JP2010206394A - Safety network apparatus and safety network - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a safety network capable of achieving target error missing rate and system failure rate. <P>SOLUTION: A safety network apparatus comprises: a bit error probability acquiring section 23 for acquiring a bit error probability on a transmission line over a safety network; an error detecting code type change section 12 for appropriately changing the type of an error detecting code to be imparted to a security message on the basis of the bit error probability notified from the bit error probability acquiring section 23; and an error detecting code type writing section 13 for calculating an error detecting code for the security message on the basis of the type of the error detecting code notified from the error detecting code type change section 12 and further generating the security message writing therein error detecting code type information indicating the type of the error detecting code and the calculated error detecting code. A transmission section 21 in a transmission layer transmits a transmission frame having stored therein the security message generated by the error detecting code type writing section 13. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a safety network device constituting a safety network.

  Conventionally, in a safety network that realizes functional safety, in order to ensure data transmission between the devices that make up the system, an error detection code, etc. is added to safety messages sent and received in the safety layer to detect bit errors during transmission. I was going. However, there is a possibility that an error that cannot be detected by the error detection code occurs depending on the occurrence state of the bit error. In a safety network, the probability of such an error being missed is defined as the error miss rate, and the system failure rate is determined based on the error miss rate and the number of messages transmitted per hour, and the system failure rate is kept at a certain level. Define risk tolerance levels to accommodate.

  The error miss rate of the safety network is calculated from the bit error probability due to the physical characteristics and signal characteristics of the transmission medium of the network, the transmission message length, and the Hamming distance of the error detection code. In the conventional safety network, the bit error probability is defined according to the type and specification of the physical layer to be adopted, and the error detection code type, the number of messages per hour, etc. are set so that the error miss rate and system failure rate fall within the target values. The parameter was determined.

"Safety Bus System for Automation" by D. Reinert and M. Schaefer, NPO Safety Engineering Laboratory, September 24, 2003, P40-41, P101

  However, according to the above-described conventional technology, since the error miss occurrence rate in the safety layer is calculated using the bit error rate defined for each transmission line, when a bit error more than expected occurs in the transmission line Has a problem that there is no basis for calculating the error miss rate, and the target error miss rate and system failure rate may not be achieved.

  The present invention has been made in view of the above, and an object of the present invention is to obtain a safety network that can achieve the target error miss rate and system failure rate even when the bit error rate is higher than expected. To do.

  Another object of the present invention is to obtain a safety network device that can easily implement a new error detection code system.

  In order to solve the above-described problems and achieve the object, the present invention provides a safety layer that performs safety control and a transmission / reception of the transmission frame in a safety network that transmits / receives a transmission frame storing a safety message between safety network devices. The transmission network includes the transmission layer, and the transmission layer includes bit error probability acquisition means for acquiring a bit error probability of a transmission path in the safety network, and the safety layer includes the bit error probability. Based on the bit error probability notified from the acquisition means, an error detection code type changing means for appropriately changing the type of the error detection code given to the safety message, and an error detection code notified from the error detection code type changing means Calculate an error detection code for the safety message based on the type, and Error detection code type information indicating the type of error detection code and error detection code information writing means for generating a safety message in which the calculated error detection code is written, and the transmission layer includes the error detection code information document. The transmission frame storing the safety message generated by the inserting means is transmitted.

  According to the present invention, it is possible to reduce the error miss rate and the system failure rate and to maintain the transmission quality of the system.

  Embodiments of a safety network according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating a configuration example of a safety network according to the present embodiment. The safety network of FIG. 1 includes a safety network device 1-M (M = 1, 2,...) And a bus system 2. In the following, a case where the bus system 2 employs a full-duplex transmission line will be described.

