JP2000278301A - Loop-shaped network communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce possibility for a frame on a transmission line to be congested or to collide in the case of transferring the frame having data on the transmission line inside a looped LAN. SOLUTION: Concerning the loop-shaped network communication system for two-way transferring the frames having data while connecting plural nodes N1, N2, N3 and N4 in the shape of loop by a transmission line 16, when the frame prepared by the transmission source node N1, for example, is retransmitted by the respective nodes N2, N3 and N4 and returned to the transmission source node N1 itself, the transmission source node N1 does not transmit the frame again. Thus, the frames transferred inside the transmission line 16 are automatically arranged and possibility for frames on the transmission line to be congested or to collide is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a loop type network communication system mainly used for a control real-time system in which a programmable controller and a computer are connected via a LAN (local area network). The present invention relates to a loop-type network communication system suitable for application to opening / closing control of a gate (sluice gate) in a dam or estuary weir.

[0002]

2. Description of the Related Art For example, in automatic control of a machine tool in a production line of a factory or automatic control in a dam system having a plurality of gates, a plurality of programmable controllers (hereinafter, referred to as PLCs) and these plurality of PLCs are concentrated. A configuration in which a computer device to be managed is connected via a local area network (hereinafter referred to as a LAN), and automatic control is performed by the PLCs on control targets such as gates constituting the machine tool and the dam system. The control system real-time system is adopted.

[0003] In such a control real-time system for controlling a control object, the LAN is required to have various things as described below.

[0004] First, data transmission can be performed according to the degree of urgency. Second, communication quality can be easily improved. Third, it is easy to improve reliability by duplicating transmission paths. Fourth, it is easy to diagnose and automatically recover from a failure.

On the other hand, the LAN has not only a control data transmission service for controlling the control target as described above, but also a voice transmission for making a call between node devices (hereinafter, simply referred to as nodes). Service, video transmission service for displaying the status image of the control object in real time,
There are also demands for various so-called multimedia services, such as a network monitoring service for monitoring the status of a LAN.

Conventionally, in a LAN of such a control real-time system, as a data link layer technology in an OSI reference model, a CSMA / CD system (Carrier
Sense Multiple Access with Collision Detection),
A token bus system, a token ring system, and the like are used.

[0007] As a technique located at the network layer or the transport layer in the OSI reference model, TCP (Transmission Control Protocol) / IP relating to so-called connection-type communication in which handshaking is performed.
(Internet Protocol) and UDP (User D) related to so-called connectionless communication without handshake.
Ata-gram Protocol) / IP is used.

Incidentally, FDDI (Fiber Distributed Data)
Interface), ATM (Asynchronous Transfer Mode)
There are backbone network technologies that use ultra-high-speed transmission lines, but the devices connected to the network are limited, and these backbone network technologies are used in LANs of control real-time systems in which information is closed within the LAN. Utilization is rare because of the high cost of hardware and software.

In these prior arts, even from the position of the reference model of OSI, the setting of urgency and reliability for each service data of various multimedia services and control of congestion are performed in layers higher than the data link layer. Generally supported by protocol.

For example, when the network layer and the transport layer protocols are used separately for each multimedia service, and data loss is allowed but urgency is given priority, UDP / IP is adopted, and reliability is more important than data urgency. When importance is placed on the characteristics, the urgency and reliability of data are differentiated for each service by adopting TCP / IP. Note that a priority is added to the header of an IP datagram to control loss or congestion of the datagram, but generally indicates a handling method on a router.

However, TCP / IP and UDP / I
Due to the nature of P, it is not easy to increase both urgency and reliability. For example, UDP / IP
If it adopts, urgency may be much better than TCP / IP, and a moving image may be able to be reproduced more clearly. However, if congestion control is not performed, the response of other service data may be deteriorated. Also, if TCP / IP is used for important data such as control data, data will almost certainly be sent to the other party, but flow control (adjusting the difference in transmission speed and transmission / reception processing capability between transmission / reception terminals). In order to maintain or maintain the throughput of the network, the network is involved until the data transfer phase, and the user's data flow
May cause a data delay due to a packet switching function for controlling the data transfer.

[0012] Further, if the data link layer close to the physical layer supports the reliability improvement measures by duplicating the transmission path, the hardware cost increases and the cost increases as the number of nodes connected to the network increases. Therefore, in order to reduce hardware cost, a measure for improving reliability by duplicating the transmission path is often realized by a protocol (software) higher than the transport layer. However, if a measure for improving reliability is realized by a protocol higher than the transport layer, a protocol for duplexing becomes complicated (for example, the number of communication sockets in TCP / IP or UDP / IP is doubled, and socket management becomes complicated). Software development costs).

[0013]

SUMMARY OF THE INVENTION The present invention has been made in consideration of such various problems, and enables efficient control of data congestion to reduce occurrence of collision on a transmission line. It is an object of the present invention to provide a loop type network communication system.

Another object of the present invention is to provide a loop-type network communication system capable of setting the urgency and reliability of data transmission with a simple protocol according to data attributes. .

Further, the present invention makes it possible to efficiently control data congestion and reduce occurrence of collisions on a transmission line even when data is looped, or to improve the urgency of data transmission. It is an object of the present invention to provide a loop-type network communication system capable of realizing setting of reliability and reliability by a simple protocol according to data attributes.

[0016]

A loop-type network communication system according to the present invention has a plurality of nodes connected in a loop by a transmission line, and a frame having data is transferred in one direction. In, comprises a source node that creates a frame having data, and each node that retransmits the frame transmitted from the source node, the source node,
When the frame created by the source node itself is retransmitted in each of the nodes and returns to the source node itself, the source node has a function of preventing the frame from being retransmitted. (The invention according to claim 1).

According to the present invention, when the frame created and transmitted by the source node returns, the source node does not retransmit the frame on the transmission path. With this simple protocol, it is possible to reduce the possibility of frame congestion and collision in the transmission path.

In this case, the transmission source node adds urgency information indicating a degree of urgently required data to reach a transmission destination node among the nodes to a header portion of the frame. By having a function of rearranging the frames received from the front node and the frames to be generated and transmitted by the node and transmitted to the rear node in the descending order of urgency based on the urgency information,
For example, a frame including highly urgent information, that is, a frame including highly urgent data can be transmitted to the destination node in a shorter time (the invention according to claim 2).

In the invention according to claim 1, the transmission source node divides the data into a plurality of frames and urgency information indicating the degree to which the data desirably reaches the destination node among the nodes. Is added to the header portion of the frame, and when transmitting the data having a high degree of urgency, the transmission source node transmits the data without dividing the data, and transmits the degree of urgency. When transmitting low data, by having a function of dividing and transmitting data, for example, a frame having newly generated high urgency data,
There is a possibility that the frame can be transmitted to the destination node in a shorter time than a frame having low urgency data generated before that (the invention according to claim 3).

[0020] In this case, the transmission source node:
Even if a frame transmitted without division has passed for a certain period,
By providing a function of retransmitting a frame having the same data from the source node when the node does not return to the source node itself, data having a high degree of urgency can be ensured, in other words, high reliability can be obtained. (Invention of claim 4).

Also, in the loop type network communication system according to the present invention, a plurality of nodes are connected in a loop by a transmission path, and the transmission path is double-looped to generate a frame having data. In a loop-type network communication system in which frames having the same data are transmitted almost simultaneously on the transmission path in both the forward and reverse directions, each node includes a node for retransmitting the frame transmitted from the source node, The source node, when the frame created by the source node itself is retransmitted in each of the nodes and returns to the source node, prevents the source node from retransmitting the frame. It has a function (the invention of claim 5).

According to the present invention, when the frame created and transmitted by the source node returns, the source node does not retransmit the frame on the transmission path. With this simple protocol, even in a so-called double-loop network communication system having a highly reliable transmission path,
It is possible to reduce the possibility of frame congestion and collision on the transmission path.

Also in this case, the transmission source node adds urgency information indicating the degree to which data desirably reaches the destination node out of the nodes to the header of the frame, and each of the nodes By having the function of rearranging the frames received from the front node and the frames generated and transmitted by the node in descending order of urgency based on the urgency information and transmitting the rearranged nodes to the rear node, for example, It is possible to transmit a frame including high information, that is, a data having high urgency to the destination node in a shorter time (the invention according to claim 6).

[0024] Further, in the invention according to claim 5, the transmission source node includes urgency level information indicating a degree of urgency of data to reach a transmission destination node among the nodes,
Adding division information indicating that the data has been divided into a plurality of frames to a frame header, the transmitting node transmits the data without dividing it when transmitting the data having a high degree of urgency, When transmitting data with a low degree of urgency, by having a function of dividing and transmitting the data, for example, a frame having newly generated data with a high degree of urgency can be generated before that. There is a possibility that the data can be transmitted to the destination node in a shorter time than the frame having the low urgency data (the invention according to claim 7).

In this case as well, if the source node does not return to the source node after a certain period of time without any division, the frame transmitted from the source node has the same data. Has a function of retransmitting the data, the data with high urgency can be transmitted reliably, in other words, with high reliability (the invention according to claim 8).

In the invention according to any one of claims 5 to 8, the transmission source node includes a frame generation order number indicating that the newly created frame is a newer frame in the header information of the frame. When a new frame is created and transmitted at the transmission source node, a frame having the latest frame generation order number obtained by updating the last frame generation order number transmitted so far is added to the source node. When transmitting in both directions of the forward loop and the reverse loop, the destination node receives a frame from both directions of the forward loop and the reverse loop, and refers to the data content of the frame in the generation order number of the received frame,
Among the frames having the same generation order number transferred from both directions, by referring to only the data content of the previously received frame, congestion and collision on the transmission line in the duplex loop network communication system can be reduced. (The invention according to claim 9).

Further, in the invention according to any one of the first to ninth aspects, a frame survival counter indicating that the frame is alive is provided in a header portion of the frame, In one of the source nodes, the frame survivor counter presets a desired count value exceeding the total number of nodes constituting the loop, and when each node receives a frame, the node survives the frame survivor counter of the frame. When the count value of the frame alive counter becomes zero at a certain node, the count value of the frame alive counter becomes zero at a certain node. By adopting a configuration having a function of preventing a frame from being retransmitted, even if the source node transmits from the source node, And even when it is not possible to reject such a frame having a data, it is possible to reliably rejecting data which becomes unnecessary by other nodes (the invention of claim 10, wherein).

[0028]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a second embodiment according to the present invention.
1 shows a control real-time system 10 to which a multiplexed loop network communication system is applied.

This control system real-time system 10
Basically, it has four nodes N1, N2, N3, N4 for creating a frame having data, and a transmission line 16 including a loop-like forward loop 12 and a reverse loop 14 for connecting adjacent nodes. . In this embodiment,
In the forward loop 12, the frame is transferred clockwise,
The frame is transferred in the counterclockwise direction in the reverse loop 14.

Each of the nodes N1, N2, N3, N4 creates a frame having data, and transmits the created frame to the transmission lines in the forward and reverse directions almost simultaneously using the forward loop 12 and the reverse loop 14. Of each node (for example, node N
1) is basically a forward node (in this case, node N
It has a function of retransmitting the frame transferred from 4) to the subsequent node (in this case, node N2). Also, each source node, when the frame created by the source node itself is retransmitted in each of the remaining nodes and returns to the source node itself, re-performs the frame at the source node. It has a function to prevent transmission.

As shown in FIG. 2, the node N1 includes a PLC unit (Programmable control unit) 20 as a control unit.
A PLC unit 20A is detachably mounted on the motherboard 22, and is mutually connected by a bus 34 to a CPU (central processing unit) unit (control unit) 24, a power supply unit 2
6, an I / O unit (input / output unit) 28 and a communication unit 40a.

Here, for convenience, the CPU unit 24, the power supply unit 26, and the I / O unit 28
called a. Therefore, the PLC unit 20A constituting the node N1 is composed of the PLC unit 30a and the communication unit 40a.
It is composed of

The I / O unit 28 includes actuators such as cylinders and motors for controlling machine tools and dam gates, not shown, and CCTV (Closed Circuit Television).
ision) Various control devices 36 such as a camera are attached.

The PLC units 20B and 20C constituting the other nodes N2 and N4 also include PLC units 30b and 30c having the same configuration as the PLC unit 20A, and communication units 40b and 40d.

As shown in FIG. 1, the node N3 is configured as a console 44 having a configuration in which a communication unit 40c is mounted on a computer device 46. In the computer device 46, a CPU, a ROM, a RAM, various interfaces, and the like are incorporated in a main body thereof, and a telephone, a television monitor, a display, a keyboard, a speaker, and the like (not shown) are connected to the main body. It has a configuration.

In the computer device 46, the operation status of each of the PLC units 30a, 30b and 30c connected to the network can be recognized in real time through the transmission line 16, and the transmission to the respective PLC units 30a, 30b and 30c is performed. Control instructions can be given through the road 16.

FIG. 3 shows a hardware configuration of the communication unit 40a. Other communication units 40b, 40
The same applies to the configurations of c and 40d.

The communication unit 40a has a bus 50,
The bus 50 includes a communication control unit 52 having the function of a computer and controlling the entire communication unit 40a, and an LS for transmitting and receiving frames on a duplex loop network.
A forward loop frame transmission / reception unit 54 and an inverse loop frame transmission / reception unit 56 configured by I (large scale integrated circuit) are connected.

A telephone 48 is connected to the bus 50 via a telephone interface 47, and the nodes N1 to N
Calls such as meetings between the four parties are possible.

The program of the communication control section 52 is stored in a program code section 58 connected to the bus 50 and constituted by a flash memory (ROM).

Further, a frame delivery table 59 connected to the bus 50 and configured by a flash memory (ROM) stores a frame received through the forward loop frame transmitting / receiving section 54 and the reverse loop frame transmitting / receiving section 56 as an O.
This is a table used to determine whether or not to hand over to the upper layer protocol of the SI reference model, in which the source node number SNO, data identifier DID, and the like of the frame referenced by the node are registered. The registration of the table contents is performed by operating a predetermined switch (not shown) of each node or by downloading from an upper layer protocol.

A forward loop transmission buffer 60 and a reverse loop transmission buffer 62 constituted by a RAM connected to the bus 50 temporarily store a frame received from a forward node and a frame newly generated and transmitted by the node. This is the buffer for recording. This buffer has a queue structure, and is arranged in descending order of urgency URG added to the frame, which will be described later.

A communication control abnormality detection unit 64 employing a watchdog timer mechanism connected to the bus 50 and the communication control unit 52 detects an operation abnormality of the communication control unit 52 and, when detecting an operation abnormality, turns off a buzzer 66. An alarm is generated by sounding or blinking the lamp 68.

The forward loop bypass switching section 7 connected between the forward loop frame transmitting / receiving section 54 and the forward loop 12
0, the reverse loop bypass switching unit 74 connected between the reverse loop frame transmitting / receiving unit 56 and the reverse loop 14,
For example, as shown in FIG. 4 in detail, the forward loop bypass switching unit 70 is configured by relay switches 71 and 72. In a normal case (normal case), the frame is transmitted from the forward node to the forward loop 12, The signal is input to the forward loop frame transmitting / receiving section 54 through the common contact 71a and the fixed contact 71b of the relay switch 71.
a, fixed contact 72b, and forward loop 12 to the rear node.

However, when the communication control abnormality detecting section 64 detects an abnormality in the communication control section 52 or when the communication control abnormality detecting section 64 detects that the node has stopped operating, the reverse loop is performed. Common contacts 71a, 7 of relay switches 71, 72 constituting bypass switching unit 74
2a are switched to the fixed contacts 71c and 72c, respectively, by the control signal from the communication control abnormality detection unit 64, and without passing through the forward loop frame transmission / reception unit 54, in other words,
The frame is sent directly to the rear node in the order of the common contact 71a and the fixed contact 71c from the front node by bypass.

The reverse loop bypass switching section 74 has the same configuration as the forward loop bypass switching section 70, and the communication control abnormality detecting section 64 controls the switching of the internal relay.

FIG. 5 shows data D (also referred to as a data part).
3 shows a configuration example of a frame 90 having T. The frame 90 constitutes a means for implementing a communication protocol in the communication unit 40a (the same applies to the communication units 40b, 40c, and 40d) shown in FIG.

The frame 90 is composed of an HDLC (High Level Data Link Control Procedure) as a basic unit of communication.
e) The frame is adopted. The frame 90 includes a flag sequence portion F (for example, 1 byte of 01111110b) indicating the start and end of the frame 90, a header portion HD having 12-byte header information, control data having a relatively high urgency level, and an urgency level. A data section DT having data such as relatively low audio data or video data,
A 2-byte flag check sequence unit FCS having error correction bits according to the CRC method. The data generated in the data part DT is data requested to be transmitted by the upper layer protocol.

FIG. 6 shows the detailed configuration of the header section HD in the frame 90. At the beginning of the header HD, a destination node number RN for receiving and processing the frame 90
O is added. The node numbers (N1, N2, N3, and N4 in this embodiment) are assigned unique numbers to each node forming the network.

As the transmission destination (reception destination) node number RNO, 32 bytes from 00 to 1Fh (h means hexadecimal notation expressed in binary coded decimal) are assigned in one byte.
However, when the frame 90 is received by a plurality of nodes, a global number FFh (a global number is generally a number in which all bits are set to 1) is used.

The source node number SNO added after the destination node number RNO is the number of the node that generates and transmits the frame 90 in response to a data transmission request from an upper layer protocol. In the example of FIG. 1, nodes N1, N2,
It is enough to have four types of numbers related to N3 and N4,
In this system, 32 bytes from 00 to 1Fh in 1 byte
Have individual parts.

The urgency information URG added after the source node number SNO indicates the degree to which data is to be urgently (as soon as possible) reached from the source node to the destination node and ranges from 00 to 0Fh. We are preparing 16 levels of urgency.

In this embodiment, 00h has the highest urgency. For example, the most urgent data for controlling a control object such as a floodgate in real time is assigned an urgency of 00h to the control data, and then the urgency of 01h is assigned to voice data by telephone or the like. Node N
An urgency of 02h is assigned to status information such as the operation status and the communication status of 1 to N4, and the lowest urgency of 03h is assigned to image data obtained by CCTV or the like.

