JP6835662B2 - Node and frame transmission control method - Google Patents

Description

The present invention relates to a frame transmission control technique for transmitting a frame between a plurality of nodes connected to a communication path by a bus.

Conventionally, BACnet (Building Automation and Control Network: registered trademark), which is a communication protocol for intelligent building networks, has been used as one of the communication methods for performing data communication between a plurality of nodes connected to a communication path by bus. It is used (see, for example, Patent Document 1).

Among such BACnets, a method called MS / TP is a master-slave communication method in which data communication is performed between a master node and a slave node, and a token passing communication method in which a token frame indicating a transmission right is circulated between nodes. This is a method of performing data communication by transmitting and receiving frames between a plurality of nodes connected to a communication path by bus in combination with.

In this MS / TP method, an address called a BACnet address is assigned in advance to each node connected to the bus connection type network. When sending a frame from an arbitrary node, the address of the node that is the destination is used as the destination address, and the own address is stored in the frame as the source address for transmission. At this time, since each node is connected to the communication path by bus, all the nodes can receive all the frames flowing on the communication path. Therefore, each node takes in the frame whose destination address matches the own node address among the received frames, and executes a predetermined application process in the upper layer.

Japanese Unexamined Patent Publication No. 2013-171388

However, in such a conventional technique, since the upper layer does not have a configuration for confirming the validity / invalidity of the address, it is actually assigned to the node at any node in response to the frame transmission request from the upper layer. There was a problem that the throughput of the entire system was reduced when the frame was sent to an invalid address.

FIG. 3 is a sequence diagram showing a conventional frame transmission operation. When a frame transmission with an invalid destination address is requested by the upper layer processing unit at an arbitrary node (step 200), the data link processing unit waits for the reception of a token from another node indicating the frame transmission authority. (Step 201), a frame is transmitted in response to the receipt of the token (step 202).

After that, a reply from the destination node is waited (step 203), but the reply does not arrive from the destination node because the destination address is invalid, and a timeout occurs. Due to this timeout, the data link processing unit determines that the transmission has failed (step 204), and transmits a token indicating the frame transmission authority to another node (step 205).
At this time, the judgment time from the frame transmission request to the transmission failure judgment is the token waiting time from the frame transmission request to the token reception, the token processing time from the token reception to the frame transmission, and the maximum reply wait from the frame transmission to the timeout. It is calculated by adding the time, and it is about 300 milliseconds in general implementation.

Therefore, during this period, the node cannot send and receive frames, and tokens cannot be passed to other nodes, so that frames cannot be sent and received by other nodes, and the throughput of the entire system is reduced by the time required for a series of determinations. Further, in the MS / TP method BACnet, if the number of nodes that cannot communicate increases for some reason, frame transmission to an invalid address may occur, and the throughput of the entire system may decrease in the same manner as described above. ..

The present invention is intended to solve such a problem, and an object of the present invention is to provide a data communication technique capable of avoiding a decrease in throughput due to frame transmission to an invalid address.

In order to achieve such an object, the node according to the present invention is used in a communication system composed of a plurality of nodes connected to a communication path by a bus, and is a communication method combining a master-slave communication method and a token passing communication method. A data link processing unit that is a node that performs data communication with each other by transmitting and receiving frames based on the above, and transmits and receives the frame to and from the node via the communication path, and the frame. By performing data communication with the node, the address information included in the upper layer processing unit that executes predetermined higher application processing and the reception frame received by the data link processing unit is acquired and used by the node. In response to a frame transmission request from the upper layer processing unit and the address management unit that manages the existing address, the destination address specified in the frame transmission request is compared with the existing address, and the destination is compared. When the address is the existing address, the frame transmission request is notified to the data link processing unit, and when the destination address is not the existing address, the transmission possibility determination unit for discarding the frame transmission request is provided. The data link processing unit transmits the specified frame to the specified destination address in response to the frame transmission request from the transmission availability determination unit.

Further, in one configuration example of the node according to the present invention, the data link processing unit designates the address of the node as a destination address and the own address as a source address. A polling frame for management is periodically transmitted, and when the address management unit acquires address information from the reception frame, the polling exchanged between nodes other than the own node received by the data link processing unit is performed. The source address is acquired from the frame and managed as the existing address.

Further, in the frame transmission control method according to the present invention, a plurality of nodes connected to the communication path by bus transmit and receive frames based on a communication method that combines a master-slave communication method and a token passing communication method. A frame transmission control method used by the node in a communication system that performs data communication between the two, a data link processing step in which the data link processing unit transmits and receives the frame to and from the node via the communication path. The upper layer processing unit executes data communication with the node using the frame to execute a predetermined upper application process, and the address management unit is the data link processing unit. The address management step that acquires the address information included in the received frame received in step 2 and manages it as an existing address used by the node, and the transmission availability determination unit respond to the frame transmission request from the upper layer processing unit. , The destination address specified in the frame transmission request is compared with the existing address, and if the destination address is the existing address, the frame transmission request is notified to the data link processing unit, and the transmission is performed. When the destination address is not the existing address, the transmission possibility determination step of discarding the frame transmission request is provided, and the data link processing step is designated in response to the frame transmission request from the transmission possibility determination unit. It includes a step of transmitting a specified frame to a destination address.

Further, in one configuration example of the frame transmission control method according to the present invention, the data link processing step specifies the address of the node as the destination address and the own address as the source address for management polling. The address management step includes a step of periodically transmitting a frame, and the address management step includes the polling frame received by the data link processing unit and exchanged between nodes other than the own node when acquiring address information from the received frame. It includes a step of acquiring the source address from the above and managing it as the existing address.

According to the present invention, the frame transmission is performed only to the valid address assigned to the actual node, and the frame transmission to the invalid address not assigned to the node is suppressed. Therefore, it is possible to avoid a decrease in throughput of the entire system caused by frame transmission to an invalid address.

It is a block diagram which shows the structure of a communication system. It is a sequence diagram which shows the processing operation of a node. It is a sequence diagram which shows the conventional frame transmission operation.

Next, an embodiment of the present invention will be described with reference to the drawings.
[Communications system]
First, the communication system 1 according to the present embodiment will be described with reference to FIG. FIG. 1 is a block diagram showing a configuration of a communication system.

As a whole, this communication system 1 is a communication system used in a monitoring control system that monitors and controls building equipment and plant equipment, and is a master-slave communication system between a plurality of nodes 10 bus-connected to the communication path L. It is a communication method that combines token passing communication methods, and has a function to perform data communication by transmitting and receiving frames.

In general, in a monitoring control system that monitors and controls building equipment and plant equipment, communication devices having various functions such as information collection function and control function are connected via a communication network as nodes, and data communication is performed between these nodes. As a result, the central monitoring device monitors and controls individual equipment. In such a monitoring control system, data communication in a higher-level application is realized by exchanging frames for data communication between each node.

A communication method such as BACnet MS / TP is a communication method that combines a master-slave communication method in which data communication is performed between a master node and a slave node and a token passing communication method in which a token frame indicating a transmission right is circulated between the nodes. It is a method.
In such a communication method, since network management such as detection of the existence of another master node is performed, each node specifies the address of the other node as the destination address and the own address as the source address for management. It has a function to periodically transmit the polling frame of. Further, since each node is connected to the communication path L by bus, it is possible to receive frames exchanged between other nodes, for example, a polling frame for management.

In the present invention, the source address included in the frame exchanged between other nodes in such a communication method, for example, the management polling frame transmitted periodically, is the node of the node actually connected to the communication path. It focuses on the address, that is, a valid existing address. Then, these existing addresses are acquired and managed in advance, and the frame is transmitted only when the specified destination address is the existing address in response to the frame transmission request from the upper layer. is there. As a result, frame transmission to an invalid address is suppressed, and as a result, a decrease in throughput is avoided.

[node]
Next, the configuration of the node 10 according to the present embodiment will be described with reference to FIG.
The node 10 is provided with a communication I / F unit 11, a data link processing unit 12, an upper layer processing unit 13, an address management unit 14, and a transmission availability determination unit 15 as main functional units. Among these functional units, the data link processing unit 12, the upper layer processing unit 13, the address management unit 14, and the transmission availability determination unit 15 are realized by an arithmetic processing unit in which the CPU and the program cooperate with each other.

