JPH0430213B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control system for bidirectional burst transmission using a two-wire transmission line, and particularly to a control system for a main device at the start of communication.

The digitalization of communication networks is progressing at a rapid pace, and the digitalization of switching equipment is already at the stage of practical use. Furthermore, in order to improve the effects of digitization or to provide advanced new services such as combined voice and data communication, it is essential to digitize subscriber terminals including subscriber lines. There are various existing digital subscriber line transmission systems using two-wire transmission lines, one of which is the bidirectional burst transmission system.

FIG. 1 shows the configuration of a conventional main device in a bidirectional burst transmission system. The main devices in FIG. 1 are a time compression circuit 1, a transmission circuit 2, a transmission/reception separation circuit 3,
It consists of a receiving circuit 4 and a time expansion circuit 5, and is connected to a slave device (not shown) via a two-wire transmission line 6. After the digital signal to be transmitted is time-compressed and bursted in the time compression circuit 1,
The signal is supplied to the transmitter/receiver separation circuit 3 via the transmitter circuit 2 which is active for the period indicated by logic level 1 in FIG. 2c. The transmission burst signal on the transmission line 6 is
This is shown in block S in Figure a. On the other hand, the received burst signal from the slave device reaches the main device via the transmission path 6 in the form shown by block R in FIG. The reception burst signal received via the transmission/reception separation circuit 3 is supplied to the reception circuit 4. In this case, if the receiving circuit 4 is made active at the same time as the burst signal transmission ends, the second
As shown by the black line in FIG. 2B, part of the energy of the transmission burst is reflected from the transmission line 6 and is supplied to the reception circuit 4. At this time, if the transmission distance is long and the attenuation of the received burst signal R is large, the received burst signal and the tail of the transmitted burst will have the same amplitude, which may lead to malfunction. Therefore, in the conventional system, the slave device provides a guard time between receiving a burst signal from the master device and transmitting the burst signal, and the master device waits for the guard time to elapse as shown in FIG. 2d. After that, start receiving. However, when a protection time is provided in this manner, the time allocated to transmission delay in the burst period becomes shorter, resulting in a problem that the maximum transmission distance of the system is shorter than when the protection time is not provided.

It is an object of the present invention to prevent part of the transmitted burst signal from being supplied to the receiving circuit without providing a protection time, or to prevent a portion of the transmitted burst signal from being supplied to the receiving circuit, or even if it is supplied, the level is sufficiently lower than that of the received burst signal so that it does not cause malfunction. An object of the present invention is to provide a control method for direct burst transmission.

In the control method of bidirectional burst transmission at the start of communication according to the present invention, at the start of communication, the main device sets a burst section in which no burst signals are sent, and performs control to prohibit sending of some burst signals, and only during the burst section. A receiving circuit is activated to detect the phase of a received burst signal from a slave device, and after detection, based on the phase, a certain receiving period is given to the receiving circuit after transmitting a certain burst signal and before transmitting the next burst signal. is made active only during the reception period, and the transmission prohibition control is canceled.

Next, the present invention will be explained in detail with reference to the drawings. An embodiment of the present invention is shown in FIG. 3, and operations at the start of communication will be explained using FIG. 4. At the start of communication, the transmission control circuit 19 sets the control output 10 to 0 and outputs the control signal 21 of FIG. 4b to the AND gate 1.
At the same time, the control signal 26 shown in FIG. The AND gate 12 is connected to the control signal 20 for limiting the burst length shown in FIG.
3 is ANDed and supplied to the control terminal of the driver 11. In this case, since the control signal 21 repeats 1 and 0 every burst period, the driver 11 becomes active every other period, and the transmitted digital signal 24 shown in FIG. As shown by block S in FIG. 4D, the signals are thinned out and sent to the transmission line 6 via the transmission/reception separation circuit 3 (in this embodiment, a transformer is used as the transmission/reception separation circuit 3). On the other hand, the received burst signal from the slave device is supplied to the transmission/reception separation circuit 3 via the transmission line 6 every burst period, as shown by block R in d of the same figure. However, receiver 1
5 is active only during the non-transmission period of the burst shown in d of the same figure, so the received digital signal 25 is thinned out as shown in f of the same figure. In this case, since no burst signal is transmitted during the burst period in which the receiver 15 is active, the influence of reflection of the transmitted burst on the transmission path 6, etc. on the burst period is extremely small. Therefore, the synchronization signal extraction circuit 17 can accurately extract the burst synchronization signal 23 as shown in FIG. The timing circuit 16 operates in synchronization with the burst synchronization signal 23 and provides the reception phase shown in FIG.
Outputs 2. The synchronization determination circuit 18 compares the burst synchronization signal 23 with the rising edge of timing 22 to determine synchronization. When the transmission control circuit 19 receives the determination result from the synchronization determination circuit 18 indicating that synchronization has been established, it sets the control output 10 to 1 and shifts to normal burst transmission control.

