JPH06315044A - Pseudo cd signal transmitter - Google Patents

Abstract

PURPOSE:To transmit a pseudo CD signal showing the change point of an RS signal applied from a data terminal without limiting the transmission rate of a transmission line by combining a transmission control means, delay means and transmitting means to respectively perform prescribed operations. CONSTITUTION:When a transmission request showing transmission start is sent from a data terminal 11, a transmitting means 19 sends that transmission request to a MODEM 13 as the pseudo CD signal. On the other hand, a transmission control means 13 generates and sends a transmission control command instructing the outgoing permission of transmitting information by delaying the transmission request. Corresponding to such a transmission control command, the data terminal 11 starts sending the transmitting information, and a delay means 17 delays that transmitting information over transmission delay time. The transmitting means 19 applies the transmitting information delayed like this to the MODEM 13 continuously to the pseudo CD signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pseudo CD signal transmission device which is arranged between a data terminal and a modem connected to an analog transmission line and has a communication interface adapted to the transmission system of the analog transmission line.

[0002]

2. Description of the Related Art In a data communication system configured via an analog communication network, for example, as shown in FIG. 3, data terminals 51 ₁ and 51 ₂ communicating with each other are respectively connected to pseudo CD signal transmission devices (hereinafter , Simply referred to as "apparatus".) 52
₁ , 52 ₂ and modems 53 ₁ , 53 ₂ , 53 ₃ , 53 ₄
Are connected to multiplex converters (MUX) 54 ₁ and 54 ₂ via a network, and these multiplex converters are mutually connected via a predetermined network.

In the data communication system having such a configuration, the modems 53 ₂ and 53 ₃ are respectively provided with the multiplex converter 5.
It operates based on the clock given from 4 ₁ and 54 ₂ .
Further, the modem 53 _1, 53 ₄ are extracted and reproduced clock based on the carrier received from the opposite modem. The data terminals 51 ₁ and 51 ₂ and the devices 52 ₁ and 52 ₂ synchronize with the opposite terminal devices based on the clocks extracted and reproduced in this way, and send and receive data based on a predetermined communication procedure. . Thus, modem 53 ₂ from the modem 53 _1, in multiplex conversion unit 54 _1, 54 ₂ and the upper and lower transmission section leading to the modem 53 ₄ through the modem 53 _3, data on the transmitting side at each connection point of the transmission device interposed In order to stabilize the synchronization with the terminal and avoid the loss of transmission information, a carrier that gives a clock that serves as a reference for the synchronization is constantly transmitted and received.

However, in general, the data terminals 51 ₁ , 51
₂ does not always operate normally under the condition that the carrier is always transmitted or received as described above. For example, the logical value of the CD (Carrier Detect) signal indicating that the carrier is received is determined by the predetermined transmission procedure. Accordingly, it is required to once become the inactive level.

In such a case, the device 52 ₁ (52 ₂ )
Is always active level RS (Request to Send) signal and ER (Equipm) to the modem 53 ₁ (53 ₄ ).
By providing a EntReady) signal, the modem 53 _1-5
3 ₄ Send and receive carriers at all times. Also, the device 5
2 ₁ (52 ₂ ) is the R given by the data terminal 51 ₁ (51 ₂ ).
The logical value of the S signal is added to the transmission information and transmitted, and the opposite device 52 ₂ (52 ₁ ) extracts the RS signal added to the transmission information in this way and sends it to the data terminal 51 ₂ (51 ₁ ). It is given as a CD signal.

Therefore, the data terminals 51 ₁ , 51
₂ can mutually perform data communication via analog transmission lines having different transmission procedures.

[0007]

By the way, in such a conventional device, since the RS signals given from the data terminals 51 ₁ and 51 ₂ are added to the transmission information and transmitted, the bit speeds higher than those of these data terminals are transmitted. It is necessary to perform transmission / reception at a rate, and the network side connecting these devices has not always performed efficient transmission according to the specific transmission capacity.

Further, a failure occurs on the network side described above, and the modem 5 ₁ (53 ₄ ) faces the modem 5 due to the failure.
The device 52 ₁ (52 ₂ ) should give to the data terminal 51 ₁ (51 ₂ ) when outputting the inactive level CD signal because it cannot receive the carrier transmitted from 3 ₂ (53 ₃ ). Since the subsequent RS signal necessary for generating the CD signal is not added to the transmission information and is not received, the matching condition of the transmission procedure between the data terminal 51 ₁ (51 ₂ ) and the network is broken and normal data is transmitted. There were cases where communication was not possible.

