GB2119204A - Telephone exchange line circuit providing special services - Google Patents

Abstract

To provide telephone users connected to analogue exchanges with certain additional facilities the circuit of the invention (1) is connected between an existing exchange line circuit (6) and the user's telephone line. By monitoring the telephone line a data processor in the circuit may distinguish service requests from telephone calls thus avoiding false traffic in the exchange. By use of a second exchange line (4) call transfer, enquiry and conference calls and call divert facilities may be provided. The data processor may also make use of a programmable repertory dialler to provide abbreviated dialling and last number redialling facilities. <IMAGE>

Description

SPECIFICATION Telephone exchange line circuits The present invention relates to telephone exchange line circuits and more particularly to such circuits for use in exchanges utilising analogue speech and/or signalling paths.

The advent of system 'x' telephone exchanges in the United Kingdom telephone network together with digital signalling from 'end to end' of the network permits the telephone authorities to provide their customers with a new range of facilities for example call diversion and conference call facilities. It is certain that once the availability of such services becomes known customers on analogue exchanges which are not scheduled for early replacement will demand some of these facilities.

To provide such facilities could prove expensive in the short term if major modifications to the exchange apparatus and/or the subscribers apparatus of analogue exchanges are required.

It is an object of the present invention to provide a telephone exchange line circuit capable of adapting outgoing lines of analogue telephone exchanges to provide some of the facilities available from a digital telephone exchange.

According to the present invention in a line circuit for connection between a telephone line to a telephone instrument and an exchange line to a telephone exchange, a data processor is arranged to determine from electric signals on the telephone line whether the signals define a telephone calll or a service request and, if the signals define a telephone call, is arranged to cause a signal generator to transmit corresponding electric signals to the exchange line whereas, if the signals define a service request, is arranged to determine the type of service requested and, if the status of the telephone line as determined by a previously received service request so requires, to cause the signal generator to transmit electric signals to the exchange line.

Preferably the line circuit is connected to a plurality of exchange lines such that, if an incoming call is received on one exchange line and the status as determined by a previously received service request is such as to diversion incoming calls, the processor is arranged to cause a further exchange line to be seized and to cause the signal generator to transmit electric signals to the further exchange line to determine the ultimate destination of the call and subsequently to cause a connection between the first exchange line and the further exchange line.

The data processor may also be arranged to monitor the telephone line when a call is in progress and, if further electric signals are received on the telephone line, may be arranged to cause a further exchange line to be seized and to cause the signal generator to transmit electric signals to the further exchange line to cause an additional call to be set up between the telephone line and a further telephone instrument.

The line circuit may be arranged such that, whilst an additional call is in progress the first exchange line is held and the connection between the first exchange line and the telephone line is disconnected. The data processor may then monitor the telephone line for further signals which determine whether the additional call is released and the connection between the first exchange line and the telephone line is re-established or whether a connection between the first exchange line, the further exchange line and the telephone line is established.

The line circuit may also include a programmable repertory dialler such that certain calls may be established by the microprocessor in dependance upon an abbreviated code received from the telephone line.

A line circuit in accordance with the invention will now be described by way of example with reference to the accompanying drawings of which: Figure 1 is a schematic diagram showing the connection of the line circuit in an exchange environment, and Figure 2 is a block schematic diagram of the line circuit.

Referring to Fig. 1 the additional line circuit 1 is interposed between a line 2 from a subscriber's telephone instrument 5 and an exchange line 3 connected to an existing conventional exchange line circuit 6.

To enable certain facilities described hereinafter to be provided the line circuit 1 is also connected to a second exchange line 4 connected to a further existing conventional line circuit 7. The line circuits 6 and 7 interact with exchange switching network 8 in the usual manner for setting up connections to other subscriber's lines (schematically shown as connections 9) and to junction and trunk routes (schematically shown as connections 10).

For reasons of economy of the line circuit 1 the exchange line circuit 7 may utilise the facility known as 'incoming calls barred' when the by-pass service (as hereinafter defined) is not specified, so that calls to the telephone instrument 5 may only be made via the exchange line circuit 6. Thus, the telephone number of the telephone 5 will be the telephone number which would normally be associated with the exchange line circuit 6. Any calls made to the telephone number usually associated with the exchange line circuit 7 are treated as calls to an unobtainable number.

Thus there is no requirement for the exchange line 4 to be busied out by the line circuit 1 when a call has been received or is in pro gress on the exchange line 3.

When the by-pass facility is specified for the exchange line circuit 7, the exchange 'incoming calls barred' facility is not used. The line circuits 6 and 7 are thus identical with each having a unique directory number. The line circuit 1 can connect incoming calls to the telephone 5 from either the line circuit 6 or 7 whilst busying out line circuit 7 or 6 respectively for the duration of the call.

To reduce the complication of the following description of Fig. 2 it will be useful to define certain terms. Reference herein to the 'called party' means a telephone instrument to which a call has been made whilst reference to the 'calling party' means a telephone instrument from which a call originated.

A by-pass call is an incoming call to the line circuit 1, established whilst diversion of incoming calls is active. Thus incoming calls to the line circuit 7 are subsequently connected to the telephone 5 whilst incoming calls on the line circuit 6 are diverted.

'A diverted call' is a call in which the calling party is not connected to the called party whose telephone number was dialled but is connected to another telephone instrument having a telephone number provided by the called party. An 'enquiry call' is a call in which either the calling party or the called party is connected to a further called party whilst the other party to the original call is still connected but not involved. A 'conference call' is a call in which three or more telephone instruments are connected.

Referring to Fig. 2 the line circuit 1 comprises a line bypass circuit 11 which is effectively a changeover switch arranged when the circuit is powered to connect the telephone line 2 through to a connection 1 2 to a line transformer 1 3 and a pulse detector 14. If the line circuit is unpowered then the line bypass 11 connects the telephone line 2 to the exchange line 3 by way of a connection 1 5 such that, in the event of a power failure to the line circuit 1 calls may still be made to and from a connected telephone instrument.

The pulse detector 14 is arranged to detect loop-disconnect dial pulses on the telephone line 2 and to convert the pulses into a suitable form for transfer to a microprocessor 16. The pulse detector may be arranged to transfer the pulses as they are received or may be arranged to detect an inter-digit pause and to assemble the received digit in binary-coded decimal form for transfer to the microprocessor 16.

It will be appreciated that the pulse detector 14 may be replaced by a tone if the telephone instrument provides signalling of digits by using multi-frequency tones.

The pulse detector 14 is also arranged to detect the presence or absence of a loop on the line 2 and to transfer the change in condition to the microprocessor 1 6.

The line transformer 1 3 prevents the generation of false calls on the exchange line 3 when for example the customer is providing a numerical code signal to the microprocessor 1 6 to change the status (hereinafter defined) of the telephone line. Thus if the handset of a telephone instrument connected to the line 2 is raised, the line 2 will be looped in the usual manner but the line transformer 1 3 prevents the loop being transferred to the exchange line 3.

The other elements of Fig. 2 will be introduced as required in the respective exemplary descriptions of six facilities readily provided by use of the line circuit. These six facilities are: A). A simple telephone call B A diverted call C Conference and enquiry calls D An abbreviated dialling call E). Repitition of the last dialled number and F). A bypass call.

When provision for bypass calls is included it should be noted that for the duration of a call using the line 3 and the line circuit 6 the private wire 28 associated with the line circuit 7 is busied out by a busying circuit 29.

Similarly the line circuit 6 is busied out for the duration of a call using the line 4 and the line circuit 7.

Taking a simple outgoing call first (that is the telephone 5 of Fig. 1 is the calling party), when the telephone handset is raised the loop on the line 2 is detected by the pulse detector 14 and is passed to the microprocessor 1 6.

The microprocessor 1 6 causes a pulsing circuit 1 7 to provide a resistive loop to the exchange line 3. The exchange line 3 being looped will cause the exchange to return dial tone to the line circuit which tone is returned to the telephone line 2 by way of the pulsing circuit 1 7 and the line transformer 13. When the pulse detector 14 detects and forwards a pulse to the microprocessor 1 6 the microprocessor causes the pulsing circuit 1 7 to disconnect the line back to the transformer 1 3. Thus although dial tone is still being provided by the exchange it is not passed to the telephone line 2.

When a sufficient number of digits have been received by the microprocessor 1 6 to permit the microprocessor to determine that the digits being dialled define a telephone call and not a service request the pulsing circuit 1 7 is caused to forward the received digits to the exchange line 3. The digits will cause the exchange to react in the normal manner.

When all of the digits received on the line 2 have been transmitted by the pulsing circuit 1 7 the microprocessor 1 6 causes the pulsing circuit to reconnect the exchange line 3 to the line transformer 1 3. Tones indicating the progress of the telephone call will now be received by the telephone line 2 from the exchange in the normal manner.

It is here noted that each time a simple outgoing call is made using the telephone line 2 the dialled number is stored by the microprocessor 1 6 in case it should be subsequently required for use as described hereinafter by the repertory dialling function.

Whilst the call is in progress the dial pulse circuit 14 continues to monitor the telephone line 2 in case the enquiry or conference call facilities (as hereinafter described) are required. It will be appreciated that the pulse detector 14 must also be used to detect cleardown of the call to enable the microprocessor 1 6 to cause the pulsing circuit 1 7 to release the exchange line 3.

Considering now the telephone connected to the line 2 as a called party when the exchange applies ringing current to the line 3 the busy condition on the p-wire 23 is detected by the p-wire detect circuit 27 which forwards a signal to the microprocessor 16.

Since the ringing current cannot be applied to the line 2 with the line transformer 1 3 in series the microprocessor 1 6 causes a metallic path to be set up bypassing the line transformer 13, and activating the ringing detector 19. The ringing current will now be supplied directly from the exchange and an answer signal from the called party will be detected by the exchange in the normal manner.The answer signal causes the exchange to disconnect the ringing current which disconnection is detected by the ringing detector 1 9. On detection of the end of the ringing signal or on detection of the line being looped by the pulse detector 14, the microprocessor 1 6 disconnects the metallic path bypassing the transformer 1 3 and commences monitoring of the line 2 for any service requests.

It is here noted that one of the facilities which may be provided is one of 'transfer if no reply'. Accordingly if the ringing current has not been removed from the line 3 within a predetermined period of time (and if the appropriate service request has been previously received from the line 2) the microprocessor causes a further call to be set up using the line 4 in the same manner as hereinafter described in respect of a diverted call.

Consider now an incoming call to the line circui 1 via the line circuit 7. The exchange applies ringing to the line 4, in the normal manner, the busy condition on the p-wire 28 is detected by the p-wire detect circuit 29, which forwards a signal to the microprocessor 1 6. The microprocessor 16, then causes a metallic path to be set up, by passing the line transformer 1 3 using the line selector 1 8 to select the incoming line 4. The call then proceeds as hereinbefore described for an incoming call on line 3, except that the diversion status is ignored.

Turning now to the diverted call facility the following further terms are used herein and are defined as follows: a "transferring party" is the telephone connected to the line 2, a "nominated number" is the telephone number of the telephone to which calls to the transferring party are to be transferred, an "original call" is a call set up between the calling party and the transferring party, and an "extended call" is a call set up between the calling party and the nominated number.

In the case of a diverted call on detection of an incoming call on the line 3 by the p-wire detect circuit 27, the microprocessor 1 6 causes the line selector 1 8 to select the line 4 and to disconnect the line 3. The change on the line 3 will not be detected by the exchange which will continue to supply ringing current to the line circuit. Since the line selector 1 8 is not connected to line 3 and the line bypass 11 is not connected to the line 3, ringing current is not applied to the line 2.

The pulsing circuit 1 7 is caused to loop the line 4 and to transmit digits defining the nominated number to the line 4. The exchange will set up a call between the transferring subscriber and the nominated number in the normal manner.

The line 4 is now monitored for an answer signal which will be in the form of either a meter pulse from the exchange which is detected by a detector circuit 20 or in the form of a line reversal detected by a respective detector circuit 21. When either detector 20 or detector 21 detects an answer signal, a signal is passed to the microprocessor 1 6 which causes the line selector 1 8 to loop the line 3 to cause the ringing current to be withdrawn and then switches the line 3 to the line 4 by way of a line transformer 22. The line transformers 1 3 and 22 are present to ensure that d.c. potentials on the pairs of lines 2, 3 and 4 are isolated.