The division information DIV added next to the urgency information URG includes whether the frame 90 is a frame 90 permitted to be divided, whether the frame 90 is the last one of the divided frames 90, and , Two-byte information indicating where the original data (data before division) is located. The division of the frame 90 is performed only on the data in which the loss of the frame 90 is allowed. Frame 90
The length of the frame 90 is limited for data that can be lost, and the frame 90 is divided when data exceeding the limit value is transmitted. The urgency URG and whether or not to divide the frame 90 are specified by an upper layer protocol of the present protocol when a data transmission request is made.

In this embodiment, the control data of the urgency information URG having the urgency of 00h is not divided because it is desired to reach the destination node as soon as possible and to prevent data loss. On the other hand, audio data, status data, and image data lower than the urgency level 01h are often allowed to be lost. Therefore, the audio data and the moving image data having such a low urgency are divided into frames 90. By dividing the frame 90,
A frame 90 having control data with a high degree of urgency, such as control information generated most recently, can be inserted between frames 90 and transmitted.

One-byte data identifier information (also referred to as data identifier) DI added after the division information DIV.
D assigns, as identifiers, 00 to 0Fh as control data, 10h as image data, 20h as audio data, and FFh as status information. The data identifier DID is provided to identify the type of data stored in the frame, and is defined by an upper layer protocol.

After the data identifier DID, the frame generation source node successively, for each node, in other words, 4-byte frame identification number information (hereinafter, also simply referred to as a frame identification number) assigned by an up-count. ) FNO is connected. The value of the frame identification number FNO is 00000
000 to FFFFFFFFh. The frame identification number FNO is a number for identifying the freshness of the frame. Each time the source node generates and transmits the frame 90, the number is incremented by one for each source node and transmitted.

After the frame identification number information FNO,
1-byte frame survival counter information FL for determining whether the frame 90 is alive, in other words, whether the frame 90 is to be transmitted to the subsequent node.
C is added. In this embodiment, the initial value is preset to 7Fh. The preset desired count value may be any number that exceeds the total number of nodes constituting the loop (for example, in the example of FIG. 1, if the total number of nodes exceeds four, FLC = 06h). The nodes are
When the frame 90 is received, the count value preset in the survival counter information FLC of the frame 90 is decremented by 1 (so-called preset down counting), and at a certain node, the count value of the frame survival counter information FLC becomes zero. 00h, the certain node
The frame 90 in which the count value of the frame survival counter information FLC becomes zero is deleted without being retransmitted.

As described above, the frame survival counter information F
LC is a counter provided in consideration of network failure. For example, in a normal case, a frame 90 is generated and transmitted at the source node, and when the frame 90 goes around the network and returns to the source node, the frame 9 is transmitted.
0 is deleted (discarded). However, as a practical matter, it cannot be said that there is no possibility that some failure occurs in the source node before the frame 90 returns to the source node, and the frame 90 cannot be discarded. In such a state, the frame 90 goes around the network forever, so that the frame in the transmission line 16 is congested, and as a result, the substantial transfer speed of the frame 90 in the network is reduced. In order to avoid this problem, when generating and transmitting the frame 90, a value larger than the number of nodes forming the network is added as a frame survival counter value, and when the frame 90 is received by another node, the counter is added. The frame 90 is deleted (discarded) at the node where the value is subtracted by 1 and the counter value becomes zero.

After the frame survival counter information FLC, 1-byte data length information LEN is added. The data length information LEN is a numerical value of 00 to 7Fh and represents a data length of 0 to 128 bytes, that is, a data size.

Next, the operation of this embodiment will be described. In the following description, an embodiment in which redundancy is taken into consideration will be described. However, for example, when a duplex loop network communication system is not required, for example, when the reliability is not so required, cost reduction can be achieved. A control real-time system 100 to which a single loop type network communication system as shown in FIG.

Actually, even in a duplex loop, a state may occur in which the frame 90 can be transferred by only one of the loops, such as a case where one of the loops is cut off. The operation can be continued in any of the loops.

FIG. 8 is a flowchart showing a receiving process of each of the communication units 40a, 40b, 40c and 40d in this embodiment. The control subject is the communication control unit 52 of each communication unit 40a, 40b, 40c, 40d.

In step S 1, when the frame 90 is transmitted from the forward node of the forward loop 12, the forward loop frame transmitting / receiving unit 54 receives the frame 90. Further, when the frame 90 is transmitted from the front node of the reverse loop 14, the frame 9 is
0 is received. The frame 90 received by the forward loop frame transmission / reception unit 54 and / or the reverse loop frame transmission / reception unit 56 is transferred to the communication control unit 52.

In step S2, the communication control unit 52 determines whether or not the frame 90 has been transmitted by the own node, based on the source node number SNO. If the frame 90 is transmitted by the own node, it is discarded (deleted) in step S3.

Next, if the determination in step S2 is negative, in step S4, the communication control unit 52 decrements the frame survival counter information FLC by one.

Next, in step S5, if the count value (count value) of the frame survival counter information FLC after the subtraction is 0, the frame 90 is determined in step S6.
Discard.

If the count value is not 0, step S
7, the communication control unit 52 determines whether the received frame 9
Whether to pass 0 to the upper layer protocol is determined by referring to the frame delivery table 59 and the frame identification number FNO of the frame 90.

That is, the frame 90 is the frame 90 registered in the frame delivery table 59, and the frame identification number F of the frame 90
If NO indicates a newer value than the frame identification number FNO of the frame 90 previously transmitted by the source node of the frame 90, the data DT included in the frame 90 is transferred to the upper layer in step S8. It is delivered to the PLC units 30a, 30b, 30c and the computer device 46 via a protocol.

In this case, the upper layer protocol is the communication unit 40a, 40b, 40d, 40c and the corresponding PLC.
Units 30a, 30b, 30c and computer device 46
Control the interface with the communication unit 4
Frames 90 received at 0a, 40b, 40c, 40d
PLC units 30a, 30b, 30c corresponding to the data in
And a data format that can be handled by the computer device 46. Further, the upper layer protocol controls a communication sequence such as a frame division process and a frame synthesis process for voice processing.

In step S8, the communication control unit 52 refers to the division information DIV and
Is a divided frame 90, the data is reassembled and delivered.

When the latestness of the frame 90 is determined by the frame identification number FNO, the communication control unit 52
It is necessary to record the latest frame identification number FNO for each transmission source node. However, instead of recording the frame identification number FNO of the transmission source node separately for the forward loop 12 and the reverse loop 14, the frame identification number FNO of the transmission source node combining both the forward loop 12 and the reverse loop 14 is recorded. The forward loop 12 and the reverse loop 14
Among them, only the frame 90 received earlier can be delivered to the upper layer protocol.

Next, in step S9, the communication control unit 52 stores the frame 90 in the forward loop transmission buffer 60 if the frame 90 has been received in the forward loop 12 irrespective of whether or not the frame 90 has been delivered to the upper layer protocol.
Is recorded, and if the frame 90 is received in the reverse loop 14, the frame 90 is stored in the reverse loop transmission buffer 62.
Record

At this time, the frames 90 are recorded in the forward loop transmission buffer 60 and the reverse loop transmission buffer 62 in descending order of urgency URG. Forward loop transmission buffer 60,
Frame 9 temporarily recorded in reverse loop transmission buffer 62
“0” is transmitted to the subsequent node in the transmission processing described below. The above is the description of the processing in frame reception.

Next, the processing of the communication control unit 52 when a data transmission request is made from an upper layer protocol will be described with reference to FIG.
This will be described with reference to the flowchart of FIG.

In step S11, when there is a data transmission request from the upper layer protocol, the communication control unit 5
In step 2, when a data transmission request is received from the upper layer protocol, the data is referred to the data identifier DID and the data length LEN, and the data is dividable and the data exceeds the maximum frame length of 128 bytes. In step S12, the frame 90 is divided into a plurality of frames with an upper limit of 128 bytes.

In step 13, a frame identification number FNO is added to each of the divided frames 90, and the number is incremented by one for each frame 90.

That is, each time a new frame 90 is generated and transmitted, the frame identification number FN obtained by adding one to the value is added.
O is added.

Next, in step S15, the communication control unit 52 records the generated frame 90 in the forward loop transmission buffer 60 and the reverse loop transmission buffer 62. In this case, a frame 90 having the same data and having the same frame identification number FNO is recorded in the forward loop transmission buffer 60 and the reverse loop transmission buffer 62. At the time of recording, the frames are recorded in the forward loop transmission buffer 60 and the reverse loop transmission buffer 62 in the order from the highest urgency URG. By doing in this way, even if a frame 90 with a low urgency URG is received from a forward node, if transmission of data with a high urgency URG occurs in the own node, the frame 90 with a high urgency URG is transmitted. Transmission can be given priority. The above is the embodiment when the data transmission request is made from the upper layer protocol.

Next, the transmission processing of each node will be described with reference to FIG.
This will be described with reference to the flowchart of FIG.

In step S16, the communication control unit 52
When determining that the frame 90 exists in the forward loop transmission buffer 60, in step S17,
The frames 90 are taken out in descending order of RG, and the frames 90 are delivered to the forward loop frame transmitting / receiving section 54 (the frames 90 are written).

Next, in step S 18, the forward loop frame transmission / reception section 54 sends the frame 9 to the rear node of the forward loop 12 via the forward loop bypass switching section 70.
Send 0.

The communication control unit 52 determines in step S19
In step S20, when it is determined that the frame 90 exists in the reverse loop transmission buffer 62, the frame 90 is taken out in descending order of the priority URG, and delivered to the reverse loop frame transmitting / receiving unit 56 (writing the frame 90).