  FIG. 2 is a block diagram illustrating a configuration example of the safety network device according to the present embodiment. The safety network device 1 -M in FIG. 2 includes a safety layer 10 and a transmission layer 20. The safety layer 10 includes an error detection code type changing unit 12 that changes the type (error detection code type) of an error detection code used in the safety layer, and an error detection code indicated by error detection code type information included in the safety message. An error detection unit 11 that performs error detection based on the type, and an error detection code type writing unit 13 that writes the type of the error detection code in the error detection code type information in the safety message. The error detection code type changing unit 12 holds a plurality of error detection code types. In addition, the transmission layer 20 includes a transmission unit 21 and a reception unit 22 that transmit and receive data to and from the bus system 2, and a bit error probability acquisition unit 23 that acquires a bit error probability of a transmission path of the safety network.

  FIG. 3 is a diagram illustrating a configuration example of the bit error probability acquisition unit 23 of FIG. The bit error probability acquisition unit 23 of FIG. 3 includes a bit error probability reading unit 31, a bit error probability calculation unit 32, and a bit error probability transmission unit 33. The bit error probability reading unit 31 reads bit error probability information indicating the bit error probability in the transmission path from the transmission frame received from the receiving unit 22. The bit error probability calculation unit 32 calculates a bit error probability based on the transmission frame received by the reception unit 22. The bit error probability transmission unit 33 stores bit error probability information indicating the bit error probability calculated by the bit error probability calculation unit 32 in a transmission frame to be transmitted. That is, the bit error probability information read by the bit error probability reading unit 31 is information transmitted from another device, and the bit error probability information that the bit error probability transmission unit 33 stores and transmits in the transmission frame is It is the calculated information.

  FIG. 4 is a diagram showing an example of a format of a transmission frame transmitted in the safety network of FIG. The format of FIG. 4 includes a destination address 41, a source address 42, a transmission frame length 43, a control flag 44, bit error probability information 45, a payload 46, and an error detection code 47. The destination address 41 stores the address of the safety network device that is the transmission destination of the transmission frame. The source address 42 stores the address of the safety network device that is the source of the transmission frame. The transmission frame length 43 stores the length of the entire transmission frame. The control flag 44 stores various information necessary for transmission. The bit error probability information 45 stores information on the bit error probability acquired by the bit error probability calculation unit 32. The payload 46 stores a safety message received from the safety layer 10 by the transmission layer 20. The error detection code 47 stores an error detection code calculated using the type of error detection code adopted by the transmission layer of each safety network device.

  FIG. 5 is a diagram illustrating an example of a format of a safety message transmitted and received between safety layers in the safety network of FIG. A destination address 51, a source address 52, a safety message length 53, error detection code type information 54, a payload 55, and an error detection code 56 are provided. The destination address 51 stores an address capable of identifying the safety layer of the destination safety network device. The source address 52 stores an address that can identify the safety layer 10 of the source safety network device. The safety message length 53 stores the length of the entire safety message. The error detection code identification information 54 stores information for identifying the type of error detection code used for the safety message. The payload 55 stores safety data to be transmitted with a safety message. The error detection code 56 stores an error detection code calculated using the type of the error detection code specified by the information stored in the error detection code identification information 54.

  Next, the operation of the safety network configured as described above will be described. Hereinafter, as an example, a case where a safety message is transmitted using a transmission frame between the safety network device 1-1 and the safety network device 1-2 in the safety network of FIG. 1 will be described.

  Here, first, a transmission frame storing a safety message is transmitted from the safety network device 1-1 to the safety network device 1-2. The error detection code type writing unit 13 of the safety layer 10 of the safety network device 1-1 creates and creates a safety message for the safety layer 10 of the safety network device 1-2 periodically or irregularly. A safety message is notified to the bit error probability acquisition unit 23 of the transmission layer 20 of the own device. In this case, in the safety message shown in FIG. 5, the error detection code type writing unit 13 uses the destination address 51 for identifying the safety layer of the safety network device 1-2 and the source address 52 for the safety layer of its own device. An address capable of identifying 10 is stored.

  The bit error probability acquisition unit 23 of the transmission layer 20 of the safety network device 1-1 outputs the safety message received from the error detection code type writing unit 13 of the safety layer 10 to the transmission unit 21, and the transmission unit 21 transmits the transmission frame. Create In this case, the transmission unit 21 of the transmission layer 20 stores the address indicating the safety network device 1-2 in the destination address 41 and the address indicating the own device in the transmission source address 42 in the transmission frame shown in FIG.

  Here, examples of the error detection code include CRC (Cyclic Redundancy Check) -CCITT. In this case, the CRC calculation target is in the range of the destination address 41 to the payload 46, and the calculation result is stored in the error detection code 47. If a bit error occurs when this transmission frame is transmitted over the network, the error can be detected by error detection processing on the receiving side. For example, when an error occurs in the CRC calculation target range, that is, in the range of the destination address 41 to the payload 46, the error can be detected by CRC calculation on the receiving side. For example, when an error occurs in the error detection code 47, the CRC calculation result on the receiving side is different from the content of the error detection code 47, so that the error can be detected.

  When the transmission frame is created as described above, the transmission unit 21 of the safety network device 1-1 sends the transmission frame to the bus system 2.

  The transmission frame transmitted from the safety network device 1-1 reaches the safety network device 1-2 via the bus system 2. When receiving the transmission frame, the receiving unit 22 of the safety network device 1-2 outputs the received transmission frame to the bit error probability acquiring unit 23 of the transmission layer 20. The transmission frame is input to the bit error probability reading unit 31 and the bit error probability calculating unit 32.

  First, the operation of the bit error probability reading unit 31 will be described. The bit error probability reading unit 31 of the safety network device 1-2 to which the transmission frame is input reads the bit error probability information 45 from the transmission frame, and the bit error probability indicated by the bit error probability information is changed to the error detection code type changing unit 12. Notify

  Since an error detection code is added to the safety message transmitted in the safety network of FIG. 1, it is possible to determine whether or not a bit error has occurred due to network transmission or the like. There are various error detection code types such as CRC-CCITT in addition to the above-mentioned CRC-CCITT, but a type having a Hamming distance necessary to achieve the target error miss rate and system failure rate is used. . If the bit error probability is high, a larger Hamming distance is required, and therefore it is necessary to use an error detection code type having a corresponding Hamming distance. As described above, the error miss rate is the probability that an error that is not detected by the error detection code will occur, and is defined by a function that uses the message length, the Hamming distance of the error detection code type, and the bit error probability as arguments.

  In general, the bit error probability of a transmission line defines an ambient environment condition such as EMI (Electro-Magnetic Interference) of the transmission line, and the bit error probability prescribed value is obtained from the worst condition among them. However, when the surrounding environment is worse than expected and the bit error probability is increased, the calculated error miss rate cannot be satisfied.

  The error detection code type changing unit 12 selects an error detection code type suitable for use in the safety message based on the notified bit error probability, and sets the current error detection code type as the newly selected error. Change to detection code type. Then, the error detection code type changing unit 12 notifies the error detection code type writing unit 13 of the fact and the changed type. Receiving this, the error detection code type writing unit 13 rewrites the error detection code type information 54 with a code indicating the changed type in the safety message transmitted by the own device, and uses the changed type to make the safety An error detection code for the message is calculated, and the calculated value is stored in the error detection code 56 of the safety message. As described above, the error detection code type of the safety message is changed.

  The error detection code type writing unit 13 of the safety layer 10 of the safety network device 1-2 sets other items to create a safety message, and the safety message is a bit of the bit error probability acquisition unit 23 of the transmission layer 20 The error probability transmission unit 33 is notified.

