JP3241104B2 - Clock supply switching method - Google Patents

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 comprising a master station and a slave station are connected in a loop by first and second transmission lines. And a clock supply switching method for switching a clock supplied to each node of a loop type 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 transmission lines, clockwise and counterclockwise, and two nodes are connected from the master station node. A clock is transmitted to each of the transmission lines of the system, and the node of the slave station selects one of the two clocks obtained from the transmission lines of the two systems, and circulates the communication data frame on the transmission line according to the clock. , Each node transmits and receives frames.

That is, a clock source is supplied from one node (master station) as a clock master in a network to another node (slave station), and synchronization in the network is performed by subordinate synchronization. Also,
In some cases, a master station node is supplied with a clock from an external network, and the entire network is synchronized with the external clock, thereby enabling subordinate 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 operation system and a standby system, in response to a failure of the transmission line clock system or a failure of the clock master or external clock supply interruption. Using a duplicated transmission line,
In addition, a countermeasure has been taken by making the clock master a dual configuration of a master station and a submaster station.

[0005]

However, in such a conventional loop type LAN, a fault in the transmission line clock system is switched from the operation system to the standby system, and a fault in the clock master is shifted from the master station to the submaster station. In this case, only a single failure can be dealt with, for example, by switching each. Therefore, a loop-type LAN capable of dealing with multiple failures has been desired.

The present invention has been made in view of such circumstances, and the priorities for all the nodes to become master stations are defined in advance, and the nodes having higher priorities are sequentially assigned as master stations. At the same time, for a node that could not become the master station, by selecting one of the clocks received from the two systems, the network can be operated even when multiple failures such as a failure in the master station or a failure in the transmission line clock system occur. And a clock supply switching method which can always establish synchronization within the clock.

[0007]

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 by first and second transmission lines. A clock is transmitted to the first and second transmission lines, and the slave station node selects one of the two clocks obtained from the first and second transmission lines, and transmits a frame of communication data according to the clock. In a loop-type LAN in which each node transmits and receives frames, thereby setting the priority order for all nodes to become master stations in advance as a clock priority, the clock priority and an external clock the existence of and transmitted to a transmission line is written to the frame, the clock each node when receiving a frame from the transmission path, which is written in the frame Sakido and by comparing the clock priority of the node, so on are sequentially updated to the highest clock priority clock priority written in the frame, with each node, the procedure of the system clock source switching arbitration
Is stored, and when a frame is received from the transmission line , the clock priority written in the frame is compared with the clock priority of the own node based on the above procedure, thereby obtaining the clock priority from the first transmission line. Clock and second
One clock is selected from the clock obtained from the transmission path of the
If an external clock is supplied to the
Is preferentially selected, and network synchronization is established in accordance with the selected clock.

[0008]

[0009]

According to the present invention, the priority order for becoming a master station is set as a clock priority for all nodes, and the clock priority and the presence or absence of an external clock are written in a frame and transmitted to a transmission line. It is transmitted and is sequentially updated to the highest clock priority. Then, the node that has received it becomes the master station if the priority of the own node is higher, selects the clock of the own node, and becomes the slave station if the priority of the own node is lower, and the first and second nodes. select one of the clocks obtained clock from the transmission path of, and outside that time, one of the nodes
If a clock is supplied, the external clock has priority
And establish network synchronization according to the selected clock.

Therefore, even if a failure occurs in a node of the master station, all nodes can become master stations in descending order of 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 one of the clocks obtained from the first and second transmission lines, so that the node always links with the master station. It is possible to switch to a new system.

Further, even when two or more network loops exist due to a failure event, the nodes having the highest priority in each loop become master stations, so that network synchronization is established in each loop unit. This makes it possible to flexibly cope with multiple failures.

In addition, in selecting a clock,
If an external clock is supplied to any of the nodes,
Presence or absence of an external clock because the clock is selected with priority
Switching between master station and slave station automatically and automatically
It is a necessary condition to operate in real time and configure the network.
Reliability in establishing clock synchronization with external networks
You.

[0013]

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

FIG. 1 is a block diagram showing a configuration of a communication node of a loop type LAN applied to the clock supply switching system of the present invention. In this figure, 1 is a communication node. The loop type LAN according to the present embodiment uses the communication node 1
Are connected by two transmission lines of the system 0 (shown by # 0 in the figure) and the system 1 (shown by # 1 in the figure), and data between the communication nodes 1 is The transmission is performed in a frame having overhead.

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

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

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

The CLK unit 4 receives an input of an external clock, and selects one clock from among a 0-system clock, a 1-system clock, and an external clock, a frequency divider 7 for the selected clock, It comprises a PLO 8 for oscillating a system clock and a detector circuit 9 for detecting 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-running (self-running) clock, an external clock, a 0-system clock, and a 1-system. It comprises an arbitration circuit 11 for selecting any one of the clocks.

As shown in FIG. 2, the overhead of a frame transmitted between the communication nodes 1 is CP-ID (Clk
Clock priority information 21 indicated by a Priority ID (Ext. Clk Enable) and EXT-EN (Ext Clk Enable)
le), the external clock monitoring information 22 shown in FIG.
(Sequence No.). External clock monitoring information 22
And the sequence information 23 are generated by the master station. Also,
The overhead frame is generated by the CSEL unit 5 and circulates through the transmission paths of the 0-system and the 1-system while relaying each communication node 1.

