JPH03117133A - Data transfer equipment - Google Patents

Abstract

PURPOSE:To prevent the transmission inhibiting period from being increased due to duration of a residual carrier, and to set the transmission inhibiting period as small as possible by measuring the duration of the residual carrier which appears at the time of receiving a reference signal, and correcting the transmission inhibiting period in a CSMA/CD channel competition control thereby. CONSTITUTION:When information of 'a fact of initialization start' from a carrier frequency converter 3 is received, a channel competition control part 19 executes preparations for measuring the time of a test pulse transmitted from the carrier frequency converter 3. In this state, duration T of a residual carrier in each transmitter/receiver 1 is calculated from length of the measured test pulse. A transmission inhibiting period obtained by correcting this duration T is set to a timer of the channel competition control part 19. In such a way, by measuring the duration of the residual carrier in each transmitter/receiver 1, and correcting the transmission inhibiting period by this measured duration, the duration portion of the residual carrier can be eliminated, and the transmission inhibiting period does not become large but can be set small exactly.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention converts the carrier frequency of a signal transmitted from each transceiver and retransmits it to each transceiver via a transmission path. The present invention relates to a data transmission device including a carrier frequency converter, each transmitter/receiver transmitting and receiving at different frequencies, and having a CSMA/CD channel contention control function.

(Prior Art) Recently, there is a bidirectional data transmission device that has a carrier frequency converter installed at one point on a data transmission path, and each transmitter/receiver has a function of transmitting and receiving at a different frequency and a CSMA/CD channel contention control function. .

When multiple transmitters and receivers are connected in parallel to the data transmission path,
The reception level of each transceiver decreases in inverse proportion to the number of connected transceivers. For this reason, in CATV lines and the like, for example, a carrier frequency converter is used to impart directionality to the transmission path, as shown in FIG. That is, the signal from each transceiver is first transmitted to a carrier frequency converter, and then retransmitted to each transceiver via the carrier frequency converter. As a result, a system is realized in which the transmission output of the carrier frequency converter is large and the transmission output of each transceiver is small, thereby making it possible to reduce the price of the entire system.

Furthermore, in a system in which a plurality of transmitters and receivers are connected in parallel, if a transmission factor occurs in the plurality of transmitters and receivers one after another, competitive transmissions occur and a collision occurs.

When a collision occurs, an error occurs in the transmitted data and the transmission fails. If contention control is not performed, this phenomenon will be repeated many times, resulting in a significant reduction in the data transmission capability of the data transmission system, or a failure in transmission.

Channel contention control functions are provided to prevent such phenomena, and include "polling/selecting method" and "rCSMA/CD channel contention control method".

In the polling/selecting method, a terminal that has become a parent device polls each terminal that has become a slave device at regular intervals, and only the polled terminals transmit data. In this method, the transmission path is considerably occupied due to polling, so the transmission efficiency is low.

On the other hand, the CSMA/CD channel contention control method is a method in which a transmitter/receiver that wants to transmit monitors the transmission path, and when it determines that the transmission path is free, starts transmission after waiting for a while. The waiting time, that is, the transmission prohibition period, is set differently for each transceiver, and the transmission is performed if no other transceiver is transmitting after the transmission prohibition period. In this case, if another transmitter/receiver is transmitting first, conflicting transmissions are prevented by repeating the process of waiting until the transmission line is free and then transmitting after the transmission line is free. . This method has higher transmission efficiency than the polling/selecting method because only the transmitter/receiver that wants to transmit exchanges signals.

Furthermore, the CSMA/CD channel contention control method includes a method in which the waiting time, that is, a transmission prohibition period, is determined using a random number and a method in which the waiting time is determined using an address. The method using random numbers allows the number of transmission start times to be less than or equal to the number of transmitters and receivers, and is therefore characterized in that the transmission prohibition period can be reduced. By the way, the transmission success rate P in this case is expressed by the following equation. Note that, in practice, when a collision occurs, a method is adopted in which the number of transmission start times is increased and the transmission is performed again.

p-Σn C1 (1/m) [(m-k)/m] where, n ""' 2 + 3.4, ...,
m is the number of transmission start times, n is the number of transceivers that have started transmission, and p is the transmission success rate (probability that only one transceiver starts transmission).

If this relationship of n+m+p is tabulated, it will look like the following table.

(Left below) From this table, it is clear that the method of calculating random numbers is not suitable for data transmission systems where a large number of transmitters and receivers frequently start transmitting at the same time. For data transmission systems where many transmitters and receivers frequently start transmitting at the same time, a method of determining from addresses is suitable.

The transmission success rate in this case is 100%.

(Problem to be solved by the invention) In the conventional data transmission device described above, the number of transmitters and receivers
If the number is increased, the number of transmission monitoring times must be increased in proportion to the number of transmission monitoring times, which causes the problem that the transmission unavailable time becomes larger and the transmission efficiency decreases in inverse proportion to this. There is.

