JPH04154241A - Bus type transmission system - Google Patents

Abstract

PURPOSE:To save transmission lines even when a failure occurs in a transmission line itself and to prepare such transmission line economically by providing a bus type transmission system with the function that to node units at stages precedent to a place where a failure occurred, one output from the center unit is input, while node units at stages following the place where the failure occurred are supplied with the other output from the center unit. CONSTITUTION:In the present bus type transmission system, both ends of bus type transmission lines 3 that consecutively inserted in node units 41-4N are supplied with output from center unit 1 so that each node receives a signal usually in one direction, while a signal is received in the opposite direction after an abnormality occurs. With this, transmission lines can be saved when an abnormality occurs therein, and since it is not necessary to duplex the entire transmission line 3, the whole transmission system can be constructed extremely economically. Furthermore, in order to back up the system when a failure occurs, since the signal receiving section of each node 41-4N can obtain nearly the similar receiving level, evenly qualified data transmission is possible.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a bus transmission system used for LAN, CATV, etc., and particularly to a system that enables backup in the event that some lines are disconnected.

``Prior art'' Conventionally, bank-up has rarely been carried out when a part of a line is disconnected in a bus-type transmission line. The only methods that have been considered are switching to a standby relay amplifier in the event of an amplifier failure, or duplicating the entire transmission line.

``Problem to be Solved by the Invention'' A method in which each node device is equipped with a spare relay amplifier and the relay amplifier is switched to the spare relay amplifier when the relay amplifier fails cannot cope with disconnections in the transmission medium itself.

Furthermore, a method of completely duplicating the entire transmission line is extremely uneconomical.

An object of the present invention is to provide a bus-type transmission line system that can be repaired even if a failure occurs in the transmission line itself and can be constructed economically.

"Means for Solving the Problem" This invention is composed of a center device and N node devices (N is an integer of 2 or more), and these N node devices are sequentially inserted in series into one transmission path. The signal output line from the center device is connected to both ends of the transmission line via a two-way splitter.

A directional coupler is connected between one end and the other end of each node device via two switches, and the switches are normally set so that the signals on the transmission line pass in the same direction. . Each node device includes a signal disconnection detection circuit that detects a disconnection of a received signal, and when the signal disconnection detection circuit detects a signal disconnection, it switches a switch to pass the signal on the transmission line from the other end to one end. Therefore, if a signal is disconnected in a node device or transmission line before the i-th node device, all node devices after the j-th node device will detect the signal disconnection and change the signal transmission direction to the opposite direction. The output from the center device is switched and the other output from the center device is input.

By connecting as described above, the node devices upstream from the point where the failure occurs receive one output from the center device until normal, and the node devices behind the point where the failure occurs receives the other output from the center device. output is supplied and rescued.

"Example" An example of the present invention is shown in FIG. The output side of the center device 1 is connected to a distributor (including a branch) 2 and connected to both ends of a transmission line 3, and the transmission line 3 has N node devices f4t~
4N are inserted in series one after another. A switch 5 is inserted in series between the Nth node device 4N and the distributor 2.

In this way, each node device 4. The arrows in ~48 indicate the direction of signal flow.

In addition, each node device 4. An example of the internal configuration of the signal receiving directional coupler 11.(i=1...N) is shown in FIG. Directional coupler for backup signal reception 12. Directional coupler for signal detection 13. Signal disconnection detection port 11rl 4° switch 15
．． ~15c, and a signal receiving section 6. Directional couplers 11, 12, and 13 each have signal input terminals X1 to X.
, signal output terminals Y1 to Ys, signal branch terminals Z, to Z,
Generally, there is a large isolation characteristic between the signal output terminal and the signal branch terminal with respect to the signal.

