JP4022206B2 - Bidirectional communication device - Google Patents

Description

  The present invention relates to a bidirectional communication device, and more particularly to a device capable of searching a target connection partner from multiple channels at high speed.

  A general CATV line is unidirectional, but in the future it is switching to bidirectional. In the case of unidirectional CATV, the subscriber only receives the broadcast / data transmitted from the broadcasting station. However, in the case of bidirectional CATV, only one unit can always transmit in one channel. However, the subscriber can send broadcast / data to the center or other subscribers.

  In order to perform bi-directional communication over the CATV line, bi-directional channels are set for the upstream and downstream bands. The number of channels to be set is determined by the number of users who can receive the interactive service at the same time, the busy hour call volume, the call loss rate, the line hold time, and the like. For example, since the transmission frequency bandwidth for data communication that can be occupied by a communication terminal with one free channel is 6 MHz, when the communication channel bandwidth is 12.5 kHz, 6 MHz ÷ 12.5 kHz = 480, which is theoretically 480. Can be obtained.

  Normally, the channels that can be used in the CATV line are as shown in FIG. 8, but in the case of a broadcasting station that is actually operated, UHF stations and satellite broadcasting stations are operated independently in addition to normal terrestrial (TV broadcasting). Broadcasting programs, municipal emergency broadcast programs, etc., the number of free channels that can be used for multiple purposes is gradually decreasing. In order to perform various services within the limited free channel, it is necessary to connect a large number of communication terminals to the CATV line.

  Conventionally, as a line connection method in a CATV line, as shown in FIG. 9, there is a method in which one communication terminal A, B,. According to this, since one communication terminal is dedicated to one channel, the time required for connection is very short, but it cannot be used by many communication terminals due to the limitation of the number of empty channels. Further, communication can be performed only between predetermined communication terminals. If you compare it to a train seat, it will not be a reserved seat where anyone can sit if you make a reservation, but it will be a fixed seat where a certain person can sit.

Therefore, a technique called MCA ( Multi Channel Access) has been considered. This divides the transmission frequency band for data communication set in the uplink / downlink into equally spaced frequency slots, and, as shown in FIG. 9B, the lines from the communication terminals A, B. Based on the connection request, the center 71 searches for an empty channel, assigns the empty channel as a communication channel to the communication terminals A, B..., And the transmitter and the receiver of each communication terminal acquire the frequency and communicate with each other. Is. MCA is likened to a free seat. In the case of a non-reserved seat, the vacant seat is searched from the end while searching for a vacancy.

  The MCA described above has an advantage that communication can be performed between arbitrary communication terminals, but there is a disadvantage that it takes a long time to connect depending on the increase in the number of communication terminals to be connected and the number of channels to be searched. . This corresponds to the fact that a vacant seat is searched from the end in the case of a non-reserved seat, so that it is difficult to find a vacancy when there are many people.

  Considering the actual operation, for example, in the case of a home medical system using a CATV line, the above-mentioned CATV principle is used. Therefore, a host station installed in a hospital sequentially connects many medical communication terminals on the CATV line. Need to poll and collect data. In such a case, it takes a time proportional to the number of times data is collected. For example, assuming 9600 BPS to communicate data of about 32 Kbytes, it takes about 35 seconds. Assuming that the loss time of the line connection in the MCA is about 25 seconds, adding the above-mentioned about 35 seconds to the loss time and setting the time required for collecting data per case to be about 1 minute, 500 pieces of data It will take about 8 hours and 20 minutes to collect. However, if the line connection loss is reduced to about 5 seconds, the same 500 data collection will be completed in about 5 hours and 30 minutes. Accordingly, it is highly desired to shorten the line connection loss.

  In the case of MCA, the number of communication terminals that can be connected to a channel is limited by the number of channels, but since the number of available empty channels is decreasing, it is expected that the number of communication terminals connected will be insufficient in the near future. There is a risk that various services cannot be received.

Further, in the case of MCA, the center bears all operations such as searching for an empty channel at the start of communication and determining a channel when communicating between communication terminals, and notifies each other's communication terminal via the center. Therefore, there is a problem that a large-scale facility is required for the center.
In addition, since the number of channels that can be used in the CATV line is gradually decreasing and must be used in the limited free channel, the CATV line tends to be blocked, and when the CATV line is blocked, a call is made. / There was a problem that communication could not be secured and service could not be improved.

  The problem described above is not limited to the bidirectional CATV line, but is common to the bidirectional wireless line.

