JPS598106B2 - Transmission control method for lines with modem interfaces - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transmission control system for a line having a modem interface.

In a system that performs transmission via a line with a modem interface, especially a data line termination device DCE, when data is transmitted from the data terminal device DTE of one's own station to the data terminal device DTE of another station, an error occurs on the side of the local station DTE. Upon receiving a send request signal (RS: SendRequest), data transmission is started.

Therefore, in a system employing a so-called half-duplex transmission system, the local station DTE and the other station DTE communicate alternately, so the RS signal is intermittently turned on or off. In other words, by turning on the RS signal, the own station D
The TE becomes the transmission mode, and by turning off the RS signal, the local DTE changes from the transmission mode to the reception mode. Since the line repeats the transmitting state and the disconnected state in this way, it is necessary to resynchronize the line every time the line changes from the disconnected state to the transmitting state. This is because the synchronization of the line is performed through data transmitted in the transmission state, and during the transition period from the disconnected state to the disputed state, there is no data that can be used as a clue for synchronization. be. Therefore, if the system employs a full-duplex transmission method, the transmitting state can be maintained at all times, and such resynchronization is not necessary. However, half 2
In the heavy-duty system, there is always a disconnection state, so it is necessary to resynchronize in the subsequent transmission state to recover from the loss of synchronization. This causes a serious problem in that data reliability is lost every time the synchronization is recovered, which can lead to fatal data errors when transmitting data information other than voice. It leads to causing. After all, it goes without saying that it would be ideal if data reliability could be achieved that is apparently equivalent to a full-duplex system even though it is a half-duplex system. Therefore, an object of the present invention is to provide a line with a modem interface that is half-duplex but does not cause synchronization like full-duplex, that is, does not deteriorate data reliability. The objective is to provide a transmission control method.

In accordance with the above object, the present invention provides a method for controlling local station DTE and other station DTE.
In a line network in which multiplexed frame data is transmitted in a half-duplex manner via the local station modem interface and the other station modem interface, the local station DTE
continuously transmitting frame synchronization pulses for synchronizing at least the multiplexed frame data transmission from the local DTE side to the other station DTE regardless of the presence or absence of a transmission request RS signal generated from the local DTE side; Information regarding the presence or absence of the transmission request RS signal is displayed and transmitted in a specific bit in each frame, and the other station DTE side continues to synchronize the line based on the frame synchronization pulse and monitors the specific bit. By doing so, the local station DTE
The present invention is characterized in that the presence or absence of the transmission request RS signal from the side is identified.

The present invention will be explained below with reference to the drawings.

FIG. 1 is a schematic block diagram showing an example of a line network to which the system of the present invention is applied.

In this figure, 11 is the data terminal device DTE on the local side;
12 is a data line termination device DCE on the local station side having a modem interface, 13 is a transmission line, 14 is a DCE on the other station side having a modem interface, and 15 is a DT on the other station side.
It is E. At least a transmission data signal SD, a transmission timing signal ST and a transmission request signal RS are sent from the DTell.
is sent to the DCEl2, converted into a serial signal along with the frame synchronization pulse F by the parallel-to-serial converter P/Sl6 in the DCEl2, and sent to the transmission line 13 via the transmission f)17. In this figure, it is assumed that the transmission data signal SD and the transmission timing signal ST employ a modulation method in which time division multiplexing is performed using asynchronous sampling. In addition to the signals F, SD, ST, and RS, the types of signals include a test signal TEST. The test signal TEST
is sent from the local DCE side to the other station DCE side when a failure occurs, and is looped back at the other station DCE side,
This is useful for performing so-called loopback tests. On the other hand, on the side of the other station DTEl5, the other station DCEl4, which is composed of the receiving section 18 and the serial-to-parallel converting section 19,
The signals from the own station are demodulated as the frame synchronization pulse F1 reception data signal RDl reception timing signal RT, and at the same time the presence of these signals is confirmed, the carrier detection signal C
Generates D. This signal CD corresponds to the signal RS on the local station side, and at the same time as the signal CD is generated, the other station DT
El5 starts receiving operation. Moreover, if the test signal TEST is transmitted from the local station side, this is also demodulated as the test signal TES'r/. In the explanation of Figure 1,
Although no mention is made of the programs 21 and 22, they will be described later as they are particularly closely related to the implementation of the present invention.