During normal operation, a signal is supplied to the terminal 10a of each node device 43, that is, in FIG. Then, the signal from the previous stage is connected to the terminal 10a of the node device.
, the A contact side of the switch 15a, the directional coupling H11 for signal reception, the A contact side of the switch 15b, and the signal transmitted to the next node device through the terminal 10b and input in this node device. Part of the signal receiving directional coupler 1
The signal passes through the A contact point of the switch 15c, the signal detection directional coupler 13, and is inputted to the signal receiving section 16 from the branch terminal Z1 of the first branch terminal Z1. Further, the presence or absence of a signal input from the previous stage is detected by the signal disconnection detection circuit 14 connected to the branch terminal Z of the signal detection directional coupler 13. When the signal disconnection detection circuit 14 is detecting a signal, the control signal P from the signal disconnection detection circuit 14 sets the switches 15a to 15c to the A contact side. In addition, in the terminal node device 4N, the switch 5 is set to the FF (off) state in normal operation by the control signal P.

For example, as shown in FIG. 3, in the event of an abnormality such as a disconnection accident occurring in the transmission line 3 between the j-th node device 4J and the preceding node device 4J-1, the node device 41 subsequent to point Q ~4N, the signal disconnection detection circuit 14 detects a signal input disconnection, and based on the detection output, immediately switches the switchers 15a to 15c to the B contact side electrically or mechanically, and switches the terminal 10b and the switch 15b. B contact side,
Directional coupler for backup signal reception 12. Switcher I5a
A passage for the terminal 10a is formed on the B contact side of the branch terminal Z of the standby signal receiving directional coupler 12.

is connected to the signal detection directional coupler 13 through the B contact side of the switch 15c. Furthermore, as shown in FIG.
The switch 5 is turned on by the control signal from the node device 4N, and the terminal 10b of the node device 4N is connected to the distributor 2. Therefore, the output of the center device 1 is the node device W4. ~4o is transmitted in the direction SL (counterclockwise in Fig. 3), which is opposite to the normal state.

The branch loss of the switched standby signal receiving directional coupler 12 is determined by the output level of its branch output terminal Zz (=reception level of the signal receiving unit 16) and the normal branch output terminal Z,
The output level is selected in advance so that the difference between the output level and the output level is not large. If the level difference can be maintained at the same level by simply connecting the signal receiving directional coupler 11 in the opposite direction, there is no need to use the backup signal receiving directional coupler 12. As shown in FIG. 5, the input terminal X1 of the signal receiving directional coupler 11 is connected to the terminal 10b through the B contact side of the switch 15b, and the output terminal Y1 is connected to the terminal 10a through the B contact side of the switch 15a. In this case, the switch 15c is omitted.

As is clear from the above description, the present invention is applicable not only to the transmission of electrical signals but also to the transmission of optical signals. Further, since the branching loss of an optical directional coupler can be selected relatively more freely than that of an electrical directional coupler, it can be said that the present invention is more suitable for transmitting optical signals.

Change■ In the above, the switch 5 may be placed anywhere between the distributor 2 and the final stage node device 4N, but due to the need to receive a switching signal in the event of an abnormality, it may be placed inside or near the node device 4N. It is preferable to place the

In the above, the switch 15b is used for the final stage node device 4N in order to have the same configuration as other node devices (Fig. 4), but this node device 4N has the terminal 10b.
Since there is no need to output a signal from the node device 48 to the distributor 2 side, the switch 15b is not necessary if the circuit is equivalent to keeping the B and C contacts of the switch 15b of this node device 48 on at all times. Furthermore, the signal receiving directional coupler 11 can also be omitted by directly connecting the A contacts of the switching devices 15a and 15c or by simply connecting them with an attenuator.

In the above, we have given examples of broadcast-type services, but FDM (frequency multiplexing) or WDM, which newly provides another frequency or wavelength for upstream signal transmission,
(wavelength division multiplexing), or by creating an additional transmission path for upstream signal transmission (SDM).
Bidirectional communication is also possible if the space division method is used.

The above can be applied to cases where signals are constantly being transmitted, such as CATV, but in systems where signals are frequently cut off even during normal operation, the switch should be turned off during predicted signal cuts. 5 is held without switching, it is possible to prevent frequent switching of the switch and loss of the first part of the transmitted data due to switching delay. For this reason, even during times when normal signal transmission is unnecessary, the center device may continue to send out signals for this purpose at certain minimum time intervals.