  Next, the operation of the bit error probability calculation unit 32 will be described. The bit error probability calculation unit 32 of the bit error probability acquisition unit 23 to which the transmission frame is input as described above calculates the bit error probability with respect to the transmission frame received by the own device, thereby causing the own device from the safety network device 1-1. The probability of bit error occurring in the transmission direction to is obtained. The bit error probability is calculated as follows, for example. First, the bit error probability calculation unit 32 refers to the transmission frame length 43 in the transmission frame, and records the transmission frame length in itself together with the time when the transmission frame is received. Also, the bit error probability calculation unit 32 performs the error detection process described above, and when an error is detected, records the reception time of the transmission frame as the error detection time. Then, the bit error probability calculation means 32 calculates the transmission frame length (cumulative transmission frame length) recorded during a certain fixed time. Then, the bit error probability is calculated by dividing the number of transmission frames in which errors are detected within the same period by the cumulative transmission frame length. The accumulated transmission frame length may be cleared every time an error is detected, and thereafter, the value of the transmission frame length 43 of the received transmission frame may be accumulated and added until the error is detected.

  The bit error probability calculation unit 32 of the bit error probability acquisition unit 23 notifies the bit error probability transmission unit 33 of the bit error probability calculated as described above.

  As described above, the bit error probability transmission unit 33 of the safety network device 1-2 obtains information on the safety message and the calculated bit error probability. The bit error probability transmission unit 33 stores the safety message notified from the error detection code type writing unit 13 in the transmission frame that is next transmitted to the safety network device 1-1. The bit error probability transmission unit 33 stores information on the bit error probability notified from the bit error probability calculation unit 32 in the bit error probability information 45 of the transmission frame. The information on the bit error probability may be a value of the bit error probability, the probability value may be expressed as a power of 10, and only the multiplier may be stored, or may be expressed by a symbol using a conversion table or the like. Then, the bit error probability transmission unit 33 notifies the transmission unit 21 of the transmission frame storing the data as described above. The transmission unit 21 stores other data, creates a transmission frame, and transmits it to the safety network device 1-1.

  The transmission frame transmitted from the safety network device 1-2 reaches the safety network device 1-1 via the bus system 2. When the bit error probability reading unit 31 of the bit error probability acquiring unit 23 in the safety network device 1-1 receives this transmission frame via the receiving unit 22, the bit error probability information 45 is read from the transmission frame, and the safety network device The bit error probability calculated and transmitted in 1-2 is acquired. In addition, the bit error probability calculation unit 32 of the bit error probability acquisition unit 23 performs the same processing as described above to obtain the bit error probability generated in the transmission direction from the safety network device 1-2 to the own device.

  Thus, in the safety network device 1-1, the bit error probability in the transmission direction from the own device to another device can be acquired. Therefore, in a full-duplex type network in which transmission paths in the transmission direction and reception direction are separate physical media, the bit error probability can be acquired for each direction individually.

  Further, the error detection unit 11 of the safety layer 10 in the safety network device 1-1 identifies the type of the error detection code with reference to the error detection code type information 54 of the safety message stored in the received transmission frame, Using this type, an error detection code for the safety message is calculated. Then, the error detection unit 11 compares the calculation result with the error detection code 56 of the received safety message, and determines that an error has occurred if they do not match.

  As described above, in the present embodiment, the bit error probability is acquired and the type of error detection code used in the safety message is changed in the safety network device configuring the safety network. This makes it possible to flexibly change the method used for error detection even when the bit error probability is higher than the expected value, thereby reducing the error miss rate and system failure rate and maintaining the system transmission quality. It becomes.

  Further, in the present embodiment, in the safety network device on the transmission side, the bit error probability is calculated from the frame length of the received frame and the error detection state, and is transmitted to the safety network device on the reception side by the transmission frame. In the safety network device on the receiving side, bit error probability information stored in the received frame is acquired. As a result, each safety network device can acquire the bit error probability in the transmission direction from its own device to the other device. Therefore, even in a full-duplex network, it is possible to grasp the bit error probability for each physical medium. Accordingly, appropriate control can be executed.

