JPH0359633B2 - - Google Patents

Description

[Detailed Description of the Invention] (1) Technical Field of the Invention The present invention relates to a subscriber circuit that interfaces with a public telephone set, and particularly to a subscriber circuit for a digital exchange that enables high-quality mutual calls between public telephone sets. This relates to a mutual communication system using communal telephones.

(2) Background of the technology Currently, communal telephones are widely used in central office telephone exchanges for subscribers who do not use telephone calls frequently. The restrictive conditions for communal telephones include the period during which one of the communal telephone subscribers is using the telephone;
Other subscribers cannot use the telephone. On the other hand, the technological development of switching equipment has recently been shifting from space-division switching to time-division switching. It is also necessary to accommodate communal telephones in time-division exchanges, and there is a need for effective implementation means that take into account connection means specific to time-division exchanges.

(3) Prior art and problems A mutual communication system between communal telephones in a conventional space division switch will be explained with reference to FIG. 1st
In the figure, 1 and 2 are public telephones, 3 is a space division switch, 4 is an outgoing register trunk (ORT),
5 indicates a ring signal trunk. Now, in Figure 1a, subscriber 1 requests a mutual call with subscriber 2, and dials the special number "112".
The originating register trunk (ORT) 4 receives this via the network (NW) 3 and notifies the control system (not shown). The connection of the outgoing register trunk (OTR) 4 to the ring signal trunk (RGT) 5 is switched by a command from the control system. The ringing signal trunk (RGT) 5 executes a 60 inter paging signal to the subscriber 1 and the subscriber 2, detects that the subscriber 2 responds, and performs a ring trip. During the call period between Party A and Party B, the ringing signal trunk (RGT) 5 monitors the call status between Party A and Party B, and the network has closed the selection route between Party A and Party B and the ringing signal trunk (RGT) 5. keep it as it is.

When subscriber 1 or subscriber 2 makes a call to a third party (not shown) via an exchange, the third trunk is used. Here, ORT4 and RGT5 are high impedance terminations for audio frequencies, and the third trunk is a matched termination. In this way, in SD exchanges, multiple types of trunk circuits with dedicated functions are connected and switched to the desired trunk at the desired timing, so during mutual calls, high impedance is applied to the voice frequency. It was easy. On the other hand, in the TD exchange
BORSCHT function (B: battery, O: overvoltage protection, R: ringing, S;
A plurality of subscriber-related functions, such as supervisory (C; codec; H; hybrid; T; test), are realized on one type of subscriber circuit. As is well known, the communication current supply circuit B
has high impedance for the audio frequency to prevent audio signal attenuation, and the 2-wire 4-wire conversion circuit H has a matched termination for the audio frequency, that is, the subscriber line has a matched termination for the audio frequency to prevent signal reflection. Terminated with characteristic impedance. Therefore, when talking to each other using a public telephone, the impedance of this 2-wire/4-wire conversion circuit affects the voice signal on the subscriber line. For this reason, there was a problem in that the audio signal level decreased and the quality of the call deteriorated.

(4) Purpose of the Invention The present invention provides a method for terminating a 2-wire and 4-wire conversion circuit in a subscriber circuit, which is always matched terminated for the voice frequency, to a high impedance termination for the voice frequency during mutual communication between communal telephones. It is an object of the present invention to provide an intercommunication system for communal telephones that enables mutual communications between communal telephones.

(5) Structure of the Invention According to the present invention, in a subscriber circuit for accommodating a subscriber line in which a plurality of telephones are connected in parallel and are made into a common telephone subscriber, in a digital exchange, the voice frequency a speech current supply circuit that is high-impedance terminated for the subscriber line and supplies speech current to the subscriber line; a two-wire four-wire conversion circuit that is matched terminated for voice frequencies; When making a call to a subscriber, connect the 2-wire 4-wire conversion circuit to the subscriber line in parallel to the call current supply circuit for matching termination, and when making calls between the plurality of communal telephones, This is achieved by providing a switching means that disconnects the two-wire and four-wire conversion circuit from the subscriber line and provides high impedance termination using the communication current supply circuit.

(6) Examples of the invention Embodiments of the present invention will be described in detail below with reference to the drawings.

