CN100556044C - Protocol control method towards wireless industrial control network - Google Patents

Abstract

The invention relates to a protocol control method oriented to a wireless industrial control network. Its communication model is made up of physical layer, data link layer and application layer, and described physical layer and application layer adopt the physical layer and application layer of international standard network interconnection model OSI respectively, it is characterized in that described data link layer It is divided into two layers: the lower sublayer uses the traditional carrier sense multiple access CSMA protocol as the wireless channel access control protocol; the upper sublayer uses a token-based control protocol to establish a Token logical ring, thereby controlling the CSMA protocol of the lower sublayer; setting a token logical ring self-healing mechanism to avoid token logical ring failure due to token loss; and determining a token logical ring expansion and contraction mechanism, so that The system can automatically adapt to the joining and exiting changes of each mobile station. The invention can avoid the collision in communication transmission and meet the real-time control requirement for industrial objects.

Description

Protocol control method for wireless industrial control network

technical field

The invention relates to a network protocol stack, in particular to a protocol stack oriented to a wireless industrial control network.

Background technique

It is difficult or even impossible to use cables for sensors on moving or rotating objects in industrial field control, handheld data acquisition equipment, and equipment that needs to be temporarily installed. At the same time, the use of wired physical media connections in extremely cold, hot, dangerous, and humid environments will also reduce the reliability of the communication system. With the development and maturity of wireless communication technology, it is possible to apply wireless communication technology to industrial control network to form a wireless industrial control network WICN (Wireless Industrial Control Network).

An important issue in its related research is the study of the data link layer protocol. The protocol problem of the data link layer has a great impact on the real-time performance and reliability of the WICN network. How to design a suitable data link layer protocol suitable for industrial field control wireless industrial control network is an important research direction in the world at present.

The real-time performance of WLAN mainly depends on the media access control at the data link layer. This problem has been studied for some time, but it is still basically limited to the traditional CSMA (Carrier Sense Multiple Access) method. This contention-based approach is a commonly used protocol for determining access to media. Although people have used various improvement measures, such as adding CA (collision avoidance) function, etc., they still cannot fundamentally avoid communication collisions during transmission, and cannot guarantee the deterministic requirements of response time in industrial control systems.

Several protocols commonly used in WLANs have different disadvantages. For example: 1. MACA (Multiple Access with Collision Avoidance) is a protocol designed for wireless LAN earlier. Its basic idea is that the sender stimulates the receiver to output a short frame, so stations near the receiver can detect this frame, so that they will not send data during the next data frame transmission. Due to the adoption of the RTS-CTS handshake mechanism, MACA reduces the collision of data packets. However, there are still conflicts in MACA, and the BEB backoff mechanism is adopted after the conflicts, so the fairness of channel access is very poor, and the real-time performance cannot be guaranteed. 2. The MACAW (MACA for Wireless) protocol has been improved on the basis of MACA. It adds carrier detection. In addition to the RTS/CTS handshake signal, it also uses other control signals (DS, ACK, RRTS). Further improve the throughput of the network. MACAW also uses the MILD backoff algorithm to replace the BEB backoff mechanism, which improves the fairness of channel access. But its excessive handshake signals increase its network overhead and transmission delay. MACA-P is an improvement based on MACA to meet the needs of multi-hop ad-hoc networks. It enhances the RTS/CTS function based on 802.11 and allows simultaneous sending and receiving, but it is not suitable for WICN networks. 3. The IEEE802.11 protocol supports two operating modes. One mode is called DCF (Distributed Coordination Function), and the other mode is called PCF (Point Coordination Function). Among them, DCF mode is the basic access mode for nodes to share wireless channels. It combines CSMA/CA (CSMA with Collision Avoidance) technology and acknowledgment (ACK) technology, and uses virtual channel monitoring mechanism and frame fragmentation technology to improve throughput of the entire network. However, the 802.11 protocol still adopts the BEB backoff mechanism, so the fairness of wireless channel access cannot be guaranteed. At present, there is no suitable protocol specifically for industrial wireless control networks.

Contents of the invention

The purpose of the present invention is to provide a protocol control method oriented to a wireless industrial control network, which can avoid collisions in communication transmission and meet the real-time control requirements for industrial objects.

In order to achieve the above object, the present invention adopts following technical scheme:

A kind of protocol control method for wireless industrial control network, its communication model is made up of physical layer, data link layer and application layer, described physical layer and application layer respectively adopt the physical layer and application layer of international standard communication model OSI, It is characterized in that the data link layer is divided into two layers: the lower sublayer uses the traditional carrier sense multiple access CSMA protocol as the actual access control protocol of the wireless channel; the upper sublayer uses a token-based control protocol , establish a token logical ring in the fully interconnected wireless distribution system, thereby controlling the CSMA protocol of the lower sublayer; set a token logical ring self-healing mechanism, to avoid the token logical ring from being invalid due to the loss of the token; and Determine a token logic ring expansion and contraction mechanism, so that the network system can automatically adapt to the changes of the joining and exiting of each mobile station.

The steps for establishing token logic in the fully interconnected wireless distribution system using the above-mentioned token-based control protocol are as follows:

(1) Initially, each station STA first enters the reset state, then listens to the channel, and waits for the invitation from the master station to join;

(2) After the main station is powered on, reset first, and then generate a token Token;

(3) The token Token is passed sequentially along the logical ring until the station waiting to send the data frame is STA to receive it, and then it sends the read frame Solicit_successor to invite other slave stations to join;

(4) After other slave stations detect Solicit_Successor, they back off for a random time slot and then send the successor station setting frame Set_successor, and the station with successful competition becomes the successor station of the master station;

(5) The successor station sets the previous successor station of the master station as its successor station. For the first joined slave station, the previous successor station of the master station is the master station itself, thus forming an initial station containing 2 token logical ring of sites;

(6) If the task queue is empty or the data frame is transmitted and processed, and the token holding time THT has not been exhausted, the master station will send Solicit_successor again to invite other slave stations to join;

(7) According to the mechanism of steps (1)-(6), after a period of time, each station in the wireless distributed system will automatically form a token logical ring, thereby forming a network system.

The self-healing steps of the above token logical ring self-healing mechanism are as follows:

(1) After the master station establishes a token logic ring, a token is generated and passed on the ring, and then the master station listens to each token sent by the slave station;

(2) Set a token recovery and maximum waiting time TRMWT in the master station, when the master station frame hears a token, it will reset TRMWT;

(3) When the TRMWT of the master station is exhausted and has not detected the next token, it considers that the token is lost, and then generates a new token according to the connection table information stored in advance and sends it to the station that lost the token .

The above token logical ring expansion and contraction mechanism determines the joining and exiting process of the slave station STA as follows:

(1) The joining process of the slave station:

① Controlled by the master station, the master station sends Solicit_Successor when the queue is empty;

②The slave station that wants to join the system sets the master station as its predecessor station after receiving the Solicit_Successor, sets the successor station of the master station as its successor station, and sends Set_Sucessor to the master station;

③ After the master station receives the Set_sucessor, it sets the slave station as its successor station, and sends the predecessor station setting frame as Set_Predecessor to its previous successor station;

④ After receiving Set_Predecessor, the former successor station of the master station sets the slave station as its predecessor station, and sends an acknowledgment frame Ack to the master station;

⑤ After the master station receives the Ack frame, it will pass the token to the newly added slave station, so far the joining process of the slave station is completed.

(2) The exit process of the slave station:

① The slave station that wants to exit sends Set_Successor to its predecessor station after receiving the token;

② After the predecessor station receives Set_Successor, set the successor station of the slave station as its successor station, and send Set_Successor to the successor station of the slave station;

③The successor station of the slave station returns the Ack frame to the slave station after receiving Set_Successor;

④After receiving the Ack frame, the slave station passes the token to its successor station and exits.

The formats of the above-mentioned token frame, request frame, successor station setting frame, predecessor station setting frame, Ack frame and data frame are as follows:

(1) The format of token frame Token: sequentially contains frame type FC, logic number Seq, table creation information SucA, local station address LA, predecessor station address PreA and token cycle number TRC;

(2) The format of the request frame Set_Successor: contains frame type FC, broadcast Br, master station successor address HSuoA and master station address HA in sequence;

(3) The successor station sets the format of the frame Set_Successor: sequentially contains frame type FC, destination address DA, successor station address SucA and the source address of the frame;

(4) The format of the frame Set-Predecessor set by the predecessor station: contains frame type FC, destination address DA, source address SA of this frame, predecessor station address PreA and Ack frame return destination address in turn;

(5) The format of the Ack frame: sequentially contains the frame type FC, the destination address DA and the source address SA of the frame;

(6) The format of the data frame: sequentially contains the frame type FC, the expected time limit Duration of the transmission of the data frame, the destination address DA, the source address SA of the frame, the priority level PC of the data, the data Data and the cyclic redundancy check code CRC.

Compared with the prior art, the present invention has the following obvious outstanding substantive features and significant advantages: the data link layer in the protocol stack provided by the present invention has added an upper sublayer, and uses a token-based control protocol to control the lower layer The sub-layer CSMA protocol prevents channel transmission from colliding and meets the real-time control requirements for industrial objects; a token logic ring self-healing mechanism is set to avoid token logic ring failure due to token loss, and the work is reliable; and Determine a token logical ring expansion and contraction mechanism, so that the system can automatically adapt to the changes of the joining and exiting of each mobile station, and improve the flexibility of the system.

Description of drawings

Fig. 1 is a schematic structural diagram of the communication model of the present invention.

Fig. 2 is a schematic diagram of the format of the token frame.

Fig. 3 is a schematic diagram of the format of the Solicit_Successor frame.

Fig. 4 is a schematic diagram of the format of the Set_Successor frame.

Fig. 5 is a schematic diagram of the format of the Set_Predecessor frame.

Fig. 6 is a schematic diagram of the format of the Ack frame.

Fig. 7 is a schematic diagram of the format of the data frame.

Fig. 8 is a schematic diagram of joining from a station.

Fig. 9 is a schematic diagram of exit from a station.

Detailed ways

A preferred embodiment of the present invention is described in detail as follows in conjunction with accompanying drawing:

Referring to Fig. 1, the protocol protocol control method for the wireless industrial control network is: in order to meet real-time requirements and reduce costs, its communication model is simplified on the basis of OSI (Open Interconnection Model). It only uses 3 layers in the OSI model, namely physical layer, data link layer and application layer.

The data link layer in this protocol stack is divided into two layers. The lower sublayer of the data link layer still uses CSMA as the actual wireless channel access control protocol. The upper sublayer of the data link layer uses a token-based control mechanism to control the CSMA of the lower layer. The basic operation process is as follows: ① Establish a token logical ring in the fully interconnected wireless distributed system. All STAs (stations) working in receiving/transmitting mode in the system must join the logical ring. After the STA gets the token, , so as to control the CSMA protocol at the lower layer to monopolize the wireless channel to specifically realize the sending of data frames, thereby avoiding the collision caused by the disorderly competition of various points in the CSMA protocol. ②In order to avoid the failure of the token logic ring due to the loss of the token, a self-healing mechanism is set in the system to ensure that the token logic ring is restored within a certain period of time. ③ It also defines the expansion and contraction mechanism of this token ring, so that the system can automatically adapt to the changes of joining and exiting each mobile station.

The significance of the present invention is to design a data link layer protocol that is compatible with and utilizes the widely used CSMA protocol and avoids its defects for the requirements of the WICN network, and can be widely used in networks such as ZigBee and WLAN. used in .

The establishment and implementation process of the token control mechanism used in the data link layer of the wireless industrial control network-oriented protocol stack will be explained in detail below.

1. Token Ring establishment process

(1) Initially, each slave station does not join the logical ring, and each station first enters the reset state, then listens to the channel and waits for the invitation from the master station (connected to the wired network) to join. (2) After the master station is powered on, it is also reset first, and then the master station generates a token Token. (3) The token is passed sequentially along the logical ring until the station STA waiting to send the data frame receives it. Then it sends the request frame Solicit_Successor, inviting other slave stations to join. (4) After the other slave stations detect Solicit_Successor, they back off for a random time slot and send the successor station setting frame Set_Successor, and the station with successful competition becomes the successor station of the master station. (5) The successor station sets the previous successor station of the master station as its successor station. For the first slave to join, the previous successor of the master is the master itself. Thus, an initial logical ring of two sites is formed. (6) When the token loops back to the master station along the token logic, the master station first processes the data transmission task in the queue (see Figure 7 for its data frame). If the queue is empty or the token holding time THT has not been exhausted after the data frame is processed, the master station will send Solicit_Successor again to invite other slave stations to join. (7) According to the mechanism of steps (1)-(6), after a sufficient period of time, the stations in the wireless distributed system will automatically form a token logical ring, thus forming a system.

2. System self-healing mechanism

(1) After the master station establishes a token logical ring, it generates a token and passes it on the ring, and then the master station listens to each token sent by the slave station. (2) Set a maximum waiting time TRMWT (TokenResume Max Wait Time) for token recovery in the master station, and reset TRMWT whenever the master station detects a token. (3) When the TRMWT of the master station is exhausted and has not detected the next token, it thinks that the token is lost, and then generates a new token according to the connection table stored in advance and sends it to the site that lost the token.

In order to ensure the real-time response, each station in the wireless industrial control network has a fixed maximum token holding time MTHT (Max Token Hold Time). When the MTHT of the station is exhausted, the token is passed to the next STA. So again and again.

In order to automatically return to normal within a certain period of time after token loss occurs, to ensure the normal operation of the protocol, it is necessary to reasonably set the maximum waiting time TRMWT for token recovery.

The maximum waiting time TRMWT for token recovery is defined as follows:

TRMWT=THT+MTTTD

Among them, THT (Token Holding Time) is the maximum token holding time of STA, and MTTTD (Max TokenTransmit Time Delay) is the maximum time required for token transmission between any two STAs on the logical ring.

If the master station has not heard the token sent by the slave station after the token is retransmitted twice, it is concluded that the slave station is out of order. The master station deletes the slave station from the logical ring, and passes the token to the successor station of the slave station.

3. The joining and exiting process of the slave station STA

(1) The joining process of the slave station: ① controlled by the master station, when the queue of the master station is empty, send Solicit_Successor; Set the successor station as its successor station, and send Set_Sucessor to the master station; ③ After the master station receives Set_sucessor, set the slave station as its successor station, and send the predecessor station setting frame as Set_Predecessor to its previous successor station; ④After receiving the Set_Predecessor, the former successor station of the master station sets the slave station as its predecessor station, and sends an acknowledgment frame Ack to the master station; ⑤The master station passes the token to the newly added slave station after receiving the Ack frame Station, so far the joining process of the human station is completed. The joining process of each slave station is shown in Figure 8.

(2) The exit process of the slave station: it is simpler than the joining process. ①The slave station that wants to exit sends Set_Successor to its predecessor station after receiving the token; ②After the predecessor station receives the Set_Successor, set the successor station of the slave station as Its successor station, and send Set_Successor to the successor station of the slave station; ③The successor station of the slave station returns the Ack frame to the slave station after receiving the Set_Successor; ④The slave station passes the token to its successor after receiving the Ack frame stand and exit. The exit process of each slave station is shown in Figure 9.

4. The six special frame formats in this embodiment are as follows:

1). The format of the token frame

As shown in Figure 2, FC (Frame Control) indicates the type of frame (token, token control frame, etc.), Seq (Sequence) is the logic number of STA, PreA (Predecessor Address) is the address of the predecessor station, LA (LocalAddress ) is the address of the local station, SucA (Successor Address) is the address of the successor station, TRC (Token RotateCounter) is the number of times the token circulates in the ring, and Res (Reserve) is a reserved field.

PreA, LA, SucA in the token frame provide information for establishing the connection table. After the master station detects the token frame, it takes out the information in the PreA, LA, SucA fields and compares it with the information in the connection table. If the information has changed, the connection table is updated, otherwise it is simply discarded. Among them, SucA also indicates the receiving station address of the token frame.

The operation of Seq is completed jointly by the master station and the slave station. The serial number of the master station is always 0. Whenever the slave station receives the token, it adds 1 to the Seq field in the token. When the token returns to the master station, the master station clears the Seq field. The serial number Seq can make the main station clearly know the number of slave stations in the current logical ring.

TRC is controlled by the master station. Whenever the master station receives the token, it adds one to the TRC, and so on.

2). The format of the Solicit_Successor frame

As shown in Figure 3, FC indicates the type of the frame, HA is the address of the master station, HSucA is the address of the successor station of the master station, and Br indicates that the frame is used for broadcasting.

3). Format of the Set_Successor frame

As shown in Figure 4, FC indicates the type of the frame, SA is the source address of the frame, DA is the destination address of the frame, and SucA is the address of the set successor station.

4). Format of the Set_Predecessor frame

As shown in Figure 5, FC indicates the type of the frame, SA is the source address of the frame, DA is the destination address of the frame, PreA is the address of the predecessor station set, and AA indicates the destination address of the Ack frame return.

5). The format of the Ack frame

As shown in Figure 6, FC indicates the type of the frame, SA is the source address of the frame, and DA is the destination address of the frame.

6). The format of the data frame

As shown in Figure 7, FC indicates the type of the frame, Duration is the expected time limit for the transmission of the data frame Duration, SA is the source address of the frame, DA is the destination address of the frame, PC is the priority level of the data packet, and Data is the data field , CRC is a cyclic redundancy check code.

Claims (2)

1. protocol control method towards wireless industrial control network, its communication model is made up of physical layer, data link layer and application layer, described physical layer and application layer adopt international standards respectively physical layer and the application layer of communication model OSI, it is characterized in that described data link layer is divided into two layers: following sublayer uses traditional carrier sense multiple access to insert the CSMA agreement as the wireless channel access control protocol; A kind of control protocol based on token is used in top sublayer, sets up a token logic box in totally interconnected wireless distribution system, thus the CSMA agreement of sublayer below the control; A token logic box self-healing mechanism is set, avoids making the token logic box lose efficacy because of losing of token; And determine a token logic box expansion and contractile mechanism, make network system can adapt to the adding of each mobile site automatically and withdraw from variation; Described use is based on the control protocol of token, and the step of setting up the token logic box in totally interconnected wireless distribution system is as follows:

When (1) initial, each site STA at first enters reset mode, intercepts channel then, waits for that the invitation of main website adds;

(2) main website gets and resets earlier after electric, generates a token Token then;

(3) token Token transmits successively along logic box, up to etc. the site STA of Frame to be sent receive it, its sends and reads to ask frame Solicit_successor then, invites other slave station to add;

(4) after other slave station listens to Solicit_Successor, keep out of the way one and send successor at random behind the time slot frame Set_successor is set, competing successful website becomes the successor of main website;

(5) successor is set to its successor in the previous follow-up station of main website again.Concerning the slave station of first adding, the previous successor of main website is exactly a main website itself, constitutes an initial token logic box that contains 2 websites thus;

(6) be that token holding time THT did not also exhaust after sky or Frame transmission disposed as if the wait task formation, main website just sends Solicit_successor again, invites other slave station to add;

(7) according to step (1)～(6) mechanism, after experience a period of time, each website in the wireless distribution system will be set up into a token logic box automatically, thereby forms a network system;

The self-healing step of described token logic box self-healing mechanism is as follows:

(1) main website generates a token and transmits on ring after setting up the token logic box, and each token that slave station sends is intercepted by main website then;

(2) in main website, set a token and recover and maximum latency TRMWT, hear a token, just TRMWT is resetted when the main website frame;

(3) also do not listen to next token after the TRMWT of main website exhausts, it just thinks token lost, and the connection table information according to storage in advance generates a new token and sends to the website of losing token then;

Described token logic box expansion and contractile mechanism, determine the adding of slave station STA and withdraw from process as follows:

(1) adition process of slave station:

1. by main website control, main website sends Solicit_Successor when formation is sky;

What 2. desire added system is made as its predecessor with main website from standing in after receiving Solicit_Successor, and the successor of main website is made as its station of continuing, and sends Set_Sucessor to main website;

3. after Set_sucessor receives in main website, this slave station is made as its successor, and sending predecessor to its previous successor, frame is set is Set_Predecessor;

4. the previous successor of main website is made as its predecessor with this slave station after receiving Set_Predecessor, and sends acknowledgement frame Ack to main website;

5. main website just passes token to this initiate slave station after receiving the Ack frame, and so far, the adition process of slave station is finished;

(2) process that withdraws from of slave station:

That 1. wants to withdraw from sends Set_Successor to its predecessor from standing in after receiving token;

2. its predecessor is received behind the Set_Successor successor that the successor of this slave station is made as it, and sends Set_Successor to the successor of this slave station;

3. the successor of this slave station is received behind the Set_Successor to this slave station loopback Ack frame;

4. slave station is received and token is passed to its successor behind the Ack frame and log off.

2. the protocol control method towards wireless industrial control network according to claim 1, it is characterized in that described token frame, claim frame, successor frame, predecessor being set, that the form of frame, Ack frame and Frame is set is as follows:

(1) form of token frame Token: contain frame type FC, logic number Seq successively, build table information SucA, this station address LA, predecessor address PreA and token period TRC;

(2) form of claim frame Set_Successor: contain frame type FC, broadcasting Br, the successor address HSuoA of main website and the address HA of main website successively;

(3) successor is provided with the form of frame Set_Successor: contain frame type FC, destination address DA, successor address SucA and this frame source address successively;

(4) predecessor is provided with the form of frame Set-Predecessor: contain frame type FC, destination address DA, this frame source address SA, predecessor address PreA and Ack frame successively and return destination address;

(5) form of Ack frame: contain frame type FC, destination address DA and this frame source address SA successively;

(6) form of Frame: priority level PC, the data Data and the cyclic redundancy check (CRC) code CRC that contain expectation time limit Duration, destination address DA that frame type FC, notebook data frame transmit, this frame source address SA, data successively.

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