The communication I / F unit 11 has a function of transmitting and receiving frames by transmitting data to and from another node 10 via the communication path L.
The data link processing unit 12 has a function of transmitting and receiving various frames to and from the other node 10 via the communication I / F unit 11 and the communication path L. At this time, the frame received from the other node 10 is transferred from the data link processing unit 12 to the upper layer processing unit 13. In addition, the data link processing unit 12 transmits the specified frame to the specified destination address in response to the frame transmission request from the transmission availability determination unit 15.

The upper layer processing unit 13 has a function of executing a predetermined upper application process by performing data communication with another node 10 using a frame, and transmits data to the other node 10 according to the upper application process. In this case, it has a function of notifying the transmission availability determination unit 15 of a frame transmission request in which the transmission destination address and transmission data are specified.

The address management unit 14 has a function of acquiring an address included in the reception frame from the reception frame received by the data link processing unit 12 and managing it as an existing address used by the other node 10. More specifically, when the address management unit 14 acquires an address from a reception frame, the source address is received from the data link processing unit 12 and is periodically exchanged between other nodes 10 for management polling frames. Has a function to acquire and manage (register) as an existing address in the storage unit (not shown). A specific example of a polling frame for management is a PFM (Poll For Master) frame used in BACnet MS / TP.

The frame for which the existing address is acquired in the address management unit 14 is not limited to the polling frame for management, and may be a data frame used for exchanging data or another management frame. .. On the other hand, by setting the polling frame for management as the target frame for acquiring the existing address, it is possible to periodically acquire a legitimate existing address with few errors. If the existing address is not updated in the address management unit 14 for a certain period of time, the existing address may be deleted. As a result, it is possible to automatically respond to node exchanges and address changes due to maintenance work.

The transmission availability determination unit 15 has a function of comparing the destination address specified in the frame transmission request with the existing address managed by the address management unit 14 in response to the frame transmission request from the upper layer processing unit 13. A function to notify the data link processing unit 12 of a frame transmission request only when the destination address is an existing address, and when the destination address is not an existing address, the frame transmission request is discarded and the frame transmission is stopped. It has a function.

[Operation of the present embodiment]
Next, the processing operation of the node 10 according to the present embodiment will be described with reference to FIG. FIG. 2 is a sequence diagram showing the processing operation of the node. Here, a case where an existing address is acquired from a PFM frame used in BACnet MS / TP and managed will be described as an example.

First, when the data link processing unit 12 receives a PFM frame transmitted from an arbitrary other node 10 to a different other node 10 (step 100), the frame data of the PFM frame is transferred to the address management unit 14. (Step 101).
The address management unit 14 acquires the source address included in the PRM frame based on the received frame data (step 102), registers it as an existing address in the storage unit (not shown) (step 103), and performs a series of series. End the address registration process.

On the other hand, when the frame transmission request is notified from the upper layer processing unit 13 (step 110), the transmission availability determination unit 15 acquires the destination address specified in the frame transmission request (step 111), and the address management unit 14 Confirms whether the address is registered as an existing address (step 112).

Here, if the destination address is not registered as an existing address (step 113: NO), the transmission availability determination unit 15 discards the frame transmission request and cancels the frame transmission (step 114).
On the other hand, when the destination address is registered as an existing address (step 113: YES), the transmission availability determination unit 15 notifies the data link processing unit 12 of the frame transmission request (step 115).

The data link processing unit 12 starts a general frame transmission process in response to the notification of the frame transmission request from the transmission availability determination unit 15.
First, it waits until the token frame is notified from the other node 10 (step 120), and in response to the reception of the token frame, generates and transmits a transmission frame based on the frame data and the destination address specified in the frame transmission request. (Step 121).

Next, the data link processing unit 12 waits until the reply frame for the transmission frame is notified from the destination node 10 (step 122), and in response to the reception of the reply frame, the frame transmission request of the frame is received. It is determined that the transmission is successful (step 123), and the success of the transmission is notified to the upper layer processing unit 13 (step 124).
After that, the data link processing unit 12 transmits a token frame to the other node 10 (step 125) in response to the arrival of the token transmission timing, and ends a series of frame transmission processes.