Figure 2 shows the block configuration of the subscriber circuit that interfaces with public telephones in the TD exchange. Although the subscriber circuit 25 has a plurality of types of subscriber-related functions, only those functions particularly required for interfacing with a public telephone set are described here. The power supply circuit 16 includes a pair of complementary transistors 12, 13 and resistors 14, 1.
5, it supplies telephone current to telephones 1 and 2 and performs subscriber monitoring (including dial pulse reception). The 2-wire 4-wire conversion circuit 18 has matching termination for the audio frequency, and is connected to the telephone 1 or 2.
It has a function that allows a telephone call to be made between the telephone and a third telephone other than telephones 1 and 2. PCM code/
The decoder 19 performs analog-to-digital conversion with the 2-wire/4-wire conversion circuit 18. switch 2
2 has a function of connecting the ringer sound source 24 to the subscriber line in conjunction with the switches 6 and 7 when a 60 inter call signal is sent to 1 and 2. Specifically, switches 6 and 7 are closed and switches 8 and 9 are opened, and switch 26 is closed to the side for 0.5 seconds.
The switch 22 is controlled to close to the side.

For the next 0.5 seconds, the switch 26 closes to the side,
The switch 22 is controlled to close to the side. Thereafter, the call signal for the 60 inters is sent out by similarly sending out the ringer sound source and the air at a 0.5 second cycle. 10 is a response detection circuit for detecting a response to the sending of a calling signal, and 11 indicates a detection output. 17 and 23 indicate batteries.

The operation of the subscriber circuit 25 during mutual communication between communal telephones will be described with reference to FIG.

In the empty state, switches 8 and 9 are closed, switch 22 is closed to the side, switch 26 is closed to the side, and switch 12 is closed to the side.
~17 enables subscriber monitoring and diamond pulse reception.

Now, dial the special number “112” from phone number 1 from 12 to
17, it notifies the control circuit of this detection.
The control circuit opens switches 8 and 9, closes switches 7 and 6, and performs the operations described above to issue a ring signal for the 60 inter. At this time, the control circuit sends out second control data indicating mutual calling together with first control data regarding other calling signals (for example, sending an IR calling signal). The second control data is made valid until the mutual communication between 1 and 2 is completed. A pair of switches 20 and 21 that connect and disconnect the two-wire and four-wire conversion circuit 18 electrically connected in parallel with the switches 12 to 17 are opened and controlled using the second control data. That is, after receiving the special number, telephone A and telephone B 1 and 2 are alternately called by the calling signal of the 60 inter, and the switches 20 and 21 are controlled to open so that the subscriber circuit 25 is switched from telephone A and telephone B 1 and 2. The impedance to the audio frequency when viewed is high impedance. As a result, telephone A and telephone B B receive DC communication current from the subscriber circuit 25, but since the subscriber circuit 25 is equivalently disconnected from the voice, a drop in the voice level is expected. It will not be possible.

As described above, in the embodiment of the present invention shown in FIG. 2, the communication current supply (BS) section is made high impedance,
Matching and termination are performed at the 2-wire and 4-wire conversion (H) section.

It goes without saying that the same effect can be obtained even if the mutual telephone communication system of the present invention is applied to subscriber circuits having other configurations.

(7) Effects of the Invention According to the present invention, even in the subscriber circuit for a TD converter, the subscriber circuit can be set to high impedance with respect to voice frequencies during mutual communication between communal telephones, so there is no drop in voice level. It is possible to make calls to.

[Brief explanation of drawings]

FIG. 1 is a block diagram for explaining mutual communication in a conventional space-division exchange, and FIG. 2 is a block diagram showing an embodiment of the present invention. In the drawing, 1 is the public telephone A, 2 is the public telephone O, 3 is the network, 4 is the outgoing register trunk (ORT), 5 is the ringing signal trunk (RGT), 6, 7, 8, 9, 20, 21 and 22 are switches, 10 is a response detection circuit, 11 is a response detection output, 12 and 13 are transistors, 14 and 15 are resistors, 16 is a communication current supply circuit, 17 and 23 are DC power supplies, and 18 is a 2-wire 4 A line conversion circuit, 19 an encoder/decoder, 24 a ringer sound source, and 25 a subscriber circuit, respectively.

Claims (1)

[Scope of Claims] 1. In a subscriber circuit for accommodating a subscriber line in which a plurality of telephones are connected in parallel and are made into a communal telephone subscriber to a digital exchange, the subscriber line is terminated with high impedance for voice frequencies, and the subscriber line is a speech current supply circuit that supplies speech current to a telephone line; a two-wire four-wire conversion circuit that is matched terminated for voice frequencies; The 2-wire 4-wire conversion circuit is connected to the subscriber line in parallel to the current supply circuit to provide a matched termination, and when the plurality of communal telephones communicate with each other, the 2-wire 4-wire conversion circuit is connected to the subscriber line in parallel to the current supply circuit. 1. A subscriber circuit for a communal telephone set, comprising switching means that is disconnected from the subscriber line and is terminated at a high impedance by the call current supply circuit.