In the above description, the switch 5 is turned off during normal operation, but it may be turned on as long as the signal transmitted from the reverse direction S does not adversely affect the transmission quality during normal operation. Therefore, in that case, the output side of the distributor 2 and the output side of the node device 4N should be directly connected, and the switch 7
H5 is unnecessary.

In the above description, only the signal receiving directional coupler 11 is cascade-connected to the transmission path of the node device, but an amplifier or the like may be cascade-connected to this directional coupler. However, when the signal is interrupted, it is necessary to reverse the direction of the amplifier together with this directional coupler.

In the above description, the extraction of the signal for detecting the presence or absence of the signal from the previous stage may be performed inside the signal receiving section 16.

"Effects of the Invention" As described above, according to the present invention, the output of the center device is supplied to both ends of a bus-type transmission line in which node devices are inserted in series, and signals from one direction are always received. However, since it is configured to receive signals from the other direction after an error occurs, it is possible to recover from an error in the transmission line, and there is no need to duplicate the entire transmission line, so the entire system is can be constructed extremely economically.

In addition, even when bus-up occurs after an abnormality occurs, the signal receiving unit of each node device can obtain the normal reception level and the reception level between the roads, so for example, video quality deterioration in the case of video signal transmission can be reduced. In addition, it is possible to perform transmission with uniform quality without causing a decrease in focus error rate during data transmission. Furthermore, since it is possible to prevent the input level at the signal receiving section from changing significantly before and after bank-up, the signal receiving section can use equipment with the same characteristics in each node device, and the receiving dynamic range can be minimized. Since it does not need to be widely used, the reception level adjustment mechanism can be omitted, adjustment can be made easier, and the configuration can be made economically.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the invention, FIG. 2 is a block diagram showing an example of the internal configuration of the first node device in FIG. 1, and FIG. 3 is a block diagram showing an example of the internal configuration of the first node device in FIG. Figure 4 is a block diagram showing the direction of the signal received by each node device in the event of an abnormality. Figure 4 is a block diagram showing the position of the switch contacts in the final stage node equipment 4M in the event of an abnormality. Figure 5 is for backup. FIG. 2 is a block diagram illustrating a configuration example of a node device that does not require a directional coupler for signal reception.

Claims (4)

[Claims] (1) N node devices (N is an integer of 2 or more) are inserted in series in a transmission line, the output end of the center device is connected to both ends of the transmission line through a distributor, and each of the above node devices is It comprises at least one directional coupler, a signal receiving section that receives a signal branched by the directional coupler, a switching means, and a signal disconnection detection circuit that detects disconnection of the received signal, and when normal. The switching means is set to pass the signal from the transmission line from one end to the other end, and when the signal disconnection detection circuit detects a signal disconnection, the switching means is switched to pass the signal from the transmission line from one end to the other end. A bus-type transmission system configured to pass from one end to the other end. (2) An always-off switch is inserted in series between the node device at the end of the signal transmission direction of the transmission path in the normal state and the distributor, and when the node device at the end detects a signal disconnection, 2. Bus type transmission system according to claim 1, characterized in that the switch is turned on. (3) The node device includes three switches as the switching means, and at the switching position of one of the two switches, the signal from one end of the node device is output to the other end through the first directional coupler. At the other switching position, the signal from the other end is output to the one end through the second directional coupler, and the remaining switch receives the signal from each branch output of the first and second directional couplers. 2. The bus-type transmission system according to claim 1, wherein the bus-type transmission system is configured to switch and supply the data to each section. (4) The node device is provided with two switches as the switching means, and one of the directional couplers is inserted between these switches, and both of these switches are connected to the directional coupler when the switch is normal. The input side of the directional coupler is connected to the above one end, the output side is connected to the above other end, and upon detection of signal disconnection, the input side of the above directional coupler is connected to the above other end, and the output side is connected to the above one end. The bus-type transmission system according to claim 1, characterized in that: