GB2084429A

GB2084429A - PBX telephone systems

Info

Publication number: GB2084429A
Application number: GB8128863A
Authority: GB
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1980-09-25
Filing date: 1981-09-24
Publication date: 1982-04-07
Also published as: FI812976L; DE3036169A1; AU7564581A; BR8106112A; EP0048924A1; NO813219L

Description

SPECIFICATION PBX telephone systems This invention relates to a telephone system for use in small private branch exchange (PBX) systems where a plurality of telephone sets is connected in a star-arrangement to a central device for digital data signal transmission. In small private branch exchanges in which it is a prerequisite for two-way alternate signalling to take place between the telephone sets and the central device common to them, this signalling takes place via an additional signalling wire pair which, together with the speech wire pair provided in the customary way, forms the relevant subscriber's line. The individual telephone sets primarily transmit information concerning the actuation of individual keys to the central device.Beside the digit selection keys, other keys can be provided which allow specific operating procedures or by whose actuation it is possible to signal the type of connection intended. It is therefore possible to distinguish, for example whether an internal connection to another telephone set of the private branch exchange is to be established or an external connection to a telephone set of the public network or to a telephone set of another private branch exchange. The central device transmits mainly connection data to the telephone sets for visual display elements fitted to them. These display elements can, for example, be in the form of light emitting diodes which by their light-emitting state can indicate to the subscriber whether the external lines of the internal lines are engaged or free. The data for all display elements provided on a telephone set can be gathered together in a data block and transmitted as binary digital signals. It is an object of the invention to provide the additional functions associated with the use of the signalling wire-pair as described with a minimum of additional complexity. According to a first aspect of this invention there is provided a telephone system for use in small private branch exchange systems, said telephone system comprising a plurality of telephone sets connected in a star-arrangement to a central device by means of a subscriber line comprising a signalling wire-pair and a speech wire-pair, each signalling wire-pair being arranged for two-way alternate transmissions of digital data signals between the relevant telephone set and the central device, for enabling actuation of manually operated elements of the telephone set to give rise to data transmission controlling functions including setting up internal and external calls, and for enabling data transmission controlling operation of elements, including visual display elements, of the telephone set,said visual display elements being arranged for indication operating states of the system or of a telephone connection and/or occupancy states of link circuits, each telephone set having a control unit for driving the visual display elements and for controlling the function sequence necessary for transmission and reception of digital data signals, the various components in the telephone set associated with the two-way alternate digital transmission comprising electronic elements or packages arranged as a digital transmission unit occupying a recess in a casing of the telephone set, the voltage supply for the unit components being arranged via the signalling wire-pair. In particular example, at least one of the telephone sets is of a type whose casing recess was intended for a digit selection unit. According to a second aspect of this invention there is provided a digital transmission unit for use in a telephone set of a system according to first aspect, said unit comprising the components associated with the two-way alternate digital transmission and capable of occupying a recess in a casing of a telephone set so as to receive power via the signalling wire-pair. An embodiment of this invention will now be described, by way of example, with reference to the accompanying drawing in which the sole figure is a block circuit diagram of a PBX system embodying this invention. The drawing shows the basic structure of a small private branch exchange (PBX) in which two-way alternate signalling takes place between a central device ZSt and individual telephone sets TS1 to TSx. The individual telephone sets TS1 to TSx are connected in radial configuration (stararrangement) to the central device ZSt common to them each view a four-wire subscriber's line. Each subscriber's line consists of a speech wire-pair a, b and a signalling wire-pair c, d. The speech data and ringing current are transmitted via the speech wire-pair concerned. The signalling wire-pair is used for two-way alternate transmission data exchange. At the same time it supplies with power the function units present in each telephone set for effecting this data exchange. A speech circuit SS is connected to the speech wire-pair leading to each telephone set, shown symbolically only as a single wire. The speech circuit SS, in conjunction with the handset HA, is used for processing the transmitted speech data and forms a line termination. Internal connections can be established between the individual telephone sets TS and there is also the possibility of being connected to one of several external lines EL. These can lead to the public telephone network or to another private branch exchange. The type of connection desired can, for example, be signalled by the actuation of a key provided for the purpose on the telephone set. For the telephone set TS 1 the possibility of initiating the transmission of certain data by the actuation of keys is indicated by the key pad TB. The key Tw is intended to indicated the presence of a standard selection keyset. The key Te represents a set of keys by means of which specific additional functions can be initiated. If it is intended to set up an external connection the appropriate information is received by the central device ZSt. Subsequent operation of one of the keys of the selection keyboard causes the control unit Pa present in the central device ZSt to output the selection data assigned. This can be affected on the external line selected for the purpose by means of normal dialling pulse generation by loop interruption with the aid of the unit IW. The control information necessary for this is supplied by the control unit Pz, which also issues the connecting commands for the switching matrix network KN.This switching matrix network then enables the connection to be switched through by appropriate actuation of its crosspoints. While active signalling from the individual telephone sets to the central device is only brought about by the actuation of a key or by the lifting of the handset, such signalling in the opposite direction, that is, from the central device to the telephone sets, must