Private branch exchange system with attendant console

Abstract: A private branch exchange system having connected thereto a telephone line (30) of a public telephone network, a plurality of extensions (50), and at least one attendant console (25), comprising: an attendant console control circuit (21) corresponding to each of the attendant consoles (25) in a main frame (10) of the private branch exchange system. A speech signal from a speech path exchange circuit and control signals are multiplexed at the attendant console control circuit (21) to be sent through a transmission line (24) to the corresponding attendant console (25), and a speech signal and control signals from the attendant console (25) are multiplexed at the attendant console (25) to be sent through a transmission line (24) to the corresponding attendant console control circuit (21).

Description: BACKGROUND OF THE INVENTION (1) Field of the Invention The present invention relates to a private branch exchange system according to the preamble of claim 1. Such a system is known from WO-A-86/06901. This document discloses an operator control system, where incoming lines and outgoing lines from a trunk circuit are inputted to a main frame switch circuit. There are several attendant consoles interconnected to the switch circuit via transmission lines. Furthermore, there are also provided multiplexes/demultiplexes that multiplex control signals from the switch circuit with some speech data received from the transmission lines. In each attendant console a multiplexer multiplexes the D-channel and the B-channel provided for data and speech, respectively. The aim is here that each of the attendant consoles be connected individually to one of the plurality of extensions (remote data bases). Thus, the voice signals pass through the trunk and the circuit switching network and the control signals from the processor are transferred through the packet switching network. The voice signal and the control signals are multiplexed in the multiplexer to be transmitted to one of the operator positions, where the voice signals are contained in the B-channels and the control signals are contained in the D-channel. In the operator position, the multiplexed signals are divided into the voice signals and the control signals. Thus, a respective multiplexer multiplexes the voice signal from the customer on line and the data signal from the data communication path and the paths of the control signals on D-channels are interconnected between the respective apparatuses, such as the processor, the operator position and the remote data bases with a protocol conversion being carried out in a separate block. With the necessary use of the D-channels such a private branch exchange system becomes bulky, costly and complicated. In private branch exchange systems, an attendant console is connected thereto for responding to an incoming call from a telephone line which is connected with a public telephone network, and calling a party on an extension to which a calling party requests to speak. Conventionally, in middle or large-size private branch exchange systems, a plurality of attendant consoles are provided in an attendant console room which is located near the main frame of the private branch exchange system. However, recently, in many factories and offices, the plurality of attendant consoles are located dispersively, for example, in reception offices and secretaries' offices in a plurality of divisions or departments. Generally, a large number of control signals are required to be transmitted between the main frame of the private branch exchange system and the attendant console through long distances. (2) Description of the Related Art Figure 1 shows a construction of a conventional private branch exchange system as disclosed in GB-A-1 577 461. In Fig. 1, reference numeral 30 denotes a public telephone line, 40 denotes the main frame of the private branch exchange system, 41 denotes a trunk circuit connecting with the public telephone line, 42 denotes a switch circuit, 431 and 432 each denote an attendant console control circuit, 44 denotes a central control circuit, 441 and 442 each denote an attendant console, 461 and 462 each denote a set of transmission lines connecting between an attendant console and the main frame of the private branch exchange system, 451 and 453 each denote a lamp indicating portion, 452 and 454 each denote a key input portion, and denotes an extension. In the construction of Fig. 1, when a call is incoming in the trunk circuit 41, the central control circuit 44 sends a control signal which indicates that a call is incoming to all the attendant consoles 441 and 442 through the corresponding attendant console control circuits 431 and 432. Responding to the signal, lamp indicators in the lamp indicating portions 451 and 453 which indicates an incoming of a call from the public telephone line 30, is turned on in each of the attendant consoles 441 and 442. When an operator at one of the attendant consoles 441 and 442 pushes a key the input from which generates a control signal which indicates that the operation at the attendant console will respond to the incoming call, the control signal from the attendant console is transmitted to the central control circuit 44 through the corresponding attendant console control circuit. Responding to the control signal which is first received in the central control circuit 44, the central control circuit 44 controls the switch circuit 42 to connect the above attendant console control circuit 431 from which the above control signal has been first sent to the central control circuit 44, to the trunk circuit 41. Thus, the operator at the attendant console 441 can speak with the calling party through the attendant console control circuit 431 and the trunk circuit 41, and can learn the party to which the calling party wishes to speak, by speaking with the calling party. When the operator at the attendant console 431 recognizes the party to which the calling party wishes to speak, the operator inputs the number of the extension of the party to which the calling party wishes to speak, from the key input portion 452. The number of the extension is transmitted from the attendant console 441 to the attendant console control circuit 431, and is transferred to the central control circuit 44. Receiving the number of the extension of the