JPH02121543A - Data transmitting device - Google Patents

Abstract

PURPOSE:To decrease the time when a transmission line is occupied by the channel conflict control by detecting a prescribed signal transmitted at the end of the transmission to detect the transmission end timing and setting a prescribed transmission inhibiting period based on the detected transmission end timing. CONSTITUTION:When a transmitting/receiving device is through with the transmission, a flag detecting pulse p1 is outputted from a counter 33 at a time point t1. The pulse p1 presets a timer circuit 37. When a prescribed transmission inhibiting period elapses, the circuit 37 has an overflow and outputs a transmission inhibiting pulse p3 at a time point t3. If no carrier exists on a CATV circuit 1 and a carrier detecting signal CD is not available at output of the pulse p3, a D flip-flop 45 is set by the pulse p3. Then a transmission grant signal is outputted from the flip-flop 45 at the time point t3. Thus the transmission of data is ready.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a data transmission device that connects a plurality of transceivers to a bidirectional CATV line in the form of a bus and transmits data via a modem. .

(Prior Art) Recently, a data transmission device has been developed in which a plurality of transmitters and receivers are connected to a bidirectional CAT line in the form of a bus and data is transmitted via a modem. In data transmission devices connected in a bus-like manner as described above, if a transmission factor occurs one after another in a plurality of transmitters and receivers, competitive transmissions occur and a collision occurs. If a collision occurs, an error will occur in the transmitted data, so
It is necessary to interrupt the transmission and retransmit it. When a conflict occurs like this, if no conflict control is done,
As described above, the operations occur repeatedly, which significantly reduces transmission efficiency. Conventionally, methods for controlling such contention include the Bolling-Selefting method and the CSMA/CD method.

The whole-selefting method is a method in which the center polls each transmitting/receiving ff1li at regular intervals, but in this method, the transmission path is always occupied due to polling, so the transmission efficiency is low.

On the other hand, in the CSMA/CD method, the transmitting and receiving devices that want to transmit constantly monitor the carrier on the transmission path, and when no Q1 glia is detected, transmission starts, and if a collision occurs, a random number or address is sent. In this method, the data is retransmitted after the time determined by E.g. Since this method does not involve the exchange of signals for polling, it has higher transmission efficiency than the hauling selective method.

Furthermore, in order to further improve the transmission efficiency in the CSMA/CD method described above, the following control is also added to the control described above. In other words, when each transmitter/receiver finishes transmitting and detects that the carrier on the transmission path has disappeared, it becomes unable to transmit for a while, but the time during which transmission is disabled varies depending on the address random number etc. It is determined for each sender/receiver. Furthermore, when it detects a carrier transmitted by another transceiver, it stops its own transmission, thereby preventing collisions due to competing transmissions.

(Problems to be Solved by the Invention) In the conventional data transmission device described above, there is a problem in that when the number of transmitters and receivers increases, the transmission unavailable time increases in proportion to the number, and the transmission efficiency decreases.

In addition, as another problem, the step size of the above-mentioned transmission unavailable time is
In addition to being long enough for each transceiver to make decisions, it also needs to be long enough to absorb deviations between each transceiver. However, when transmission ends and the carrier on the transmission path disappears, The carrier does not immediately disappear, but in a transmission device using a modem, there is a residual carrier, and this residual carrier increases the above-mentioned deviation, and as a result, the above-mentioned non-transmission time increases, and the transmission efficiency decreases. There's a problem.

More specifically, in a data transmission system that transmits data via a modem, even if the transmitter stops transmitting carriers, residual carriers remain on the transmission path. The attenuation of this carrier is approximately several db/μ5ec (in the modem of the reference transmission equipment, it is approximately -4db/μ5 from -20dbm to -60dbm).
the rate r decay of u sec). On the other hand, the threshold level for Ki A/Rear detection on the receiving d side is 10 d.
bm (-80dbm for the reference modem),
A time difference occurs in the timing of transmission end detection depending on the difference in attenuation in the transmission path between the transmitter and the receiver. The relationship between this time difference and the difference in attenuation of the transmission line is several hundred n5ec/
db (with the reference transmission equipment, the difference in the transmission path difference is at most 40 db, and there is a difference of about 10 db at the timing of the end of transmission).
), this relationship t is the 6th
The figure shows carrier strength versus time t from carrier transmission stop F.
It is reduced as d.