Next, burst transmission according to the present invention in normal times will be explained with reference to FIGS. 5 and 6. First, a case where the transmission distance is relatively long will be explained. The control output 10 of the transmission control circuit 19 is 1
Therefore, the output of OR gate 13 becomes 1,
The AND gate 12 supplies the control signal 20 as it is to the control terminal of the driver 11. Therefore, the driver 11 remains active during the period indicated by the logic level 1 in FIG. 5B, and sends out the transmission digital signal 24 shown in FIG. That is, burst signal transmission stop control is prohibited. The transmitted burst signal is shown by block S in FIG. On the other hand, the data selector 14 selects the timing 22 shown in d in the figure and supplies it to the control terminal of the receiver 15. Therefore, all received burst signals or block R from the slave device are received. In this case, the period in which the receiver 15 is active is limited in length, and there is a time interval between the period in which the receiver 15 is active and the transmission period given by the control signal 20.
The tail of the transmission burst shown by the black line is not received.

Since the slave device sends a signal to the main device, that is, a reception burst signal R, in synchronization with the reception phase of the transmission burst signal S from the main device, the transmission burst signal S and the reception burst signal R are synchronized with each other as shown in the basic principle in Fig. 2. The time difference with the burst signal R is given by the round trip time between the main device and the slave device based on the transmission delay time. Therefore, when the distance between the main device and the slave device is short, the above-mentioned transmission delay time becomes small. Since no protection time is provided between the transmitted burst signal S and the received burst signal R, both burst signals are
Approach as shown in Figure a. Therefore, even if the active period of the receiver 15 is limited as shown in FIG. 2B, the tail of the block S is received by the receiver 15 as shown by the black line in FIG. But in this case,
Since the transmission distance is short, the attenuation of receiving block R due to transmission loss is small, and the amplitude of block R is sufficiently larger than that of the tail of block S. That is, even if a part of the transmission burst signal is supplied to the receiving circuit, malfunction will not occur.

In addition, in the main device using a transformer as the transmitting/receiving separation circuit 3, in order to further reduce the influence of the transmitting burst on the receiving circuit, the receiver is activated after transmitting, as described in Patent Application No. 149174/1983. The winding on the main unit side of the transformer may be shorted to ground during this period.

As described above, according to the present invention, there is no need to provide a protection time between a transmitting burst and a receiving burst in bidirectional transmission using a two-wire transmission line, so that the possible transmission distance can be extended. The application range of digital subscriber systems using the transmission method can be expanded.

[Brief explanation of drawings]

FIG. 1 shows the configuration of a conventional main device of a bidirectional burst transmission system. 2a-d show the timing of the main device of FIG. FIG. 3 shows an embodiment of the main device according to the invention. Figures 4a-h, Figure 5a
-e and FIGS. 6a-c show the timing in the main device of FIG. 1 and 3, 1 is a time compression circuit, 2 is a transmission circuit, 3 is a transmission/reception separation circuit, and 4 is a time compression circuit.
is a receiving circuit, 5 is a time expansion circuit, 6 is a transmission line, 11 is a driver, 12 is an AND gate,
13 is the OR gate, 14 is the data selector,
15 is the receiver, 16 is the timing circuit, 1
7 is a synchronization signal extraction circuit, 18 is a synchronization determination circuit, and 19 is a transmission control circuit.

Claims (1)

[Claims] 1. In a communication system that performs bidirectional burst transmission using a two-wire transmission line, at the start of communication, the main device establishes a burst section in which no burst signals are sent, performs control to prohibit transmission of some burst signals, and Activates the receiving circuit only to detect the phase of the received burst signal from the slave device, and after detection, based on the phase, a certain receiving period is given after transmitting a certain burst signal and before transmitting the next burst signal. A control method for bidirectional burst transmission at the start of communication, characterized in that a circuit is made active only during the reception period and the transmission prohibition control is canceled.