party to which the calling party wishes to speak, the central control circuit 44 controls the switch circuit 42 to connect the extension of the party to which the calling party wishes to speak, to the trunk circuit 41. In the above operation, the man-machine interface at the attendant consoles 441 and 442 is realized by the keys in the key input portions 452 and 454 and the lamp indicators in the lamp indicating portions 451 and 453. The lamp indicators turn on and off responding to pushing of the keys, and it is required that the delay of the turn-on or turn-off of the lamp indicators in the response to the pushing of the keys is less than 200 msec so as to be natural to the operator. In the prior art, the CCITT V.11 system is utilized for transmission of control signals between attendant console control circuits and corresponding attendant consoles. According to the CCITT V.11 recommendation, a balanced cable is used for transmission of control signals in each direction from an attendant console control circuit to a corresponding attendant console, and from the attendant console to the corresponding attendant console control circuit, i.e., a pair of balanced cables are laid between each of the attendant consoles 441 and 442 and the main frame 40 of the private branch exchange system, in addition to transmission lines for transmitting speech signals between each of the attendant consoles 441 and 442 and the main frame 40 of the private branch exchange system. As mentioned before, recently, the attendant consoles are located dispersively around the main frame of the private branch exchange system, and therefore, the distances between the attendant consoles and the main frame 40 of the private branch exchange system are large. However, generally, the above V11 system requires additional equipment for a long distance transmission, and the provision of the additional equipment increases cost for construction. Further, when the distances between the attendant consoles and the main frame 40 of the private branch exchange system are large, the cost in constructing the whole private branch exchange system is increased due to the above laying of the pair of balanced cables. SUMMARY OF THE INVENTION The object of the present invention is to provide a private branch exchange system having connected thereto an attendant console and a plurality of extensions, wherein transmission between a main frame of the system and the attendant consoles can be carried out using a small number of transmission lines, such that the cost for constructing the whole system is reduced. This object is solved by a private branch exchange system as defined in claim 1. According to one aspect of the present invention, there is provided a private branch exchange system connecting a telephone line of a public telephone network and a plurality of extensions thereto, comprising: a main frame, at least one attendant console, and a transmission line, provided for each attendant console. The main frame comprises a trunk circuit, a switch circuit, a central control circuit, and at least one attendant console control circuit. Each of the above attendant console responds to an incoming call, receives a speech signal from a calling party, sends a speech signal to the calling party, inputs control information for transferring an incoming call to one of the plurality of extensions, sends control signals to the central control circuit, and receives control signals from the central control circuit. Each of the transmission line connects the attendant console with the corresponding attendant console control circuit, transmits the control signals between the attendant console with the corresponding attendant console control circuit. The trunk circuit is connected to the telephone line of the public telephone network, receives an incoming call through the public telephone network, and transmits an incoming and outgoing speech signal. The switch circuit connects the trunk circuit with one of the attendant console and the plurality of extensions under control of the central control circuit. The central control circuit sends control signals to the attendant console and receives control signals from the attendant console, and controls the switch circuit to connect the trunk circuit with one of the attendant consoles and the plurality of extensions according to the control signal from one of the attendant consoles. Each of the attendant console control circuits comprises a first multiplex transmission circuit which multiplexes the speech signal from the switch circuit and the control signals from the central control circuit, and transmits the multiplexed signal on the transmission line, and the first multiplex transmission circuit further receives a signal from the transmission line, and demultiplexes the received signal into a speech signal which is to be sent to the switch circuit, and control signals which are to be sent to the central control circuit. The attendant console further comprises a second multiplex transmission circuit which multiplexes the speech signal from the switch circuit and the control signals from the central control circuit, and transmits the multiplexed signal on the transmission line, and the second multiplex transmission circuit further receives a signal from the transmission line, and demultiplexes the received signal into a speech signal and control signals. Further, the above first and second multiplex transmission circuits alternately and periodically send and receive the multiplexed signal through the transmission line. Alternatively, the first and second multiplex transmission circuits send and receive the multiplexed signals through the transmission line so that the multiplexed signals from the first and second multiplex transmission circuits are transmitted simultaneously on the transmission line as a frequency division multiplex transmission. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Figure 1 is a block diagram of the conventional private branch exchange system having connected thereto an attendant console and a plurality of extensions; Figure 2 is a block diagram of a private branch exchange system having connected thereto an attendant console and a plurality of extensions, in an embodiment of the present invention; and Figure 3 shows the data format and timing in the transmission between an attendant console control circuit in the main frame of the private branch exchange system and an attendant console in the construction of Fig. 2. DESCRIPTION OF THE PREFERRED EMBODIMENTS Figure 2 is a block diagram of a private branch exchange system having connected thereto an attendant console and a plurality of extensions, in an embodiment of the present invention. Only the construction including an attendant console and a corresponding attendant console control circuit, is shown in Fig. 2, and the construction of the private branch exchange system in the embodiment of the present invention which is not shown in Fig. 2, is the same as the construction of Fig. 1. In Fig. 2, reference numeral 10 denotes the main frame of the private branch exchange system, 22 denotes a switch circuit, 21 denotes an attendant console control circuit, 23 denotes a central control circuit, 25 denotes an attendant console, 24 denotes a two-wire transmission line connected between the attendant console 25 and the main frame 10 of the private branch exchange system, 211 and 251 each denote a time compression multiplex transmission control circuit, 212 and 253 each denote an asynchronous transmission control circuit, 252 denotes a speech signal transformation circuit, 254 denotes a lamp indication control circuit, 255 denotes a key input control circuit, 214 and 256 each denote a microprocessor unit, 213 and 257 each denote a memory, and 258 denotes a headset comprising a microphone and an ear receiver. In the construction of Fig. 2, the central control circuit 23 holds all the statuses of the private branch exchange system, sends control signals of the statuses to the attendant console control circuits (including the attendant console control circuit 21), receiving control signals which are generated by key operations at the attendant consoles (including the attendant console 25), and controls the switch circuit 22 to connect the trunk circuit with one of the attendant console control circuits or extensions according to an incoming call or the control signals from the attendant consoles. When the microprocessor unit 214 in the attendant console control circuit 21 receives a control signal from the central control circuit 23 through the interface circuit 215, the microprocessor unit 214 stores the status which is indicated by the received control signal in a corresponding address in the memory 213. The memory 213 in the attendant console control circuit 21 holds the statuses of the private branch exchange system which are necessary for the corresponding attendant console 25. The statuses held in the memory 213 are periodically sent to the corresponding attendant console 25 through the asynchronous transmission control circuit 212, the time compression multiplex transmission control circuit 211, and the two-wire transmission line 24. Each byte of the above statuses held in the memory 213 is read and is sent to the asynchronous transmission control circuit 212 as control signals in the form of parallel data under control of the microprocessor unit 214. The asynchronous transmission control circuit 212 transforms the received parallel data comprised of each eight bit portion of the above statuses, into a serial form, and sends the serial data as control signals to the time compression multiplex transmission control circuit 211 as an asynchronous transmission, for example, a start-stop transmission. The time compression multiplex transmission control circuits 211 and 251 are provided for controlling the transmission of the control signals between the attendant console control circuit 21 and the attendant console 25 through the two-wire transmission line 24. Figure 3 shows the data format and timing in the transmission between the attendant console control circuit 21 in the main frame 10 of the private branch exchange system and an attendant console 25 in the construction of Fig. 2. As shown in Fig. 3, the transmission between the attendant console control circuit 21 and the attendant console 25 is carried out periodically in the period of T=125 msec. Transmission of a downstream frame from the attendant console control circuit 21 to the attendant console 25 is carried out in the first half cycle of each cycle T in a burst mode, and transmission of an upstream frame from the attendant console 25 to the attendant console control circuit 21 is carried out in the second half cycle of each cycle T in a burst mode. In each of the downstream frames and the upstream frames, "F" denotes a frame synchronization pattern, "B1" denotes a B1 channel, "B2" denotes a B2 channel, and "D" denotes a D channel, i.e., each transmission frame contains three channels. Each of the B1 and B2 channels contains 8 bits, and the D channels contains 2 bits. Namely, the transmission rate of each of the B1 and B2 channels is 64 Kbps, and the transmission rate of the D channel is 16Kbps. The time compression multiplex transmission control circuit 211 in the attendant console control circuit 21 receives digital speech signal (PCM signal) which has been transmitted from the calling party through the telephone line, the trunk circuit, and the switch circuit 22, and the above control signals from the asynchronous transmission control circuit 212, multiplexes the received signals in the frame as shown in Fig. 3, and sends them through the two-wire transmission line 24 to the corresponding attendant console 25, in the above first half cycle, and the time compression multiplex transmission control circuit 211 receives the multiplexed signal in the frames as shown in Fig. 3 through the two-wire transmission line 24 from the corresponding attendant console 25, demultiplexes the received signal into the digital speech signal (PCM signal) and the above control signals, and sends the digital speech signal (PCM signal) to the switch circuit 22, and the control signals to the asynchronous transmission control circuit 212, in the above second half cycle. The digital speech signal is transmitted to the calling party through the switch circuit 22, the trunk circuit, and the telephone line. The above digital speech signals are transmitted through the B1 channel, and the above control signals are transmitted through the B2 channel. The D channel is not used. The asynchronous transmission control circuit 212 transforms the control signals which are received from the time compression multiplex transmission control circuit 211 