According to the present invention, a pseudo CD signal indicating a change point of an RS signal given from a data terminal is transmitted without imposing a restriction on the transmission speed of the transmission path, and when the failure of the transmission path is ensured, the pseudo CD signal is reliably transmitted to the data terminal side. Pseudo CD that can match the transmission procedure
An object is to provide a signal transmission device.

[0010]

FIG. 1 is a block diagram showing the principle of the present invention. The present invention relates to a pseudo CD signal transmission device that uses a communication interface between a data terminal 11 and a modem 13 connected to an analog transmission line that requires constant transmission of a carrier during transmission. A transmission control command for delaying the transmission request and instructing the data terminal to permit transmission of the transmission information, and transmitting the transmission information in accordance with the status information obtained via the modem 13 when the analog transmission line fails. Transmission control means 15 withdrawing the transmission control command indicating permission, and transmission control means 15
By delaying the transmission information transmitted from the data terminal 11 for a time longer than the transmission request delay time, and adding the transmission request before and after the transmission information delayed by the delay means 17 on the time axis. It is characterized in that it is provided with a transmitting means 19 for giving to the modem 13.

[0011]

In the pseudo CD signal transmission device according to the present invention,
When a transmission request indicating the start of transmission is sent from the data terminal 11, the transmitting means 19 transmits the transmission request to the opposite data terminal via the analog transmission line in a pseudo CD signal indicating that the carrier has been received in a pseudo manner. Is sent to the modem 13. Further, the transmission control means 15 delays the transmission request described above for a time corresponding to the transmission delay of the analog transmission path, thereby generating and transmitting a transmission control command instructing permission to transmit the transmission information. The data terminal 11 starts transmitting the transmission information in response to such a transmission control command,
The delay means 17 delays the transmission information for a time longer than the above-mentioned transmission delay time. The transmission means 19 gives the transmission information delayed in this way to the modem following the above-mentioned pseudo CD signal, and further, the transmission request transmitted by the data terminal 11 to indicate the completion when the transmission is completed is described above. It is added to the end of the transmission information as a pseudo CD signal for notifying the opposite data terminal that the carrier is not received in a pseudo manner, and is given to the modem 13.

That is, since the pseudo CD signal is transmitted to the analog transmission line via the modem 13 at the permissible delay time of the transmission start command for the transmission request and the time after the transmission of the transmission information is completed, the transmission speed should be changed. Instead, it is possible to perform data transmission at the transmission rate required by the data terminal 11.

Further, the transmission control means 15 withdraws the transmission control command for permitting the transmission of the transmission information to the data terminal 11 in accordance with the status information obtained via the modem 13 when the analog transmission path has a fault, so that the analog transmission path Inconsistency in the transmission procedure between the data terminal 11 and the data terminal 11 is reliably avoided.

[0014]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 2 is a diagram showing an embodiment of the present invention.

In the figure, the device according to this embodiment is
The transmission control unit 21 and the reception control unit 22 are arranged in place of the devices 52 ₁ and 52 ₂ shown in FIG. In addition,
Below, the ER signal, the RS signal, the SD (Send Data) signal, the transmission clock ST1 output from the data terminal 51 ₁ (51 ₂ ) side, and the DR to be given to these data terminals.
(Data Set Ready) signal, CS (Clear to Send) signal,
Transmission clock ST2, CD signal, RD (Receive Data)
Regarding the signal and the reception clock RT, the two letters for identifying the signal are shown with a subscript " _T " added, and the ER signal, the RS signal, the SD signal, and the transmission to be given to the modem 53 ₁ (53 ₂ ) are shown. The clock ST1 and the DR signal, CS signal, and transmission clock ST output from these modems
2. Regarding the CD signal, the RD signal, and the reception clock RT, the suffix “ _M ” is added to the two letters that similarly identify the signals.

