JPH04213942A - Line concentrator for dual loop local area network - Google Patents

Abstract

PURPOSE:To send a data signal surely to a low-class line concentrator even when a fault takes place in a sub line when a dual loop local area network is constituted by combining a high class line concentrator having a loopback function and a low class line concentrator not having a loopback function. CONSTITUTION:Even when a fault takes place in a sub line Lb, control circuit sections 4, a, 4b for high class line concentrators are provided with external switches 6a, 6b generating a latch signal to maintain the connection state of main lines LA without being affected by the fault and a data signal is always sent to a low class line concentrator through a main line La.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a line concentrator for a double-loop local area network (hereinafter referred to as LAN).

0002

[Prior Art] In general, a LAN in which line concentrators are connected in a loop via transmission lines has advantages such as fewer restrictions on communication distance, communication speed, etc. compared to star configurations or bus configurations. have

In this type of loop-type LAN, if a transmission line is suddenly disconnected, the local failure spreads throughout the network, making data transmission impossible. In order to avoid such a situation, conventionally, the line concentrators are connected in advance with double transmission lines, one as the main line and the other as the sub line, and in the event of a failure, the signals to be transmitted are routed to the point where the failure has occurred. A configuration is adopted in which a detour is made before the failure occurs to prevent the occurrence of a failure from spreading to the entire network.

On the other hand, as mentioned above, the individual line concentrators are equipped with a so-called automatic loopback function (hereinafter referred to as High-grade line concentrators) have complicated circuit configurations, making the entire device expensive. Therefore, in the past, inexpensive and simple line concentrators (hereinafter referred to as low-grade line concentrators) that do not require a power source and do not have the above-mentioned automatic loopback function have also been provided.

[0005]

[Problem to be Solved by the Invention] By the way, when a double-loop type LAN is constructed by combining the above-mentioned high-grade line concentrator with a loopback function and a low-grade line concentrator without a loopback function, the following problem occurs. cause problems.

[0006] Now, as shown in FIG. 5, four line concentrators N10 to N40 are connected by a main line La and a sub line Lb to form a network, of which the one indicated by reference numeral N20 is a low-grade line concentrator. So, the rest are N10 and N30.
, N40 are all high-grade line concentrators, data signals are transmitted counterclockwise on the main line La, and pilot signals are transmitted clockwise on the sub line Lb.

[0007] Here, the sub line Lb is a low-grade line concentrator N20.
If a disconnection occurs between the main line La and the high-grade line concentrator N10 on the left side (point p in the figure), transmission of this pilot signal will be lost, so the high-level line concentrator N10 on the left side responds by internally connecting the main line La and the secondary line La. The line Lb is connected to each other. Then, the data signal is no longer input to the high-grade line concentrator N30 on the right side of the low-grade line concentrator N20 via the main line La, so this high-grade line concentrator N30 also detects this and internally switches the main line La and the sub line Lb. and to each other.

As a result, the centrally located low-grade concentrator N
20 becomes independently disconnected from the left and right high-grade line concentrators N10 and N30, and it becomes impossible to send data signals to the workstation w connected to this low-grade line concentrator N20.

[0009]

[Means for Solving the Problems] The present invention has been made in view of the above problems, and when a double loop type LAN is constructed by combining a high-grade line concentrator and a low-grade line concentrator, This allows data signals to be reliably transmitted to the low-grade line concentrator even if a failure occurs in the sub-line.

Therefore, the present invention includes a first signal detection section that detects the presence or absence of a signal transmitted to the main line that transmits the signal in one direction of circulation, and a sub-signal detection section that transmits the signal in the circulation direction opposite to the main line. In response to the detection signals output from the second signal detection unit that detects the signal transmitted to the line, and the first and second signal detection units, the main,
In a double-loop type LAN concentrator comprising first and second control circuit units that switch the connection state of sub-lines to each other, the presence or absence of the detection signal is determined for the first and second control circuit units. Regardless of whether these first and second control circuit sections are
The present invention is characterized in that first and second external switches are provided, each of which generates a latch signal to maintain the individual connection state of the sub-line.