Therefore, in the conventional system, the signals RS, TE
ST and CD, TEST/ are these programs 21
and other signals F, SD, without passing through 22.
It is treated in the same way as ST, F, RD, and RT. The scheme of the present invention will be apparent by reference to the timing charts shown in FIGS. 2A and 2B.

FIG. 2A is a timing chart for explaining the conventional transmission control method in an easy-to-understand manner, and FIG. 2B is a timing chart for explaining the transmission control method of the present invention in an easy-to-understand manner. Referring to FIG. 2A, conventionally, DTEl
In response to the transmission request signal RS turning on 50N'' at 1 (see FIG. 2A) (see FIG. 2A), DCEl2 (
Fig. 1) is the multiplexed frame data signal FD (Fig. 2A b).
(see). This signal FD is formed by multiplexing at least three types of signals: a frame synchronization pulse F, a transmission data signal SD, and a transmission timing signal ST, and a large number of frames are successively transmitted with these as one frame. However,
Normally, specific bits are assigned for transmitting the test signal TEST to perform the loopback test. The other station side that receives the frame data signal FD of FIG. 2A b demodulates these signals and generates a carrier detection signal CD (see FIG. 2A c).

This signal CD informs the other station that the transmission request signal RS has been generated on the local station side, and in conjunction with this, the other station performs synchronization pull-in and enters the reception mode. In this way, the reason why synchronization must be performed every time the signal RS is generated is because the frame data signal FD no longer exists on the line every time the signal RS turns off 80FF.
This is because the other stations end up being out of synchronization each time. Therefore, in the present invention, basically, at least the frame synchronization pulse F continues to be transmitted to the other station regardless of the presence or absence of the transmission request signal RS (see [F] in FIG. 2B c).

This allows the other station to escape from the out-of-synchronization state based on the frame synchronization pulse F. However, if this is done, the other station will be placed in a state as if it were constantly receiving the transmitted frame data signal FD, and would therefore constantly generate the carrier detection signal CD, so it would have to perform its original transmitting and receiving operations. I end up not being able to do anything. For this reason, the present invention further takes the following measures. That is, information indicating the presence or absence of the transmission request signal RS is attached to each frame that is continuously transmitted without pause. However, it is uneconomical to provide a new bit area within one limited frame for this purpose, so the vacant bit area of the test signal TEST, which has a low utilization rate, is used. However, if there is room for bit allocation, a separate RS display area may be provided as a specific bit. FIG. 2B is a timing chart for explaining the method of the present invention. With the generation of the original signal RS (see FIG. 2B a), the pseudo transmission request signal PRS
(see FIG. 2B, b), and multiplexes and inserts it into, for example, the test signal TEST bit area in the transmission frame data FD. This pseudo-transmission request signal PRS consists of, for example, a continuous pattern of 1010, . . . . The reason why this continuous pattern of 1010 . . . is preferable will be described later. On the other hand, when the other station monitors the test signal bit area and demodulates the signal PRS, it determines that data has been transmitted from the own station and generates a carrier detection signal CD (see Figure 2B, d). . In this way, half-duplex data transmission and reception is possible without causing an out-of-synchronization state on the other station side and without losing the ability to identify the presence or absence of a transmission request.

To implement the operation illustrated in FIG. 2B, the blocks 21 and 22 shown in FIG. 1 are required.

The block 21 is a so-called RS/TEST switching circuit, and the block 22 is a so-called CD/TEST separating circuit. In other words, the RS/TEST/switching circuit 21 receives the signal RS
When the test signal TEST is generated, the pseudo transmission request signal PRS is output, while when the test signal TEST is generated, it is output as is. Also, CD/TEST・
The separation circuit 22 determines whether the test signal TEST bit area indicates the original test signal or whether the signal PR
This is to separate whether a carrier detection signal corresponding to S is being displayed. Former RS/TEST/switching circuit 2
1 is realized, for example, by the circuit shown in Fig. 3, and the latter CD/TE
The ST/separation circuit 22 is realized, for example, by the circuit shown in FIG. In FIG. 3, the circuit 21 is connected to the original test signal TE.
An inverter 31 receives ST, receives a transmission request signal RS and an output signal of an oscillator 34, and generates a pseudo transmission request signal P.
NAND gate 32 and NAND gate 33 that output RS
Consisting of The NAND gate 33 allows the continuous "r" level test signal TEST to pass through as it is, and when the test signal TEST does not exist, it passes the continuous "0" level test signal TEST.
゛゜When it is a level signal, the NAND gate 32
It allows the signal PRS from to pass through. Note that either signal TEST or PRS is inserted into the test signal bit area. In addition, the signal PR from the NAND gate 32
Since S is the output signal from the oscillator 34, it becomes a continuous pattern of 1010... as described above. On the other hand, the CD/TEST/separation circuit 22 in FIG. 4 receives the test signal TESTV (see TES'T' in FIG. 1) from the test signal TEST bit area in FIG. A carrier detection signal CD corresponding to the transmission request signal PRS is separated.

