JP2006003118A - Method for synchronizing clock time - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a clock time synchronizing method capable of establishing clock time synchronization in a network. <P>SOLUTION: In the method for synchronizing clock times of the network of a tree structure constituted of a plurality of nodes, a parent node leads a clock of the parent node for very carrier sense, generates clock time information on the basis of a lead time, and transmits the clock time information to a child node. The child node performs delay correction of the amount of one hop on the clock time information. By setting the time of the child node, it is possible to establish clock time synchronization in the network. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a clock time synchronization method.

Establishing clock time synchronization in the network is essential for parallel processing of scheduled tasks between nodes. For example, like a wireless sensor network, there is a system in which each node is equipped with a sensor, performs sensing at a predetermined time, and transfers the data to a route.
As a conventional method, there is a method of transmitting clock time information between a route and a node and performing delay correction according to the number of hops at the node, or a method of transmitting clock time information in which the delay time to the node is previously corrected by the route (For example, refer to Patent Document 1).

FIG. 2 is a diagram illustrating a configuration example of a network. FIG. 3 is a diagram showing a conventional example of the clock time synchronization method, and FIG. 3 is a diagram showing another conventional example of the clock time synchronization method.
For example, in the network shown in FIG. 2, consider establishing clock time synchronization between node 0 and node 2 that are routes. The route transmits clock time information to the node 2. The clock time information transmitted by the node 0 is relayed by the node 1 and received by the node 2. When delay correction for two hops is performed in advance in the route, the node 2 writes the received clock time information to the clock of its own node (node 2). When delay correction is performed at node 2, the result of delay correction for two hops is written to the clock of the own node.

Further, as a conventional method, there is a method in which clock synchronization is sequentially performed between nodes in a network in which a plurality of wireless nodes are distributed. This method is used for the purpose of synchronizing transmission / reception timing between nodes by time division duplex (see, for example, Patent Document 2).
Further, as another conventional method, there is a method of synchronizing time in a CSMA / CD LAN (see, for example, Patent Document 3).
JP 2003-317180 A Japanese Patent Laid-Open No. 2003-274349 JP-A-4-273737

However, in the prior art described in Patent Document 1 described above, when using communication means using carrier sense or retransmission such as radio, as shown in FIG. 3, not only the delay time according to the number of hops but also the relay node. It is necessary to correct the generated carrier idle time and retransmission time.
In addition, in the method in which delay correction is performed in advance in the route, the carrier idle waiting time and the retransmission time cannot be corrected. Further, in the method of performing delay correction at the node, it is necessary to newly add the carrier waiting time generated at the relay node and the time information required for retransmission in addition to the clock time information of the route to the signal.

On the other hand, in the method described in Patent Document 2, the delay time due to carrier sense for signal collision avoidance and retransmission at the time of signal collision is not considered.
Further, in the method described in Patent Document 3 described above, it is necessary to transmit delay information generated by the CSMA / CD method in addition to the clock time information.
Therefore, an object of the present invention is to provide a clock time synchronization method capable of establishing clock time synchronization in a network.

  In order to solve the above-mentioned problem, according to the first aspect of the present invention, in the clock time synchronization method of a network having a tree structure composed of a plurality of nodes, the parent node sets the clock of the parent node for each carrier sense. Read, generate clock time information from the read time, transmit the clock time information to the child node, the child node performs a delay correction of one hop on the clock time information, and sets the clock of the child node It is characterized by setting.

  According to the first aspect of the present invention, the parent node transmits its own clock time information to the child node, and the child node performs delay correction for one hop, thereby establishing clock time synchronization in the network. be able to. The reason is that the parent node clock is read for each carrier sense between the parent node and the child node, clock time information is generated, and transmitted to the child node.

  According to a second aspect of the present invention, in the first aspect of the invention, each child node downstream of the child node performs delay correction for one hop on the clock time information, and each child downstream of the child node A node clock is set.

  According to a third aspect of the present invention, in the first or second aspect of the invention, each of the child nodes transmits a clock time setting completion signal to the parent node when the clock time setting is completed. .

  According to a fourth aspect of the present invention, in the clock time synchronization method of a mesh type network composed of a plurality of nodes, the parent node reads the clock of the parent node for each carrier sense, and clock time information is obtained from the read time. , And assigns a sequence number to the clock time information, transmits the clock time information to the child node, and the child node uses the sequence number to perform a delay correction for one hop on the clock time information. And setting a clock of the child node, and transmitting clock time information to the downstream child node.

  According to a fifth aspect of the invention, in the fourth aspect of the invention, each child node downstream of the child node performs a delay correction for one hop on the clock time information using the sequence number, and the child node The clock of each child node on the downstream side of the node is set.

  The invention according to claim 6 is the invention according to claim 4 or 5, wherein when the parent node newly establishes clock time synchronization in the network, the child node receives clock time information to which another sequence number is assigned. It is characterized by transmitting to.

  The parent node transmits the clock time information of its own node to the child node, and the child node performs a delay correction for one hop so that the parent node clock is read for each carrier sense between the parent node and the child node. Since clock time information is generated and transmitted to the child node, clock time synchronization in the network can be established.

  In the clock time synchronization method for a network having a tree structure constituted by a plurality of nodes, the present invention reads the clock of the parent node for each carrier sense, generates clock time information from the read time, The clock time information is transmitted to a child node, and the child node performs delay correction for one hop on the clock time information, and sets the clock of the child node.

(Features of the present invention)
Consider a tree (tree) structure network composed of a plurality of nodes as shown in FIG. 1, and synchronize the clock of the network node with the clock of the root (node 0 in FIG. 1). Each node performs signal collision prevention by carrier sense during signal transmission.
In the present invention, the parent node reads the clock for each carrier sense, generates clock time information, and transmits the clock time information between the parent node and the child node. The child node performs delay correction for one hop and sets the clock.

FIG. 4 shows the concept of one embodiment of the clock time information synchronization method of the present invention.
In FIG. 4, the node 0 reads the clock for each carrier sense, generates clock time information, and transmits it to the node 1. The node 1 receiving the clock time information from the node 0 writes the result of delay correction for one hop to the clock. Thus, the node 0 and the node 1 establish clock time synchronization.
Next, the node 1 reads the clock for each carrier sense, and transmits the clock time information of the node 1 to the node 2. The node 2 receiving the clock time information from the node 1 writes the result of delay correction for one hop to the clock. Thus, node 1 and node 2 establish clock time synchronization.
Finally, the node 1 reads the clock for each carrier sense, and transmits the clock time information of the node 1 to the node 3. The node 3 receiving the clock time information from the node 1 writes the result of delay correction for one hop to the clock. Node 1 and node 3 establish clock time synchronization, and as a result, the clock of node 0, which is the root, and the clocks of node 1, node 2, and node 3 have established synchronization. Thus, even when each node uses carrier sense in a tree structure network composed of a plurality of nodes, the parent node always transmits its own clock time information for each carrier sense, and the child node sets 1 to the clock time information. The network clock time synchronization can be established by performing delay correction for hops and setting the clock of the own node.

Next, an embodiment of the clock time synchronization method of the present invention will be described.
(Configuration of Example)
Each node shown in FIG. 1 has a read / write clock. Clock time information can be acquired by reading the clock, and the clock time can be corrected by writing the time to the clock. Further, the route information held by each node is shown in FIGS. 5 (a) to 5 (d).
The processing of the parent node will be described using the flowchart of FIG.
The parent node reads the clock of its own node and generates clock time information (step S1).
After generating the clock time information, the parent node performs carrier sense and determines whether or not carrier detection has been performed (step S2).
If the parent node finds a carrier (step S2 / No), it waits for a predetermined time (step S6), reads the clock again to generate clock time information (step S1), and performs carrier sense (step S2). ).
If the parent node has not found a carrier (step S2 / Yes), it transmits clock time information to the child node (step S3).
The parent node determines whether or not a clock setting completion signal is received (step S4), and determines whether or not another child node exists (step S5).
When the parent node receives the clock setting completion signal from the child node (step S4 / Yes) and has another child node (step S5 / Yes), the same processing is performed for the other child nodes. carry out.
If the parent node has no other child nodes (step S5 / No), the process ends.
When the parent node cannot receive the clock setting completion signal from the child node (step S4 / No), the parent node determines whether or not a reception timeout has occurred (step S7).
If the parent node fails to receive within the predetermined time, it times out (step S7 / Yes), and determines whether or not the number of retransmissions exceeds the predetermined number (step S8).
If the number of retransmissions is within the predetermined number (step S8 / No), the parent node performs the process again from the timepiece read.
When the number of retransmissions exceeds the predetermined number (step S8 / Yes) and the parent node has another child node (step S5 / Yes), the same processing is performed on the other child node, If there is no child node (No in step S5), the process is terminated.

Next, child node processing will be described with reference to the flowchart of FIG.
When the child node receives the clock time information from the parent node (step T1), the child node performs a delay correction for one hop (step T2), and transmits a clock time setting completion signal to the parent node (step T3).
The child node determines whether or not it has another child node (step T4).
If the child node has an entry of the child node in the path information (if it has another child node: Step T4 / Yes), the child node performs the process shown in FIG. 6 on the child node (Step T5).
If there is no child node entry in the route information (if no other child node is present: Step T4 / No), the child node ends the process.

