JPH0621955A - Clock supply switching system - Google Patents

Abstract

PURPOSE:To turn all the nodes into a master station by setting priority to the nodes as clock priority, transmitting a frame while writing the priority, and defining the reception node of the higher priority as the master station by comparing the priority of the node itself. CONSTITUTION:The priority is set to a register 10 of a CSEL part 5 at each node as the clock priority, and the frame written the priority is transmitted through an IF part 2 of a '0' system transmission line or an IF part 3 of a '1' system transmission line. Concerning the reception nodes, the node having the higher priority is defined as the master station and the node having the lower priority is defined as a slave station by comparing the priority of the node themselves. Therefore, all the nodes can become the master stations, the synchronism of a network can be always established, the synchronism of the network can be established for the unit of each loop even when over two fault network loops exit and even the multiple amounts of faults can be flexibly deal with.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a loop type LAN (local area network) in which a plurality of nodes consisting of a master station and a slave station are connected in a loop by two transmission paths of a first system and a second system. , A clock supply switching method for switching a clock supplied to each node of a loop LAN.

[0002]

2. Description of the Related Art In a loop type LAN as described above, a plurality of nodes consisting of a master station and a slave station are connected in a loop by two clockwise and counterclockwise transmission lines, and two nodes are connected from the node of the master station. A clock is sent to each transmission line of the system, and at the node of the slave station, one of the two clocks obtained from the transmission lines of the two systems is selected, and a frame of communication data is circulated in the transmission line according to the clock, Thus, each node transmits / receives a frame.

That is, a clock source is supplied from one node (master station) as a clock master in the network to another node (slave station) to perform intra-network synchronization by subordinate synchronization. Also,
In some systems, a clock is supplied to the node of the master station from an external network and the entire network is synchronized with the external clock to enable slave synchronization with the external network.

In such a conventional loop type LAN, the clock system of the transmission line is divided into two systems, an operating system and a standby system, for a failure of the transmission path clock system and a failure of the clock master or external clock supply interruption. Using the duplicated transmission line
Further, the clock master has been dealt with by adopting a dual configuration of a master station and a sub-master station.

[0005]

However, in the conventional loop type LAN as described above, the failure of the transmission line clock system is changed from the active system to the standby system, and the failure of the clock master is changed from the master station to the sub-master station. Since only a single failure can be dealt with such as switching to each, a loop type LAN capable of dealing with multiple failures has been desired.

The present invention has been made in consideration of such a situation. Priorities for becoming master stations are defined in advance for all nodes, and nodes having higher priorities are sequentially designated as master stations. At the same time, for the node that could not become the master station, by selecting one of the clocks received from the two systems, even if there is a multiple failure such as failure of the master station or failure of the transmission line clock system, It is intended to provide a clock supply switching system capable of always establishing internal synchronization.

[0007]

SUMMARY OF THE INVENTION According to the present invention, a network is constructed by connecting a plurality of nodes consisting of a master station and a slave station in a loop with first and second transmission lines. A clock is sent to the first and second transmission lines, and at the slave station node, one of the two clocks obtained from the first and second transmission lines is selected, and the frame of communication data is transmitted according to the clock. In a loop-type LAN in which a node circulates around a path, whereby each node transmits and receives frames, the priority order for becoming a master station is set in advance as clock priority for all nodes, and the clock priority is set for the frame. When each node receives a frame from the transmission line after writing and sending it to the transmission line, the clock priority written in the frame and the clock of its own node are written. Clock priority, the clock priority written in the frame is sequentially updated to the highest clock priority. At each node, when the frame is received from the transmission line, it is written in the frame. By comparing the existing clock priority with the clock priority of the own node, one clock is selected from the clock obtained from the first transmission line, the clock obtained from the second transmission line, and the clock of the own node. The clock supply switching method consists of establishing network synchronization according to the selected clock.

In the above method, when an external clock is supplied to a specific node from an external network, the node to which the external clock is supplied writes the frame to the frame when the frame is received from the transmission line. By comparing the clock priority with the clock priority of its own node, one clock is selected and selected from the clock obtained from the first transmission line, the clock obtained from the second transmission line, and the external clock. Establish network synchronization according to the clock.

[0009]

According to the present invention, the priority order for becoming the master station is set as the clock priority in all the nodes, and the clock priority is written in the frame and sent out to the transmission line, which is the highest. The clock priority is updated in sequence. Then, the node that receives it becomes the master station to select the clock of its own node if the priority of its own node is higher, and becomes the slave station if the priority of its own node is lower. One of the clocks obtained from the transmission line is selected, and network synchronization is established according to the selected clock.

Therefore, even if a failure occurs in the node of the master station, all the nodes can become master stations in the order of high priority, so that network synchronization can always be established. Further, even if a failure occurs in the transmission line clock system, each node of the slave station can select either one of the clocks obtained from the first and second transmission lines, so that it always links with the master station. It is possible to switch to a new system.

Further, even when two or more network loops are present due to a failure event, the node having the highest priority in each loop becomes the master station, so that network synchronization is established for each loop. This makes it possible to flexibly cope with multiple failures.

