CN116647605A - OPC UA efficient communication implementation method based on improved KCP - Google Patents

Abstract

The invention discloses an implementation method of OPCUA high-efficiency communication based on improved KCP. The invention uses KCP and UDP to combine to replace TCP transmission protocol in original transmission layer. The communication architecture of the client and the server is as follows: the request of the application program is firstly converted into an OPCUA message by the OPCUA communication stack and then transmitted to the KCP communication stack, and the KCP communication stack encapsulates the KCP communication stack into KCP data packets in a fragmentation way and transmits the KCP data packets to the wide area network. Once the KCP communication stack receives the KCP data packet from the wide area network, the KCP communication stack reassembles the KCP data packet into the OPCUA message. Finally, the OPCUA message is converted into a common message format which is easy to process through the OPCUA communication stack. The KCP communication improvement comprises the design of the KCP protocol data segment head, the adoption of a randomly initialized serial number to ensure the communication security, the prevention of serial number wrapping by a record timestamp, and the use of a piggyback message to reduce the transmission quantity of data. Compared with common OPCUA communication, the method can ensure lower communication delay and has great practical significance.

Description

OPC UA efficient communication implementation method based on improved KCP

Technical Field

The invention belongs to the field of industrial Internet, and relates to an OPC UA communication method, which can reduce the reduction of communication efficiency and ensure the accurate transmission between data especially under the condition of poor network conditions.

Background

The OPC UA protocol, which is an industry 4.0 standard, solves the problem of the platform restrictions of the OPC standard, which is located above the application layer, and between the transport layers of which a TCP protocol is used for the connection. The conventional TCP protocol has some problems such as, for example,

(1) The implementation of TCP is often embedded in the system kernel, and if new functions need to be implemented, the system kernel needs to be modified, so that the upgrade is very difficult, and other unknown errors are easy to occur.

(2) The delayed ACK response strategy employed by TCP may result in the sender waiting time exceeding the timeout retransmission time. In this case, the receiving end does not receive the ACK, and the transmitting end must retransmit the data packet, thereby increasing network traffic and reducing network efficiency.

(3) The congestion control of TCP avoids network congestion and ensures reliability and performance of the network, but may also cause delay in network transmission, and increases transmission time due to the need to wait for acknowledgement messages before transmitting data.

Furthermore, TCP's congestion control is poorly adapted to high-speed networks, which limits the sending rate at the beginning of data transmission, thus affecting the throughput of the overall network. It is difficult to guarantee a deterministic transfer between data if connectionless, unreliable UDP connections are used at the transport layer, which is a fatal disadvantage in industry where extremely high accuracy requirements are present.

Disclosure of Invention

The invention aims at overcoming the defects of the prior art, and provides an OPC UA efficient communication implementation method based on improved KCP. The invention overcomes the defects of the traditional TCP or UDP by replacing the TCP protocol in the OPC UA protocol. The OPC UA server adopts the scheme of UDP communication protocol in the communication between the transmission layers, and adds a KCP protocol on the basis of UDP, the KCP is used for wasting partial bandwidth at the cost of 30-40% faster transmission speed than TCP, and the transmission delay is greatly reduced. By adopting the realization method, the data transmission efficiency can be improved, and the communication delay is reduced, so that the normal operation and the high-efficiency operation of the whole system are ensured. Such protocols have value for industrial production and business operations.

The invention provides a brand new implementation method of OPC UA high-efficiency communication based on improved KCP, and redesigns part of KCP protocol according to the actual situation of OPC UA, the technical problem scheme comprises the following steps:

and (1) initializing an OPC UA server according to the configuration information, and attempting to establish connection between the OPC UA client and the KCP.

OPC UA clients map IP addresses, port numbers to thirty-two unsigned integers through FNV hash algorithm to act as session ids.

The KCP sends a message to create a connection request to the OPC UA server listening port.

After receiving the connection request, the monitoring port of the OPC UA server creates a new communication port for the OPC UA client, and returns a confirmation message by using the communication port.

And (2) the OPC UA client side indicates that the connection is successfully created after receiving the confirmation message from the communication port of the OPC UA client side. The OPC UA client sends a Hello message containing information about the maximum message size, the data block size and the number.