  In the above-described embodiment, the case where the bus system 2 employs a full-duplex transmission line has been described. However, the above-described configuration can also be applied when a half-duplex transmission line is employed. In the case of half duplex, since the same transmission path is used in both the transmission direction and the reception direction from the own apparatus to the other apparatus, the bit error probability calculation unit 32 sends the calculated bit error to the bit error probability reading unit 31. Notify the probability. Then, the bit error probability reading unit 31 compares the bit error probability indicated by the bit error probability information acquired from the transmission frame with the bit error probability notified from the bit error probability calculating unit 32, and has a larger value (transmission). The error detection code type changing unit 12 is notified of the bit error probability. Then, the error detection code type changing unit 12 changes the error detection code type using the notified bit error probability.

Embodiment 2. FIG.
In the first embodiment, the case where one of error detection methods prepared in advance is selected has been described. However, in this embodiment, a new error detection method can be added, and a new method can be included. Will be described.

  FIG. 6 is a block diagram illustrating a configuration example of the safety network device according to the present embodiment. Compared to the safety network device 1-M in FIG. 1, the safety network device 1B-M in FIG. 6 replaces the safety layer 10 and the error detection code type change unit 12 with a safety layer 10B and an error detection code type change unit 12B. And an error detection code type adding unit 14 and an error detection code information storage unit 15 for storing a Hamming distance and an algorithm used for error detection are different. The error detection code type changing unit 12B can select the type of the error detection code not only from the type of the error detection code held by itself but also from the type provided in the error detection code information storage unit 15. The error detection code type adding unit 14 can add hamming information and an algorithm to the error detection code information storage unit 15 for one or more error detection methods. The error detection code information storage unit 15 stores hamming information and algorithms for one or more error detection methods.

  Further, the safety network device 1B-M of the present embodiment is used in place of the safety network device 1-M, and constitutes a safety network (not shown) similar to FIG.

  Next, the operation in the safety network configured as described above will be described. As a premise, the error detection code type changing unit 12B of the safety network device 1B-M, as described in the first embodiment, generates a corresponding error based on the bit error probability calculated and notified by the bit error probability acquiring unit 23. An error detection code type having a Hamming distance is selected and used for error detection of a safety message.

  Here, in addition to the error detection code type held by the error detection code type changing unit 12B itself, as a new error detection code type, for example, a type having a short code length and a long Hamming distance and an error detection code are derived. It is assumed that the calculation procedure for simplifying the calculation procedure and the type with reduced processing load are stored in the error detection code type adding unit 14.

  The error detection code type adding unit 14 of the safety network device 1B-M stores the type of hamming information and algorithm in the error detection code information storage unit 15. When the bit error probability is notified from the bit error probability acquisition unit 23, the error detection code type change unit 12B changes the type of the error detection code based on the bit error probability. At this time, in determining the error detection code type to be used, the error detection code information storage unit 15 is referred to, and the error detection code type held by itself and the newly added error detection code type are selected. decide.

  In the determination, the error detection code type changing unit 12B considers the safety message length, the Hamming distance, and the like in addition to the notified bit error probability. When the hamming distance depends on the safety message length, the error detection code information storage unit 15 may store information on the correlation between the safety message length and the hamming distance. Further, as information for comparing and selecting the error detection code types, the error detection code information storage unit 15 may further include information such as a calculation amount for calculating the error detection code. The error detection code changing unit 12B holds an algorithm for comparing error detection code types and the like, evaluates these parameters, and selects an appropriate error detection code type. In general, the calculation of an error detection code requires many calculation procedures. In particular, since an error detection code with a long Hamming distance tends to have a long code length, the error detection code type changing unit 12B also considers the processing load. Can be selected.

  As described above, in this embodiment, a function unit for adding a new error detection method is provided. As a result, an error detection method can be easily added, and the error detection method can be selected more flexibly.

  As described above, the safety network device according to the present invention is useful when used in a safety network, and is particularly suitable for a case where it is desired to achieve a target error miss rate and system failure rate regardless of the bit error probability. Yes.

2 is a diagram illustrating a configuration example of a safety network according to Embodiment 1. FIG. FIG. 3 is a block diagram illustrating a configuration example of a safety network device according to the first embodiment. It is a figure which shows the structural example of the bit error probability acquisition part of FIG. It is a figure which shows the structural example of the format of the transmission frame transmitted in the safety network of FIG. It is a figure which shows an example of the format of the safety message transmitted / received between safety layers in the safety network of FIG. 6 is a block diagram illustrating a configuration example of a safety network device according to a second embodiment. FIG.

1, 1B Safety Network Device 2 Bus System 10, 10B Safety Layer 11 Error Detection Unit 12, 12B Error Detection Code Type Change Unit 13 Error Detection Code Type Write Unit 14 Error Detection Code Type Addition Unit 15 Error Detection Code Information Storage Unit 20 Transmission layer 21 Transmission unit 22 Reception unit 23 Bit error probability acquisition unit 31 Bit error probability reading unit 32 Bit error probability calculation unit 33 Bit error probability transmission unit 41 Destination address 42 Source address 43 Transmission frame length 44 Control flag 45 Bit error probability Information 46 Payload 47 Error detection code 51 Destination address 52 Source address 53 Safety message length 54 Error detection code type information 55 Payload 56 Error detection code

Claims (6)

In a safety network for transmitting and receiving a transmission frame storing a safety message between safety network devices, the safety network device comprising a safety layer for performing safety control and a transmission layer for transmitting and receiving the transmission frame,
The transmission layer is
Bit error probability acquisition means for acquiring a bit error probability of a transmission line in the safety network;
With
The safety layer is
Based on the bit error probability notified from the bit error probability acquisition means, error detection code type change means for appropriately changing the type of error detection code to be given to the safety message;
Based on the error detection code type notified from the error detection code type changing means, an error detection code for the safety message is calculated, and further, error detection code type information indicating the type of the error detection code and the calculation Error detection code information writing means for generating a safety message in which the error detection code is written;
With
The safety network device, wherein the transmission layer transmits a transmission frame storing a safety message generated by the error detection code information writing means. The bit error probability acquisition means includes
Bit error probability reading means for reading first bit error probability information which is a bit error probability in the transmission direction from the own device to another device from the received transmission frame;
Bit error probability calculation means for calculating the bit error probability in the transmission direction from the other device to the own device based on the received transmission frame;
Second bit error probability information indicating the bit error probability calculated by the bit error probability calculation means and a safety message generated by the error detection code information writing means are stored in a transmission frame transmitted to another apparatus. Bit error probability transmission means;
With
The transmission layer further transmits a transmission frame storing the second bit error probability information in addition to the safety message generated by the error detection code information writing means. The described safety network device.   3. The bit error probability acquisition unit, wherein the bit error probability reading unit notifies the error detection code type changing unit of a bit error probability indicated by the first bit error probability information. Safety network equipment. The bit error probability calculating means further notifies the calculated bit error probability to the bit error probability reading means,
The bit error reading means further compares the bit error probability calculated by the bit error probability calculating means with the bit error probability indicated by the first bit error probability information read by itself, and has a high probability. The safety network device according to claim 2, wherein the bit error probability of the other is notified to the error detection code type changing means. An error detection code type addition means capable of adding a Hamming distance and an algorithm for the type of error detection code;
Error detection code information storage means for storing the Hamming distance and algorithm for the type of error detection code;
Further comprising
The error detection code type changing means selects an error detection code type used in the safety layer from among the error detection code types stored by itself and the error detection code information storage means. Item 5. The safety network device according to any one of Items 1 to 4. The safety network device according to any one of claims 1 to 5,
A safety network comprising a plurality of devices.

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