The extended call will continue until one or other of the calling party or nominated number clears. A normal cleardown sequence will then be initiated by the exchange. It will be noted that when a call is transferred the calling party will be charged in the normal manner for the call from the calling party to the transferring party. The transferring party will be charged for the call from the transferring party to the nominated number.

When transfer is selected by a user of the telephone connected to the line 2 the micro processor 1 6 is arranged to cause all calls to the transferring party to be directed to the nominated number. So that the transferring party is aware that the facility has been re quested if the handset of the telephone con nected to the line 2 is raised, the microproces sor 1 6 causes a special dial tone to be sent.

Provided that there is not an extended call in progress at the time the handset is raised the line circuit will permit a simple call as previously described to be made. If an ex tended call is in progress then the user of the telephone may make service requests to the line circuit but may not make an outgoing call.

If a service request is made which either cancels the transfer facility or changes the nominated number, the change of status does not become effective until the extended call in progress has ended.

In the ensuing description of conference and enquiry calls it is assumed that the calling party is the telephone attached to the line 2 whilst the called party is connected by way of the exchange line 3. However, the sequence of conference and enquiry calls is identical regardless of which of the two is the called or the calling party. A connection by way of the line 4 is referred to as a connection to a "third party".

Assuming that a connection has been established between the calling party and the called party in the manner hereinbefore described for a simple outgoing call, the pulse detector 14 is monitoring the line 2 for any further dial pulses. If a subsequent signal is detected by the pulse detection circuit 1 4 the microprocessor 1 6 is alerted to a service request. If the request is for an enquiry or conference call the ensuing digits will define the telephone number of a third party. The line selector 1 8 is caused to loop the line 3 (to hold the original call) and to connect the line 4 to the pulsing circuit.The call by way of the line 4 is now set up in the manner described above for a transferred call except that when all of the digits have been transmitted the line 2 is connected to the line 4 by way of the line transformer 1 3 and the line selector 1 8.

This is the enquiry call stage of the connection. The pulse detector 1 4 monitors the line 2 for a subsequent digit to pass to the microprocessor 1 6 which in dependance on the digit dialled either disconnects the line 4 thus releasing the enquiry call and reconnects the original call or causes the line selector to connect the line 3 to the line 4 by way of the line transformer 22 and connects the line 2 to lines 3 and 4 by way of the transformer 1 3.

In the latter case a conference call is in progress.

A further signal detected by the pulse detector 14 in the conference call may indicate either that the call on the line 3 is to be released or that the call on the line 4 is to be released leaving the calling party connected to either the third party or the called party respectively. A further conference or enquiry call may then be made using whichever of the lines 3 and 4 has been released. If the line 3 is released it is necessary to prevent incoming calls. Accordingly a busy indication is applied to the exchange private wire 23 by a busying circuit 24. This indicates to the exchange that the line is not available.

It will be realised that digits received on the line 2 indicate either a service request or a part of a telephone number. Accordingly if a digit is received by the line circuit from the line 2 within, say, five seconds of a previously received digit it is deemed a part of a telephone number and is transmitted to the ex-change accordingly. If the period since receipt of a preceding digit exceeds five seconds then the digit is determined as a further service request.

To provide an abbreviated dialling facility a repertory dialler 26 is provided in the present circuit having the ability to store up to ten twenty digit telephone numbers, selectable by the telephone user. It will be appreciated that a larger capacity repertory dialler could be employed. However, if the capacity of the repertory dialler 26 is too great the service request code plus the code to define which of the telephone numbers in the library of the repertory dialler is required may exceed the number of digits in the telephone number.

On detection of the appropriate service code the microprocessor 1 6 requests the telephone number from the repertory dialler 26 and causes the number to be transmitted to the line 3 for the exchange to effect the connection in the same manner as previously described for the setting up of a simple outgoing call.

It is possible to combine a number of service requests. For example in the case of an enquiry call the calling party may dial the service code for an enquiry call followed by the service code for abbreviated dialling of one of the ten numbers held in the repertory dialler 26.

Similarly the telephone number to which diverted calls are to be made may be defined by use of the service code.

Having thus far described some of the facilities provided by the line circuit it is convenient to mention a suitable coding arrangement for the service codes.

The microprocessor is programmed to recognise '13' as initial digits for requesting a service when a call is not in progress. If the following digit is a 'one' then the request is to activate a certain facility (for example the 'transfer' or 'transfer of no reply' facility). If the following digit is a zero ('ten') then the request will be to de-activate a certain facility.