SUMMARY OF THE INVENTION An object of the present invention is to provide a bidirectional communication device that can automatically switch from a CATV line to a general line (NTT) when the CATV line cannot be used , by solving the above-mentioned drawbacks of the prior art. There is.

  According to a first aspect of the present invention, there is provided a bi-directional communication device that performs bi-directional communication between a plurality of communication terminals connected to a CATV line via a center. When not in use, a general telephone line is connected to the communication terminal in addition to the CATV line so that the CATV line can be used preferentially over the general telephone line. This is a bidirectional communication device that automatically switches the communication terminal on the receiving side from a CATV line to a general telephone line when the call channel is in use.

  A second invention is a communication device of a bidirectional line which is a wireless line in place of the CATV line in the first invention.

  According to the present invention, when the CATV line cannot be used, the CATV line can be automatically switched to the general line (NTT). Therefore, the user is not kept waiting.

  Furthermore, according to the present invention, the present invention is not limited to a bidirectional CATV line, but can also be applied to a bidirectional wireless line.

  An embodiment in which a bidirectional line communication apparatus of the present invention is applied to a bidirectional CATV line will be described below with reference to the drawings.

  As shown in FIG. 7, a signal (upstream signal) from the communication terminal to the broadcasting station and a signal (downstream signal) from the broadcasting station to the communication terminal are distinguished from each other at 60 MHz. Broadcasts such as TV broadcast programs and satellite broadcast programs are downstream signals, and reports related to home security, home medical system data, home video games and online karaoke requests are upstream signals. In order to perform bidirectional communication between a center connected by a CATV line and a plurality of communication terminals, or between a plurality of terminals, as shown by the dotted lines in FIG. An uplink data communication transmission frequency band 51 and a downlink data communication transmission frequency band 52 for communication are set.

  A large number of channels are obtained by dividing the set transmission frequency bandwidth for data communication at equal intervals by the call channel bandwidth. Among these, a call channel for performing a call is set to n lines, and at least one inquiry channel for transferring call channel information from each communication terminal is set. If the transmission frequency bandwidth for data communication is 6 MHz and the communication channel bandwidth is 12.5 kHz, the number of channels obtained is 480 as described above, but some of these are inquiry channels, and the rest Is a call channel.

  Here, as shown in FIG. 1 (a), in order to search for an unspecified communication partner on the CATV line, one communication channel (transmission / reception call) is used while the number of communication terminals A, B. One communication terminal is assigned to (channel). Here, S1 to Sn are call channels, and R1 is an inquiry channel.

  Further, when the number of communication terminals A, B,... In the entire system increases beyond the n-line communication channels S1 to Sn, as shown in FIG. Assign multiple units and consider this as a group. For example, 2 to 3 units.

  Such allocation of communication channels to communication terminals is managed by a database to be described later.

  A unique identification number ID is assigned to each communication terminal. Then, the n communication channels S1 to Sn are assigned to the unique identification numbers ID of the communication terminals A, B,... And the database 3 is created by associating the assigned communication channels with the identification numbers. Is set on the computer 2.

  FIG. 2 shows a specific example of the database 3 corresponding to FIG. Each of the two empty channels is divided into 480 channels, and the reception / transmission frequency is assigned to the identification number ID of each communication terminal. The reception frequency and the transmission frequency are paired, and the reception frequency is obtained by frequency conversion of the transmission frequency at a certain rate. This fixed ratio is not common to any broadcasting station, but is a value specific to the broadcasting station to be installed. In the case of FIG. 2, the frequency obtained by adding 94 MHz to the upstream frequency is returned as downstream.

  In the table, the reception / transmission frequencies assigned to IDs 0000 0000 to 0000 0007 are used for inquiry frequencies, system management, and emergency broadcasting. In addition, when considering a home medical care system, if the common identification number ID of the communication terminal is the same as the last eight digits (39814131) of the home phone number (for example, 03 (3981) 4131), it is very understandable. Cheap.

  In FIG. 1 (a), when the communication terminal on the calling side of the call is A and the communication terminal on the receiving side is G, the communication channel assigned to the communication terminal G from the communication terminal A to the center 1 In order to know S7, the identification number 007 of the communication terminal G is notified through the inquiry channel R1. The center 1 notified of the identification number 007 of the communication terminal G searches the database 3 for the communication channel S7 corresponding to the identification number 007 of the communication terminal G, and finds the communication channel S7 corresponding to the identification number 007 of the communication terminal G. When the communication terminal G having the identification number 007 corresponding to the communication channel S7 is not busy, the communication channel A of the communication terminal G is notified to the communication terminal A.

