JPH11298503A - Monitoring system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a monitoring system by avoiding collision of transmission from each node and eliminating missing of transmission data if the collision should occur when simultaneous multiple address communication is conducted by using a user datagram protocol UDP/Internet protocol IP. SOLUTION: An Ethernet interface 3 for personal computers 1A, 1B and programmable controllers 21 -2N is provided with a simultaneous multi-address communication function 35 . This simultaneous multi-address communication function 35 specifies a transmission size, assigns a block number being an identifier of the transmission data, decides a data transmission interval and a data transmission period depending on the block number and sets/revises a transmission interval of its own node based on a relation between presence of reception of simultaneous multi-address communication data and a time limit of a transmission wait timer from the block number and other node to avoid collision of transmission data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a monitoring system in which computers are connected to each other via a network via Ethernet, and more particularly, to a data collision avoidance process in broadcast in the system.

[0002]

2. Description of the Related Art Ethernet uses a coaxial cable as a data transmission medium, and enables communication between computers through a CSMA / CD (collision detection type carrier wave multiplexing LAN access) interface.

In the monitoring system, a personal computer is used as a host computer in place of a conventional workstation or minicomputer, and a monitoring controller is connected to the programmable controller by Ethernet to communicate monitoring information.

These personal computers and programmable controllers use a TCP / IP protocol (Transmission system) as an interface for communication using Ethernet.
onControlProtocol / Interne
When implementing tProtocol), a broadcast function for sharing the same data among the nodes is provided by UDP / IP (U
This is realized by using “serDatagramProtocol”.

[0005]

In the Ethernet, when the transmission of each node collides, the collision is detected at the LSI level of the Ethernet and the transmission timing is shifted to prevent the loss of the frame data.

[0006] For this reason, when simultaneous broadcast communication is performed using UDP / IP, it is common that transmission timing is not defined between nodes that transmit simultaneous broadcast data. As a result, in the worst case, the transmitted data may not be received by the partner node.

SUMMARY OF THE INVENTION An object of the present invention is to provide a monitoring system which performs simultaneous broadcast communication using UDP / IP, avoids collisions in transmission from each node, and eliminates loss of transmission data even in case of collision. To provide.

[0008]

According to the present invention, in order to solve the above-mentioned problems, a plurality of nodes to be a computer or a programmable controller are connected by Ethernet, and each node has a UD having an Ethernet interface.
In a monitoring system for performing broadcast using P / IP, each interface of each of the nodes defines a transmission size of broadcast transmission data and assigns a block number serving as an identifier of the transmission data; Processing means for determining a data transmission interval determined by the block number and a transmission cycle determined by the maximum value of the block number; and setting a time limit of a transmission wait timer longer than the transmission cycle and starting up, and When the broadcast data is not received from the node, the data of the block number of the own node is transmitted, and the basic block number is set to the block number assigned to the own node, and the time limit of the transmission waiting timer is defined as the transmission period. The first initial processing means, and the time limit of the transmission wait timer, which is set longer than the transmission cycle, is activated, and another transmission is started within the transmission cycle. The block number of the data received when the broadcast data from the broadcast node is received is used as the basic block number, and the size of this basic block number is compared with the block number of the local node. When the transmission timer expires after the second initial processing means to be activated and the processing by the first or second initial processing means are completed, the data of the block number of the own node is transmitted and the time limit of the transmission timer is transmitted. Restarts at the cycle, and receives broadcast data from another node before the transmission timer expires, and sets the time limit of the transmission wait timer when the received block number matches the basic block number set in the local node. Normal processing means for resetting and restarting.

[0009]

FIG. 1 is a block diagram of a main part of a monitoring system according to an embodiment of the present invention. PC 1A, 1B
It was a host computer, programmable controller 2 ₁ to 2 _N is an Ethernet connection.

The personal computers 1A and 1B and the programmable controllers 2 ₁ to 2 _N are connected to the programmable controller 2
_As shown in FIG. ₁ , an Ethernet interface 3 for obtaining an intercommunication function is provided. The illustrated interface 3 shows only a broadcast function using UDP / IP. Further, the processor 4 shows only a user memory 5 for storing transmission / reception data in the broadcast communication.

[0011] interface 3, in addition to the physical layer 3 ₁ and the data link layer 3 ₂ and IP3 ₃ and UDP3 _4, in this embodiment provided with a broadcast function ₃₅ all together at the junction of the processor 4. The broadcast function 3 to _5, the data link layer 3 ₂ and I
It is the same way software configuration and P3 ₃ and UDP3 _4.

[0012] Each node broadcast function ₃₅ provided (PC 1A, 1B, the programmable controller 2 ₁ to 2 _N), respectively, in order to avoid transmission collisions, comprising means for each node creates a transmission timing in each . For this reason, the concept of the block number BN is introduced into the broadcast transmission data.

The block number BN is an identifier of data, so that there is no duplicate block number in one network. That is, when a certain node transmits data of block number BN = X, other nodes in the same network are prohibited from transmitting data of block number BN = X.

The block number BN defines the offset position of the memory shared by each node in the broadcast function, and is also a factor for defining the transmission size.

FIG. 2 shows an example of assigning a block number to the broadcast shared memory (4096 words). One block is defined as 128 words, and the maximum value of the block number is 32. Each block numbers 1 to 32, for example, assign a block number BN = 1 on the transmission region of the PC 1A, assigning a block number BN = 3 in the programmable controller 2 _1. FIG. 3 shows an example of this assignment.

The broadcast function ₃₅ avoids collision of transmission data by controlling the block number BN assigned to each node as the transmission order. The control of the transmission order is determined by the transmission interval and the transmission cycle. The transmission interval is specified time T between block number N and block number N + 1.
The transmission cycle is a cycle of the broadcast communication represented by a time obtained by multiplying the maximum block number BN _MAX in the network by the transmission interval T.