into parallel one-byte data, and transfers the parallel data (control signals) to the microprocessor unit 214. When the microprocessor unit 214 receives the control signals from the asynchronous transmission control circuit 212, the received control signals are once stored in the memory 213 as a part of the statuses, and are then transferred to the central control circuit 23 through the interface circuit 215. In the attendant console 25, the time compression multiplex transmission control circuit 251 functions in a similar manner to the above time compression multiplex transmission control circuit 211. The time compression multiplex transmission control circuit 251 receives the above multiplexed signal in the frame as shown in Fig. 3 through the two-wire transmission line 24 from the corresponding attendant console 25, demultiplexes the received signal into the digital speech signal (PCM signal) and the above control signals, and sends the digital speech signal (PCM signal) to the speech signal transformation circuit 252, and the control signals to the asynchronous transmission control circuit 253, in the above first half cycle. The speech transformation circuit 252 receives the digital speech signal from the time compression multiplex transmission control circuit 251, and transforms the received digital speech signal into an analog speech signal. The analog speech signal is supplied to the ear receiver in the headset 258. An analog speech signal which is generated in the microphone in the headset is input into the speech signal transformation circuit 252, and is transformed to a digital speech signal to be supplied to the time compression multiplex transmission control circuit 251. The key input control circuit 255 is provided for generating a key input signal responding to a key operation by an operator. The key input signal is once stored in the memory 257 under control of the microprocessor unit 256 as control information, and the control information which is held in the memory 257 is then transferred to the asynchronous transmission control circuit 253 as control signals under control of the microprocessor unit 256 in a parallel form. When the asynchronous transmission control circuit 253 receives the parallel control signals from the memory 257, the asynchronous transmission control circuit 253 transforms the parallel control signals into a serial form, and the control signals in the serial form are transferred to the time compression multiplex transmission control circuit 251. The time compression multiplex transmission control circuit 251 receives the above digital speech signal from the speech signal transformation circuit 252, and the control signals from the asynchronous transmission control circuit 253, multiplexes the received signals in the frame as shown in Fig. 3, and sends the multiplexed signals through the two-wire transmission line 24 to the corresponding attendant console control circuit 21, in the above second half cycle. When the asynchronous transmission control circuit 253 receives the above control signals from the time compression multiplex transmission control circuit 253 in a serial form, the control signals are transformed into a parallel form, and are then transferred to the memory 257 as statuses to the microprocessor unit 256 as an asynchronous transmission. The microprocessor unit 256 stores the received control signals in the memory 257, and controls the lamp indication control circuit 254 to turn on the light indicators according to the statuses which are held in the memory 257. In the above construction, the control signals which are transmitted from the central control circuit 23 to the attendant console 25 include, for example, a status signal indicating that a call is incoming, and the control signals which are transmitted from the attendant console 25 to the central control circuit 23, include, for example, dialing information which has been input from the key input portion of the attendant console 25 by the operator, and is transmitted from the attendant console 25 to indicate a number of an extension of a party to which a calling party wishes to speak. All control signals are repeatedly transmitted between the attendant console control circuit 21 and the attendant console 25, and each status held in each of the memories 214 and 256 in the attendant console control circuit 21 and the attendant console 25, is renewed every time a corresponding control signal is received in the attendant console control circuit 21 and the attendant console 25, respectively. Thus, even if a bit of the control signals is erroneously transmitted, an erroneous status corresponding the erroneously transmitted bit is once written in the memory 214 or 257, however, it is then renewed by a correct status when a correct bit corresponding to the above erroneously transmitted bit is transmitted in the next transmission cycle. Using the above construction for the transmission between the attendant console control circuit and the attendant console, an operation for attending to an incoming call in the private branch exchange system which is similar to the operation explained before with reference to Fig. 1, is carried out in the embodiment of the present invention. As explained above, according to the present invention, both the speech signals and the control signals can be transmitted through a common transmission line as a time-divisionally multiplexed signal between the attendant console and the attendant console control circuit. Therefore, the number of the cables which are necessary to be laid between the attendant console and the attendant console control circuit, can be reduced, and the cost for constructing the whole private branch exchange system is reduced. Further, according to the above time compression multiplex transmission system, the transmission of the speech signals and the control signals in both directions between the attendant console and the attendant console control circuit can be carried out using only a two-wire transmission line. Although the time compression multiplex transmission is used in the above embodiment, any other transmission system wherein transmission of signals in both directions is possible using only one transmission line, for example, a frequency division multiplex transmission system, can be used instead of the time compression multiplex transmission system.