be carried out considerably more frequently. The data transmitted by the central device related primarily to connection information for visual display elements. These visual display elements are shown for the telephone set TS 1 as LED's L1 to Ln. They can be used to indicate, for example, the engaged condition of the individual external lines or the engaged condition of the internal lines. The appropriate control information is applied to the signalling line concerned in the form of binary digital signals, it being possible to form the binary values by modulation of the signalling line voltage.For example, the active binary value corresponding to a "logl" - bit can, for example, be formed by a determinate drop of the signalling pair voltage. The binary value corresponding to a "logO"-bit can be characterized by the quiescent voltage state of the signalling line concerned. In small private branch exchanges the same data in most cases has to be transmitted to the individual telephone sets. This can be effected by means of a common sending circuit Sz, which is controlled by the control unit Pz provided in the central device ZSt. This sending circuit is multiple-connected at the output end to one wire, for example the c-wire, of each signalling wire-pair. The bit pattern corresponding to the information to be transmitted within a data block which has been formed is transmitted to this sending circuit by the control unit Pz by means of a corresponding transmitter bit timer.The sending circuit then effects the appropriate modulation of the signalling line voltage. The signalling line quiescent voltage is supplied in the same way as the supply voltage for the unit SE to be connected to the speech wire-pair for supplying the microphone with power. This SE can, for example, represent a current transformer to be supplied with mains voltage. If it is intended for the individual telephone sets to receive different data, this can be achieved using the common sending circuit Sz by means of a simple selection circuit S1 to Sx, arranged in the central device for each telephone set. By means of this selection circuit it is possible to insert an additional data bit in a predefined place in the data block transmitted by the common sending circuit. This can be effected for example by a voltage drop on the c/-wire which leads to the telephone set which is to receive the information. Consequently, the total information contained in the data block concerned is only evaluated by the evaluation circuit provided for the purpose in this assigned telephone set. For the telephone set TS 1, the units associated with the digital signalling and the visual display elements are combined in a digital transmission unit BS. The same applies to the other telephone sets. These function units are constructed with the least possible circuit complexity. Electronic components or packages are used as far as possible. The individual function units are combined into this unit with regard to spatial dimensions in such a way that they can be inserted in the casing recess, provided in a standard mass-produced conventional telephone set, for accommodating the number selection keyboard. A receiving circuit Et is used for evaluating the voltage variations which occur on the signalling wire-pair.The receiving circuit Et converts the bit pattern transmitted from the central device ZSt by modulation of the line voltage into an appropriate pulse train and passes this on to control unit Pt. This recognizes the information contained in the pulse train and supplies, for example, the drive commands for the LED's L1 to Ln. These LED's can be supplied with power via the regulator circuit IR2. Those LED's which for example should be switched off can be effectively bypassed by an electronic switch controller accordingly by the control un Pt. The data to be transmitted from the telephone set is transmitted by modulation of the current flowing on the signalling line. The binary values of the digital data to be transmitted are formed by a current drop, which can correspond to a "logl"-bit, and by the quiescent current value of the signalling line, which then corresponds to the "logO"-bit. This data can be gathered separately in a data block, one data block then being transmitted alternately to the central device ZSt and from the central device ZSt to the telephone set concerned. The data can also be interleaved with the data transmitted from the central device ZSt bit-by-bit within a data block which is to be formed on reception. Actuation of one of the keys of the key pad or lifting of the handset is registered by the control unit Pt. Besides a timing unit TG, this control unit also contains a microprocessor MP.Transmission of the data formed by current modulation is effected by a sending unit S, which in turn is controlled by the control unit Pt. The sending unit S can basically consist of an electronic switch, by means of which for example a regulator unit IR1 is switched off. This regulator unit is used in the practical example for supplying power to the control unit Pt. During the time that the regulator unit IR1 is switched off, this supply can be maintained by a storage element contained in it. By switching the regulator unit off, the current flowing in the signalling wire-pair is reduced by the current value otherwise consumed by this regulator unit. With the current drop which takes place, an appropriate data bit within each data block can be sent to the central device ZSt. The digital data transmitted from the telephone set in the manner described is registered in the common facility by a receiving circuit E1 to Ex in each case coupled to a respective wire of each signalling line and passed to the control unit Pz. This then initiates the functions which are to follow. Electronic components and packages are used as far as possible for the construction of the individual function units which are additionally provided in each telephone set for the purposes of the digital data transmission. This consequently reduces the space requirement for these addtional function units. Moreover these function units are coupled spatially to the set of selection keys in such a way that the entire digital transmission unit can be fitted in place of the key-board provided in a mass-produced conventional telephone set. Consequently, a telephone set is obtained which can provide additional functions without changes to its external form and dimensions. This is advantageous as compared with the obvious solutions, namely of accommodating the additional function units in an auxiliary device coupled to the telephone set or completely redesigning the casing with due regard to the additional functions. The digital transmission unit, besides the actuating elements for number selection or for issuing other control information, consists of the receiving and sending units necessary for data exchange and a control unit which controls their functions This control unit can contain a timing unit and a microprocessor. In addition, units can be provided which regulate the current consumption of individual function units.