Furthermore, the difference in transmission start times needs to be of a length that can be determined by each transceiver. That is, it needs to be long enough to absorb the timing difference between each transmitter and receiver. The timing deviation between each transmitter and receiver is caused by residual carriers on the transmission path. Even when a transmitter/receiver finishes transmitting, the residual carriers on the transmission path do not immediately drop below the threshold, but gradually attenuate, indicating that the transmitter/receiver that was transmitting has stopped transmitting. Despite this, the receiving side mistakenly assumes that the transmission is continuing. However, in a data transmission device using a modem, there is always a residual carrier. Furthermore, the length of time that this residual carrier lasts varies depending on the reception level of the transceiver, which further causes a timing difference between each transceiver. This deviation is included in the width of the transmission prohibition period, and as a result, the transmission prohibition period becomes very long, resulting in a problem that the transmission efficiency becomes very low.

More specifically, in a data transmission device that transmits data via a modem, the carrier on the transmission path attenuates at -several tens of db/μsec when the transceiver stops transmitting. In addition,
The modem of the reference transmission device has a range of 20 dbm to 60 dbm.
bm at a rate of approximately -4 db/μsec. Also, the carrier detection threshold level of each transceiver is approximately −
Since it is several tens of dbm (-80 dbm in the reference modem), a time difference occurs in the timing of transmission end detection depending on the difference in signal level between each transmitter and receiver. The relationship between this time difference and the difference in signal level on the transmission path is several hundred nanometers/day.
bm.
A time difference of 0 μsec occurred). FIG. 3 shows the relationship between the signal level at the receiving end and the elapsed time from the stop of transmission to the disappearance of the carrier.

Note that in data transmission lines such as CATV lines, the transmission line has directionality as shown in Figure 1, and all signals sent from each transceiver are first sent to the carrier frequency converter.
It is retransmitted from the carrier frequency converter to each transceiver.

In Figure 4, the shaded area shows the delay in the timing of the end of transmission due to the residual carrier when transmitting data from one transceiver to another. It can be seen that this is caused by a shift in the transmission end timing due to residual carriers when being sent from the converter to each transceiver. Note that this difference in the delay in the end of transmission due to the residual carrier is because the reception level differs for each terminal.

Recently, there have been systems in which devices for transmitting data over CATV lines are used as data transmission systems such as management systems and message exchange systems in apartment complexes, housing complexes, and the like. In this case, the number of transmitters and receivers increases from several tens to 1,000 to 2,000, so the time that the data transmission path for CSMA/CD channel contention control is occupied becomes very long, and the transmission efficiency is very low. (In the reference transmission device, if you create a system consisting of 1000 transceivers, the transfer rate is 64 Kbps, and 1 packet is 64 bytes, and the time difference from carrier disappearance to transmission is possible is 20 μsec) The transmission capacity decreases to 36%.Furthermore, if one packet is 16 bytes under the same conditions, the transmission capacity decreases to 2%).

The present invention has been made in view of the above, and an object of the present invention is to provide a data transmission device that improves the transmission efficiency of a transmission line by reducing the difference in the timing of the end of transmission between each transmitter and receiver. It is in.

[Configuration of the Invention (Means for Solving the Problem) In order to achieve the above object, the data transmission device of the present invention comprises:
A carrier frequency converter is installed that converts the carrier frequency of the signal transmitted from each transceiver and retransmits it to each transceiver via a transmission path, and each transceiver transmits and receives at a different frequency. /
A data transmission device having a CD channel contention control function, wherein the carrier frequency converter has transmitting means for transmitting a predetermined reference signal to each transceiver, and each transceiver has a carrier frequency converter. a receiving means for receiving the reference signal transmitted from the receiving means; a measuring means for measuring the duration of residual carrier appearing when the receiving means receives the reference signal; and a duration of the residual carrier measured by the measuring means. The gist of the present invention is to include a correction means for correcting a transmission prohibition period in CSMA/CD channel contention control based on time.

(Function) In the data transmission device of the present invention, each transceiver receives a predetermined reference signal transmitted from a carrier frequency converter, measures the duration of a residual carrier that appears when receiving this reference signal, The transmission prohibition period in CSMA/CD channel contention control is corrected based on the measured residual carrier duration.

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

FIG. 1 is a block diagram showing the overall configuration of a data transmission device according to an embodiment of the present invention. The data transmission device shown in the figure is applied to, for example, a CATV line,
As shown in FIG. 2(b), the signal transmitted from each transceiver 1 is sent to the carrier frequency converter 3 via the transmission line 5, and the carrier frequency converter 3 sends the signal to each transceiver 1. The carrier frequency of the transmitted signal is converted and transmitted again to each transceiver 1 via the transmission line 5. Further, each transceiver 1 performs transmitting and receiving operations at different frequencies and has CSMA/CD channel contention control.

