JP4237693B2 - Communication control method - Google Patents

Description

  The present invention relates to a communication control method in a system that performs periodic communication at high speed on a network in which a plurality of nodes are connected. Such a communication control method is applied to control of a communication unit for a plant monitoring / control system, for example.

In a fixed-cycle communication system, each device (node) connected to a network transmits and receives data at a fixed cycle. As a communication control method in such a fixed cycle communication system, there is one having the following procedure.
(1) A unique number called a network address is assigned to each node.
(2) The leading node performs data transmission in the cycle of its own node.
(3) When a node other than the head receives data transmitted by a node having an address immediately before itself, it determines that a transmission right (token) has been granted and performs data transmission.
An example of such a communication control method is disclosed in, for example, Japanese Patent Laid-Open No. 2000-216786 (Patent Document 1). Although not described in Patent Document 1, UDP / IP, which is an Internet communication protocol, can be used in the communication control method. In this case, the network address assigned to each node is a so-called IP address.

In the periodic communication system as described above, a node having a high communication processing capability (for example, a monitoring / control unit equipped with a dedicated real-time OS; hereinafter referred to as a high-speed communication node) and a node having a low communication processing capability (for example, commercially available) Consider a case in which a personal computer equipped with a multitasking OS (hereinafter referred to as a low-speed communication node) is mixed. In such a case, conventionally, communication has been performed by the following method.
(Method 1) The communication cycle of all nodes is lengthened according to the low-speed communication node.
(Method 2) The high-speed communication node performs fixed-cycle communication, and the low-speed communication node performs communication while ignoring the cycle.
(Method 3) In the low-speed communication node, data thinning is performed by appropriately discarding the contents of received data at the application level.

  Method 3 will be described in more detail using UDP / IP as an example. In UDP / IP, an IP packet is reconstructed into UDP level data by a driver, an operating system, or a high-level processing system equivalent thereto. This reconfiguration process is performed on all data sent from other nodes at a fixed period. However, in the case of a low-speed communication node, there is no ability to capture and process all the data by an application. Therefore, the application captures data at a period longer than the fixed period and discards other data, thereby thinning out the data and reducing the processing load.

JP 2000-216786 A

  In the method 1, the communication cycle of all the nodes is lengthened for some nodes having low communication processing capacity, so that the entire system cannot exhibit the required performance.

  In Method 2, since the transmission right management using tokens is incomplete, there is a possibility that a packet transmitted by a high-speed communication node at a fixed period and a packet transmitted randomly by a low-speed communication node will collide on the network. There is. In order to avoid this, network access control such as CSMA / CD (Carrier Sense Multiple Access with Collision Detection) is required, and particularly when the number of nodes is large, the utilization efficiency of the transmission capability of the network is significantly reduced. Sometimes.

  In Method 3, although the communication processing load is reduced to some extent by thinning out data, a packet that is not used in the application is finally passed to the UDP level processing. Since such a wasteful process occurs, a significant load reduction effect cannot be expected.

  The present invention has been made to solve the above-described problems, and its purpose is to consider the communication processing capability of each node in a system that performs periodic communication including a high-speed communication node and a low-speed communication node. Accordingly, it is an object of the present invention to provide a communication control method capable of reducing the communication processing load of a low-speed communication node while effectively utilizing the transmission capability of the network by operating all the nodes in cooperation.

The communication control method according to the present invention made to solve the above problems is as follows.
In a communication control method for a periodic communication system including a plurality of nodes connected to a data communication network and each assigned a unique address,
A procedure for dividing the plurality of nodes into a high-speed node group composed of nodes with high communication processing capacity and a low-speed node group composed of nodes with low communication processing capacity;
A procedure for setting a high-speed node designation address for uniformly transmitting data to each node included in the high-speed node group to each node included in the high-speed node group;
A procedure for setting all nodes designated addresses for transmitting data to all nodes in the network, and
A procedure for designating the first node to perform data transmission first in the high-speed node group and causing the node to perform data transmission at a certain period.
With
The first node sets two or more times of data transmission as one cycle, sets the destination of each data in each cycle to either the high-speed node designation address or the all-node designation address according to a predetermined schedule,
Each node other than the first node receives data addressed to the group designation address corresponding to the node group to which the node belongs and data addressed to all the node designation addresses, and next time based on predetermined transmission right information included in the data. If there is a right to transmit data, and if the user has the right to transmit data, the data is transmitted to the same destination as the destination set in the received data. Features.

  In the communication control method according to the present invention, communication in the network is performed using a UDP / IP protocol, a multicast address is assigned to the high-speed node group as the group-designated address, and all the node-designated addresses are the network-designated addresses. A broadcast address can be used.

  Also, in the communication control method according to the present invention, the transmission right information is a source address of received data, and each node is determined to perform data transmission immediately before the source address of the data. If it matches the address of the selected node, it can be determined that it has the transmission right.