In addition, the equipment that transmits data on the CATV line is
It is a system that has a repeater in the center, converts the signal sent from the transmitting side to a different frequency (which may also be converted to a different modulation) and transmits it, and this signal is received by the receiving side. , the time difference between the transmission end detection timings on each receiving side due to the amount of attenuation of the transmission path described above is doubled.

Furthermore, recently, such data transmission equipment has been installed as a BBS (B, ULLET BOARD SY) in apartment complexes, housing complexes, etc.
There are systems used as bucket 1 data transmission devices such as STEM (e.g., electronic circulation board systems, message transfer systems), and management systems. In this case, the number of transceivers increases from several tens to 1,2000, so the time that the transmission path is occupied during channel contention time becomes very good, and the transmission rate becomes low. In particular, since such data transmission equipment mainly transmits data in short packets (256 by 1 or less), most of the transmission path is used for channel contention, and as a result, transmission efficiency decreases. (In the reference transmission device, i
If a device consisting of ooo transmitters and receivers is created, the transfer rate is 54 kbps, 1 packet is 64 bytes, and the time difference from carrier extinction to transmission ready is 30 μsec, the transmission efficiency will drop to 21%.

The present invention has been made in view of the above, and its purpose is to reduce the difference in the timing of transmission end detection between each transmitting and receiving c, and to reduce the proportion of the C1 transmission line used for channel contention. An object of the present invention is to provide a data transmission device that improves the transmission efficiency of a transmission line.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the data transmission device of the present invention has the following features:
Two-way 0ATVIT! lI! A data transmission device that connects multiple transmitters and receivers in a bus-like manner and transmits data using the C3MA/CD method via a modem, and detects the timing of the end of transmission by detecting a predetermined signal sent at the end of transmission. The gist of the present invention is to provide a detection means for detecting the transmission end timing, and a setting means for setting a predetermined transmission prohibition period based on the transmission end timing detected by the detection means.

(Function) The data transmission device of the present invention detects the timing of the end of transmission by detecting a predetermined signal transmitted at the time of end of transmission,
A predetermined transmission prohibition period is set based on the detected transmission end timing.

(Example) Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a block diagram showing the configuration of a remote system of a data transmission device according to an embodiment of the present invention. In the data transmission device shown in the figure, a plurality of transceivers 3 are connected to a CΔTV line 1 in a bus-like manner, and a repeater 5 is connected on the CATV line 1 between these transceivers 3.

Each transmitter/receiver 3 is connected to information equipment, etc. via an interface (not shown), and is connected to a transmission serial control processing device 7 having a transmission processing control 2IIR function, and the transmission control processing device 7 and C
The transmission control processing device is connected between the ATV line 1 and modulates the transmission signal sent from the transmission control processing device 7 and transmits it to the CATV line 1, or demodulates the signal received from the CA TV line 1. It consists of a modem 9 that supplies power to the network 7.

The repeater 5 is for changing the frequency of the modulated transmission signal from the modem 9, and in some cases further changing the modulation method, and retransmitting it to the CAT line 1.

FIG. 2 is a block diagram showing the configuration of each transceiver 3 shown in FIG. 1. This transceiver 3 includes a parallel input/output device r111N connected to an interface of information equipment, a processing device 13 connected to the parallel input/output device 11 and having a processing function, and a buffer device connected to the processing device 13. 15. Connected between the processing device 13 and the modem 9, converting the parallel signal from the processing device 13 into a serial signal and supplying it to the modem 9, converting the serial signal from the modem 9 into a parallel signal and processing it. Parallel/serial converter 17, C8M△/CD chip 1 to supply to device 13
The present invention is comprised of one CSMA/CD channel contention processing device having a channel contention processing capability and the modem 9.

FIG. 3 shows the CSMA/CD channel conflict filter shown in FIG. 2. It is a block diagram showing the configuration of Hii'ff19. This C3MA/CD channel conflict processing head 19
includes a flag detection device 21 that receives received data RXD supplied from the modem 9 and detects specific flags generated at the start and end of data transmission; a flag detection signal from the flag detection device 21; A transmission prohibition period setting timer 23 receives the carrier detection signal CD from the modem 9 and sets a transmission prohibition period; It is composed of an AND circuit 25 that performs an AND operation on the transmission request signal RTS-. Note that a clock signal is supplied to the flag detection device 21 and the transmission prohibition period setting timer 23, and the transmission prohibition period setting timer 2
3 is supplied with a setting value for setting the transmission prohibition period.

FIG. 4 shows a circuit of a transmission signal end detection device that achieves a transmission signal end detection device composed of the flag detection device 21 and the transmission prohibition period setting timer 23 of the CSMA/CD channel conflict processing device 19 shown in FIG. FIG. 2 is a block diagram showing the configuration. The transmission signal end detection device shown in the same figure is HDLC (1-1high 1evel [)a
ta 1ink Control Pr.

The configuration is shown for the case of the cedure) protocol.

FIG. 5 is a timing diagram of this embodiment, and the transmission signal end detection device of FIG. 4 will be explained with reference to this timing diagram.

HDLC is designed to send a special flag or character with the content "rolllllloj" only at the beginning and end of data transmission. Therefore, this special flag r01111110J is sent to the C3MA/CD channel conflict processing device 19 as received data RXD as shown in FIG. 5(b) via the modem 9, specifically, to the AND circuit shown in FIG. 3
1 is received and calculated by the counter 33 via the special flag r01111110J, and when the counter 33 detects that 5 or more ``1''s continue, and 5 or more ``1''s continue, the counter 33 One pulse, the Zunawara flag detection pulse p1, is output as shown by <d) in FIG. In this case, the AND circuit 31 is supplied with the carrier detection signal CD shown in FIG. It is also supplied to the divider 41, and from the divider 41 (C
) is the special flag r01111.
This pulse po is output in response to "1" of 110J.
is supplied to the clock terminal of the counter 33.

Note that the clock terminal of the divider 41 is supplied with a clock that is 0 times the transfer frequency.

Further, the flag detection pulse p1 outputted from the counter 33 is sent to the timer circuit 37 via three inverters, sets the D free knob 70 knob 35, and is sent to the timer circuit 37 via the AND circuit 43. supplying a clock, thereby activating the timer circuit 37;
;:j55 After a predetermined transmission prohibition period as shown in (e) of FIG. 5, a transmission prohibition pulse p3 shown in (f) of FIG. 5 is outputted from the timer circuit 37. The output of the D flip-flop 35 is set by the flag detection pulse p+ from the counter 33, and then reset by the transmission prohibition pulse p3 of the timer circuit 37, and the output pulse p2 corresponding to the transmission prohibition period during this period is set by the flag detection pulse p+ from the counter 33. is generated as shown in FIG. 5(e).

The transmission inhibit pulse p3 from the timer circuit 37 is supplied to a clock terminal of a D flip-flop 45 via an inverter 47. In addition, the D flip-flop 45
data input 9η: Since the carrier detection signal CD is supplied to the child via the inverter 49, when the transmission inhibit pulse p3 is supplied to the D flip-flop 45 and there is no carrier detection signal CD, The D flip-flop 45 outputs a transmittable signal as shown in (1) in FIG. It is designed to be output as a transmission request signal RTS.

Next, the operation of this embodiment, particularly the operation of CSMA/CD channel contention control in the case of HDLC, will be explained with reference to the timing diagram of FIG. 5.