If the signal TES'r/ is a continuous "F" level test signal TEST, the bottom detector 41 will not detect the 01 level, so the original test signal TEST
can be determined. Note that a normal diode clamp circuit may be used as the bottom detector. If the signal TES'T/ is 101
If the pseudo transmission request signal PRS is a continuous pattern of 0......, at least one of them is ``0''.
The bottom detector 41 detects ゜゛ and outputs the test signal TE.
It is determined that there is no ST. Instead, monostable multicircuit 4
2 is designed as a circuit having a time constant with a period longer than the period of the continuous pattern of 1010......, so the continuous pattern of 1010...... , into a continuous 1r'' level signal CD, and outputs the signal PRS. In this way, TEST and CD can be separated. As explained above, according to the present invention, regarding line synchronization, half-duplex type However, it can produce the same effect as the full-duplex method, and without increasing the hardware, it suppresses the deterioration in data reliability caused by resynchronization as in the conventional method. be able to.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram showing an example of a line network to which the method of the present invention is applied, FIG. 2A is a timing chart for explaining the conventional transmission control method in an easy-to-understand manner, and FIG. 2B is a transmission control method of the present invention. A timing chart for explaining the control system in an easy-to-understand manner. Figure 3 is a circuit diagram showing an example of the RS/TEST switching circuit in Figure 1. Figure 4 is a circuit diagram showing an example of the RS/TEST switching circuit in Figure 1.
FIG. 2 is a circuit diagram showing an example of an EST/separation circuit. In the figure, 11 is the local station DTE, and 12 is the local station DCEl.
4 is another station DCEl5 is another station DTEl2l is RS/TE
ST/switching circuit, 22 is CD/TEST/separation circuit, F
is a frame synchronization pulse, RS is a transmission request signal, PRS is a pseudo transmission request signal, SD is a transmission data signal, ST is a transmission timing signal, and TEST and TEST' are test signals, respectively.

Claims (1)

[Scope of Claims] 1. The data terminal device DTE of the local station and the data terminal device DTE of the other station perform half-duplex communication with each other via the data line terminating device DCE of the local station and the data line terminating device DCE of the other station each having a modem interface. In a line network that performs multiplexed frame data transmission according to the formula, the local station DTE
At least a frame synchronization pulse F for synchronizing the multiplexed frame data transmission is continuously transmitted from the local station DTE side to the other station DTE side regardless of the presence or absence of the transmission request signal RS generated from the transmission request signal RS. , and transmits information regarding the presence or absence of the RS signal in a specific bit area in each frame as a false transmission request signal PRS, and
The TE side continues to synchronize the line based on the frame synchronization pulse F, and also monitors the specific bit to identify the presence or absence of the RS signal from the local DTE side and outputs a carrier detection signal CD. 1. A transmission control method for a line having a modem interface, characterized in that transmission is controlled to occur on a line having a modem interface. 2. Each frame is formed by multiplexing at least transmission data SD, transmission timing ST, and test signal TEST into corresponding bit areas, and the multiplexed bit area of the test signal TEST is used as a specific bit area. The method described in Section 1. 3. The system according to claim 2, wherein the own station DCE has an RS/TEST switching circuit, and the other station DCE has a CD/TEST separation circuit. 4 RS signal and TEST signal are each RS/T
The EST switching circuit outputs the 1010... continuous pattern signal or continuous "1" level signal, while the CD/TEST separation circuit outputs the 1010...
....The continuous pattern signal is selectively reproduced as a continuous "1" level CD signal, and the TEST signal is alternatively reproduced as a continuous "1" level signal. Method described in section.