Hereinafter, the communication control method according to the present invention will be described in detail by taking the case where the communication protocol is UDP / IP as an example.
(1) All nodes in the network are divided into a group of high-speed communication nodes and a group of low-speed communication nodes, and the data transmission order within each group is determined. As a whole, the order of data transmission is determined so that each node in the high-speed node group performs data transmission first, and then each node in the low-speed node group performs data transmission.
(2) A unique IP address is assigned to each node. Here, it is assumed that the IP address is assigned so that the address value increases by 1 according to the data transmission order. The node with the smallest IP address becomes the first node.
(3) A multicast address corresponding to a group of high-speed communication nodes is set. This multicast address corresponds to the high-speed node designation address of the present invention.
(4) A broadcast address for transmitting data to all nodes is set. This corresponds to the all node designation address of the present invention.
(5) Using a timer, the head node is caused to execute data transmission at cycle T. At this time, two or more predetermined data transmission operations are collectively defined as one cycle. For example, when three data transmissions are defined as one cycle, the cycle of one cycle is 3T.
(6) The leading node sets the data destination at the time of each data transmission to either a multicast address or a broadcast address. A schedule is determined in advance and stored in the head node as to which address is selected as a destination at the time of data transmission in one cycle.
(7) When each node other than the head node receives a packet of data transmitted by another node, it checks the source address, and the address is the address immediately before itself (that is, here, from its own address) If the address is the same as (one smaller address), it is determined that the data transmission right has been transferred to itself, and data transmission is performed. The destination of the transmission data at this time is the same as the destination of the previously received data. That is, if the destination of the received data is a multicast address, the destination of the transmission data is also the same multicast address, and if the destination of the received data is a broadcast address, the destination of the transmission data is also a broadcast address.

  An example of the operation of the periodic communication system controlled by the above method is shown below.

(First operation example)
In this operation example, the head node performs two data transmission operations with a period T in one cycle.
At the first data transmission, the leading node sets the broadcast address as the destination. Accordingly, the packet of transmission data is received by all nodes in the network. Next, the second node having an IP address that is one greater than the first node transmits its own data to the broadcast address. The packet of transmission data is received again by all nodes. Next, a third node having an IP address that is one greater than that of the second node similarly transmits data to the broadcast address. In this way, each node sequentially transmits its own data to the broadcast address. When the data transmission of the last node is completed, the first data transmission is completed. After that, it waits until the second data transmission by the head node.
The second data transmission is performed when time T has elapsed from the start of the first data transmission. At the second data transmission, the leading node sets the multicast address as the destination. Therefore, only the nodes included in the high-speed node group receive the transmission data packet. Thereafter, each node included in the high-speed node group sequentially transmits its own data to the multicast address in the same procedure as the first data transmission. When data transmission of the last node of the high-speed node group is completed, one cycle is completed.

  When the above control is performed, the high-speed communication node transmits data at a cycle T, while the low-speed communication node transmits data at a cycle 2T. In this way, the objectives of effective utilization of network transmission capability by cooperative operation of all nodes and reduction of communication processing load of the low-speed communication node are achieved.

(Second operation example)
In this operation example, the head node performs three data transmission operations with a period T in one cycle. The leading node sets the broadcast address as the destination at the first data transmission, and sets the multicast address as the destination at the second and third data transmissions. In this case, the data packet transmitted for the first time is received by all the nodes in the network, and the data packet transmitted for the second and third times is received only by the high-speed communication node. In each data transmission, a process in which a node that receives a packet sequentially transmits its own data is as described in the first operation example. When the above control is performed, the high-speed communication node transmits data at a cycle T, while the low-speed communication node transmits data at a cycle 3T.

  According to the communication control method according to the present invention as described above, in a system that performs periodic communication including a high-speed communication node and a low-speed communication node, by cooperating all the nodes while considering the communication processing capability of each node. The communication processing load of the low-speed communication node can be reduced while effectively utilizing the transmission capability of the network.

  An embodiment of a communication control method according to the present invention will be described with reference to the drawings.

  FIG. 1 shows a schematic configuration of a system to which the communication control method of this embodiment is applied. The system of FIG. 1 includes eight nodes 1 to 8 connected to a data communication network 10 such as a LAN. Four nodes from node 1 to node 4 are high-speed communication nodes that can communicate at a fixed cycle T, and four nodes from node 5 to node 8 are low-speed communication nodes that can communicate at a fixed cycle 2T. The communication protocol between nodes is UDP / IP. Nodes 1 to 8 are assigned IP addresses 192.168.0.11 to 192.168.0.18, respectively, and node 1 functions as a leading node. A multicast address 224.0.0.100 is assigned to the high-speed node group 20 including the high-speed communication nodes 1 to 4, but no multicast address is set to the low-speed node group 22 including the low-speed communication nodes 5 to 8. The broadcast address is 192.168.0.255.

  Next, the operation of the system of FIG. 1 will be described.