Next, in step S 21, the reverse loop frame transmission / reception section 56 sends the frame 9 to the rear node of the reverse loop 14 via the reverse loop bypass switching section 74.
Send 0.

Next, the retransmission processing of the frame 90 will be described with reference to the flowchart of FIG. In step S22, the communication control unit 52 determines that the frame transmitted by the own node does not return after a certain period of time due to the loss of the frame 90 (however, the forward loop 12, the reverse loop 1
If the frame 90 returns in any one of the four cases, it means that the frame has gone around the network. ), The frame 90 is stored in step S
In step 24, if the frame is not permitted to undergo data division in step 23,
Retransmit 0.

When the data is not lost and when the frame 90 permits data division, the process returns to the step S11 without retransmitting in the step S25.

The reason why the data is not retransmitted in the case of the frame 90 permitting the data division is to provide a simple retransmission procedure. Normally, when the upper layer protocol requests the data transmission of the data identifier DID to be retransmitted at present, the control data in the control real-time system discards old data, At this point, retransmission is terminated because the contents of the data must be transmitted in real time (immediately).

As described above, according to the above embodiment,
A header section HD is provided in the frame 90 having the data DT, and an urgency URG, a data identifier DID indicating a data type, a frame survival counter, and the like can be added to the header section HD. For this reason, it is possible to give the degree of urgency, the degree of reliability, or the like as an attribute of the frame 90 according to the content of the data DT. In a communication system, there is a possibility that optimal data transmission with less frame congestion and collision can be performed.

The present invention is not limited to the above-described embodiment, but can adopt various configurations without departing from the gist of the present invention.

[0091]

As described above, according to the present invention, the source node does not retransmit on the transmission path when the frame created and transmitted by the source node returns. Is adopted. By adopting this protocol, frames transferred in the transmission path are automatically arranged, and the effect of reducing the possibility of frame congestion or collision on the transmission path can be achieved.

Further, according to the present invention, it is possible to set urgency and reliability for each multimedia service, and to operate the system urgently and reliably from the source node to the destination node. When transmitting important data that the user wants to reach, it is possible to increase both the urgency and reliability by increasing the urgency and transmitting the data without dividing the frame. The reliability can be further improved by forming the data into a double loop.

Further, when most of the present protocol is realized by software, the communication protocol is simplified, and the effect of reducing software development costs is achieved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of a control real-time system to which a duplex loop network communication system according to an embodiment is applied.

FIG. 2 is a block diagram illustrating a configuration example of a node related to a PLC in the example of FIG. 1;

FIG. 3 is a block diagram showing a configuration of a communication unit in the example of FIG. 1;

FIG. 4 is a block diagram showing a configuration of a forward loop bypass switching unit in the example of FIG. 3;

FIG. 5 is an explanatory diagram showing a structure of a frame for transferring a loop.

FIG. 6 is an explanatory diagram showing a structure of a header portion in a frame.

FIG. 7 is a block diagram showing a configuration of a control real-time system to which a loop type network communication system without a double loop is applied.

FIG. 8 is a flowchart provided to explain an operation at the time of frame reception in the example of FIG. 1;

FIG. 9 is a flowchart (1/3) used to describe an operation at the time of frame transmission in the example of FIG. 1;

FIG. 10 is a flowchart (2/3) used to describe an operation at the time of frame transmission in the example of FIG. 1;

FIG. 11 is a flowchart (3/3) used to describe an operation when transmitting a frame in the example of FIG. 1;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Real-time system 12 ... Forward loop 14 ... Reverse loop 16 ... Transmission line 20A-20C ... PLC unit 22 ... Motherboard 24 ... CPU unit 26 ... Power supply unit 28 ... I / O unit 30a-30c
... PLC units 34, 50 ... buses 40a to 40d
... Communication unit 46 ... Computer device 52 ... Communication control unit 54 ... Forward loop frame transmission / reception unit 56 ... Reverse loop frame transmission / reception unit 58 ... Program code unit 59 ... Frame delivery table 60 ... Forward loop transmission buffer 62 ... Reverse loop transmission buffer 64 ... Communication control abnormality detection unit 66 Buzzer 68 Lamp 70 Forward loop bypass switching unit 71, 72 Relay switch 74 Reverse loop bypass switching unit 90 Frame N1, N2, N
3, N4 node DT data (data portion) F flag sequence portion FCS flag check sequence portion HD header portion