First, when a certain transceiver 3 starts transmission, a start flag consisting of the special flag r01111110J is output, and this flag is detected by the counter 33 via the AND circuit 31 in FIG. 4 as reception data RXD, and the special flag When “1” of “[01111110”] continues for five or more times, the flag detection pulse p1 is output from the counter 33 at time t.
This flag detection pulse p1 presets the timer circuit 37, and the D
The flip 70 knob 35 is set and a clock is supplied to the timer circuit 37 via the AND circuit 43, thereby starting the timer circuit 37.

When a predetermined transmission prohibition period has elapsed, the timer circuit 37 overflows and outputs a transmission prohibition pulse p3 at time t3-. However, at this timing, since transmission is in progress, this transmission inhibit pulse p3 is ignored. Note that if the end flag arrives before the timer circuit 37 overflows and generates the transmission prohibition pulse p3, the timer circuit 37 is reset in the same way, and the end flag processing described below is performed. be exposed.

Next, when the transmitter/receiver 3 that was transmitting ends the transmission, an end flag consisting of the special flag r01111110J is output, and this flag is processed as received data RXD by the counter 33 via the AND circuit 31 as in the case described above. Detected and the special flag r01111110J is set to “1”
continues for five or more times, the flag detection pulse p1 is output from the counter 33 at time t1, and the flag detection pulse p1 presets the timer circuit 37, sets the D flip-flop 35, and outputs the AND circuit 43. A clock is supplied to the timer circuit 37 via the clock, and the timer circuit 37 is thereby activated. When a predetermined transmission prohibition period has elapsed, the timer circuit 37 overflows and outputs a transmission prohibition pulse p3 at time t3.

When this transmission prohibition pulse p3 is output, if there is no carrier on the CATV line 1 and there is no carrier detection signal CD, the D flip-flop 45 is set by the transmission prohibition pulse p3, and the D flip-flop 45 is set by the transmission prohibition pulse p3.
As shown in ((+) in FIG. 5, a send ready signal is output from time t3, and the send ready state is entered.The send ready signal is then passed through the AND circuit 25 shown in FIG. 3 to become a send request signal. It is output as RTS.If another transceiver 3 starts transmitting the start flag before the timer circuit 37 times out and outputs the transmission prohibition pulse p3, the timer circuit 37 outputs the transmission prohibition pulse p3. Since p3 is not output, transmission is not possible, and processing is performed in the same manner as in the case where the start flag is received as described in (e) above.

[Effects of the Invention] As described above, according to the present invention, the timing of the end of transmission is detected by detecting a predetermined signal transmitted at the end of transmission, and the timing of the end of transmission is detected based on the detected timing of end of transmission. Since the prohibition period is set, the transmission prohibition period after the end of transmission can be determined without being affected by residual carriers, and can be set to a very small value of, for example, 1 μsec or less, so the transmission path is not occupied for channel contention control. The transmission time can be reduced, and the transmission efficiency can be greatly improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the overall system configuration of a data transmission device according to an embodiment of the present invention, and FIG. 2 is a block diagram showing the configuration of a transceiver used in the data transmission device of FIG. 1. 3 is a block diagram showing the configuration of the C8M/CD channel contention processing device used in the transceiver shown in FIG. 2, and FIG. Fig. 5 is a timing diagram showing the operation of the data transmission equipment shown in Figs. FIG. 3 is a diagram showing how the time from when the transmitter/receiver ends transmission until the receiver detects the end of transmission differs depending on the receiver. 1... CATV line 3... Transmitter/receiver 7... Transmission control processing device 9... Modem 19... CSMA/CD chitunnel conflict processing device 21
... Flag detection device 23 ... Transmission prohibition period setting timer 33 ... Counter 37 ... Timer circuit 45 ... D flip-flop

Claims (1)

[Claims] A data transmission device that connects multiple transmitters and receivers in a bus-like manner to a bidirectional CATV line and transmits data using the CSMA/CD method via a modem.The transmission ends when a predetermined signal that is sent at the end of transmission is detected. What is claimed is: 1. A data transmission device comprising: a detection means for detecting the timing of the transmission; and a setting means for setting a predetermined transmission prohibition period based on the transmission end timing detected by the detection means.