  The first data transmission operation will be described with reference to FIG. At the time of the first data transmission, the leading node 1 sets the broadcast address (192.168.0.255) as the destination. Accordingly, the transmission data packet is received by all the nodes 1 to 8 in the network 10 (step S11). Next, the second node 2 having an IP address larger by 1 than the first node 1 transmits its own data to the same destination as the previously received packet, that is, to the broadcast address (192.168.0.255). Accordingly, the packet of transmission data of the second node 2 is received again by all the nodes 1 to 8 (step S12). Next, the third node 3 having an IP address 1 higher than that of the second node similarly transmits data to the broadcast address (192.168.0.255) (step S13). In this way, the nodes 1 to 8 sequentially transmit their own data to the broadcast address (192.168.0.255) (in FIG. 2, the data transmission steps of the nodes 4 to 7 are omitted). When the data transmission of the last node 8 is completed (step S18), the first data transmission is completed. After that, it waits until the second data transmission by the leading node 1.

  Next, the second data transmission will be described with reference to FIG. The second data transmission is performed when time T has elapsed from the start of the first data transmission. At the time of the second data transmission, the leading node 1 sets the multicast address (224.0.0.100) as the destination address. Therefore, only the nodes 1 to 4 included in the high-speed node group 20 receive the transmission data packet (step S21). Thereafter, the nodes 1 to 4 included in the high-speed node group 20 sequentially transmit their own data to the multicast address (224.0.0.100) in the same procedure as the first data transmission (steps S22 to S24). When the data transmission of the last node 4 of the high-speed node group 20 is completed (step S24), one cycle is completed. Thereafter, the second and subsequent cycles are repeated at a period of 2T according to the above-described procedure.

  As a result of the control described above, the high-speed communication nodes 1 to 4 belonging to the high-speed node group 20 transmit data at the cycle T, while the low-speed communication nodes 5 to 8 transmit data at the cycle 2T. Thus, since each node operates in cooperation, there is no possibility of packet collision.

  In the network configuration of FIG. 1, there is no routing device such as a router between the group of high-speed communication nodes 1 to 4 and the group of low-speed communication nodes 5 to 8, so the packet addressed to the multicast address (224.0.0.100) Reaches not only the high-speed communication nodes 1 to 4 but also the low-speed communication nodes 5 to 8. However, the low-speed communication nodes 5 to 8 discard the packet addressed to the multicast address (224.0.0.100) at the IP layer, and do not perform the process of reconfiguring the packet at the UDP level. Accordingly, the processing load is reduced accordingly.

  As mentioned above, although one Embodiment of the communication processing method concerning this invention was described, it cannot be overemphasized that embodiment is not restricted above.

  For example, the reduction of processing load in a low-speed communication node is not so important, and when the collision avoidance of a packet in the network is the most important issue, the present invention can be implemented using the port number used in the UDP layer. Is possible. Specific examples of this form are listed below.

(1) A port number P1 (for example, 8192) is assigned to data transmission addressed to all nodes, and a port number P2 (for example, 8193) is assigned to data transmission for only the high-speed node group.
(2) The head node sets the combination of the broadcast address and port number P1 as the destination when transmitting data to all nodes, while the broadcast address and port when transmitting data only to the high-speed communication node A combination with the number P2 is set as the destination. The packet of transmission data reaches all nodes.
(3) Among the nodes other than the head node, the low-speed communication node reconstructs the received packet into UDP level data, and then examines the port number. To pass. On the other hand, the high-speed communication node reconstructs all packets into UDP level data and passes them to the upper layer.

  According to the above method, it is possible to implement the present invention while keeping the processing load of the low-speed communication node at least as high as the method 3 described in the related art.

  In the above embodiment, UDP / IP is used as an example of the communication protocol. However, the present invention can be implemented using other communication protocols as long as the protocol has an address group concept.

  In addition to the above, various embodiments are conceivable within the spirit and scope of the present invention.

1 is a schematic configuration diagram of a system to which an embodiment of a communication control method according to the present invention is applied. The figure which shows the procedure of the data transmission operation | movement of the 1st time by the system of FIG. The figure which shows the procedure of the data transmission operation | movement of the 2nd time by the system of FIG.

Explanation of symbols

1 to 4 ... high speed communication nodes 5 to 8 ... low speed communication node 10 ... network 20 ... high speed node group 22 ... low speed node group

Claims (1)

In a communication control method for a periodic communication system including a plurality of nodes connected to a data communication network and each assigned a unique address,
A procedure for dividing the plurality of nodes into a high-speed node group composed of nodes with high communication processing capacity and a low-speed node group composed of nodes with low communication processing capacity;
A procedure for setting a high-speed node designation address for uniformly transmitting data to each node included in the high-speed node group to each node included in the high-speed node group;
A procedure for setting all nodes designated addresses for transmitting data to all nodes in the network, and
A procedure for designating the first node to perform data transmission first in the high-speed node group and causing the node to perform data transmission at a certain period.
With
The first node sets two or more times of data transmission as one cycle, sets the destination of each data in each cycle to either the high-speed node designation address or the all-node designation address according to a predetermined schedule,
Each node other than the first node receives data addressed to the group designation address corresponding to the node group to which the node belongs and data addressed to all the node designation addresses, and next time based on predetermined transmission right information included in the data. If there is a right to transmit data, and if the user has the right to transmit data, the data is transmitted to the same destination as the destination set in the received data. A communication control method.

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