In the transmission control unit 21, the ER _T signal is given to one input of the OR gate 23 and the output thereof is DR.
_{The T} signal is obtained. The other input of the OR gate 23 is D
R _M signal is supplied, ER _M signals and RS _M signal is fixed set to active (low) level. Delay circuit 24
To the one input of the input and the OR gate 25 of given RS _T signal, the output of the delay circuit 24 is connected to the input of one input and the inverter 27 of the OR gate 26. The other input of the OR gate 26 is given CS _M signals, CS _T signal is obtained at its output. The output of the inverter 27 is connected to the other input of the OR gate 25, and its output is connected to one input of the AND gate 28. The SD _T signal is given to the data input of the shift register 29,
Its output is connected to the other input of AND gate 28. At the output of the AND gate 28, the SD _M signal is obtained. The transmission clock ST is input to the changeover switch 30.
1 _T and ST2 _M are provided, and the transmission clock ST2 _T is obtained at its first output. The transmission clock ST1 _M is obtained at the second output of the changeover switch 30, and the third output thereof is connected to the clock input of the shift register 29.

In the reception controller 22, the CD _M signal is given to one input of the OR gate 31, and its output is connected to the inputs of the flip-flop (FF) 32 and the delay circuit 33 to output the CD _T signal. . The RD _M signal is applied to the data input of the shift register 34, and its parallel output is connected to the inputs of the OR gate 35 and the AND gate 36. The output of the AND gate 36 is connected to one input of the AND gate 37, and the output of the flip-flop 32 is connected to the input of the inverter 38 and one input of the OR gate 39. The output of the inverter 38 is the AND gate 37.
Of the OR gate 39 and its output is connected to the other input of the OR gate 39. The output of the OR gate 39 is connected to one input of the AND gate 40, and the output of the OR gate 35 is connected to the other input. The output of the AND gate 40 is connected to the other input of the OR gate 31,
The output of the delay circuit 33 is connected to one input of the OR gate 41. The serial output of the shift register 34 is connected to the other input of the OR gate 41, and the RD _T signal is obtained at its output. The clock input of the shift register 34 is supplied with the reception clock RT _M , and the reception clock is output as the reception clock RT _T.

Regarding the correspondence between this embodiment and the block diagram shown in FIG. 1, the data terminal 51 ₁ (51 ₂ ) corresponds to the data terminal 11, and the modem 53 ₁ (53 ₄ ) corresponds to the modem 13.
The delay circuit 24 and the OR gate 26 correspond to the transmission control means 15, the shift register 29 and the changeover switch 30 correspond to the delay means 17, and the delay circuit 2
4, the OR gate 25, the inverter 27 and the AND gate 28 correspond to the transmitting means 19.

The operation of this embodiment will be described below. In addition,
In the following, regarding the logical value of each signal related to the modem interface, the active (on) level is represented by a low level and the inactive (off) level is represented by a high level based on CCITT's V series recommendation, and each logical value is represented. The circuit operates in positive logic with respect to such a logical value, and the transmission clocks ST1 _M , ST2 _T and the reception clock RT
_T is obtained by transparently transmitting the transmit clock ST1 _T, ST2 _M and receive clock RT _M through a device according to the present embodiment, respectively, and the shift register 29 of the transmit clock ST1 _T, ST2 _M, changeover switch It is assumed that 30 operates in synchronism with one selected according to the form of the network.

In the modem 53 ₁ (53 ₂ ), although not shown, the DR _M signal is fixedly set to the active level, and the transmission control unit 21 fixedly sets the ER _M signal and the RS _M signal to the active level. So data terminal 5
The 1 ₁ (51 ₂ ) side always recognizes that it is operating normally and constantly sends out the carrier. Therefore, the modem 53
Between _{1-53 2,} the carrier is transmitted and received continuously.

Further, the data terminal 51 ₁ (51 ₂₎ sets the logical value of the ER _T signal becomes the inoperable state to the inactive level, the modem 53 ₁ (53 ₄₎ or become data transmission incapable state an undeliverable status when DR _M signal and CS
Set the logical value of the _M signal to the inactive level. OR gate 23, ER _T signals and DR also logical value of _M signal any outputs a DR _T signal of active level as long as an active level, one of the logical values of ER _T signals and DR _M signal in the opposite non When an active level to set the logical value of the DR _T signal inactive le level. Further, the OR gate 26 sets the logical value of the _CST signal to the inactive level in response to the CS _M signal which has become the inactive level. Therefore, the data terminal 51
Due to the failure of ₁ (51 ₂ ) or the modem 53 ₁ (53 ₄ ), the transmission procedure between the data terminal 51 ₁ (51 ₂ ) and the modem 53 ₁ (53 ₄ ) may fall into an inconsistent state. Avoided.