FIG. 4 shows the relationship between the transmission interval and the transmission cycle, where the maximum block number BN _MAX = 5 at a transmission interval of 30 ms.
In this case, the transmission cycle is 150 ms.

[0018] By setting the allocation and transmission period, the transmission interval of the block number to above, the broadcast function _35, normal shown in processing and 6 at initial shown in Figure 5 for collision avoidance of transmission Perform processing. These processes will be described in detail below.

In FIG. 5, first, the transmission waiting timer is set to a time period slightly longer than the transmission cycle and started (S1).
It monitors data reception from other nodes and checks whether there is simultaneous broadcast reception (S2).

When there is no broadcast data reception and the transmission waiting timer times out (S3), it is determined that the own node has started up first in the same network, and the data of the block number BN assigned to the own node is transmitted. Then, the data that becomes the basic block number is set as the block number of the own node (S5). Then, the timer is restarted with the time limit of the transmission waiting timer set as the transmission period (S6).

As a result, the own node is assumed to have started up first, the time limit of the transmission wait timer is set to a minimum value (transmission cycle), and simultaneous broadcast is permitted during this minimum time.

In step S2, if simultaneous broadcast reception is performed before the transmission wait timer expires, it is determined that another node has already been started, and transmission of the own node is performed based on the block number of that node. In order to create the timing, first, the transmission waiting timer is stopped (S7). Then, the block number of the received broadcast data is set as the basic block number (S8).

Next, it is checked whether or not the basic block number is smaller than the block number assigned to the own node (S9).

[0024]

[Equation 1] (block number of own node−basic block number) × transmission interval is reset, and a transmission waiting timer is started (S10).

Conversely, when the basic block number is larger than the block number of the own node, the time limit of the transmission wait timer is set as follows:

[0026]

[Equation 2] (maximum block number− (basic block number−block number of own node)) × transmission interval is reset, and a transmission waiting timer is started (S11).

Therefore, when a broadcast is received from another node, the timer period of the own node is set based on the difference from the block number of the other node and the transmission interval, and the broadcast in this timer period is performed. Allowed.

FIG. 6 shows the broadcast processing after the timer time limit is set by the processing of FIG. In FIG.
It is checked whether or not the transmission wait timer has expired (S21). When the time has expired, the data of the block number of the own node is transmitted (S22), the time limit of the transmission wait timer is set to the transmission cycle, and the timer is restarted. Start (S2
3) Wait for the next time-up (S21).

When the transmission waiting timer has not expired, the apparatus waits for simultaneous broadcast reception (S24). When simultaneous broadcast reception has occurred, the reception block number and the processing S5 or S8 are performed.
It is checked whether the basic block number matches the basic block number set in step (S25). If not, the broadcast data of the basic block number is received as it is while the transmission wait timer is operating (S21).

When the reception block number matches the basic block number, the time limit of the transmission waiting timer is processed in step S10 or S10.
The value is reset to the value set in 11 (S26).

With the above-described normal processing, the broadcast data is transmitted at the shortest transmission cycle when the transmission waiting timer expires (S22, S23). Then, when broadcast data is received from another node while the transmission waiting timer is waiting for time-up, the time limit of the transmission waiting timer of the own node is reset (S24 to S26). Thus, the deviation of the accuracy of the timer clock between the nodes is corrected within one cycle of the broadcast, always starting from the reception of the basic block number.

[0032]

As described above, according to the present invention, the transmission interval of each node is specified by the block number, so that the transmission from each node does not collide and the loss of the transmission data is ensured. There is an effect that can be prevented.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram showing an embodiment of the present invention.

FIG. 2 is an area of a broadcast shared memory according to the embodiment;

FIG. 3 is an example of assignment of block numbers BN in the embodiment.

FIG. 4 is a diagram illustrating a relationship between a transmission interval and a transmission cycle in the embodiment.

FIG. 5 shows an initial processing procedure of a broadcast function in the embodiment.

FIG. 6 shows a normal processing procedure of a broadcast function in the embodiment.

[Explanation of symbols]

1A, 1B ... PC _{2 1, 2 2, 2 N} ... Programmable controller 3 ... interface 3 ₅ ... broadcast function 4 ... Processor

Claims (1)

[Claims] 1. A method in which a plurality of nodes to be a computer or a programmable controller are connected to each other via Ethernet,
Each node has a U
In a monitoring system for performing broadcast using DP / IP, each interface of each of the nodes defines a transmission size of broadcast transmission data and assigns a block number serving as an identifier of the transmission data; A processing means for determining a data transmission interval determined by the block number and a transmission cycle determined by the maximum value of the block number; and setting a time limit of a transmission wait timer longer than the transmission cycle and starting up. When the broadcast data is not received from the node, the data of the block number of the own node is transmitted, and the basic block number is set to the block number assigned to the own node, and the time limit of the transmission wait timer is defined as the transmission cycle. A first initial processing means for setting the time limit of the transmission wait timer to be longer than the transmission cycle, The block number of the data received when broadcast data from another node is received is used as the basic block number, and the time limit of the transmission wait timer is set by comparing the size of this basic block number with the block number of the own node. A second initial processing means for restarting, and after the processing by the first or second initial processing means, when the transmission timer times out, transmits the data of the block number of the own node and sets the time limit of the transmission timer. Restart after the transmission cycle, receive the broadcast data from another node before the transmission timer expires, and set the time of the transmission wait timer when the received block number matches the basic block number set in the local node. A normal processing means for resetting and restarting the system.