Once the OPC UA server receives the Hello message, it returns an Acknowledge message to the OPC UA client.

The Acknowledges message contains information of the maximum message size, data block size and number that the server can handle, and the protocol version number supported by the server.

If the OPC UA client and the server can agree with each other through the Hello message and the Acknowledges message, the connection is considered to be successful, otherwise, the connection is failed.

If the OPC UA server or the OPC UA client receives the corresponding data message for a plurality of times, the error is reported and the KCP connection is closed. If the OPC UA server does not receive the Hello message, the OPC UA server automatically disconnects the KCP after a user-defined time interval.

And (3) after the OPC UA client obtains the Acknowledges message sent by the OPC UA server, sending the security policy, the security mode, the digital certificate and the random number information of the OPC UA client as Open Secure Channel message. The OPC UA server verifies whether the digital certificate and security policy of the client meet the requirements, and if so, returns a Open Secure Channel Response message. The OPC UA client and the OPC UA server carry out encrypted communication by generating a symmetric key through random numbers.

After opening the secure channel, the OPC UA client sends a Create Session Request message to the OPC UA server, which contains the client's application name, URI, session name, session timeout time, maximum request message size, and information of a random number Nonce that can only be used once. After receiving the Create Session Request message, the OPC UA server signs the Nonce for proving itself to the client as the required target server. While verifying Create Session Request that the message meets the specifications, and if so, returning Create Session Response message with signature information.

After receiving the response of the Create Session Response message returned from the server, the OPC UA client generates a signature using the authentication token and sends Activate Session Request a message to the server, where the message contains the signature of the client and information of the user identity. The OPC UA server verifies whether the signature and user identity of the client are valid, and if so, sends a Activate Session Response message to the client and allocates a set of available subscription ID and node ID resources to the client. And then the OPC UA client and the server can perform data reading, writing, subscribing and publishing operations through the session message.

And (6) improving the traditional KCP transmission communication from four aspects, namely, improving the design of the header of the KCP protocol data segment again, adopting the randomly initialized serial number to ensure the communication safety, recording the time stamp to prevent the serial number from wrapping, and reducing the transmission quantity of the data by using the piggyback acknowledgement message.

The further detailed implementation of step (6) is as follows:

the re-modification of the KCP protocol data segment header design is illustrated in detail in fig. 3.

The improved KCP specifies that each connection randomly generates an initial sequence number, and in order to ensure randomness and unpredictability of the sequence numbers, the improved KCP sequence numbers employ a dynamic scheme including time, port number, IP address as input for initialization, as shown in equation 1 below,

where the division of the current timestamp value time by 4 indicates that the sequence number increases by 1 every four microseconds. H is calculated by an FNV hash algorithm through the IP address and the port number of the client.

The sequence number of KCP is represented by an unsigned integer of four bytes, meaning that when more than 2 ³² The problem of sequence number wrapping occurs at-1, so that when improving KCP communication, the receiver will save the timestamp of the current receive window start packet, denoted as rts. The receiver compares the timestamp value time in the just received packet with the rts value. If the time is less than rts, indicating that the packet has expired, the receiver will discard the packet.

The improved KCP adds a new message type, namely data and acknowledgement messages. When KCP sends acknowledgement message, if there is data message to be sent to opposite side, the acknowledgement message is attached to initial part of data in data message so as to reduce quantity of transmission data. In order to avoid confusion between data and confirmation messages and common data messages, a sequence is designed in cmd fragments of the message header to indicate that the message is a data and confirmation message, and the data part in the data and confirmation type message should start from 24 bytes of the normal data part.

The beneficial effects of the invention are as follows:

if the transmission layer in the seven-layer network architecture uses TCP for communication, the bottom layer in the OPC UA three-layer communication architecture can ensure the accuracy of data transmission, but the communication efficiency is greatly reduced under the condition of poor network conditions. The invention provides an OPC UA communication protocol based on improved KCP, which uses a scheme of combining KCP and UDP in a transmission layer. Compared with the original OPC UA protocol, the protocol shows more excellent performance in a complex network environment, and can effectively improve the performance and stability of OPC UA communication, thereby better meeting the requirements of practical application.

Drawings

FIG. 1 is an OPC UA communication architecture based on an improved KCP;

FIG. 2 is a detailed communication sequence of OPC UA based on improved KCP;

FIG. 3 is a diagram of three different message header designs;

FIG. 4 is a comparison of average communication delays between an OPC UA server and a client using TCP and KCP, respectively;

fig. 5 is a graph of the cumulative distribution of requests between an OPC UA server and a client using TCP and KCP, respectively.

Detailed Description

The invention is further described below with reference to the drawings and examples.

The invention discloses an OPC UA high-efficiency communication realization method based on improved KCP. The invention uses KCP and UDP to combine to replace TCP transmission protocol in original transmission layer. The communication architecture of the client and the server is as follows: the request of the application program is firstly converted into an OPC UA message by an OPC UA communication stack and then transmitted to a KCP communication stack, and the KCP communication stack encapsulates the fragments into KCP data packets and transmits the KCP data packets to the wide area network. Once the KCP communication stack receives the KCP data packet from the wide area network, the KCP communication stack reassembles the KCP data packet into an OPC UA message. Finally, OPC UA messages are converted into the usual message formats that are easy to handle by means of an OPC UA communication stack. Meanwhile, the traditional KCP communication is improved in the following four aspects, namely, the design of the header of the KCP protocol data segment is improved again, the communication safety is ensured by adopting a randomly initialized serial number, the serial number is prevented from being rewound by recording a time stamp, and the transmission quantity of data is reduced by using a piggyback confirmation message. Experiments prove that the communication scheme of OPC UA based on improved KCP can ensure lower communication delay compared with common OPC UA communication, and has great practical significance.

Fig. 1 is a basic communication architecture of OPC UA based on KCP, and the communication architecture is mainly divided into OPC UA communication stacks and KCP communication stacks. The OPC UA communication stack translates the request of an application into OPC UA messages. The OPC UA message is then passed to the KCP communication stack, which encapsulates its fragments into KCP packets and sends them to the wide area network. When a KCP packet is received from the wide area network, the KCP communication stack reassembles the KCP packet into an OPC UA message. The OPC UA message is then converted by the OPC UA communication stack into a data format understandable to the application and the application is notified of the processing.

Fig. 2 is a detailed communication sequence of KCP-based OPC UA, and is also a main process of KCP-based OPC UA communication. The communication process is the steps (1) to (5) described above, and mainly includes the processes of establishing KCP connection, hello call and Acknowledge response, opening a secure channel, creating a session, and activating the session. The specific implementation steps of the OPC UA communication connection based on the improved KCP are as follows:

the KCP communication Connection is managed by a UA_connection object, and consists of a socket used for UDP communication, a KCP object responsible for carrying out fragmented retransmission on a data packet, and a timer part for executing update. A timer is used in the UA Connection to determine when to invoke update. The timer traverses the data segment in the sending cache space, records the time point closest to the current time, and judges the time point as the next time of invoking update. The KCP communication periodically judges the reception and transmission of the data packet by calling the update function.

The update internally calls a flush function that is used to send KCP packets into the wide area network. Firstly, the acknowledgement message to be sent in the ack_list is sent to the communication terminal. ack_list is a linked list storing acknowledgement messages to be sent to the communication end, and whenever the KCP receives a data packet, the sequence number and the timestamp recorded by the KCP are inserted into the linked list. And when the confirmation response message is sent, detecting whether the data message needs to be sent or not, and if so, combining the data message and the confirmation message into data and the confirmation message and sending the data and the confirmation message to the wide area network.

3. The sender judges whether to send the detection window message according to the value of remote_receiver_window, and the parameter stores the size of the receiving window of the receiver. When remote_receive_window is zero, the sender continuously sends the detection window message according to the probe_interval until receiving the response window message sent by the receiver. Wherein the value of probe_interval is the time interval for sending the probe window message.