On the other hand, when the data terminal 51 ₁ (51 ₂ ) is not performing data communication, the modem 53 ₁ (53 ₄ ) is activated in response to the RS _M signal fixedly set to the active level as described above. Output the level CS _M signal,
Data terminal 51 ₁ in response to the signal (51 ₂₎ and outputs the RS _T signal inactive level. OR gate 25
Since the two signals of different logic values according to steady the logical values of the above-mentioned RS _T signal is input, it outputs a high level signal to the AND gate 28. Further, the OR gate 26 is set since the inactive level RS _T signals via the active level of the CS _M signal and the delay circuit 24 described above in its input is given, the logic value of CS _T signal inactive level To do. Therefore, the data terminal 51 ₁ (51 ₂₎ is responsive to such a CS _T signal S
The logical value of the D _T signal is set to the inactive level, and the AND gate 28 outputs the SD _M signal of the inactive level in response to such an SD _T signal provided via the shift register 29.

Further, the data terminal 51 ₁ (51 ₂ ) receives the ER _T signal and the R when the data communication is started.
Set the logical value of the S _T signal to the active level. Delay circuit 24, the delay time of the circuit is set to the carrier on time in compliance with the recommendations described above (RS-CS delay time), active level logical values of CS _T signal in response to the active level RS _T signal Set to. Therefore, the data terminal 51 ₁ (51 _2), SD _T signal indicating serial transmission information in response to the active level DR _T such CS _T signal and the OR gate 23 outputs in response to ER _T signal ( It does not include the RS _T signal.) to the.

The shift register 29 has the number of stages corresponding to the carrier-on time, takes in the SD _T signal in synchronization with the transmission clock given through the changeover switch 30, delays it, and inputs it to the other input of the AND gate 28. introduce.

On the other hand, the OR gate 25, although RS _T signal changes to the active level one input thereof is supplied directly, the RS _T signal to the other input of the delay circuit 2
4 and the inverter 27, the signals are delayed and provided, so that a low-level signal is output within the delay time width.
Therefore, the output of the AND gate 28 becomes an active (low) level with a pulse width substantially equal to the carrier on time, and the serial transmission information output from the shift register 29 with the passage of the carrier on time is obtained as the SD _M signal. . In the following, a plurality of active level bits preceding the transmission information in this way are referred to as "RS ^- information".

When the data terminal 51 ₁ (51 ₂ ) finishes the transmission, it sets the logical value of the SD _T signal to the inactive level after transmitting the last bit of the transmission information, and further, RS _T Set the logic value of the signal to the inactive level. AND gate 28 via the OR gate 25 is given RS _T signal such non-active level,
In response to the signal, the SD _T signal provided through the shift register 29 is sent out as the SD _M signal. Therefore, the logic level of the SD _M signal becomes a constant inactive (high) level in the time subsequent to the last bit of the above-mentioned transmission information. In the following, a plurality of inactive-level bits following the transmission information in this manner will be referred to as “RS ⁺ information”.

On the other hand, in the reception control unit 22, the modem 5
If the configuration of the device facing each other through 3 ₁ and 53 ₄ is the same as the device according to the present embodiment, the logical value of the CD _M signal is active by the carrier that is constantly received via the modem 53 ₁ (53 ₄ ). The logic value of the RD _M signal in the state where the level is reached and the data communication is not performed is set to the inactive level. The shift register 34 is supplied to the OR gate 41 is delayed such RD _M signal.

The flip-flop 32 stores the logical value of the CD _T signal applied to the data terminal 51 ₁ (51 ₂ ) in advance, and when the logical value is an inactive level, the delay circuit 33 is activated. The corresponding input of OR gate 41 is also set to the inactive level via. Therefore, the OR gate 41 outputs the inactive RD _T signal. Further, the AND gate 37 is a flip-flop 32.
Is closed by a low level signal supplied from the inverter 38 to the output of the OR gate 39 is set to a high level according to the inactive level CD _T signal directly supplied from the flip-flop 32. Therefore, the AND gate 40 is opened by the OR gate 39.