  The communication terminal A that has received the communication channel S7 of the communication terminal G performs a transmission operation to the communication terminal G through the communication channel S7 of the communication terminal G. When the communication terminal G performs an incoming call operation, the communication terminal A notifies the communication terminal G of the call channel S1 corresponding to the identification number 000 of the communication terminal A. The communication terminal G notified of the call channel S1 performs a transmission operation to the communication terminal A through the call channel S1 of the communication terminal A, thereby realizing a call between the communication terminal A and the communication terminal G.

  Also, in FIG. 1B, when communication terminal A performs a call operation within the group, communication channel S4 assigned to this group is used by another communication terminal B within the group. The terminal A makes a call within a range in which ± 1 to ± m (m is an integer smaller than n and a value within the moving range of the frequency of the one call channel) channel is added to the call channel S4 assigned to the group. Check channel availability. If it is available, the call channel S4 of the communication terminal A is changed to the available call channel, for example, S3, and the changed call channel S3 of the communication terminal A is notified to the center 1 through the inquiry channel R1, Transmission operation to the communication terminal G is performed. After that, the communication terminal A and the communication terminal G check the unique identification numbers 000 and 026 between the communication terminal A on the calling side and the communication terminal G on the receiving side. carry out. After the call is finished and after the communication of the other communication terminal B in the group is finished, the changed call channel S3 of the communication terminal A is returned to the original call channel S4, and at the same time the database 3 of the center 1 using the inquiry channel. Update.

  The present invention is just a reserved seat when compared to a train seat. FIG. 1A shows a case where only one person is reserved for one channel. However, since normal communication is not performed all day, it is not preferable from the viewpoint of efficiency to always have one channel occupied by one person. Therefore, as shown in FIG. 1B, the reserved seat is treated like a group seat. Look at the volume of calls per channel and assign several people to one channel. Look at the reserved seat and use it as it is if no one is using it. If someone is using it first, search for a vacancy near the reserved seat. Even if your reserved seats are in use, the seats right next to them are often vacant. In this case, the longer the search range, the longer it takes to find “vacant”, but the smaller the search range, the less time it takes to find “vacant”.

  Here, when the communication channel S4 assigned to the group is used by another communication terminal B in the group, the number of channels to be moved in addition to the call channel S4 assigned to the group is ± 1 to ± m ( The reason why m is an integer smaller than n and is within the range of the frequency movement range of the one call channel is to reduce the connection loss and speed up the search. If m = n This is because the connection loss increases as in the case of MCA, and if m = 0, the state does not change from the state of FIG. Practically, about ± 1 to ± 3 is preferable.

  In the present invention, the communication terminal A, not the center, searches for an empty channel at the start of communication, notifies the communication terminal G of the communication channel S1 corresponding to the identification number 000 of the communication terminal A, or calls assigned to groups. Check the availability of the communication channel within the range of adding ± 1 to ± m (m is an integer smaller than n and a value within the moving range of the frequency of the one communication channel) to the channel S4, or a communication terminal Since the determination of the channel when communicating with each other is borne on behalf of the center, the burden on the center is reduced and the center can be operated with simple equipment. This increases the burden on the communication terminal, but the increased burden can be easily absorbed by the advancement, higher functionality, and lower cost of the electronic devices that make up the communication terminal.

  Hereinafter, a bidirectional CATV communication system will be described in detail.

  As shown in FIG. 3, the center 1 has a CATV broadcasting facility 4 and a management computer 2. A plurality of communication terminals 6 are connected to the center 1 through a wireless or wired CATV line 5. The plurality of communication terminals 6 have a function of transmitting / receiving data between arbitrary communication terminals 6 and transmitting / receiving data for communication from the management computer 2 of the center 1. The communication terminal 6 has a mechanism capable of setting at least the transmission frequency and the reception frequency from software uniquely installed in the CPU or a management computer, for example, a preset mechanism for fixing a specific frequency to the PLL.