The reason for sending the probe window message is that when remote_receiver_window is zero, in order to continue sending data to the receiver, the sender needs to wait for the response window message from the receiver to update remote_receiver_window. Even if the receiving party can resend the message after the receiving window is recovered, the response window message may be lost in the network transmission process, so that the sending party cannot update the receiving window size of the opposite communication end. At this time, if the sender does not actively send the detection window message, the sender will continuously wait for the response window message of the receiver. The receiver will consider that the sender has successfully received the response window message and updated the remote_receive_window while waiting for the sender's data message. This situation where two parties wait for each other to enter a deadlock will result in the inability of data transmission to take place.

4. Finally, the size of the transmission window needs to be updated. The value of the transmission window is the minimum value among the transmission window size send_window and remote_receive_window set by the user. And calculating the sequence number at the tail end of the window according to the size of the transmission window, and transferring the KCP data packet with the sequence number smaller than the value in the transmission queue into a transmission buffer space. And then, the newly added KCP data packet in the transmission buffer space is transmitted, whether the transmitted KCP data packet triggers a timeout retransmission mechanism or a quick retransmission mechanism is judged, and if so, the transmission is carried out again.

Fig. 3 is a diagram of three different message header designs. The KCP messages can be classified into four types, namely, acknowledgement messages, user data messages, probe window messages, and response window messages. The invention redesigns the respective data header formats for the messages according to different application scenes. Fig. 3 (a) retains only ts and sn fields for accurate RTT calculation and acknowledgement of receipt of the packet, and deletes the len and frg fields associated with the relative order of the data that need not be acknowledged, for the header format of the acknowledgement message. Fig. 3 (b) is a data message header format, the type of message header being identical to the original message header. Fig. 3 (c) is a probe window message and response window message header format. When the sender finds that the remote receiving window is zero, the detection window message is sent regularly until the response window message is received, so that the type of message can directly remove irrelevant ts and sn fields. Each type of message header has a ack, cmd, and wnd. Wherein the ack is used to update the send window quickly. cmd is used to distinguish message types. The wnd is used to inform the communication partner of the remote receiving window size.

Fig. 4 is a diagram showing communication using OPC UA protocol based on modified KCP and OPC UA protocol based on TCP under different network environments, respectively, and recording communication delay thereof in milliseconds. When the network delay is 100 milliseconds, the average communication delay pair of two protocols is like a graph under the condition of different packet loss rates. It is clearly seen that the communication efficiency of the KCP-based OPC UA protocol is higher than that of the TCP-based OPC UA protocol. And as the packet loss rate increases, the communication delay of the former increases by a smaller magnitude than the latter.

Fig. 5 is a cumulative distribution diagram of two protocols under different packet loss rates. The x-axis in the cumulative profile is the communication delay in milliseconds. The y-axis is the percentage of the total number of requests that is less than a certain communication delay value. In fig. 5 (a), only one point is shown, because the KCP-based OPC UA protocol and the TCP-based OPC UA protocol can ensure that the data is successfully transmitted once when the packet loss rate is zero, i.e., the transmission time is equal to the network delay, so that the communication delay of the two is not changed. As the packet loss rate increases, the communication efficiency of the two protocols is different. As can be seen from fig. 5 (b), 5 (c) and 5 (d), the OPC UA protocol based on the modified KCP has more requests for communication delay than the OPC UA protocol based on the TCP, and this gap is continuously enlarged as the packet loss rate increases.

Claims (10)

1. An OPC UA high-efficiency communication realization method based on improved KCP is characterized in that the method overcomes the defects of the traditional TCP or UDP by replacing the TCP protocol in the OPC UA protocol, improves the data transmission efficiency and reduces the communication delay; the OPC UA server adopts UDP communication protocol in communication between transmission layers, and adds an improved KCP protocol on the basis of UDP.

