JPS61283253A - Transmission control system - Google Patents

Abstract

PURPOSE:To execute a fault countermeasure by detecting a check signal and changing the transmission transition depending on the detection state to apply quick loopback with a simple procedure. CONSTITUTION:Separate section command signals (a, b) are inputted to link switches 3, 4 from a selection control circuit 7 and a transmission signal received by an active link 1 or a transmission signal received from a stand-by link 2 or a test signal C is selected by the link switches 3, 4. The detection state of detection circuits 5, 6 is inputted to the selection control circuit 7 of the link switch as detection signals (d, e). The test signal C is a signal as a conduction test signal of the transmission line.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to countermeasures against failures in network transmission paths, and particularly to a transmission control method for relieving failures on transmission paths in a ring network using a loopback method.

[Prior Art J] With the rise in office automation in recent years, so-called local area networks (LANs) have been developed to connect and communicate with various office equipment in the office using inexpensive networks.
) have been widely put into practical use, and in particular, ring-shaped networks are becoming more widespread due to advances in optical fiber technology.
In contrast to AN, where the transmission path is formed only with so-called passive elements such as coaxial or stranded cables, ring type L
In an AN, so-called active elements such as a photoelectric conversion module and a data buffer circuit such as a shift register are incorporated in series in a transmission path, so failures are likely to occur.

For this reason, in a ring type network, the transmission paths of the rings are duplicated, and the transmission paths are provided in opposite directions, and one is used as a working ring and the other is used as a backup ring.

Now, as shown in Figure 1 (A), when a transmission path failure occurs between node 100 and node n in the ring network, the 7
A so-called loopback method is used in which the transmission path is returned to nodes 100 and 7-n to isolate the faulty part and maintain the ring. What is difficult to understand in this method is to detect which node or between which node and which node the fault in the transmission path occurred, and if this is detected, the fault can be removed. Loopback can be achieved by connecting the working and backup transmission lines at the nodes at both ends of the chain.

Isolation of a faulty part by loopback is generally performed in the following manner.

As shown in FIG. 2(A), when a failure occurs in the transmission path at the node 202, as shown in FIG. 2(B), the node 202
With 0 as the master node, create a loopback loop between nodes 201 and 205 that are closest to node 200, and after confirming that communication is not interrupted in that loop, next create a loop that includes nodes 202 and 204. Configure and check if it is normal. In this case, node 20
2 is included, this loop does not operate normally.Therefore, a loop is constructed excluding either node 202 or node 204, which has been newly included in the loop, and it is checked whether communication can be performed normally. In this case node 202
When node 203 is removed from the loop, normal communication becomes possible, and a loop including the primary node 203 is configured and a similar test is performed.In this way, at a certain stage, communication in that loop inevitably gets interrupted. When this happens, the process returns to the previous stage loop, assumes that the loopback has been completed, fixes the loop as shown in FIG. 2(C), and moves on to restarting the network.

Today, microcomputers and the like are used to control network nodes, and most of the above procedures are performed by software control. First, a Loop Back command is sent from a specific node to the nodes on both sides of it. After issuing a communication test and verifying that there is no abnormality, these nodes receive 87p.
There is a method of issuing an ass command to release the loopback, and then repeating the same procedure for the next 7-de to extend the loopback step by step.

However, such a procedure is very complicated, and when there are many nodes in the network, it takes a lot of time to completely recover the network by loopback, so it has the disadvantage that it has a large impact on the user's work. there were.

EObjective J The present invention has been made in view of the above-mentioned drawbacks, and is designed to output test signals to duplicated transmission paths by changing directions when a transmission failure occurs, and to output test signals in a network equipped with means for detecting the test signals. The object of the present invention is to provide a transmission control method that allows each transmission device to easily and quickly configure a loopback and recover from a failure by changing the transmission path depending on the detection state of each transmission device.

E Example” Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 3 is a block diagram of the network transmission/reception circuit in each node, where 1 represents the working ring which is the network transmission path, and 2 represents the protection ring, the working ring l.
3 and 4 in the figure are the working ring and the spare ring, respectively. A signal selection switch circuit provided in the transmitting section of
It is possible to switch and transmit several signals to each ring. Hereinafter, these switch circuits will be referred to as link switches.

Although the above two link switches are represented by mechanical symbols in the figure, they are electrically operated (e.g. by logic elements).
It doesn't matter if it's a switch.

Separate selection instruction signals a and b are input from the selection control circuit 7 to the link switch 3.4, and either the transmission signal received from the working ring 1 or the transmission signal received from the protection ring 2, or as will be explained later, is input to the link switch 3.4. , one of the test signals C generated from the test signal generation circuit 8 is selected by the link switch 3.4.
6 is a detection circuit that detects the test signal C when it is sent from another node via the working or backup ring, and the detection state is sent to the link switch selection control circuit 7 as detection signals d and e. As will be described later, the 0 selection control circuit 7 input to the 0 selection control circuit 7 only needs to have a relatively simple logic judgment function, and this can be a logic circuit or a microcomputer for communication control as described above. Also good.