  From the communication terminal 6, transmission data is sent from the CPU 7 through the modem 8. The transmission data enters the LPF 9 through the modem 8, and after unnecessary components in the high band are removed by the LPF 9, the FM modulator 10 performs FM modulation on the designated FM broadcast band, and the FM signal passes through the BPF 11 to generate unnecessary waves. Removed. The signal from which the unnecessary wave has been removed is mixed with the oscillation signal of the VCO 14 adjusted to the transmission frequency setting signal by the PLL 13 by the mixer 12 and converted into an adjustment frequency set in advance by CATV. After conversion, unnecessary components in the high band are removed by the LPF 15 and then sent to the RFAMP 16 to be amplified to a predetermined level necessary for sending to the center 1. The gain of the RFAMP 16 is controlled by an AGC voltage supplied from the CPU 7 through the modem 8. The amplified signal passes through the RFGATESWITCH 17 for protecting from transmission errors due to inflow noise controlled to be closed by the transmission control signal, and is sent to the center 1 through the DUPLEXER 18 through the CATV line 5.

  On the other hand, the data signal output from the center 1 is input from the DUPLEXER 18 to the communication terminal 6, mixed with the signal of the oscillator 20 by the mixer 19, and the mixer 19 when the carrier of the data signal matches the set reception frequency. Is taken out of. The frequency of the oscillator 20 is controlled by phase-detecting the local oscillation signal and the reception frequency setting signal generated by the oscillator 20 by the PLL 21 and extracting the error voltage to feed back to the oscillator 20.

  The first intermediate frequency signal (10.7 MHz) is extracted from the signal output from the mixer 19 by passing through the first-stage BPF 22, and further the IF center frequency ± 455 kHz for removing adjacent interference at the second-stage BPF 23. The selectivity characteristics above a predetermined level can be obtained. Then, the FMDET 24 detects a change in frequency as a change in voltage, and a part of the detected signal removes unnecessary noise in the squelch circuit 25 and removes unnecessary high-frequency components through the LPF 26, and then receives the modem 8 as received data. Through the CPU 7 and processed.

  When a plurality of communication terminals are connected to a single channel as shown in FIG. 1 (b) in the CATV line having the above-described environment, an actual communication terminal (hereinafter referred to as a call station) 4), although a part of the procedure for communication by connecting a line with a communication terminal on the receiving side (hereinafter called a called station) is omitted, it is roughly as shown in FIG. Here, for convenience, uplink / downlink attached to a channel is referred to as transmission / reception, and a channel without limitation of transmission / reception means both transmission / reception.

  (1) The call station starts transmission (401), selects the called station (402), and then sets the reception frequency to one of several transmission inquiry channels to which the reception frequency is assigned in advance. The PLL 21 is set (preset), the presence or absence of the carrier received through the DUPLEXER 18 is determined by the CPU 7, and it is confirmed whether the transmission inquiry channel of the one frequency is not used by another communication terminal (403). In the case where a plurality of communication terminals are assigned to one call channel, it is necessary to confirm this since one or more communication terminals cannot simultaneously transmit to the same channel. If it is in use, the setting of the reception frequency is set to the next frequency of the transmission inquiry channel and the same is confirmed.

  Here, if an unused transmission inquiry channel can be confirmed, the confirmation is stopped, the frequency of the transmission inquiry channel is stored in the CPU 7, and the same frequency as that is set as the transmission frequency in the PLL 13 on the transmission side. Transmission operation is possible for the inquiry channel. In addition, in order to set a reception inquiry channel on the reception side, the reception frequency obtained by frequency conversion of the transmission frequency at a certain rate is set in the PLL 21 on the reception side to prepare for reception of an inquiry response. If all are in use, the call station user is notified that the call is busy and the process ends (405).

  (2) The call station transmits inquiry data about the frequency of the called station to the center 1 through the above-described transmission inquiry channel via the DUPLEXER 18 (404). In the center, from the database on the computer 2 for system management, information on the call channel for receiving / transmitting the called station and information on whether or not the called station is currently talking are sent from the receiving side through the reception inquiry channel to the CPU 7. (406). At this point, it is determined whether the called station exists (412) or the called station is not in use (413). If the called station is not registered or is busy, both The call station user is notified that the call is in progress and ends (405).

  (3) Next, the call station uses the pre-assigned transmission call channel as the main, and checks whether the transmission call channel is used by other communication terminals in the same group in the same manner as in (1). To do. Again, when a plurality of communication terminals are assigned to one call channel, one or more communication terminals cannot transmit to the same channel at the same time.

  (4) Here, when the transmission call channel is being used, the reception frequency setting value of the PLL 21 on the receiving side is moved, and several channels before and after the main transmission call channel, for example, the main transmission call channel are ± The usage status of the channels in the range including 1 to ± 3 channels is sequentially confirmed, and an unused transmission call channel is detected and determined from the status (see FIG. 1B). If all are in use at this time, the user of the call station is notified that it is busy, and the process ends.