When an external clock is supplied to the node of the master station from the external network, subordinate synchronization with the external network becomes possible.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the embodiments shown in the drawings. The present invention is not limited to this.

FIG. 1 is a block diagram showing the structure of a loop type LAN communication node applied to the clock supply switching system of the present invention. In this figure, 1 is a communication node. The loop type LAN of this embodiment is the communication node 1
Are connected by two transmission paths in the reverse direction of the 0-system (shown as # 0 in the figure) and the 1-system (shown as # 1 in the figure). It is designed to be transmitted in a frame having an overhead.

The communication node 1 includes a 0-system transmission line IF unit 2,
1-system transmission line IF unit 3, CLK unit 4, and CSEL unit 5
It consists of

The 0-system transmission path IF unit 2 receives a frame from the transmission path # 0, performs REC detection, transmission path clock extraction, and reception overhead separation, and
The transmission overhead is multiplexed and output again to the transmission path # 0.

The 1-system transmission path IF unit 3 receives a frame input from the transmission path # 1, performs REC detection, transmission path clock extraction, and reception overhead separation.
The transmission overhead is multiplexed and output again to the transmission line # 1.

The CLK section 4 receives an input of an external clock and selects one clock from 0-system clock, 1-system clock and external clock, a frequency dividing circuit 7 for the selected clock, It is composed of a PLO 8 which oscillates a system clock and a detector circuit 9 which detects an external clock.

The CSEL unit 5 includes a register 10 in which the priority order for the communication node 1 to become a clock master is stored in advance as clock priority data, a free-run (self-running) clock, an external clock, a 0-system clock, and a 1-system clock. It is composed of an arbitration circuit 11 which selects any one of the clocks.

The overhead of the frame transmitted between the communication nodes 1 is, as shown in FIG. 2, CP-ID (Clk
Clock priority information 21 indicated by Priority ID, and EXT-EN (Ext Clk Enab)
le), the external clock monitoring information 22 and SEQ
It is composed of the sequence information 23 indicated by (Sequence No.). External clock monitoring information 22
The sequence information 23 is generated by the master station. Also,
This overhead frame is generated by the CSEL unit 5 and circulates the transmission lines of the 0-system and the 1-system in a form of relaying each communication node 1.

Of the information included in the overhead frame, the clock priority information 23 is the reception clock priority information # 0 / # 1 of the 0-system and 1-system, and CSEL when the frame is received by each communication node 1. Register 1 in part 5
The clock priority data set to 0 are compared, and the higher priority value is written and relayed.

As the external clock monitoring information 22, the master station writes and transmits the state (enable: '1', disable: '0') of the external clock enable signal, and the communication node 1 of each slave station only monitors. To relay.

The sequence information 23 is transmitted by writing a sequence number in the communication node 1 of the master station, which is updated every time the circulating frame is transmitted again, and the communication node 1 of each slave station relays it only by monitoring. To do. The overhead frame is used for each communication node 1.
When receiving with, a certain protection is taken, and reception enable is valid in the enabled state.

In the CSEL unit 5, the 0-system transmission line IF unit 2
Reception enable signals # 0 / # 1 of the 0 system and 1 system extracted by the transmission path IF unit 3 of the 1 and system 1 and the received 0 system and 1 of the 1 system, respectively.
The system 0 based on the information obtained from the overhead # 0 / # 1 of the system frame, the external clock enable signal extracted by the CLK unit 4, and the clock priority data set in the register 10 in the CSEL unit 5. Clock, 1-system clock, external clock supplied from external network, and C
One of the PLO free-run clocks mounted on the SEL unit 5 is selected and used as the supply source of the system clock generated by the CLK unit 4.

As described above, the system clock supply source options of the communication node 1 are switched as four state transitions of a free-run clock, a 0-system clock, a 1-system clock, and an external clock as shown in FIG. And, as shown in FIG. 5, CP-IDM (clock priority data) CP-ID0 (0 system reception clock priority information) CP-ID1 (1 system reception clock priority information) CP-EN0 (0 system reception overhead enable) ) (Reception enable, sequence information) CP-EN1 (1 system reception overhead enable) (Reception enable, sequence information) EXT-EN (external clock enable) EXT-EN0 (0 system external clock synchronization enable) EXT-EN1 (1 system External clock synchronization enable) Give 9 parameters of previous state Arbitrate by.
Of the four states, the free-run clock and the external clock are 0 when the communication node 1 operates as a master station.
The state of the system clock and the system clock is the communication node 1
Will operate as a slave station.

The operation of this embodiment will be described below in the case where six communication nodes A to F are connected and the clock priority is defined as A → F → B → E → C → D in descending order. This will be described with reference to five cases shown in FIGS. 6 to 10.

FIG. 6 shows an example in which the communication nodes A to F are turned on in this order and all the communication nodes A to F have normally started up. The communication node A is in the free-run state because its own station is the highest in the clock priority in the loop, and operates as a master station. In the communication nodes B to F, the reception enable is enabled from the 0-system of the transmission path clock system, and since the clock priority is lower than that of the communication node A, the 0-system clock state is obtained.
It operates as a slave station of the communication node A.