Now, regarding the test signal C, this is a signal used as a so-called "continuity test signal" for the transmission line. Therefore, it is necessary for this signal to be one that cannot pass through the location where the transmission path failure has occurred, and one that is easy to detect.
It is necessary to select according to the circumstances of each network. For example, when an AC signal is used as the test signal, the detection circuit 5.6 for the test signal C may be configured to detect the AC signal by using a differentiation circuit or a one-shot circuit that is sensitive to changes in the signal. It has become.

FIG. 4 shows an example of the logic circuit of the selection control circuit 7.

Here, lO~12 is an inverter circuit, 13~18 are AN
The D circuit 19 is a switch that instructs the output of the test signal C as a loop master, and Table 1 shows the relationship between these signals. Note that these operations will be described in detail later.

! = Signal present, 0: No signal, X: Either 0 or 1 is fine.

Table 1 Figure 5 shows an example of the detection circuits 5 and 6, and Figure 6 shows the signal waveforms of each part. It is differentiated and becomes a signal 3o. This signal 30 is converted into a pulse 31 by a comparator 33 and input to a retriggerable one-shot circuit 34. Since the output pulse width of this one-shot circuit 34 is set to a time T that is slightly longer than the period of the input test signal C, the output pulse width of the one-shot circuit Q remains constant while the AC signal continues to be input. The detection signals d and e are kept at high level. Note that in this circuit, depending on the test signal C, the differentiating circuit and the comparator 33 may be omitted.

Now, in addition to the hardware described above, in the present invention, the following operations are performed at the nodes in the network. First, when a fault occurs on the network transmission path, each node independently detects this. An example of a detection means is, for example, in a ring-shaped network using a token passing method in which tokens circulate within the network at any time, the token code does not flow on the transmission path even after a certain specified period of time has elapsed, in other words, the token has disappeared. There is a method to detect the occurrence of a failure.

When a failure is detected, the current communication operation is stopped and all nodes in the network take one of the following two actions. In this node, the test signal generating circuit 8 is connected to link switches 3 and 4 for both the working and backup rings.
Switching to (a) and (f) respectively, the test signal C is sent to the working ring and the backup ring, respectively.

This situation is shown in FIG. 7, where the test signal C is transmitted to the working and backup rings in opposite directions centering on the loopback master 700.

(As shown in Figure 1 below, the test signal C is transmitted from this loopback master to the working ring L in a counterclockwise direction, and the test signal C is transmitted to the backup ring 2 in a clockwise direction. (The nodes in the clockwise direction are called downstream nodes, and the nodes in the counterclockwise direction are called upstream nodes.) The second operation is performed by a node other than the loopback master, and is performed by a node other than the loopback master. The sent test signal Ct is monitored using the two detection circuits 5.6, and depending on the detection state, the following link switch 3
．． 4 selection control is performed.

(a) If the test signal C is received in the working ring 1 and detected by the detection circuit 5, the link switch 3 of the working ring transmitter is switched to (b), and the received test signal C
The receiver passes it as is to the next upstream node.

(b) When the test signal C is received by the backup ring 2 and detected by the detection circuit 6, the link switch 4 of the backup ring transmitter is similarly switched to (e), and the received test signal is transmitted to the next downstream node. Pass the uke.

(C) If the test signal C is detected by the detection circuit 5 on the working ring l, but not detected on the protection ring 2, that is, by the detection circuit 6, the link switch 4 of the protection ring transmitter is ) to (d), the test signal C is sent back.

(d) If the test signal C is detected by the detection circuit 6 on the spare ring 2, but not detected in the working ring l, that is, by the detection circuit 5, the link switch of the working ring transmitter is turned on (b). By switching to (c), the test signal C is sent back.

Figures 8 (A) to (1) show the movements of the link switches in each 7-door during the J$2 operation described above.As mentioned above, the working ring l is on the upstream side of the loopback master, and the standby ring is on the downstream side of the loopback master. Since test signal C is sent to ring 2, as shown in Fig. 8 (
The waveform mark in the diagram shows that the test signal C is flowing on the ring. First, let us explain the upstream node.
FIG. 8(A) shows a state in which the test signal C from the loopback master is waited for.

FIG. 8(B) shows that the test signal C is detected in the working ring 1,
According to the operation in section (a) above, the link switch 3 is switched to (b), and the test signal C is passed to the next working ring l.

In FIG. 8(C), the test signal C has not yet appeared on the backup ring 2, so the link switch 4 is activated in order to pass the test signal C received on the working ring 1 to the backup ring 2 (according to section C). Switch to (d).