  (5) The call station stores the call channel in the CPU 7, sets the frequency of the transmission call channel as the transmission frequency in the PLL 13, and is assigned to the called station that is the call partner notified from the system management computer 2. An outgoing call operation is performed for a call channel (407).

  Data to be transmitted for establishing communication here includes a unique identification number ID on the call station side, a unique identification number ID on the called station side, a transmission / reception call channel on the call station side, spare data for future expansion, communication Checksum data for confirming the accuracy of the contents. The reason why the call station sends the other party's ID and own ID is that the application used may use it.

  (6) After receiving the data from the call station (416), the called station B in the reception standby state (415) checks the transmitted unique identification number ID (417), and the ID is its own If it does not match the unique identification number ID, the incoming call is abandoned, and the next unique identification number ID frame is waited for. The matched called station notifies the calling station that the start of the call is permitted (418). At the same time, information such as the transmission / reception call channel on the called station side is also notified. Here, the called station confirms the ID because there is a possibility that another communication terminal is connected to one call channel, and it is necessary to select one of the target terminals.

  In addition, when a plurality of communication terminals are connected to the receiving side and the received plurality of communication terminals are other than their own IDs, the following (a) Alternatively, the operation (b) is performed.

  (A) When it is desired to transmit, as described above, an empty range is searched for within a range of about ± 1 to ± 3 of the set call channel, and the operation shifts to a transmission operation.

  (B) When waiting for reception Continues reception using the calling channel set in the inquiry channel, and waits until it is called. If the call is not called from another communication terminal, when the call on the originally assigned call channel ends, the call is waited on the assigned call channel. When called from another communication terminal, the call channel is used to search for a vacant channel within the range of ± 1 to ± 3 of the allocated call channel, and the result is reported to the center. Receive and wait to be called. When the call is over, it waits for the next call on the originally assigned call channel.

  (7) When the call station receives a permission notice from the called station, both the calling station and the called station open the lines (409, 419), and start communication / communication (410, 420).

  (8) After the call ends, the call channel to which the call station has moved is returned to the original setting value. Here, the reason why the call channel is returned to the original setting value is to prevent the channel allocated to the communication terminal subscribed to the CATV broadcasting station from being shifted. This is because, if the “vacant” seat that was discovered by accident is set as a reserved seat for one person, the number of reserved seats for one seat can be shifted, which is inconvenient.

  As described above, the correspondence between the unique identification number of the communication terminal and the frequency is stored in the database 2 on the computer 2 that manages the communication system, and communication with the communication terminal of the connection partner is performed in response to a request from the communication terminal. Necessary data is exchanged using a database, so the target connection partner can be searched at high speed.

  In addition, since the connection relationship of the communication terminals can be easily changed by simply rewriting the contents of the database, in order to search for an unspecified communication partner on the CATV line, there is only one communication terminal with a small number of communication terminals. One unit can be assigned to a channel, and two or three communication terminals can be assigned to one channel as the quantity increases. In particular, when a plurality of communication terminals are assigned to one channel, it is possible to connect more communication terminals than the number of channels. Can also be supported.

  In addition, when 2 to 3 communication terminals are assigned to one channel, if a preset channel is used according to the line usage status, the channel moves by itself and finds an empty channel within the movement range. Since it did in this way, compared with MCA which moves all the channels, the target connection partner can be searched at higher speed. For this reason, for example, in a home medical system using a CATV line, even when a host station installed in a hospital needs to poll a large number of medical communication terminals on the CATV line in order and collect data, a line connection loss occurs. Because it is shortened, it takes less time to collect data.

  Further, the present invention is not limited to a bidirectional CATV line, but can also be applied to a bidirectional wireless line. This is because there is no difference in circuit / configuration between the two, which is wired or wireless.

  In the above embodiment, a plurality of communication terminals are assigned to one call channel and grouped. However, this group is not fixed. The allocation of communication terminals to channels can be freely changed by rewriting the database, and the change can be made flexibly according to the usage frequency of CATV. In an extreme example, if a communication terminal of a certain channel uses a majority of the day for communication, the channel is allocated to only that one communication terminal, and the frequency of use is almost the same for other channels. It is also possible to assign several communication terminals to a channel that does not have any. The management computer 2 of the center 1 plans the channel assignment in this way so that all the communication terminals can talk on the same chance.

  In the embodiment shown in FIG. 1B, the case where only one communication terminal Z is connected to the channel on the incoming side has been described for the sake of convenience. However, the transmission side to which a plurality of communication terminals A and B are connected is described. Of course, the present invention can also be applied to a case where a plurality of communication terminals other than the communication terminal Z are connected to the receiving side.

