CALL HAND UNIT routine is initiated. This allows for one of four possible states: a SMART CODE at step 185, a DIALLED EXTENSION number having a different ID to that of the base unit at step 186, a GENERAL ON HOOK

condition at step 187 and a HAND UNIT OPEN or EXTENSION OFF HOOK condition 192 (shown in Fig. 7c).

When at step 187, a GENERAL ON HOOK condition is detected, this means that all local extension units are hung up, implying that the local extension unit which initiated the outgoing call has had second thoughts about transferring the call to the cordless telephone 16 and has simply hung up. In this case, a step 188, the ringer of the hand unit is stopped and, at step 189, control branches to START.

When at step 185 a SMART CODE is detected, this again implies that the local extension unit which attempted to transfer the call has had second thoughts and decided not to transfer the call after all. In this case, at step 190 the ring signal to the hand unit is stopped and, at step 191, control branches to the OUTGOING CALL routine allowing the whole cycle to be repeated. Exactly the same happens when, at step 186, another local extension unit is dialled in pulse mode only, the base unit detects an extension number having a different ID to its own ID, and this indicates that the transferring extension has decided, for whatever reason, to transfer the call to a different local extension unit. In this case, also, at step 190 the ringer stops and at step 191 control branches to the OUTGOING CALL routine. If, in the CALL HAND UNIT routine, a HAND UNIT OPEN state is detected at step 192 denoting that the hand unit 41 is off-hook, then at step 193 the ring signal to the hand unit 41 is interrupted and the HAND UNIT CONNECT routine is executed.

Referring now to Fig. 7d the logic associated with the hand unit 41 will now be described. In the initial condition, labelled START there exist five possible states: EXTENSION OFF HOOK 195, RING SIGNAL DETECTED BY BASE UNIT 196, MESSAGE SIGNAL OFF" 197, MESSAGE SIGNAL "ON" 198 and PUSH-BUTTON DEPRESSED 199. The logic associated with each of these states will now be described.

At step 195, an EXTENSION OFF HOOK state is detected conse¬ quent to the hand unit 41 being off hook. In this case, a step 200 the hand unit 41 is connected to the line and at step 201 control branches to HAND UNIT OFF HOOK having two possible states: EXTENSION ON HOOK 202 and PUSH-BUTTON DETECTED 203. When, at step 202, EXTENSION ON HOOK state is detected, this means that the hand unit 41 has been replaced and control branches at step 204 to START. Otherwise, when at step 203 the Push-Button is detected, this means that the Push-Button 52 in the hand unit 41 has been depressed thereby allowing INTERCOM MODE to be initiated between the hand unit 41 and the base unit 40. In this case, at step 205 an RF signal is sent to the base unit in order for the base unit 40 to send a SMART CODE to the line, and at step 206 control reverts to the HAND UNIT OFF HOOK routine allowing repetition of the cycle.

When at step 196 a RING SIGNAL is sent by the base unit 40, then at step 207 the ringer in the hand unit is sounded in order to alert the hand unit 41 that a call awaits it. If the hand unit does not respond within a reasonable time or, for any other reason, the base unit has second thoughts, such that at step 208 the RING SIGNAL is OFF, then at step 209 control branches to START. Otherwise, if at step 210 an EXTENSION OFF HOOK state is detected, this is because the hand unit was lifted and, in this case, the HAND UNIT OFF HOOK routine described above is executed.

When at step 197 a MESSAGE SIGNAL "OFF" state is detected, then at step 211 the message indication lamp in the hand unit is switched off and at step 212 control branches to START. Likewise, when at step 198 the MESSAGE SIGNAL "ON" state is detected, then at step 213 the message indication lamp in the portable hand unit 41 is switched on and at step 214 control branches to START.

When at step 199 the PUSH-BUTTON DEPRESSED state is detected, then at step 215 an RF signal is transmitted from the hand unit 41 to the

base unit 40 for the purpose of initiating INTERCOM MODE between them. If at step 216 an EXTENSION ON HOOK state is detected, this implies that the hand unit 41 was replaced and, in this case, control branches at step 217 to START. Referring now to Figs. 8a to 8d of the drawings, the logic associated with the enhanced answerphone 17 as shown in Fig. 2 will now be described. The initial condition is that the answerphone extension is On Hook and this is denoted in Figs. 8a and 8b at step 220 also labelled START. In this state, the answerphone can detect three different states: RING DETECT 221, GENERAL ON HOOK 222 and GENERAL OFF HOOK 223.

At step 221 a RING DETECT state is detected, thus denoting an incoming call. The micro-controller 57 is awakened at step 224 thus initiating a routine labelled RECORD STANDBY allowing for the possibility that an incoming call will be recorded in the answerphone. Three possible states can now be detected: GENERAL OFF HOOK 225, MINIMUM NUMBER OF RINGS COUNTED 226 and DIRECT CALLER SELECTION 273. When at step 225 a GENERAL OFF HOOK state is detected, DTMF is awakened at 227 and one of four possible states is awakened: GENERAL ON HOOK 228, "#" plus the answerphone ID extension 229, SMART CODE followed by the answerphone ID number 230 and the answerphone ID number unprefixed by either a "#" or by a SMART CODE 231. The GENERAL ON HOOK state 228 indicates that none of the local extension units has been lifted, i.e. the incoming call has not yet been answered. In this case, at step 232 control branches to START. When at step 229 the user ID of the answerphone 17 is detected prefixed by DTMF "#", this is ignored, for the reasons explained above, because it derives from a SMART CODE having been sent by the calling party in order to transfer his local call to a local extension unit at the remote end

having the same ID as the answerphone. In this case, no action is taken and at step 233 control branches to RECORD STANDBY.

When at step 230, a SMART CODE followed by the ID number of the answerphone is detected, or when at step 231 an unprefixed ID corresponding to the ID of the answerphone is detected, then at step 234 the answerphone 17 is operated in order to record the incoming message until one of three states is encountered: DISCONNECT TONE 235, SMART CODE 236 or the ID of the answerphone 237. When at step 235 DISCONNECT TONE is encountered, this means that the calling party has hung up and the disconnect tone is sent down the line by the central exchange. In this case, at step 238 control reverts to START. Otherwise, when SMART CODE or the same ID as the answerphone are encountered at step 236 or 237, this indicates that a local extension which wished the conversation to be recorded by the answeφhone and so transferred the call thereto, by pressing its Push- Button and dialling the ID of the answeφhone, now wishes to stop the recording process and to this end has either depressed the Push-Button in order to generate a SMART CODE or, alternatively, has dialled the ID number of the answerphone 17. In either case, at step 239 the recording process stops, the answeφhone 17 goes ON HOOK and awaits one of four states: DTMF "#" plus ID 240, SMART CODE PLUS ID 241, the ID of the answer¬ phone unprefixed by the SMART CODE or by DTMF "#" 242 and GENERAL ON HOOK 243.

When, at step 240, the ID of the answeφhone is detected prefixed by DTMF "#", then for the same reasons as explained above, this is ignored and at step 244 control branches to RECORD STANDBY so as to allow either an incoming call to be recorded or a locally initiated outgoing call to be directed also to the answeφhone 17. When at steps 241 or 242 the ID of the answeφhone is detected either prefixed by a SMART CODE or unprefixed, this indicates that a local extension unit has transferred the call to the

answerphone 17 for the purpose of recording the conversation in progress and, in this case, at step 245 control branches to RECORD MESSAGE. When at step 243 a GENERAL ON HOOK condition is detected, this means that all local extension units have shut down and, at step 246 control branches to START.

If after step 224, the MINIMUM NUMBER OF RINGS are counted at step 226, this means that no local extension unit answered the incoming call within the pre-set number of rings, whereupon at step 248, the answerphone goes off-hook and the normal answerphone mode becomes active. Alternatively, following step 224, DIRECT CALLER SELECTION

273 may be initiated as described below with reference to Fig. 8d of the drawings.

It will be appreciated from the foregoing description that, according to the logic shown in Fig. 8a, it is not possible for another local extension unit both to transfer a call to a local extension unit and also to record the conversation in progress on the answerphone. This follows, because the very act of attempting to transfer a call is accomplished first by depressing the Push-Button and this generates a SMART CODE which, at step 236, stops the recording process in the answerphone. If desired, step 236 can be dispensed with so that the recording process will be stopped at step 239 only when the ID number of the answerphone is received by the answerphone at step 237 during the RECORD MESSAGE routine.