FIG. 7 shows a case where a failure occurs in the 0-system of the transmission path clock system between the communication node A and the communication node B, and an example showing a case where a single-system failure occurs in the transmission path. The communication node B switches to the 1-system clock state when the 0-system reception enable is disabled. The communication nodes C to F are switched to the 1-system clock state when the 0-system sequence synchronization is lost.

In FIG. 8, the 0 line of the transmission line clock between the communication node B and the communication node C has a fault, and the 1 line system of the transmission line clock between the communication node E and the communication node F has a fault. This is a case, and is an example showing a case where both system failures occur in the transmission path. The communication node F switches to the 1-system clock state because the 0-system clock priority is lower than that of the 1-system clock. The communication nodes C to E form an isolated loop, and the communication node E switches to the free-run state and operates as a master station because its own station is the highest in the priority of the clock in the isolated loop. The communication node C switches to the 1-system clock state when the 0-system reception enable is disabled. The communication node D switches to the 1-system clock state when the 0-system sequence synchronization is lost.

FIG. 9 shows an example in which the communication node A, which is the master station, leaves the transmission line due to a failure. Since the communication node F has the second highest clock priority after the communication node A, the communication node F switches to the free-run state and operates as a master station. The communication nodes B to E are switched to the 1-system clock state when the 0-system sequence synchronization is lost.

FIG. 10 shows an example in which a failure occurs in the external clock supplied to the communication node A which is the master station. The communication node A transmits the external clock monitoring information in the disabled state because the external clock enable is disabled, but nevertheless,
Since the external clock monitoring information is received in the enabled state from the first system, it switches to the first system clock state and operates as a slave station. Since the external clock monitoring information from both systems is disabled and the external clock enable is enabled, the communication node F enters the external clock state and operates as a master station. The communication nodes B to E are out of sequence synchronization once at the time when the master station is switched, and are switched to the system which has received the clock priority information from the communication node F earlier.

[0032]

As described above, according to the present invention,
Since the priority order to become the master station is preset in all nodes as the clock priority, even if the network is not completely looped due to various failure events, if there are two or more nodes, the master You can configure nodes for stations and slave stations. Further, even if there is only one normal node, since it operates as a master station itself, data communication is possible on the path line within the range of that node. Therefore, no matter what kind of multiple failures occur, network synchronization can always be established, which greatly contributes to improving the reliability of the network and facilitating maintenance.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a communication node of a loop type LAN applied to the present invention.

FIG. 2 is a configuration diagram of an overhead frame.

FIG. 3 is a system clock supply source switching state transition diagram.

FIG. 4 is an explanatory diagram of system clock supply source switching arbitration.

5 is an explanatory diagram of system clock supply source switching arbitration subsequent to FIG. 4. FIG.

FIG. 6 is an explanatory diagram showing a case where all communication nodes have normally started up.

FIG. 7 is an explanatory diagram showing a case where a one-sided failure occurs in a transmission path.

FIG. 8 is an explanatory diagram showing a case where a failure of both systems occurs in a transmission path.

FIG. 9 is an explanatory diagram showing a case where a communication node A leaves the transmission line due to a failure.

10 is an explanatory diagram showing a case where a failure occurs in the external clock supplied to the communication node A. FIG.

[Explanation of symbols]

 1 Communication Node 2 0 System Transmission Line IF Unit 3 1 System Transmission Line IF Unit 4 CLK Unit 5 CSEL Unit 6 Selector 7 Dividing Circuit 8 PLO 9 Detector Circuit 10 Register 11 Arbitration Circuit 21 Clock Priority Information 22 External Clock Monitoring Information 23 Sequence information

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masashi Hirome 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited

Claims (2)

[Claims] 1. A network is constructed by connecting a plurality of nodes consisting of a master station and a slave station in a loop with first and second transmission lines, and the nodes from the master station to the first station
And a clock to the second transmission line, the slave station node selects one from the two clocks obtained from the first and second transmission lines, and sends a frame of communication data to the transmission line according to the clock. In a loop-type LAN in which the nodes are circulated and thereby transmit and receive frames at each node, the priority order to become the master station is set in advance as clock priority for all nodes, and the clock priority is written in the frame. When sending out to the transmission line and each node receiving the frame from the transmission line, the clock priority written in the frame is compared with the clock priority of the own node to determine the clock priority written in the frame. It updates sequentially to the highest clock priority, and each node writes the frame when it receives it from the transmission line. By comparing the built-in clock priority with the clock priority of the own node, one clock is obtained from the clock obtained from the first transmission line, the clock obtained from the second transmission line, and the clock of the own node. A clock supply switching method consisting of selecting a clock and establishing network synchronization according to the selected clock. 2. An external clock is supplied to a specific node from an external network, and a node to which the external clock is supplied, when receiving a frame from a transmission line, sets the clock priority written in the frame to the clock of its own node. By comparing with the priority, the clock obtained from the first transmission line and the second
2. The clock supply switching system according to claim 1, further comprising: selecting one clock from the clock obtained from the transmission line and the external clock, and establishing network synchronization according to the selected clock.