In FIG. 8(D), the test signal C is transmitted from the upstream node to the backup ring 2 and is detected.
In FIG. 8(E), the link switch 4 is switched to (e) in order to pass the spare ring reception signal to the downstream node according to the above-mentioned (b). If there is a transmission path failure at a node one level upstream of a certain node (or around it), the node upstream of the failure location cannot enter the positions shown in Figures 8(E) and 8(C). In addition, the node one downstream of the failure point cannot detect the test signal C on the backup ring z, and the state shown in FIG. 8(D) does not occur, so this node
remain in state C).

Regarding FIGS. 8(CF) to 8(I)K, explanations thereof will be omitted since they can be considered by replacing the working ring with a spare ring.

Therefore, at the node immediately before the node with the transmission path failure (or the transmission path around it),
), and all other nodes except the master node and the faulty node are in the state shown in Figure 8 (E) or Figure 8 (
I) becomes worse. This can be represented graphically as shown in FIG. 9(A).

That is, nodes 902 and 904 in the network with node 900 as the master node are the failed nodes 903
The transmission path is returned to the other node 901 .
905 causes the signal to be transmitted to the next node, at which point the loopback is completed as shown in Figure I89 (CB). At this point, the status of all link switches is fixed and the network is restarted.

The test signal is propagated in the form of receiving and passing at each node as shown in Figure 8 (B) or Figure 8 (F), and as shown in Figure 8 (C).
Alternatively, as shown in Figure 8 (G), the signal from another ring is transmitted back, and the transmitted test signal is judged and further transmitted to the next node. It takes some time for the state transition of the link switch of the node to finally settle down. Of course, this is quite a short time compared to the conventional example. Therefore, it is preferable to fix the states of all link switches as described above after a period of at least the maximum transition time after starting the loopback process.

Now, in the circuit configuration of FIG. 3, the test signal generation circuit 8 is not required at nodes other than the loopback master, but
When considering the reliability of the network as a system, there are cases where it is advantageous to have nodes other than the loopback master have the same circuit configuration as shown in Figure 883. This is because if a network has only one loopback master, it cannot output a test signal when a transmission line failure occurs in the loopback master.

Rescue by loopback becomes impossible and the network goes down. Therefore, all nodes or two or more nodes should have the same circuit configuration as the loopback master.
It is possible to prevent this case by using one of them as a loopback master and operating the network.

For this purpose, the control circuit 7 may be provided with operation switching means, such as the switch means shown in this embodiment, so that the switching can be performed manually or automatically by a control signal from a microcomputer or the like.

[Effects] As described above, according to the present invention, when a transmission failure occurs, test signals are output to the duplicated transmission paths in different directions,
By detecting the test signal in each transmission device in the network and changing the transmission progress depending on the detection state, there is an effect that loopback can be quickly performed with a simple procedure and countermeasures against failures can be implemented.

[Brief explanation of the drawing]

881 (A), CB) and Figure 2 (A). (B) and (C) are conceptual diagrams showing the principle of loopback. FIG. 2 is an explanatory diagram showing an example of a conventional loopback method, FIG. 3 is a circuit block diagram of a node transmitting/receiving section as an embodiment of the present invention, and FIG. 4 is a diagram of a selection control circuit as an embodiment of the present invention. Logic circuit diagram, Fig. 5 is a signal detection circuit diagram which is an embodiment of the present invention, Fig. 6 is a signal waveform diagram of each part of Fig. 5, Fig. 7 and Fig. 9 (A), CB) are the main A conceptual diagram showing the operation of the invention. FIGS. 8(A) to 8(I) are explanatory diagrams showing the operation sequence of the link switch in the present invention. Here, l... working ring, 2... spare ring, 3
．． 4... Link switch circuit, 5, 6... Signal detection circuit, 7... Selection control circuit, 8... Test signal generation circuit, 19... Loop master instruction switch, 34...
-Retriggerable one-shot circuit. Patent applicant: Canon Co., Ltd. Figure 1 (B) Figure 2 Figure 3 Figure 4 Roof 08° Master No. 8 rIA (A) Upstream 4th line No. 8 rIA (8) Figure 8 CD)

Claims (3)

[Claims] (1) In a ring-shaped network including a first transmission path and a second transmission path, a test signal is output from the test signal generating means to the first and second transmission paths in mutually different directions, and the network each transmission device is provided with a detection means for detecting the arrival of the test signal on the first and second transmission paths,
A transmission control system characterized by comprising a switching means that switches transmission paths depending on the detected state. (2) The transmission control system according to claim 1, wherein the test signal generating means is a specific transmission device within the network. (3) When detecting the arrival of the test signal on the first transmission path, the switching means connects the receiving section of the first transmission path and the transmitting section of the second transmission path, and connects the receiving section of the first transmission path and the transmitting section of the second transmission path. When the arrival of the test signal is detected, the receiving section of the first transmission path and the transmitting section of the second transmission path are separated, and the second transmission path is completed. A transmission control method according to claim 1.