  By the way, in the communication procedure of FIG. 4 described above, when all the call channels are in use or the other party is in a call, the call station user is notified that the call is in progress and is terminated. However, in this case, it is very convenient to automatically switch from the blocked CATV line to the general telephone line (NTT) instead of terminating the communication. Therefore, the main part of the communication terminal 6 is improved as shown in FIG. 5 and a general telephone line modem 27 is connected to the CPU 7 in the communication terminal 6 of FIG. 3 in addition to the CATV line modem 8. This connection allows the CATV line 5 to be used preferentially over the general telephone line 28. If the other party of the CATV line 5 is in a call or if all the call channels are in use, the general telephone line 28 is used. Automatically switch to outgoing calls. The flow of this switching process will be described with reference to FIG. In FIG. 6, parts corresponding to those in FIG.

  When the called station is not in use (413), the center notifies the calling station of the channel of the called station (414) as in FIG. However, when the called station is in use, that is, when the called station is in a call, or all the CATV line call channels are in use, the center searches the telephone number of the general public line from the already registered database. The call station is notified (421). The call station receives the searched telephone number of the general public line (422). Here, the call station notifies the user that “it is connected to the general public line because it is busy” (423), and then terminates the CATV line (424). The call station automatically makes a call to the general public telephone number received at 422 (425). The subsequent processing is the same as normal telephone processing.

  As described above, when the CATV line is blocked, it is automatically switched to the general public line. Therefore, even if the CATV line is blocked, the call / communication can be secured, so that the service can be further improved and it is convenient.

BRIEF DESCRIPTION OF THE DRAWINGS It is a principle figure of the system of the communication apparatus of the bidirectional line of this invention, (a) is explanatory drawing in case one communication terminal is allocated to one call channel, (b) is the whole system more than a call channel It is explanatory drawing when the number of communication terminals increases and a plurality of communication terminals are allocated to one call channel. It is a correspondence table of a communication terminal specific number (ID), reception frequency, and transmission frequency showing a specific example of the database of the present embodiment. 1 is a system configuration diagram of a center side and a communication terminal side connected by a CATV line for implementing a bidirectional line communication apparatus of the present embodiment. FIG. It is explanatory drawing which shows the flow of a process until the communication terminal of the transmission side by this Embodiment connects a line | wire with the communication terminal of the receiving side via a center. It is a principal part block diagram of the communication terminal to which the general telephone line modem by this Embodiment was added. FIG. 6 is an explanatory diagram showing a flow of processing for automatically switching connection from a CATV line to a general public line when all the CATV lines according to the embodiment of FIG. 5 are used or during a call. It is explanatory drawing which shows the example of a band division | segmentation of the bidirectional transmission path of our country. It is a channel CATV reception frequency list of our country. The principle figure of the system of a prior art example is shown, (a) is a one-to-one system, (b) is an MCA system.

Explanation of symbols

1 Center 3 Database 5 CATV line 7 CPU
8 CATV line modem 27 General line modem 28 General telephone lines A, B, G Communication terminals S1 to Sn Call channel R1 Inquiry channel

Claims (2)

A plurality of communication terminals in which a CATV line and a general telephone line are switchably connected, a center for performing bidirectional communication between the plurality of communication terminals via the CATV line, and the plurality of communication terminals provided in the center A bidirectional line communication apparatus that performs bidirectional communication between a plurality of communication terminals connected to the CATV line via the center, and a database that registers telephone numbers of general public lines of communication terminals.
The center determines whether the communication terminal on the incoming side that is trying to connect the line from the communication terminal on the outgoing side is in a call or the call channel is in use,
If the communication terminal of the called party is other than the case of a call or during a call channel is used, the communication terminal of the called side from the communication terminal of the calling side, preferentially connecting the CATV line than the public telephone line And let
Wherein when receiving communication terminal is busy or speech channel in use, the the source communication terminal of the called side from the communication terminal, and automatically switched let from the CATV line to the public telephone line, the Connect a regular telephone line,
Said telephone number of the general public line of the called communication terminal searches from the database, the communication terminal of the calling side, so as to automatically transmitted to the receiving-side communication terminal having the telephone number of the general public line, which is search Two-way communication device. When the center automatically switches and connects the incoming communication terminal from the CATV line to the general telephone line, the center notifies the calling communication terminal of a message to switch to the general public line. The bidirectional communication device according to claim 1.

Images