[Effect of this embodiment]
As described above, in the present embodiment, the address management unit 14 acquires an address from the reception frame received by the data link processing unit 12, manages it as an existing address used by the other node 10, and determines whether transmission is possible. 15 compares the destination address specified in the frame transmission request with the existing address in response to the frame transmission request from the upper layer processing unit 13, and requests frame transmission only when the destination address is the existing address. Is notified to the data link processing unit 12.

As a result, the frame is transmitted to the destination address specified in the frame transmission request only when the destination address specified in the frame transmission request is registered as an existing address, and the transmission is not registered as an existing address. If the destination address is specified, frame transmission in response to the frame transmission request will be canceled. As a result, the frame is transmitted only to the valid address assigned to the actual node 10, and the frame transmission to the invalid address not assigned to the node 10 is suppressed. Therefore, it is possible to avoid a decrease in throughput of the entire system caused by frame transmission to an invalid address.

Further, in the present embodiment, when the address management unit 14 acquires an address from the reception frame, the source address is acquired from the management polling frame exchanged between the other nodes 10 received by the data link processing unit 12. However, it may be managed as an existing address.
As a result, it is possible to periodically acquire a legitimate existing address with few errors, and it is possible to more accurately suppress frame transmission to an invalid address.

[Extension of Embodiment]
Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the structure and details of the present invention within the scope of the present invention.

1 ... Communication system, 10 ... Node, 11 ... Communication I / F unit, 12 ... Data link processing unit, 13 ... Upper layer processing unit, 14 ... Address management unit, 15 ... Transmission availability determination unit, L ... Communication path.

Claims (4)

Used in a communication system consisting of a plurality of nodes connected to a communication path by bus, data communication is performed with each other by transmitting and receiving frames based on a communication method that combines a master-slave communication method and a token passing communication method. A node
A data link processing unit that transmits and receives the frame to and from the node via the communication path, and
A higher layer processing unit that executes predetermined higher application processing by performing data communication with the node using the frame, and
An address management unit that acquires address information included in a reception frame received by the data link processing unit and manages it as an existing address used by the node.
In response to the frame transmission request from the upper layer processing unit, the destination address specified in the frame transmission request is compared with the existing address, and if the destination address is the existing address, the frame transmission is performed. It is provided with a transmission availability determination unit that notifies the data link processing unit of the request and discards the frame transmission request when the destination address is not the existing address.
The data link processing unit is a node that transmits a designated frame to a designated destination address in response to the frame transmission request from the transmission availability determination unit. In the node according to claim 1.
The data link processing unit periodically transmits a management polling frame in which the address of the node is designated as the destination address and the own address is designated as the source address.
When the address management unit acquires the address information from the receiving frame, the address management unit acquires the source address from the polling frame received by the data link processing unit and exchanged between nodes other than the own node, and obtains the existing source address. A node characterized by being managed as an address. In a communication system in which a plurality of nodes connected to a communication path by bus transmit and receive frames based on a communication method that combines a master-slave communication method and a token passing communication method, data communication is performed between these nodes. It is a frame transmission control method used in
A data link processing step in which the data link processing unit transmits and receives the frame to and from the node via the communication path, and
A higher layer processing step in which the upper layer processing unit executes a predetermined upper application process by performing data communication with the node using the frame, and
An address management step in which the address management unit acquires the address information included in the received frame received by the data link processing unit and manages it as an existing address used in the node.
The transmission availability determination unit compares the destination address specified in the frame transmission request with the existing address in response to the frame transmission request from the upper layer processing unit, and the destination address is the existing address. In this case, the data link processing unit is notified of the frame transmission request, and if the destination address is not the existing address, the frame transmission request is discarded.
The data link processing step is a frame transmission control method including a step of transmitting a designated frame to a designated destination address in response to the frame transmission request from the transmission availability determination unit. In the frame transmission control method according to claim 3,
The data link processing step includes a step of periodically transmitting a management polling frame in which the address of the node is designated as a destination address and the own address is designated as a source address.
In the address management step, when acquiring address information from the receiving frame, the source address is acquired from the polling frame received by the data link processing unit and exchanged between nodes other than the own node, and the existing address is acquired. A frame transmission control method including a step of managing as an address.

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