Claims

1. A telephone system for use in small private branch exchange systems, said telephone system comprising a plurality of telephone sets connected in a star-arrangement to a central device each by means of a subscriber line comprising a signalling wire-pair and a speech wire-pair, each signalling wire-pair being arranged for two-way alternate transmission of digital data signals between the relevant telephone set and the central device, for enabling actuation of manually operated elements of the telephone set to give rise to data transmission controlling functions including setting up internal and external calls, and for enabling data transmission controlling operation of elements, including visual display elements, of the telephone set, said visual display elements being arranged for indicating operating states of the system or of a telephone connection and/or occupancy states of link circuits, each telephone set having a control unit for driving the visual display elements and for controlling the function sequences necessary for transmission and reception of digital data signals, the various components in the telephone set associated with the two-way alternate digital transmission comprising electronic elements or packages arranged as a digital transmission unit occupying a recess in a casing of the telephone set, the voltage supply for the unit components being arranged via the signalling wire-pair.

2. A telephone system according to claim 1 wherein at least one of said telephone sets is of a type whose casing recess was intended for a digit selection unit.

3. A telephone system according to claim 1 or claim 2 wherein said visual display elements are incorporated in the digital transmission unit.

4. A telephone system according to any one of the preceding claims wherein at least one of the telephone sets provides a loud-speaker and/or a handsfree facility.

5. A telephone system for use in small private branch exchange systems, said telephone system being substantially as described herein with reference to the accompanying drawing.

6. A digital transmission unit for use in a telephone set of a system according to any of the preceding claims, said unit comprising the components associated with the two-way alternate digital transmission and capable of occupying a recess in a casing of a telephone set so as to receive power via the signalling wire-pair.

7. A digital transmission unit according to claim 6 wherein the unit can occupy the casing recess of a conventional telephone set intended for the digit selection unit.

8. A digital transmission unit for use in a telephone set of a system according to any one of claims 1 to 5, said digital transmission unit being substantially as described herein with reference to the accompanying drawing.

9. A method of constructing a telephone set for use in a system according to any one of claims 1 to 5, said method including the steps of inserting a digital transmission unit according to any one of claims 6 to 8 into a recess in a casing of the telephone set.

10. A method according to claim 9 wherein the digital transmission unit is inserted into a casing recess of a conventional telephone set and intended for a digit selection unit.

11. A method of constructing a telephone set for use in a system according to any one of claims 1 to 5, said method being substantially as described herein with reference to the accompanying drawing.

12. A telephone set for use in a system according to any one of claims 1 to 5, said telephone set including a digital transmission unit according to any one of claims 6 to 8.

13. A telephone set according to claim 12 wherein the set is constructed by a method according to any one of claims 9 to 11.

14. A telephone set for use in a system according to any one of claims 1 to 5, said telephone set being substantially as described herein with reference to the accompanying drawing.