JPH04112534U - data transmission equipment - Google Patents

Abstract

(57) [Summary] [Purpose] To avoid communication deadlock without application intervention even when a specific control signal in a communication protocol causes an error. Structure: A text end signal detection circuit 12 detects a text end signal indicating the end of text of transmission data, and a start signal detection circuit 22 detects a transmission start signal indicating the start of transmission in received data. Then, the monitoring circuit 18 monitors the time from the detection of the text end signal to the detection of the transmission start signal, and if the transmission start signal is not detected even after counting a predetermined time or more, it is determined that an error has occurred in the text end signal. As a prerequisite, the text end signal generation circuit 14 re-outputs the text end signal to continue communication.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

The present invention relates to data transmission equipment, especially when specific control signals are required on a communication protocol. Data transmission that avoids communication deadlock even when an error occurs. Regarding the sending device.

0002

[Conventional technology]

Traditionally, data transmission equipment that performs half-duplex communication using telephone lines has a variety of Data communication is performed using a communication protocol. Such data communication applications Applications range from simple one-way file transfers to two-way transfers. Various applications including multi-processing applications such as transferring files between exists. On the other hand, the communication protocols that support such applications are , BSC (binary synchronous communication) and HDLC (high level data link control) ), and both host computers and terminal devices must comply with this standard. communication protocol.

0003 By the way, when data is transmitted using a telephone line, data errors may occur. The occurrence of this cannot realistically be avoided. The probability of error occurrence depends on line conditions Basically, it occurs on any line, and it depends on the communication protocol itself. Does not exist. The communication protocol checks for errors in this transmission and resends the data. It is designed to be able to be recovered using methods such as

0004

[Problem that the idea aims to solve]

However, for example, with the BSC communication protocol, files are transferred between each other. When data communication occurs, it may not be possible to deal with such errors. . In other words, in applications that perform bidirectional file transfer, The concept of reversal of transmission rights is used when switching between transmission rights. And this cut During the exchange, the sender sends an EOT (end of text signal) indicating the end of the sent text. It is designed to transmit a control signal. On the receiving side, this end-of-text signal When it receives the file, it becomes the sender and transfers the file.

[0005] However, if this end-of-text signal itself is sent incorrectly due to a transmission error, , it becomes impossible to deal with this. In other words, if you were the sender, the text When a termination signal is sent, the right to transmit is relinquished under the assumption that the transmission was successful. and enters the state of waiting for reception. On the other hand, on the side receiving the data, the end of the text Since no acknowledgment signal has been sent, it is assumed that the reception status is still continuing. It is in a state of waiting for reception. If an error occurs in the end-of-text signal in this way, both The other side enters the waiting state, and a kind of protocol deadlock occurs. cormorant. The higher-level application detects that communication is no longer occurring and aborts it. The communication will be cut off by the code timer.

[0006] In this way, communication protocols originally require error correction to compensate for errors in the transmission path. The compensation function may not work in certain conditions. This way In this case, you can restart the file transfer by resending the file using the application. can. However, when transferring large files, this is difficult to use. Very inconvenient.

[0007] Therefore, the purpose of this invention is to detect errors caused by specific control signals on the communication protocol. Even in cases where communication deadlocks can be avoided without application intervention. To provide a data transmission device with

[0008]

[Means to solve the problem]

In this invention, we have developed a system that detects a text end signal indicating the end of text of transmitted data. Detects the transmission end signal detection means and the transmission start signal indicating the transmission start in the received data. Detection of the transmission start signal from the detection of the text end signal a clocking means for measuring the time up to a predetermined time; A text that outputs the text end signal again when the transmission start signal is not detected. The data transmission device is provided with a strike end signal re-output means.

[0009] In other words, in the present invention, after the text end signal is sent, the receiving side Measure the time it takes for the transmission start signal to be sent from If the transmission start signal is not sent, an error occurs in the text end signal. The above-mentioned purpose is achieved by retransmitting this as if it were sent.

0010

【Example】

The present invention will be described in detail with reference to Examples below.

[0011] Figure 1 shows the main part of the circuit configuration of a data transmission device in an embodiment of the present invention. It is something. This data transmission device transmits data 11 sent from a terminal device. Text end signal detection circuit 12 for detecting text end signal 12 in It is equipped with The end-of-text signal, like other control signals, is composed of a specific code string. data, and can be distinguished from general data and detected. send The data 11 is also input to a transmission data selection circuit 13. this The transmission data selection circuit 13 receives a text end signal from the text end signal generation circuit 14. No. 15 is supplied, and any data or signal can be selected. The signal is supplied to a modulation/demodulation circuit (MODEM) 16. This modulation/demodulation circuit 1 6 is a commonly used modulation/demodulation circuit, which demodulates the data or signal described above. In addition to modulating the transmission data sent from a terminal device (not shown), it modulates the reception data It is designed to be output as data 17.

0012 Selection control of the transmission data selection circuit 13 is performed by a monitoring circuit 18. This monitoring circuit 18 includes a text end signal detection circuit 12 that detects a text end signal. This detection signal 19 is input every time the signal is output. Also, the end of the text A text end signal that instructs the end signal generation circuit 14 to generate a text end signal 15. In addition to outputting a completion signal generation instruction signal 21, a start signal receives reception data 17. Detection signal 2 output when the detection circuit 22 detects a transmission start signal from the partner station 4 is input. The transmission start signal is as if the transmission right were reversed. It starts with a special code such as "ENQ" (enquiry character).

[0013] The monitoring circuit 18 performs a process from detecting the text end signal 15 to detecting the transmission start signal. This is a circuit that monitors time. The monitoring time is, after detecting the text end signal 15, If the other station receives this correctly, it will predict the transmission start signal that will be sent back. The time T is set as the sum of the measured time and the delay time of the transmission path. this If the transmission start signal is not detected until time T has elapsed, the monitoring circuit 18 The text end signal generation instruction signal 21 described above is output. end of text The signal generation circuit 14 receives a text end signal generation instruction signal 21 from the monitoring circuit 18. When input, it generates the same end-of-text signal 15 as the terminal. Also, this supervisor The output of the visual circuit 18 is supplied to the transmission data selection circuit 13 as a switching signal 25. As a result, the transmission data is The selection circuit 13 selects this text end signal 15 and sends it to the modulation/demodulation circuit 16. It turns out.

[0014] Next, the sequence control of the data transmission device of this embodiment will be explained using FIG. conduct. Figure (A) shows the case where sequence control is performed normally. . The device shown in the upper part of this figure (A) (the first terminal device) is initially used as the sending device. The query shall be performed before sending “ENQ” and starting sending data. Have a meeting. The device shown at the bottom of this figure (A) (second terminal device) is initially It shall act as a device on the receiving side, and shall respond to the “ACK” (acknowledge character) signal. Therefore, an affirmative response is made. This allows the data (DATA) to be sent from the first terminal device. The communication is performed, and the second terminal device sends an "ACK" in response. first terminal When the device receives this, it sends an end-of-text signal (EOT) 15 and ends the transmission. Let me know what you did.

[0015] At this stage, the second terminal device switches to the sending side and sends “ ENQ". The first terminal device returns "ACK" in response. When the terminal device No. 2 receives this, it transmits data (DATA). Same as below be.

[0016] Figure 2 (B) shows what happens when an error occurs at the stage of sending the text end signal. This is a representation of conventional sequence control for reference. The section shown at the top in this figure Transmission of data (DATA) from one terminal device to the second terminal device shown below Suppose that was done. In response, the second terminal device returns "ACK". 1st When the terminal device receives this, it sends out a text end signal. However, this text It is assumed that an error occurs in data transmission at the stage of sending the text end signal.

[0017] The first terminal device has sent this text end signal, so it relinquishes the right to send it and receives it. The terminal then waits for "ENQ" to be sent from the second terminal device. Also, The second terminal device waits for an “ENQ” or end-of-text signal to be returned. However, neither signal is returned. Therefore, the transmission of the first terminal device is It is assumed that the message is still in progress and is still in the waiting state. in this way, In this state, both terminal devices are in a state of waiting for reception, which is a kind of protocol-based A deadlock will result. The upper level application continues to be in a state of no communication. However, communication is cut off by the abort timer (marked with an x in the diagram).

[0018] In contrast, FIG. 2(C) shows that the text ends in the data transmission device of this embodiment. This shows a case where an error occurs at the stage of signal transmission. Same figure (B) Similarly, data (DATA) is transmitted from the first terminal device to the second terminal device. The second terminal device returns "ACK" in response. first terminal device receives this and sends an end-of-text signal. of sending this end-of-text signal. It is assumed that an error occurs in data transmission at this stage.

[0019] The monitoring circuit 18 (FIG. 1) disposed on the first terminal device side detects the end of text signal. Is it the time when the text completion signal detection circuit 12 detects the signal and inputs the detection signal 19? When the clocking operation is started and the above-mentioned time T is clocked, a text end signal 15 is sent. to end the transmission. By retransmitting this text end signal 15, the second terminal device If the second terminal device is able to receive this, the second terminal device sends “ENQ”. After that, if “ACK” is returned, data transmission will start. can do. In this way, the monitoring circuit 18 monitors the transmission of the text end signal of its own station. By sending this text end signal 15 again in consideration of errors, it is possible to deadlock can be avoided.

[0020]

[Effect of the idea]

In this way, according to the present invention, there is a special restriction that cannot be retransmitted on the protocol. If an error occurs in the control signal, the data transmission equipment side retransmits the signal. It is possible to avoid communication deadlock and realize smooth data communication.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing main parts of a circuit configuration of a data transmission device.

[Figure 2] (A) is a sequence diagram of the data transmission device of this embodiment when sequence control is performed normally, and (B) is a sequence diagram when an error occurs at the stage of sending a text end signal. FIG. 4 is a sequence diagram showing for reference the conventional sequence control in the case where the text end signal is sent, and FIG.

[Explanation of symbols]

12 Text end signal detection circuit 13 Transmission data selection circuit 14 Text end signal generation circuit 16 Modulation/demodulation circuit 18 Monitoring circuit 22 Start signal detection circuit

Claims (2)

[Scope of utility model registration request] 1. Text end signal detection means for detecting a text end signal indicating the end of text of transmission data; transmission start signal detection means for detecting a transmission start signal indicating the start of transmission in received data; and said text end signal. and a text end signal for re-outputting a text end signal when the transmission start signal is not detected even after the timer measures a predetermined time or more. 1. A data transmission device comprising: re-output means. 2. Inputting transmission data and a text end signal generated by the text end signal re-output means,
Selection means for selecting one of these and inputting it to the modulation/demodulation circuit, and switching control for switching the selected output of this selection means to the text end signal side at the timing when the text end signal is output by the text end signal re-output means. 2. The data transmission device according to claim 1, further comprising: means.