[0011]

[Operation] In the above configuration, the second external switch is operated for the high-grade line concentrator on the left adjacent to the low-grade line concentrator, and the first external switch is operated for the high-grade line concentrator on the right, respectively. A latch signal is always generated to keep the main and sub lines connected separately.

[0012] As a result, even if a fault occurs in the sub-line, the first and second control circuit sections of the high-grade line concentrator maintain the connection state between the main lines without being affected by this, so that the main line The data signal is transmitted to the low-level concentrator through.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing how a double loop type LAN is constructed by combining a high-grade line concentrator with a loop-back function and a low-grade line concentrator without a loop-back function.

In this embodiment, four concentrators N1 to N
4 are connected by the main line La and the sub line Lb to form a network, of which the one indicated by the symbol N2 is a low-grade line concentrator, and the remaining ones N1, N3, and N4 are all high-grade line concentrators. Under normal conditions with no failures, the main line L
It is assumed that a data signal is transmitted counterclockwise to line a, and a pilot signal is transmitted clockwise to subline Lb.

FIG. 2 is a block diagram showing the entire high-grade line concentrators N1, N3, and N4.
3 and N4 both have the same configuration.

In the figure, 1a is a first signal detection unit that detects the presence or absence of a signal transmitted via the main line La, and 1b
is a second signal detection unit that detects the presence or absence of a signal transmitted via the sub line Lb, and both signal detection units 1a and 1b detect whether any signal is transmitted to the main line La or the sub line Lb. When there is no signal transmission, a high level detection signal is output, and when there is no signal transmission, a low level detection signal is output.

Reference numeral 2 denotes a pilot signal generating section for transmitting a pilot signal when a failure occurs in the sub-line Lb.

4a responds to the high level detection signal output from the first signal detection unit 1a, and connects the main and sub lines La and L.
The first control circuit section 4b switches from the individual connection state of the main and sub lines La and Lb to the mutual connection state of the main and sub lines La and Lb in response to the high level detection signal output from the second signal detection section 1a. , main, from the individual connection status of sub-line La, Lb
This is a second control circuit unit that switches the mutual connection state of sub-lines La and Lb.

6a and 6b are first and second control circuit sections 4a,
4b, the first and second control circuit sections 4a and 4b are connected to the main and sub-line La and Lb individually, regardless of the presence or absence of detection signals from the first and second signal detection sections 1a and 1b. These are first and second external switches that are operated to generate a high-level latch signal when the connection is maintained.

Reference numeral 8 denotes a workstation connection section to which the workstation w is connected.

As shown in FIGS. 3(a) and 3(b), the above-mentioned first and second control circuit sections 4a and 4b include line changeover switches 10a and 10b, signal selection switches 12a and 12b, and an OR gate 14a, Consisting of 14b.

When the first and second external switches 6a and 6b are turned off, a high level latch signal is output.
This signal is applied to the line changeover switches 10a and 10b via the OR gates 14a and 14b, so that the line changeover switches 10a and 10b are connected to the first and second signal detection units 1a,
Regardless of the signal output of the detection signal from 1b, the state of connection between the main lines La (connection between contacts c and x) is always maintained as shown in the figure.

Conversely, the first and second external switches 6a, 6b
When turned on, these first and second switches 6a, 6
A low level signal is output from the terminal b, and this is sent to the line changeover switches 10a and 10a through the OR gates 14a and 14b.
0b, this line changeover switch 10a
, 10b, the connection state is switched according to the output level of the detection signal from the first and second signal detection sections 1a and 1b. That is, when a high-level detection signal is output from the first and second signal detection sections 1a and 1b due to the presence of a transmission signal, the line changeover switches 10a and 10b connect the main lines La (contact points). connection between main line La and sub line Lb (
(connection between contacts c and y).