Further, as shown in FIG. 1, the carrier frequency converter 3 includes a modulator 31, a demodulator 33, and an initial setting signal generator 35.
has. Each transceiver 1 is connected to a carrier frequency converter 3 via a transmission path 5, and connected to a modem 11 that performs modulation and demodulation processing, and is also connected to external information equipment, etc. via an interface. It has a transmission control processing device 14 that performs data transmission processing and channel access control.

FIG. 2 is a block diagram showing the configuration of each transceiver 1 shown in FIG. 1. As shown in the figure, each transmitter/receiver 1 includes the modem 11 connected to the transmission path, a serial number 1014 connected to the modem 11, a parallel number 1015 connected to the interface of information equipment, etc. It has a buffer 17 between the serial I1015 and the serial I1014, a channel contention control section 19, and a CPU 21 that controls the overall operation. In FIG. 2, solid lines indicate the flow of data, and dotted lines indicate the flow of control.

FIG. 5 shows the configuration of the initial setting signal generator 35 of the carrier frequency converter 3 shown in FIG.
FIG.

The initial setting signal generator 35 includes a control section 37 that controls the initial setting signal generation operation, a counter 39, a flip-flop 41, gated buffers 43 and 45, and an OR circuit 47.4.
It has 9.

When the control unit 37 of the initial setting signal generator 35 attempts to initialize each transceiver 1, it first sets the test 0 signal line to a high level as shown in FIG. modulator 31 as transmission request signal RTS via 47
6(f) as shown in FIG. 6(f), and then outputs the information "to be processed by each transceiver" from the signal line of the test TXD as shown in FIG. 6(b). This information is transmitted via the gated buffer 43 and the OR circuit 47 and further via the modulator 31 to the transmission path 5 as shown in FIG. 6(g), and is transmitted to each transceiver 1.

Then, set the test 0 signal line to low level.
Next, the time for sending out the test pulse is set in the counter 39. In this case, the count N1 set in the counter 39 is as follows.

N 1 = t o /t 1 where tn is the time (seconds) for the carrier frequency converter 3 to send out the test pulse, and tl is the time (in seconds) for the counter 3 sorant to send out the test pulse.

Then, in order to send out a test pulse, the control unit 37 first sets the count N1 in the counter 39. Then, the signal line of the test l-1 is set to a high level as shown in FIG. 6(C). Set. As a result, the flip-flop 41 is preset, and its output Q is as shown in FIG. 6(e).
becomes high level, and a test pulse is sent from the modulator 31 to the transmission line 5 via the OR circuit 49. At the same time, the counter 39 is triggered from the test 1 signal line and starts counting. When the test pulse transmission time elapses, the value of the counter 39 becomes O, and the counter 39 outputs a Z signal as shown in FIG. 6(d), thereby clearing the flip-flop 41 and transmitting the test pulse. ends.

Next, set the test 0 signal line to high level and test T
The xD transmits information ``initializing each transceiver'' 5 , lowers the test 0 signal to a low level, and thereafter the carrier frequency converter 3 returns to normal operation.

Figure 7 shows the CSMA/CD of each transceiver 1 shown in Figure 2.
FIG. 2 is a block diagram showing the configuration of one channel contention control unit that implements channel contention control. The channel contention control unit 19 shown in the figure includes a counter 51 that measures the length of the test pulse transmitted from the carrier frequency converter 3, flip-flops 5B and 55 that detect the beginning and end of the test pulse,
It has an AND circuit 57, an inverter 59, a prescaler 6 which supplies the clock pulse φ2 of the counter 51, a buffer 63, and an inverter 65 which supplies and clears the test signal from the CPU 21 to the clear terminal of the flip-flop 53.55. Traditional CSM
Timer 67, flip-flop 69, AND circuits 71, 75, and inverter 73.7 that realize A/CD control function
It has 7.

FIG. 8 is a time chart showing the operation of the channel contention control unit 19 shown in FIG. When receiving the information "initial settings start", first the CPU 21
The test signal on the test signal line is controlled as shown in Fig. 8(b).
Set the flip-flop 53 to high level as shown in
．． 55 and also clears the counter 51,
This makes preparations for measuring the time of the test pulse that will be transmitted next from the carrier frequency converter 3. Then, when the test pulse is transmitted from the carrier frequency converter 3, the flip-flop 5
3 is set, its output Q2 becomes high level, and the AND circuit 57 outputs an output signal P1 as shown in FIG. A clock φ2 is supplied to the counter 51 via the buffer 63 as shown in FIG. 8(f), and the counter 51 measures the length of the test pulse. When the test pulse from the carrier frequency converter 3 ends, the output Q3 of the flip-flop 55 becomes a low level as shown in FIG. 8(d), so that the AND circuit 57 no longer outputs the output signal P]-. , the clock φ to the counter 51 is also stopped. Counter 51 finishes measuring the length of the test pulse.