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yasushi Takizawa 5-1-1 Shimorenjaku, Mitaka City, Tokyo Japan Radio Co., Ltd. (72) Inventor Eiji Ikari 5-1-1 Shimorenjaku, Mitaka City, Tokyo Japan Radio (72) Inventor Hiroyasu Shibata 2-10-19 Ueda, Ueda City, Nagano Prefecture Inside Ueda Nippon Radio Co., Ltd. (72) Inventor Takehiro Shimizu 2-10-19, Ueda City, Nagano Prefecture Ueda Within Nippon Radio Co., Ltd. (72) Inventor Kazuto Ogawa 2-10-19, Ueda-shi, Nagano Prefecture Inside Ueda Nippon Radio Co., Ltd. No. Ueda Nihon Radio Co., Ltd. F term (reference) 5K030 GA03 HA08 HB15 HB17 HC14 JA07 KA03 LA01 LC18 LE14 5K031 AA01 CB01 CB09 CB10 CC04 DA12 DB11

Claims (10)

[Claims] 1. A loop-type network communication system in which a plurality of nodes are connected in a loop by a transmission path and a frame having data is transferred in one direction, a transmission source node for creating a frame having data, Each node for retransmitting a frame transmitted from a source node, wherein the source node retransmits a frame created by the source node itself in each node, and the source node itself A loop-type network communication system having a function of preventing the source node from retransmitting the frame when returning to the above. 2. The loop-type network communication system according to claim 1, wherein the transmission source node transmits, to the transmission destination node among the nodes, urgency information indicating the degree to which data is desirably urgently transmitted. Each node has a function of rearranging a frame received from a front node and a frame generated and transmitted by the node in descending order of urgency based on the urgency information, and transmitting the rearranged node to the rear node. A loop type network communication system characterized by the above-mentioned. 3. The loop-type network communication system according to claim 1, wherein the transmission source node transmits a plurality of pieces of urgency information and data indicating the degree to which the data desirably reaches the transmission destination node among the nodes. And adding division information indicating that the frame has been divided into a header portion of the frame, the transmission source node transmits the data without dividing when transmitting the data having a high degree of urgency, and A loop-type network communication system having a function of dividing and transmitting data with low urgency. 4. The loop type network communication system according to claim 3, wherein the source node does not return to the source node itself even if a frame transmitted without division has passed for a predetermined period. A loop-type network communication system having a function of retransmitting a frame having the same data from a transmission source node. 5. A transmission path in a forward direction and a reverse direction from a transmission source node that creates a frame having data, wherein a plurality of nodes are connected in a loop by a transmission path, and the transmission path is double-looped. A loop type network communication system in which frames having the same data are transmitted substantially simultaneously, comprising: a node for retransmitting a frame transmitted from the transmission source node; wherein the transmission source node is the transmission source node itself. Wherein the loop created by the above-mentioned node has a function of preventing the frame from being retransmitted at the source node when the frame is retransmitted at each node and returned to the source node. Communications system. 6. The loop type network communication system according to claim 5, wherein the transmission source node transmits urgency information indicating a degree of urgently required data to reach a transmission destination node among the nodes, in a header portion of the frame. Each node has a function of rearranging a frame received from a front node and a frame generated and transmitted by the node in descending order of urgency based on the urgency information and transmitting the rearranged node to a rear node. A loop type network communication system characterized by the above-mentioned. 7. The loop-type network communication system according to claim 5, wherein the transmission source node includes a plurality of pieces of urgency information indicating a degree of urgency of the data to reach a transmission destination node among the nodes. And adding division information indicating that the data has been divided into frames to a frame header. When transmitting the data having a high degree of urgency, the source node transmits the data without dividing the data, A loop-type network communication system having a function of dividing data when transmitting low-grade data and transmitting the divided data. 8. The loop-type network communication system according to claim 7, wherein the transmission source node returns to the transmission source node when the frame transmitted without division has not returned to the transmission source node even after a certain period has elapsed. A loop-type network communication system having a function of retransmitting a frame having the same data from a transmission source node. 9. The loop type network communication system according to claim 5, wherein the transmission source node sets a frame generation order number indicating that the newly created frame is a newer frame. A function of adding to the header information of the frame, a new frame generation sequence number that updates the last frame generation sequence number transmitted so far when a new frame is created and transmitted at the source node. Is transmitted in both directions of the forward loop and the reverse loop, and the destination node receives frames from both directions of the forward loop and the reverse loop, and generates frame data in the generation order number of the received frame. When referring to the contents, of the frames received from both directions and having the same generation order number, Loop network communication system, characterized in that reference only. 10. The loop type network communication system according to claim 1, wherein a frame survival counter indicating that the frame is alive is provided in a header portion of the frame, In the transmission source node that is the generation source of, the frame survival counter is preset with a desired count value exceeding the total number of nodes constituting the loop, and when each node receives a frame, When the count value of the frame alive counter becomes zero at a certain node, the certain node determines that the count value of the frame alive counter is zero. A loop-type network communication system having a function of preventing retransmission of a frame having a value. Stem.