Among the information included in the overhead frame, the clock priority information 23 includes, when the communication node 1 receives the frame, the received clock priority information # 0 / # 1 of the 0-system and the 1-system, and CSEL. Register 1 in unit 5
The clock priority data set to 0 is compared, and the higher priority value is written and relayed.

The external clock monitoring information 22 is transmitted by writing the state of the external clock enable signal (enable: "1", disable: "0") in the master station, and the communication node 1 of each slave station only monitors. To relay.

The sequence information 23 is written and transmitted in the communication node 1 of the master station such that the sequence number is updated each time the circulating frame is transmitted again, and the communication node 1 of each slave station relays only by monitoring. I do. Note that the overhead frame is stored in each communication node 1
When receiving the data, certain protection is taken, and the reception is enabled when the reception enable is enabled.

In the CSEL unit 5, the 0-system transmission line IF unit 2
And the 1-system reception enable signal # 0 / # 1 extracted by the transmission-line IF unit 3 of the 1-system and 1-system, respectively.
Based on the information obtained from the overhead # 0 / # 1 of the frame of the system, 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, the system Clock, first system clock, external clock supplied from an external network, and C
One of the free-run clocks of the PLO mounted on the SEL unit 5 is selected and used as a 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 the free-running clock, the 0-system clock, the 1-system clock, and the external clock as shown in FIG. As shown in FIG. 5 and 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.
Among the four states, the states of the free-running clock and the external clock indicate that the communication node 1 operates as a master station,
The status of the system clock and the system clock is determined by the communication node 1
Will operate as a slave station.

Hereinafter, the operation of this embodiment will be described in the case where the clock priority is defined as A → F → B → E → C → D in the configuration in which six communication nodes A to F are connected, in the order of higher priority. This will be described with reference to five cases shown in FIGS.

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

FIG. 7 shows a case where a failure has occurred in the system 0 of the transmission line clock system between the communication node A and the communication node B, and shows an example in which a single system failure has occurred in the transmission line. The communication node B switches to the state of the system 1 clock when the reception enable of the system 0 is disabled. The communication nodes C to F switch to the state of the system 1 clock when the sequence synchronization of the system 0 is lost.

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

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

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

[0032]

As described above, according to the present invention,
Since the priority order for becoming the master station is set in advance for 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 Station and slave station nodes can be set. Further, even if the number of normal nodes becomes one, since the node itself operates as a master station, data can be communicated on a path line within the range of the node. Therefore, even if any multiple failures occur, network synchronization can always be established, which greatly contributes to improvement of network reliability and easiness of maintenance. Moreover, in the selection of the clock,
If an external clock is supplied to any of the nodes,
Presence or absence of an external clock because the clock is selected with priority
Switching between master station and slave station automatically and automatically
It is a necessary condition to operate in real time and configure the network.
Reliability in establishing clock synchronization with external networks
You.

[Brief description of the 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 transition diagram of a system clock supply source switching state.

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

FIG. 5 is an explanatory diagram of arbitration for switching system clock supply sources following FIG. 4;

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

FIG. 7 is an explanatory diagram showing a case where a single-system failure has occurred in a transmission line.

FIG. 8 is an explanatory diagram showing a case where a two-way failure has occurred in a transmission path.

FIG. 9 is an explanatory diagram showing a case where a communication node A has left a transmission path due to a failure.

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

[Explanation of symbols]

 REFERENCE SIGNS LIST 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 frequency divider 8 PLO 9 detector circuit 10 register 11 arbitration circuit 21 clock priority information 22 external clock monitoring Information 23 Sequence information

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masashi Hirome 1015 Uedanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (56) References JP-A-3-71746 (JP, A) JP-A-4- 51627 (JP, A) JP-A-2-257733 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04L 12/42

Claims (1)

(57) [Claims] 1. A network is formed by connecting a plurality of nodes consisting of a master station and a slave station in a loop by first and second transmission lines, and a first node is connected to the first node by a node of the master station.
And a clock is transmitted to the second transmission line. The slave station node selects one of the two clocks obtained from the first and second transmission lines, and transmits a communication data frame to the transmission line in accordance with the clock. In a loop-type LAN in which each node transmits and receives frames, whereby the priority order for becoming a master station is set in advance for all nodes as a clock priority, and the clock priority and the presence or absence of an external clock are set. Is written to the frame and sent to the transmission path.When each node receives the frame from the transmission path, the clock priority written in the frame is compared with the clock priority of the own node, and the so on are sequentially updated to the highest clock priority clock priority are, in each node, the system clock source switching tone Stop hand
The order is stored, and when a frame is received from the transmission line , the clock priority written in the frame is compared with the clock priority of the own node based on the above procedure, so that the first transmission line the resulting clock and with selecting one clock from the clock of the clock and the local node obtained from the second transmission path, either Roh
If an external clock is supplied to the external clock,
Clock supply switching method , which preferentially selects the clock and establishes network synchronization according to the selected clock.