As shown in Fig. 8b of the drawings, a GENERAL OFF HOOK condition detected at step 223 denotes that a local extension unit wishes to initiate an outgoing call. In this case, all remaining local extension units go into STANDBY MODE, permitting the call to be transferred thereto by the particular extension unit which initiated the call. The micro-controller is awakened at step 247 and at step 249 DTMF is awakened, whereupon one of three states is awaited: GENERAL ON HOOK 251 , PULSE DIALLED USER ID

NUMBER 252 or SMART CODE PLUS ID 253. As before, the GENERAL ON HOOK condition at step 251 indicates that all local extension units have hung up and, in this case, at step 254 control branches to START. Otherwise, the presence at step 253 of a SMART CODE followed by the ID number of the answerphone or a step 252 of the pulse-dialled answerphone ID, indicates that the local extension unit which initiated the outgoing call wishes to record the call in progress. Therefore, at step 255 the normal answerphone procedure is initiated and the answerphone goes off hook. One of three states is now awaited: DISCONNECT TONE 256, SMART CODE PLUS ANSWERPHONE ID 257 and pulse-dialled answeφhone ID 258. When, at step 256, the DISCONNECT TONE is detected, this means that the calling party has hung up and the disconnect tone is sent down the line by the central exchange. In this case, at step 259, the answerphone goes on-hook and at step 260 control branches to START. When at steps 257 or 258 a SMART CODE followed by the answeφhone ID or the pulse-dialled answer¬ phone ID are received, then, for the reasons explained above, the local extension unit which transferred the call to the answeφhone now wishes to abort the recording process and, in this case, at step 261 recording stops, the answeφhone goes on-hook and at step 262 control reverts to ANSWERPHONE STANDBY.

Referring now to Fig. 8c of the drawings, the logic associated with the ALERT EXTENSION UNITS routine will be described. There are two possible initial states: NO MESSAGES RECORDED 263 or MESSAGES STORED 264. When at step 263 no prior messages are recorded in the answerphone, this means that none of the message indication lamps in the local extension units is yet illuminated and so the answeφhone 17 must send a message indication signal to all the local extension units connected in the system and record the fact so that only one indication signal is sent by the answeφhone and so as to avoid getting into a closed loop. Thus, at step 265, an UPDATE

SIGNAL NOT YET SENT state is detected and, in this case, at step 266 a MESSAGE "OFF" signal is sent by the answerphone to all the local extension units and at step 267 control branches to START. Otherwise, at step 268 an UPDATE SIGNAL ALREADY SENT state is detected and, in this case, there is obviously no need again to send the MESSAGE "OFF" signal to the local extension units and at step 268 control branches directly to START.

When at step 264, MESSAGE(S) ALREADY STORED state is detected, this indicates that a message has been recorded in the answerphone and suitable action must be taken according to whether all the local extension units in the system have been alerted to this fact. Therefore, if at step 268 an UPDATE SIGNAL NOT YET SENT state is detected, then at step 269 a MESSAGE "ON" SIGNAL is sent to all of the local extension units in the system and, at step 270 control branches to START. Alternatively, when at step 271 an UPDATE SIGNAL ALREADY SENT state is detected, there is no need to transmit any further MESSAGE "ON" SIGNAL to the local extension units and, at step 272, control branches to START.

Referring now to Fig. 8d, DIRECT CALLER SELECTION 273 will be described. At step 274 a pre-recorded message is sent to an incoming caller prior to transmission of the dial tone informing the remote caller what DTMF number to send down the line so as to connect directly to a specific local extension unit. If at step 275, no DTMF signal were received, then at step 276 the normal answeφhone process ensues, whereafter at step 277, control reverts to ANSWERPHONE MODE.

If at step 278, a DTMF ID is received, then the pre-recorded message is interrupted allowing one of three states: GENERAL OFF HOOK 280, TIMEOUT 281 and DISCONNECT TONE 282. If GENERAL OFF HOOK is detected at step 280, this means that the requested local extension unit answered and, in this case, control branches to RECORD STANDBY at step 283 so as to allow the local extension unit now on line to transfer the call

to another local extension unit. If at step 281, the called extension does not respond within a pre-set time interval, then TIMEOUT occurs and at step 284 the incoming call is recorded by the answerphone in the normal manner. Thereafter, at step 285, control branches to the RECORD STANDBY routine described above with reference to Fig. 8a of the drawings.

If at step 282, the DISCONNECT TONE is heard meaning that the remote caller hung up, then at step 286 control branches to START. From the foregoing description, it will be clear that the GENERAL OFF HOOK and ZERO VOLT PULSE Detector 34 shown in Fig. 3 must be capable of discrimi- nating between an initial drop in voltage across the line, corresponding to a General Off Hook condition and a still further drop in the voltage across the line corresponding to a Zero Volt Pulse, when a "smart code" is sent down the line. Although throughout this description reference has been made to a Zero Volt Pulse, in fact the voltage level of the signal which is sent down the line consequent to activating the push-button switch 36 can be larger than zero providing that it is susceptible to discrimination from the voltage across the line corresponding to a General Off Hook condition. In practice, however, it is easier to employ a pulse whose voltage level is zero, or substantially zero. Voltage detection circuits inevitably apply a load across the line and infer the line voltage from the current which thus flows through the load. In order for such measurement to be accurate and to avoid loading the line, the load impedance must be as high as possible, theoretically infinite. In practice, of course, the load impedance is less than infinite and as will further be appreciated if more than one voltage signal is to be measured, each by applying a separate load across the line, then the net load impedance will fall even further because the combined impedance of two parallel loads is always less than the individual impedance of each load. Thus, when a large number of telephone extension units are connected across the same

