JPH07162447A - Data transmission system - Google Patents

Abstract

PURPOSE:To eliminate the wait time for a local station address which is necessary for a conventional polling/selecting system by allowing sequential access from a slave station DTE on condition that a line is in a free state wherein a communication is not in processing. CONSTITUTION:The DTE interface 43 of a slave station DCE 4 receives a transmission request signal from the slave station DTE5 and sends a clear-to- send signal(CS) when the signal from a clear-to-send judging circuit 44 indicates a line free state wherein transmission is allowed, so that the slave station DTE5 can have a communication with a master station DTE1. The clear-to-send signal(CS) is not sent out when the signal indicates an in-communication state wherein the transmission is disallowed. The procedure for a connection between the slave station DTE5 and DC4 is based upon the CCITT.V24.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data transmission system, and more particularly to a data transmission system in which a master station communicates with a plurality of slave stations having a branch type by polling / selecting.

[0002]

2. Description of the Related Art Conventionally, this type of data transmission system is
Through the master station terminal device (master station DTE), the master station line terminating device (master station DCE) that converts the signal on the master station DTE side into the signal on the transmission path side, the communication line that is the transmission path, and this communication line A plurality of terminals are respectively connected to a plurality of terminal lines branched from a slave station line terminating device (slave station DCE) for converting the transmitted signal of the master station DTE into a signal on the DTE side and branching the line into a plurality of terminal lines. And a slave station terminal device (slave station DTE).

Normally, the communication procedure is to select a slave station DTE by polling / selecting from the master station DTE, and then perform communication between the master station DTE and the slave station DTE. That is, the master station DTE sequentially transmits the station address of the slave station DTE to the slave station DTE, and the slave station DTE performs communication after confirming reception of its own station address. When a voice analog line is used for the communication line, the DCEs of both stations include a modem. The DCE also includes other functions necessary for signal transmission such as error correction.

The master station DTE has a function of performing broadcast communication with all the slave stations DTE or designating a specific slave station DTE for communication.

[0005]

As described above, according to the conventional technique, the slave station DTE can perform communication only when there is polling from the master station DTE, and the slave station DTE attempts to transmit data. In this case, it is necessary to wait for the polling of the own station address, and this extra waiting time is required. In addition, in order to secure the origination of the slave station in this way, it is necessary to always secure a communication line between the terminal device on the master station side and the terminal device on the slave station side in the polling selecting method, which is a waste of communication cost. There is a problem that it takes.

[0006]

SUMMARY OF THE INVENTION A data transmission system of the present invention includes a master station terminal device, a master station line terminating device for converting a signal on the master station terminal device side into a signal on the transmission line side, and a communication which is a transmission line. A line and a slave station line terminating device for converting the signal of the master station line terminating device transmitted via this communication line into a signal on the terminal side and branching the line into a plurality of terminal lines and a plurality of the terminal lines, respectively. In a data communication system comprising a plurality of slave station terminal devices connected to each other, wherein the master station terminal device communicates with the slave station terminal device by polling / selecting, the slave station line terminating device is the master station. The communication state between the terminal device and the slave station terminal device is monitored, and when there is no communication, the transmission request signal transmitted from the slave station terminal device is accepted and the master station terminal device side And a means for sending a signal for inhibiting the transmission request to the other of said slave station terminal apparatus except for the performed simultaneously calling slave station channel connection.

Further, the connection procedure for the transmission request signal between the slave station line terminating device and the slave station terminal device is CCITT Recommendation V.26. 24 or a system conforming to the CCITT recommendation of the same type.

[0008]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a block diagram showing the system configuration of this embodiment.

In the figure, the master station DTE1 is a terminal device on the master station side, the master station DCE2 is a line terminal device on the master station side for performing signal format conversion and the like, and the communication line 3 uses an analog dedicated line in the voice band, The slave station DCE4 is a slave terminal side line terminating device that performs signal format conversion, line branching and terminal side transmission control, and the slave station DTE5 is n slave station side terminal devices that communicate with the master station DTE. The master station DTE1 and each slave station DTE5 perform data communication in the half-duplex mode.

The internal configuration of the slave station DCE4 includes a LINE interface 41 including a modem for converting the signal on the communication line 3 side into a signal on the terminal side, and a branch circuit for branching the terminal line into n terminal lines in a direct current manner. 42, each child station DT
The n DTE interfaces 43 for interfacing signals with the E5, the communication signals are monitored through the respective DTE interfaces 43, and the presence or absence of the communication signals is detected, and the slave station DTE
When there is a transmission request from 5, the transmission permission / inhibition is determined, and the determination result is notified to each slave station DTE 5 via each DTE interface 43.