Claims: A private branch exchange system having connected thereto a telephone line (30) of a public telephone network and a plurality of extensions (50), comprising: a) a switch circuit (22); b) a central control circuit (23); c) at least one attendant console control circuit (21); d) at least one attendant console (25) respectively connected with a corresponding one of said attendant console control circuits (21), for responding to an incoming call, receiving a speech signal from a calling party, sending a speech signal to the calling party, sending control signals to said central control circuit (23) and receiving control signals from said central control circuit (23); and e) a transmission line (24) provided for each attendant console (25) for connecting a respective attendant console (25) with the corresponding attendant console control circuit (21), for transmitting said control signals between the attendant console (25) and the corresponding attendant console control circuit (21); f) said switch circuit (22) connecting said telephone line (30) with one of said attendant consoles (25) and said plurality of extensions (50) under control of said central control circuit (23); g) said central control circuit (23) sending control signals to said attendant console (25) and receiving control signals from said attendant console (25), and controlling said switch circuit (22) to connect said telephone line (30) with one of said attendant console (25) and said plurality of extensions (50) according to a control signal from one of said attendant console (25); h) each of said attendant console control circuits (21) comprising a first multiplex transmission circuit (211) for multiplexing said speech signal from the switch circuit (22) and said control signals from said central control circuit (23) and transmitting said multiplexed signal on said transmission line (24); and for receiving a multiplexed signal from the transmission line (24) and demultiplexing said received signal into a speech signal which is to be sent to the switch circuit (22), and control signals which are to be sent to said central control circuit (23); i) said attendant console (25) comprising a second multiplex transmission circuit (251) for multiplexing said speech signal to be sent to the switch circuit (22) and said control signals to be sent to said central control circuit (23) and transmitting said multiplexed signal on said transmission line (24), and for receiving a multiplexed signal from the transmission line (24) and demultiplexing said received signal into a speech signal and control signals; characterized in that j) transmission of said multiplexed signals over said respective transmission lines (24) between each attendant console control circuit (21) and a respective attendant console (25) is carried out in transmission frames (F, B1, B2, D) with said respective control signals being transmitted in one (B2) of the B-channels (B1, B2) of the respective transmission frame and said speech signals being transmitted through the other one (B1) of said B-channels (B1, B2) of said transmission frame and with D-channels (D) not being used. A private branch exchange system according to claim 1 characterized in that transmission of a downstream transmission frame from a attendant console control circuits (21) to a attendant console (25) is respectively carried out in the first half cycle of each cycle (T) in a burst mode, and transmission of an upstream transmission frame from the attendant console (25) to the attendant console control circuit (21) is carried out in the second half cycle of each cycle (T) in a burst mode, whereby said first and second multiplex transmission circuits (211, 251) alternately and periodically send and receive said multiplexed signal to said transmission line (24). A private branch exchange system according to claim 1, wherein said first and second multiplex transmission circuits (211, 251) send and receive said multiplexed signals through said transmission line (24) so that the multiplexed signals from the first and second multiplex transmission circuits (211, 251) are transmitted simultaneously on the transmission line (24) as a frequency division multiplex transmission. A private branch exchange system according to claim 1, characterized by a trunk circuit (41) connected to said telephone line (30) of said public telephone network for receiving said incoming call through said public telephone network and transmitting said incoming and outgoing speech signals; said switch circuit (22) connecting said trunk circuit (41) with one of said attendant console (25) and said plurality of extensions (50) under control of said central control circuit (23); and said central control circuit (23) sending to and receiving from said attendant console (25) control signals, and controlling said switch circuit (22) to connect said trunk circuit (41) with one of said attendant console (25) and said plurality of extensions (50) according to the control signal from one of said attendant console (25).

Inventors: HIOKI SATOSHI, ISHIBASHI MASAAKI, SHIMASUE TSUTOMU, SHIMAZAKI KAZUHISA, HIOKI, SATOSHI, ISHIBASHI, MASAAKI, SHIMASUE, TSUTOMU, SHIMAZAKI, KAZUHISA
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1990
Main classification: H04M3
IPC codes: H04Q3, H04Q11, H04M3