On the other hand, each signal selection switch 12a, 12b
, when a high-level signal indicating the presence of a transmission signal is output from the first and second signal detection units 1a and 1b, the connection between the sub-lines La (contact c
and x connection) state is maintained. Further, when low level signals are output from the first and second signal detection sections 1a and 1b, the line changeover switches 10a and 10b are switched to the main line La.
When it is in the connection state, the connection state with the pilot signal generator 2 (connection between contacts c and z) is selected, and the line changeover switches 10a and 10b are in the connection state between the main line La and the sub line Lb. Sometimes, the connection state between contact point c and midpoint y is selected.

FIG. 4 is a block diagram showing the configuration of the low-grade line concentrator N2.

This low-grade line concentrator N2 has a workstation connection section 16 interposed to the main line La, and
The sub line Lb is directly connected as is.

When constructing the double-loop type LAN shown in FIG. 1 using each of the line concentrators N1 to N4 having the above configuration, the first high-grade line concentrator N1 on the left side adjacent to the low-grade line concentrator N2 is The external switch 6a is turned on and the second external switch 6b is turned off. Further, regarding the high-grade line concentrator N3 on the right side, the first external switch 6a is turned off and the second external switch 6b is turned on in advance. Regarding the remaining high-grade line concentrator N4, both the first and second external switches 6a and 6b are turned on. Therefore, the line changeover switch 10b in the second control circuit section 4b of the high-grade line concentrator N1 always connects the main lines La to each other (contact points) as shown, regardless of the output level of the second signal detection section 1b. (connection between c and x) maintains the state. In addition, the line changeover switch 10a in the first control circuit section 4a of the high-grade line concentrator N3 always connects the main lines La to each other as shown in the figure, regardless of the output level of the first signal detection section 1a.
The state of the connection between contacts c and x is maintained.

Next, the operation of each part in the above configuration depending on whether or not a line failure occurs will be explained.

(1) In a normal state with no failures In this case, the data signal is transmitted to the main line La, and the pilot signal is transmitted to the sub line Lb. Therefore, each concentrator N1 to N4 first and second signal detection units 1a,
A high-level detection signal is output from each of the terminals 1b. As a result, the line changeover switches 10a and 10b of the first and second control circuit sections 4a and 4b maintain the connection state of the main line La, while the signal selection switches 12a and 12b
Connection of sub line Lb as shown (connection between contacts c and x)
held in state.

Therefore, focusing on one high-grade line concentrator N1, for example, data signals input to this line concentrator N1 via the main line La are transferred via the line changeover switch 10a of the first control circuit section 4a. and is taken into the workstation w from the workstation connection section 8. Further, the data signal from this workstation w is outputted to the next low-grade line concentrator N2 via the line changeover switch 10b of the second control circuit section 4b. The data signal transmitted to the low-grade line concentrator N2 is taken into the workstation w via its workstation connection 16.

Furthermore, the pilot signal input to the low-grade line concentrator N2 passes through this and is connected to the sub line L.
The signal is transmitted to the next stage high-grade concentrator N1 via line b. The pilot signal input to this high-grade line concentrator N1 is
The signal is further output to the next high-grade line concentrator N4 via the signal selection switch 12b of the control circuit section 4b, the signal selection switch 12a of the first control circuit section 4a, and the sub line Lb.

(2) When a failure occurs in the sub-line that connects the high-grade line concentrator and the low-grade line concentrator For example, if a failure occurs at point p of the sub-line Lb shown in FIG. Since the pilot signal is no longer input to the line concentrator N1, the output of the second signal detection section 1b becomes low level, but the second external switch 6b is set to off in advance and a high level latch signal is output. , the line changeover switch 10b connects the main line La (
The connection between contacts c and x) is maintained as it is. Therefore, the data signal is sent to the next stage low-grade line concentrator N2 via this second control circuit section 4b, and furthermore, the data signal sent from this low-grade line concentrator N2 is sent to the main line La.
The signal is transmitted to the next stage high-grade line concentrator N3 via.