The '131' or '130' codes are chosen as unused codes in a telephone network. It will be realised that any "free" digit combination may be used.

Having received a '131' or '130' code the microprocessor 1 6 awaits a service code. For example to activate the transfer service a user will dial '13121' followed by the telephone number to which calls are to be transferred.

The telephone number is stored in the microprocessor 1 6 and is used as required.

The microprocessor 1 6 is arranged such that if ' 1 3121 is received without a following telephone number incoming calls are connected to the last telephone number nominated with a transfer request. If no previous transfer service request has been received the request will be ignored.

"21" being the service code for transfer the facility is cancelled by the user dialling '13021'. The transfer on no reply' service is requested by the user dialling '13122' and is cancelled by '13022'.

For abbreviated dialling the user dials '13' (the service request), '3' (abbreviated dialling service code) and 'n' (where n is in the range '1' to 'O') to define which of the ten numbers held in the repertory dialler 26 is required.

To insert a telephone number in the library of the repertory dialler 26 the user dials '13151 n' followed by the telephone number.

If all of the numbers in the library are to be cancelled a code of '130051' is dialled whilst to cancel one of the numbers in the library a code of '13051 n' is used.

If a repetition of an immediately preceding dialled number is required a code of '134' is used.

When a call is in progress and a digit is received on the line 2 an enquiry call request is indicated. It is convenient to use the digit '1' this being the shortest digit. The digit will be followed by either the telephone number or an abbreviated dialling request.

Once an enquiry call has been established digit '1' releases the enquiry call and recon nects the original call and digit '2' causes the establishment of a conference call.

When a conference call is in progress digit '42' releases the third party call and digit '41' releases the original call.

Claims (9)

1. A line circuit for connection between a telephone line to a telephone instrument and an exchange line to a telephone exchange wherein a data processor is arranged to determine from electric signals on the telephone line whether the signals define a telephone call or a service request and, if the signals define a telephone call, is arranged to cause a signal generator to transmit corresponding electric signals to the exchange line whereas, if the signals define a service request, is arranged to determine the type of service requested and, if the status of the telephone line as determined by a previously received service request so requires, to cause the signal generator to transmit electric signals to the exchange line.

2. A line circuit as claimed in Claim 1 which is also arranged for connection to a second exchange line to a telephone exchange and the data processor is programmed such that, if an incoming call is received on one of the exchange lines and the status of the line circuit as determined by a previously received service request is such as to divert incoming calls to a different telephone, the other exchange line is seized by the line circuit and the signal generator is caused to transmit electric signals to said other exchange line which signals determine the ultimate destination of the call, the processor also being arranged to cause a subsequent connection between the two exchange lines.

3. A line circuit as claimed in Claim 2 wherein the data processor is also arranged to monitor the telephone line when a call is in progress using one of said exchange lines and, if further electric signals are received on the telephone line, is arranged to cause the other exchange line to be seized and to cause the signal generator to transmit electric signals to said other exchange line to cause an additional call to be set up between the telephone line and a different destination.

4. A line circuit as claimed in Claim 3 wherein the circuit is arranged such that when an additional call is in progress said one of said exchange lines is held and the connection between that exchange line and the telephone line is disconnected, and a connection is effected between the telephone line and said other exchange line.

5. A line circuit as claimed in Claim 4 wherein the data processor is also arranged whilst an additional call is in progress to monitor the telephone line for further signals which signals determine either whether the additional call is released and the connection between the first said exchange line and the telephone line is re-established, or whether a connection between both exchange lines and the telephone line is established.

6. A line circuit as claimed in any precedinc claim including a programmable repertory dialler wherein the data processor is responsive to signals received on the telephone line to establish certain telephone calls in response to an abbreviated code.

7. A line circuit as claimed in any preceding claim wherein the data processor is a microprocessor.

8. A line circuit as claimed in any one of claims 2 to 7 wherein the data processor is arranged to cause the connection of any incoming call on said additional exchange line to the telephone line regardless of whether the status of the line circuit as determined by a previously received service request is such as to divert incoming calls.

9. A line circuit substantially as hereinbefore described with reference to Fig. 2 of the accompanying drawings.