The duration T of the residual carrier in each transceiver 1 is calculated from the length of the test pulse measured as described above using the following equation.

T=t2 Φn-t3 Here, t2 is the time (seconds) of one clock of clock φ
n is the count value measured by the counter 51, and t3 is the time (seconds) for the carrier frequency converter 3 to send out the test pulse.

Note that each transceiver 1 stores the time at which the carrier frequency converter 3 sends out the test pulse.

A transmission prohibition period obtained by correcting this duration T is set in the timer 67 of the channel contention control section 19. The setting value N2 for this transmission prohibition period is as shown in the following equation.

N2=(to,, + address φt4 T)/ls, where fall is the offset (seconds) of the transmission pause period t4
is the increment (seconds) of the transmission pause period, t is the time (seconds) of one count of the timer 67, and address is the own address of the transceiver 1.

The setting value N2 for the transmission prohibition period calculated as above is:
The timer 67 is set under the control of the CPU 21 after initialization and when a carrier appears on the transmission line 5. When the carrier on the transmission path 5 becomes low level, the timer 67 starts counting time and measures the transmission prohibited period.

If the timer 67 times out before the other transceiver 1 transmits, the signal from the output terminal zc of the timer 67 becomes high level, which sets the flip-flop 69 and causes the CPU 21 The signal to the AND circuit 71 that masks the transmission request signal RTS' from the transmission control processing device 13 via the transmission control processing device 13 is set to high level to remove the mask, and when the transmission request signal RTS' is at high level, A signal is sent to the transmission line 5 via the modem 11 to start data transmission.

In addition, if the other transceiver 1 starts transmitting earlier and the own transceiver 1 finishes transmitting (residual carrier is in the data), the transmission request signal RTS is at a low level and the carrier detection CD is Since the level is high, the flip-flop 69 is cleared, and the transmission request signal RTS' sent through the CPU 21 is masked by the flip-flop 69 again.

As described above, by measuring the duration of the residual carrier in each transceiver 1 and correcting the transmission prohibition period based on the measured duration, the duration of the residual carrier indicated by diagonal lines in FIG. 4 is removed. Therefore, the transmission prohibition period can be appropriately set to a small value without increasing it, and transmission efficiency can be improved. For example, conventional CS
In MA/CD channel contention control, the increments of the transmission pause period are 10 μSee, but the time width that the IC for the timer 67 can recognize is several hundred nanometers for TTL, for example.
It is possible to realize a data transmission device that can be made as small as approximately e, and the transmission efficiency does not decrease even when a large number of transmitters and receivers are connected.

0 [Effects of the Invention] As explained above, according to the present invention, each transceiver receives a predetermined reference signal transmitted from a carrier frequency converter, and receives the residual carrier that appears when receiving this reference signal. The duration of the residual carrier is measured, and the transmission prohibited period in CSMA/CD channel contention control is corrected based on the measured residual carrier duration. This prevents the transmission prohibited period from increasing due to the residual carrier duration, and It is possible to minimize the inhibition period and improve transmission efficiency.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a data transmission device according to an embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of a transceiver used in the data transmission device of FIG. 1, and FIG. A diagram showing the change in signal level at the receiving end from the end of transmission,
FIG. 4 is a diagram showing the timing deviation due to the influence of residual carriers, FIG. 5 is a block diagram showing the configuration of the signal generator for initial setting of the carrier frequency converter of FIG. 1, and FIG.
1 Timing diagram showing the operation of the initial setting signal generator shown in Figure 1.
FIG. 7 is a block diagram showing the configuration of the channel contention control section of the transceiver shown in FIG. 1, and FIG. 8 is a timing chart showing the operation of the channel contention control section of FIG. 7. 1... Transmitter/receiver 3... Carrier frequency converter 5... Transmission line 19... Channel competition control section 35... Initial setting signal generator 37... Control section 39... Counter 51 ...Counter 67...Timer

Claims (1)

[Claims] A carrier frequency converter is provided to convert the carrier frequency of the signal transmitted from each transceiver and resend it to each transceiver via a transmission path, and each transceiver transmits and receives at a different frequency. A data transmission device having a CD channel contention control function, wherein the carrier frequency converter has transmitting means for transmitting a predetermined reference signal to each transceiver, and each transceiver has a carrier frequency converter. a receiving means for receiving the reference signal transmitted from the receiving means; a measuring means for measuring the duration of residual carrier appearing when the receiving means receives the reference signal; and a duration of the residual carrier measured by the measuring means. CSMA/by time
A data transmission device comprising: a correction means for correcting a transmission prohibition period in CD channel contention control.