line, it is desirable to maximize as much as possible the load impedance connected across the line by each telephone extension unit in order that the net load impedance across the line does not fall below accepted values. In practice, a significantly reduced loading is normally permissible across the telephone line during a General Off Hook condition than in the opposite case of a General On Hook condition.

Referring to Fig. 9, there is shown a circuit diagram of a General Off Hook and Zero Volt Pulse Detector designated generally as 300 and which comprises a bridge rectifier 301 connected across the tip and ring connections of the telephone line, designated 302 and 303, respectively. A positive rail of the bridge rectifier 301 is connected to GND whilst a negative rail thereof is connected to GND via a voltage divider comprising resistors 304 and 305. A common junction between the resistors 304 and 305 is connected to the non-inverting input 306 of a comparator 307 whose inverting input 308 is connected to a reference voltage V _REF . An output 309 of the comparator 307 constitutes the General Off Hook signal and indicates whether the voltage across the line corresponds to a General Off Hook condition.

A similar circuit is employed for the Zero Volt Pulse Detector and this is connected also between GND and the negative output of the bridge rectifier 301 via a normally open switch 310 which is coupled to the output 309 of the comparator 307 and is responsive to a General Off Hook condition for closing so as to connect the Zero Volt Pulse Detector across the line in parallel with the General Off Hook Detector. Thus, the Zero Volt Pulse Detector also comprises a voltage divider comprising resistors 311 and 312, a common junction of which is connected to the non- inverting input 313 of a comparator 314 whose inverting input 315 is connected to a voltage reference, also designated V _REF , it being understood that this may or may not be the same as the reference voltage employed in

the General Off Hook Detector depending on the relative values of the resistors in the respective voltage dividers. An output 316 of the comparator 314 is representative of the Zero Volt Pulse detection signal. Thus, in normal conditions when the handset is ON HOOK, there is no signal at the output 309 of the comparator 307 and so the normally open switch contact 310 remains open. Under these conditions, the Zero Volt Pulse Detector is completely inactive and disconnected from the line, such that the line sees only the impedance of the General Off Hook Detector. Only when the telephone handset is lifted, giving rise to a GENERAL OFF HOOK condition at the output 309 of the comparator 307, is the switch contact 310 closed, thereby connecting the Zero Volt Pulse Detector across the line.

Thus, by means of the arrangement shown in Fig. 9, the number of loads connected across the line at any given time will be significantly reduced, even when multiple telephone extension units are connected across the same line. Moreover, such an arrangement allows for the loading across the line to be dependent on whether the telephone handset is lifted or not so as to conform with FCC and other similar standards. It will be understood that the normally open switch contact 310 is shown schematically in Fig. 9 and may, in practice, be constituted by a normally open relay contact or by a semiconductor switch as is well known in the art.

Likewise, other modifications to the logic described in detail with reference to the Figures will be apparent to those skilled in the art without departing from the principal inventive concept which allows a telephone extension unit to discriminate between whether a telephone call has been initiated locally or remotely and for processing a detected call signal differently according to whether the signal derives from a locally or remotely initiated call.

In the preferred embodiment, the required discrimination between an incoming and outgoing call is based on the fact that an incoming call is characterized by first receiving a ring signal and this being followed by lifting of the handset. On the other hand, an outgoing call is characterized by first lifting the handset and only then producing a ring signal. However, other forms of discrimination are also feasible. For example, the required discrimination can be effected on the basis that an outgoing call inevitably results in there being produced a dialling signal shortly after lifting the handset whilst, of course, no such dialling signal is produced when the handset is lifted responsive to an incoming call.

It will also be understood that whilst the invention has been described with particular regard to an enhanced answering machine or cordless telephone, permitting a conventional or enhanced telephone extension unit to be connected across a common telephone line for receiving an incoming call and to direct the incoming call to the enhanced telephone extension unit, the latter may also be a facsimile machine or, indeed, any other suitable telephone extension unit. Thus, for example, the invention allows for an enhanced facsimile machine to be connected to the line and for somebody lifting his handset responsive to an incoming facsimile call to direct the call to the facsimile machine, thus obviating the caller the need to redial.