Further, the signal selection switch 12b of the high-grade line concentrator N1 is configured such that even if the output of the second signal detection section 1b is at a low level, the line changeover switch 10b is set to the main line La.
Since the connection state is maintained, the connection state with the pilot signal generating section 2 (connection between contacts c and z) is selected. Therefore, the pilot signal from the pilot signal generator 2 is sent out to the sub line Lb via the signal selection switch 12b, and further outputted from the first control circuit section 4a to the next stage high-grade line concentrator N4.

In this way, even if a failure occurs in the sub-line Lb connecting the high-grade line concentrator N1 and the low-grade line concentrator N2, the data is reliably transmitted to the low-grade line concentrator N2 via the main line La. A signal is transmitted.

(3) When a failure occurs in the main line that connects high-grade line concentrators For example, if a failure occurs at point q of the main line La shown in FIG. Since the data signal is no longer input to the high-grade line concentrator N1, the first signal detection unit 1
The output of a becomes low level. At this time, since the first external switch 6a is set to ON, its output is at a low level. Therefore, the line changeover switch 10a of the first control circuit section 4a is switched to a state where the main line La and the sub line Lb are connected (the contacts c and y are connected). Also, the first
The signal selection switch 12a of the control circuit section 4a has a contact c connected to a middle point y.

Furthermore, since the main line La and sub-line Lb of one high-grade line concentrator N1 are connected to each other, the pilot signal from this line concentrator N1 is no longer input to the other high-grade line concentrator N4. The output of the second signal detection section 1b of this high-grade line concentrator N4 becomes low level. At this time, since the second external switch 6b is set to be on, its output is at a low level. Therefore, the second
The line changeover switch 10b of the control circuit section 4b is connected to the main line L.
The state changes to a state where a is connected to the sub line Lb (connection between contacts c and y). Further, the contact c of the signal selection switch 12b of the second control circuit section 4b is connected to the middle point y.

Therefore, with the failure point q as a boundary, in one high-grade line concentrator N1, the line changeover switch 10a of the first control circuit section 4a switches to the other high-grade line concentrator N4.
Then, each data signal is detoured at the line changeover switch 10b of the second control circuit section 4b.

[0038]

According to the present invention, when a double loop type LAN is configured by combining a high-grade line concentrator and a low-grade line concentrator, the low-grade line concentrator can be isolated from the network even if a failure occurs in the sub line. This avoids the inconvenience of being disconnected, and data signals can be reliably transmitted.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the overall connection state of a double loop LAN according to an embodiment of the present invention.

FIG. 2 is a block diagram showing the configuration of a high-grade line concentrator.

FIG. 3(a) is a block diagram of a first control circuit section of the high-grade line concentrator.

FIG. 3(b) is a block diagram of a second control circuit section of the high-grade line concentrator.

FIG. 4 is a block diagram showing the configuration of a low-grade line concentrator.

FIG. 5 is a block diagram showing the overall connection state of a conventional double-loop LAN.

[Explanation of symbols]

N1, N3, N4...high-grade line concentrator, N2...low-grade line concentrator, 1a, 1b...first, second signal detection section, 4a, 4b...first, second control circuit section, 6a, 6b...first, first 2 external switch.

Claims (1)

[Claims] 1. A first signal detection unit that detects the presence or absence of a signal transmitted to a main line that transmits a signal in one direction of circulation, and a first signal detection unit that transmits a signal to a sub line that transmits a signal in a circulation direction opposite to the main line. a second signal detection section that detects a signal that is detected;
first and second control circuit units that switch from individual connection states of the main and sub lines to mutual connection states of the main and sub lines in response to a detection signal output from the second signal detection unit; In a line concentrator for a double-loop local area network, the first and second control circuits are connected to the main and sub lines regardless of the presence or absence of the detection signal. 1. A line concentrator for a double-loop local area network, comprising first and second external switches that generate latch signals to maintain individual connection states.