When the modem 53 ₁ (53 ₂ ) receives the RD _M signal containing RS ⁻ information in such a state, the shift register 34 takes in the RD _M signal and performs serial-parallel conversion. When the RS ^- signal is detected by such serial-parallel conversion, its output is set to the low level. Therefore, the OR gate 31 uses the above-mentioned active-level CD _M signal as the CD _T signal as the data terminal 51.
₁ (51 ₂ ) and the logical value of the CD _T signal is stored in the flip-flop 32.

The delay circuit 33 has a delay time corresponding to the bit length of RS ^- information, and when such a delay time elapses from the time when the logical value of the CD _T signal changes to the active level, it passes through the OR gate 41. Setting to output the RD _M signal (not including RS ⁻ information) transmitted through the shift register 34 as the RD _T signal.

During data communication, the AND gate 37 is opened via the inverter 38 by the active level CD _T signal held in the flip-flop 32. The inclusion of RS ⁺ information RD _M signal received in such a state, the information is parallel conversion by the shift register 34, and after being converted into a high-level signal through the AND gate 36 gates 37 And is transmitted to the AND gate 40 via the OR gate 39. Further, the output of the OR gate 35 is set to a high level in response to the RS ⁺ information converted in parallel by the shift register 34. Therefore, CD _M
The signal is output as a CD _T signal through the OR gate 31 which is set to the passing state by the AND gate 40,
And it is stored in the flip-flop 32 again and the subsequent RS
^- used in the preparation to detect the information.

In this embodiment, a digital circuit such as a combination circuit or a shift register is used to provide an interface related to the RS signal between the modem side and the data terminal side. Not limited to the configuration, if the response speed adapted to the transmission procedure can be obtained,
For example, the transmission control means 15, the delay means 17, the transmission means 1
9. Other units may be realized by controlling software, or an analog delay element may be used instead of the delay element such as a shift register.

[0033]

As described above, according to the present invention, the pseudo C
The D signal is transmitted to the analog transmission line by using the permissible delay time of the transmission start command given as a response to the transmission request sent by the data terminal and the time after the data terminal has completed transmitting the transmission information. Therefore, the data transmission can be performed at the transmission rate required by the data terminal without changing the transmission rate. Further, when there is a failure in the analog transmission line (network side), the transmission control means 15 sends a transmission control command to the data terminal 11 to permit transmission of the transmission information, according to the status information obtained via the modem in response to the failure. Since it is withdrawn, inconsistency in the transmission procedure between the analog transmission line side and the data terminal side can be reliably avoided.

Therefore, in the data transmission system to which the present invention is applied, the reliability of the transmission line can be improved while maintaining the transmission efficiency.

[Brief description of drawings]

FIG. 1 is a principle block diagram of the present invention.

FIG. 2 is a diagram showing an embodiment of the present invention.

FIG. 3 is a diagram showing a configuration example of a data communication system using an analog communication network.

[Explanation of symbols]

11, 51 Data terminal 13, 53 Modem 15 Transmission control means 17 Delay means 19 Transmission means 21 Transmission control section 22 Reception control section 23, 25, 26, 31, 35, 39, 41 OR gate 24, 33 Delay circuit 27, 38 Inverter 28, 36, 37, 40 AND gate 29, 34 Shift register 30 Changeover switch 32 Flip-flop 52 Pseudo CD signal transmission device 54 Multiplex conversion device (MUX)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location 9371-5K H04L 13/00 309A

Claims (1)

[Claims] 1. A pseudo CD having a communication interface between a data terminal (11) and a modem (13) connected to an analog transmission line for which carrier transmission is always required during transmission.
In the signal transmission device, the transmission request sent from the data terminal (11) is delayed to send a transmission start command to the data terminal to instruct whether to permit transmission of transmission information, and the modem is used when the analog transmission line fails. Depending on the status information obtained via (13), the transmission control means (15) withdrawing the transmission start command indicating the transmission permission of the transmission information, and the time for which the transmission control means (15) delays the transmission request or more. Delay means (17) for delaying the transmission information sent from the data terminal (11) over the time of, and the transmission request is added before and after the transmission information delayed by the delay means (17) on the time axis. Said modem (13)
And a sending means (19) for giving to the pseudo CD signal transmitting apparatus.