2. The method for implementing OPC UA efficient communication based on improved KCP as claimed in claim 1, comprising the steps of:

initializing an OPC UA server according to configuration information, and attempting to establish connection between an OPC UA client and an improved KCP;

the OPC UA client maps the IP address and the port number into thirty-two unsigned integers through the FNV hash algorithm to serve as a session id;

the KCP sends a message for creating a connection request to an OPC UA server monitoring port;

after receiving the connection request, the monitoring port of the OPC UA server creates a new communication port for the OPC UA client and returns a confirmation message by using the communication port;

step (2), after receiving the confirmation message from the communication port of the OPC UA client, the OPC UA client indicates that the connection is successfully created; the OPC UA client sends a Hello message, and once the OPC UA server receives the Hello message, an Acknowledgemessage is returned to the OPC UA client;

if the OPC UA client and the server can agree with each other through the Hello message and the Acknowledges message, the connection is considered to be successful, otherwise, the connection is failed;

after the OPC UA client obtains the Acknowledges message sent by the OPC UA server, the OPC UA client sends the security policy, security mode, digital certificate and random number information as Open Secure Channel message; the OPC UA server verifies whether the digital certificate and the security policy of the client meet the requirements, and if the digital certificate and the security policy of the client pass the verification, a Open Secure Channel Response message is returned; the OPC UA client and the OPC UA server generate a symmetric key through random numbers to carry out encryption communication;

after opening the secure channel, the OPC UA client sends a Create Session Request message to the OPC UA server, after receiving Create Session Request the OPC UA server signs the random number Nonce in the message, if passing the verification, returns Create Session Response the message;

after receiving the response of the Create Session Response message returned by the server, the OPC UA client generates a signature by using the authentication token and sends Activate Session Request a message to the server, wherein the message contains the signature of the client and the information of the user identity; the OPC UA server verifies whether the signature and the user identity of the client are valid, if so, a Activate Session Response message is sent to the client, and a group of available subscription ID and node ID resources are allocated to the client; and then the OPC UA client and the server can perform data reading, writing, subscribing and publishing operations through the session message.

3. The method according to claim 2, wherein the Hello message in step (2) contains information of a maximum message size, a data block size and a number.

4. The method according to claim 2, wherein the Acknowledge message in step (2) contains information of the maximum message size, the data block size and the number that the server can process, and the protocol version number supported by the server.

5. The method for implementing OPC UA efficient communication based on improved KCP according to claim 3 or 4, wherein if the OPC UA server or OPC UA client receives the corresponding data message multiple times, the error is reported and the KCP connection is closed; if the OPC UA server does not receive the Hello message, the OPC UA server automatically disconnects the KCP after a user-defined time interval.

6. The method of claim 5, wherein the Create Session Request message in step (4) includes information about the client's application name, URI, session name, session timeout time, maximum request message size, and a random number Nonce that can only be used once.

7. The method for implementing OPC UA efficient communication based on improved KCP as claimed in claim 2, wherein the improvement of KCP transmission communication comprises: the KCP protocol data segment head design, adopting random initialized serial number to ensure communication safety, recording time stamp to prevent serial number from wrapping, using piggyback message to reduce data transmission quantity.

8. The method for implementing OPC UA efficient communication based on improved KCP as claimed in claim 7, wherein the improved KCP is implemented as follows:

the improved KCP specifies that each connection randomly generates an initial sequence number, and in order to ensure randomness and unpredictability of the sequence numbers, the improved KCP sequence numbers employ a dynamic scheme including time, port number, IP address as input for initialization, as shown in equation 1 below,

wherein, the division of the current timestamp value time by 4 represents that the sequence number increases by 1 every four microseconds; h is calculated by an FNV hash algorithm through the IP address and the port number of the client;

the sequence number of KCP is represented by an unsigned integer of four bytes, meaning that when more than 2 ³² -1, a problem of sequence number wrapping occurs, so that when improving KCP communication, the receiver will save the timestamp of the current reception window start packet, denoted as rts; the receiver compares the timestamp value time with the rts value in the data packet just received; if the time is less than rts, indicating that the packet has expired, the receiver will discard the packet.

9. The method for implementing OPC UA efficient communication based on improved KCP as claimed in claim 8, wherein the improved KCP adds a new message type, namely data and acknowledgement message; when KCP sends acknowledgement message, if there is data message to be sent to opposite side, combining acknowledgement message and data message into data and acknowledgement message.

10. The method according to claim 9, wherein in order to avoid confusion between data and acknowledgement messages and normal data messages, a sequence is designed in cmd slices of the packet header to indicate that the message is a data and acknowledgement message, and the data portion in the message should start 24 bytes after the normal data portion.