(Description of operation of the embodiment)
An operation example of the embodiment will be described with reference to FIG.
FIG. 8 shows a timing chart of each node in FIG.
The root node 0 attempts to establish clock time synchronization with the child node 1.
Node 0 performs carrier sense after reading the clock of its own node and generating clock time information.
Since node 0 did not find a carrier, it transmits clock time information to node 1.
The node 0 waits for the clock setting completion signal from the node 1, but since it has timed out, it reads the clock of its own node again, generates clock time information, and performs carrier sense.
Since node 0 did not find a carrier, it transmits clock time information to node 1 and receives a clock setting completion signal from node 1.
Since node 0 has no other child nodes, the process ends.
When the node 1 receives the clock time information from the node 0, the node 1 performs a delay correction for one hop and writes the clock time information to the clock of its own node.
The node 1 transmits a clock setting completion signal to the node 0.
Since node 1 has node 2 and node 3 as child nodes, it attempts to establish clock time synchronization for these nodes 2 and 3.
Node 1 reads the clock of its own node, generates clock time information, performs carrier sense, does not find a carrier, transmits clock time information to node 2, and completes clock setting from node 2. Receive a signal.
Since the node 2 has no child node, the process ends.
Node 1 attempts to establish clock time synchronization with node 3.
The node 1 reads the clock of its own node, generates clock time information, and then performs carrier sense. Since the carrier is found by carrier sense, it waits for a predetermined time, reads the clock of its own node again, generates clock time information, and then performs carrier sense.
Since node 1 did not find a carrier, node 1 transmits clock time information to node 3 and receives a clock setting completion signal from node 3.
Since node 1 has no other child nodes, the process is terminated.
Since the node 3 has no child node, the process ends.
As described above, clock time synchronization is established in the network.

(Explanation of effect)
According to the present invention, when a communication means using carrier sense or retransmission is used in a tree structure network composed of a plurality of nodes, the parent node transmits its own clock time information to the child node, and the child node has one hop. By performing the minute delay correction, clock time synchronization in the network can be established. The reason is that between the parent node and the child node, the clock of the parent node is read for each carrier sense, clock time information is generated, and transmitted to the child node.

The concept of another embodiment of the clock time synchronization method of the present invention is shown in FIG.
In FIG. 9, it is considered that the clock in the network is synchronized with the clock of the node 0 in the mesh type network.
In this embodiment, in the clock time synchronization method of the mesh type network configured by a plurality of nodes, the parent node reads the clock of the parent node for each carrier sense, generates clock time information from the read time, A sequence number is assigned to the clock time information, and the clock time information is transmitted to the child node. The child node performs a delay correction for one hop on the clock time information using the sequence number, and sets the clock of the child node. The clock time information is transmitted to the downstream child node.
In this example, synchronization with the clock of the node 0 is shown as an example, but the same applies to other nodes. Node 0 assigns a sequence number to the clock time information. Node 0 uses the same sequence number for the adjacent node, and the received node uses the sequence number to read the clock of its own node to the adjacent node and transmit the clock time information. For example, if node 0 transmits sequence number 1 and its own clock time information to node 1, node 1 transmits sequence number 1 and its own clock time information to adjacent node 2. In order to prevent a clock time information loop, when the same sequence number is received repeatedly, the clock time information is not transmitted to the adjacent node. When node 0 wants to newly establish clock time synchronization in the network, node 0 gives another sequence number and transmits clock time information.

It is a figure which shows the Tree (tree) structure network comprised from several nodes. It is a figure which shows the prior art example of a clock time synchronization system. It is a figure which shows the other conventional example of a clock time synchronous system. It is a conceptual diagram of an example of the clock time synchronization method of this invention. (A)-(d) is a figure which shows the routing information which each node hold | maintains. It is a flowchart which shows the process of a parent node. It is a flowchart which shows the process of a child node. 5 is a timing chart of each node in FIG. 4. It is a conceptual diagram of the other Example of the clock time synchronization method of this invention.

Claims (6)

In a clock time synchronization method for a network having a tree structure composed of a plurality of nodes,
The parent node reads the clock of the parent node for each carrier sense, generates clock time information from the read time, transmits the clock time information to the child node,
The clock time synchronization method, wherein the child node performs a delay correction for one hop on the clock time information, and sets the clock of the child node.   The child node downstream of the child node performs delay correction for one hop on the clock time information, and sets the clock of each child node downstream of the child node. Clock time synchronization method.   3. The clock time synchronization method according to claim 1, wherein each of the child nodes transmits a clock time setting completion signal to the parent node when the clock time setting is completed. In the clock time synchronization method of a mesh type network composed of a plurality of nodes,
The parent node reads the clock of the parent node for each carrier sense, generates clock time information from the read time, assigns a sequence number to the clock time information, and transmits the clock time information to the child node ,
The child node performs delay correction for one hop on the clock time information using the sequence number, sets the clock of the child node, and transmits the clock time information to the downstream child node. Clock time synchronization method to be used.   Each child node on the downstream side of the child node performs delay correction for one hop on the clock time information using the sequence number, and sets the clock of each child node on the downstream side of the child node. The clock time synchronization method according to claim 4.   6. The clock time synchronization according to claim 4 or 5, wherein when the parent node newly establishes clock time synchronization in the network, the parent node transmits clock time information to which another sequence number is assigned to the child node. Method.

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