Next, each DTE interface 43 of the slave station DCE4, whose operation will be described, monitors whether or not each branch line is in communication, and sends the result to the transmission availability determination circuit 44. Further, each DTE interface 43 is in a state in which a signal from the master station DTE1 is allowed to pass and polling / selecting is possible while each line is not communicating, and at the same time, a standby state is received for an outgoing signal from the slave station DTE5. .

In this state, for example, the slave station DTE5a
When there is an outgoing signal from the slave station DC in the connection procedure shown in FIG.
A transmission enable signal (CS) is sent from the E4 to the child station DTE5a. FIG. 2 shows CCIT between the slave station DCE4 and the slave station DTE5.
T. It is a time chart figure which shows the connection procedure by a V24 interface. That is, when the ready signal (ER) is first transmitted from the slave station DTE5a, the DTE of the slave station DCE4 is transmitted.
The interface 43 prepares for reception, and after this is completed, returns a data set ready signal (DR). Subsequently, when the transmission request signal (RS) is transmitted from the slave station DTE 5a, the determination result from the transmission permission / inhibition determination circuit 44 is acceptable on the DTE interface 43 side unless each line is in communication. If there is no abnormality in the side line, the transmission enable signal (CS) is returned. As a result, the slave station DTE5a
Makes a transmission request to the master station DTE1 to enable communication.

On the other hand, when any one of the slave stations DTE5 transmits without knowing this while the line is in communication, the transmission enable / disable signal (CS) indicates that the transmission enable / disable determining circuit 44 gives a negative result. It is prohibited to send. Therefore, this slave station DTE5 cannot perform transmission and cannot communicate with the master station DTE1. That is, when the slave station DTE5a starts the connection procedure, the transmission signal is detected and the line becomes in communication, so that the transmission from the subsequent slave station DTE is suppressed and only the communication of the preceding slave station DTE5a is suppressed. Reserved.

Similarly, when there is a slave station DTE that is in communication by conventional polling / selecting, similarly, a later-originating slave station DTE cannot receive the transmission enable signal (CS), so that transmission is suppressed.

The software for the connection procedure between the master station DTE1 and the slave station DTE5 is the normal polling / selecting software to which the above-mentioned software for transmitting the slave station DTE is added.

[0016]

As described above, the present invention is provided with a circuit which accepts the transmission request signal from the slave station DCE and enables this access when the line is not in communication. Therefore, from the slave station DTE side. Can be transmitted at any time, and there is no need to wait for reception of its own address by conventional polling / selecting. Therefore, there is an effect that this waiting time at the time of transmitting the DTE on the slave station side becomes unnecessary.

The connection procedure between the slave station DCE and the slave station DTE is CCITT. Since it conforms to the V24 interface, it has the effect of simplifying the DTE operation without much changing it from the conventional one.

[Brief description of drawings]

FIG. 1 is a block diagram showing a system configuration of an embodiment of the present invention.

FIG. 2 is a time chart showing a connection procedure of a child station DTE in FIG.

[Explanation of symbols]

 1 Master station DTE 2 Master station DCE 3 Communication line 4 Slave station DCE 5 Slave station DTE 41 LINE interface 42 DC branch circuit 44 Transmission permission judgment circuit 43 DTE interface

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location 9371-5K H04L 13/00 307 Z

Claims (2)

[Claims] 1. A master station terminal device, a master station line terminating device for converting a signal on the master station terminal device side into a signal on a transmission line side, a communication line which is a transmission line, and the parent transmitted via this communication line. It is composed of a slave station line terminator for converting the format of the signal from the station line terminator into a signal on the terminal side and branching the line into a plurality of terminal lines, and a plurality of slave station terminal devices respectively connected to the plurality of terminal lines. In the data communication system in which the master station terminal device communicates with the slave station terminal device by polling / selecting, the slave station line terminal device is in a communication state between the master station terminal device and the slave station terminal device. When there is no communication, the transmission request signal transmitted from the slave station terminal device is accepted and the line connection with the master station terminal device side is performed, and at the same time, the other slaves other than the transmitting slave station are connected. A data communication system comprising means for transmitting a signal for suppressing a transmission request to a station terminal device. 2. The connection procedure for the transmission request signal between the slave station line terminating device and the slave station terminal device is C
CITT Recommendation V. 24. The data transmission system according to claim 1, wherein the data transmission system complies with the CCITT Recommendation 24 or the like.