JPS60189344A - Data communication system and its equipment - Google Patents

Abstract

PURPOSE:To improve transmission efficiency by outputting a token frame of a preamble which is longer than other transmission frame, when switching a network system of a random access type CSMA/CD system to a dispersion control type token passing system. CONSTITUTION:A transmission origin address prepared in advance from an address storage part 5 is read out, and this address is set to a destination address 303 of the top priority token 300. Also, a self-address of a storage part 5 is set to a transmission origin address 304 of the top priority token 300. In such a state, the first priority token 300 is transmitted, and whether the token 300 has been transmitted normally or not is checked, and in case that it has not been transmitted normally, the top priority token 300 is transmitted again. Also, in order to obtain preferentially a right of transmission, a preamble 301 which is longer than other transmission frame is provided. When this token 300 is transmitted normally, the own communicating mode flag is set to a token mode and the processing is executed.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a data communication method and device for a network system in which a plurality of transmission devices are connected to a bus-type communication medium.
CSMA/C is said to be the most efficient, especially at low loads.
It enables the combination of the D method and the token passing method, which is said to be most efficient at high loads, and allows other transmissions as token frames when switching the communication mode from the C3MA/CD method at low loads to the token passing method at high loads. The present invention relates to a data communication system and device that outputs a preamble token frame that is longer than a frame.

[Prior Art] In network systems using path-type communication media, the random access type C5MA/CD method and the distributed control type token passing method are mainly used, but each has its advantages and disadvantages. The C3MA/CD method requires a frame collision detection circuit, but the control for obtaining communication rights is simpler than the token passing method. However, when the transmission path becomes highly loaded, collisions of information frames occur frequently, and the transmission efficiency is extremely reduced. On the other hand, although the token passing method does not require a frame collision detection circuit, the control to obtain communication rights is more complicated. In the I-kun passing method, after a device that currently has communication rights has completed its own transmission, it holds the address of the 1-kun transmission destination for the next device to which it should pass the communication rights (hereinafter referred to as a token). need to be. Therefore, when a device is installed or removed from a system operating using the token passing method, other connected devices must reconfigure their own token transmission destination addresses. No. If the system is not reconfigured, tokens will not be sent to devices that are installed in the system forever, and even if tokens are sent to devices that are removed from the system, the tokens will not be passed to the next device. This results in problems.

Moreover, since a wide variety of devices can be connected to a network system, powering on or adding new devices can
Alternatively, the need for such address reconfiguration frequently occurs due to power-off or removal of already connected equipment due to failure, etc.

In the token passing method, frame collisions do not occur, so transmission efficiency does not decrease even if the transmission path becomes highly loaded. However, in general, when the load is low, the transmission efficiency is lower than that of the C3MA/CD method due to overhead processing such as 1-kun delegation. For these reasons, conventional network systems intended for low-load 11j7 communications have adopted the C3MA/CD method, while network I/work systems designed to handle high loads have adopted the 1-Kun passing method from the beginning. It was selectively adopted. It is also conceivable to be able to switch between both types depending on the load. However, for example, when the load is low, the C5MA/CD method is used for communication, and when the load is high, the data communication method is switched to the token passing method.
Even if a high load condition is detected under communication control using the D method, frame collisions occur frequently, so there is a drawback that notification to switch the communication control method cannot be promptly transmitted to devices throughout the network.

[Objective] The present invention has been made in view of the above-mentioned drawbacks of the prior art, and its purpose is to improve communication control and token passing using the C3MA/CD method in a network system using a bus-type communication medium. Considering both advantages of communication control using this method, quick switching is possible using a method that outputs a token frame with a preamble longer than other transmission frames as a 1. The object of the present invention is to provide a data communication method that enables communication with high data transmission efficiency at all times.

Another object of the present invention is to provide a data communication device with C3MA/CD.
The communication control means according to the CS MA/CD method is equipped with a communication control means according to the CS MA/CD method, a communication control means according to the token passing method, and a preamble generation means capable of outputting a token frame with a preamble longer than other transmission frames. By outputting a token frame with a longer preamble than other transmission frames as a token frame when switching from the C3MA/CD method under low load to the token passing method under high load, communication with high data transmission efficiency is always maintained. The purpose of the present invention is to provide a data communication device that enables the following.

[Embodiment] Hereinafter, a data communication system and device according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows the main configuration of a transmission device (hereinafter referred to as the present embodiment device) used to implement a data communication method according to an embodiment of the present invention (hereinafter referred to as the present embodiment method). FIG. In the figure, l is a frame transmission circuit, 2
is a frame reception circuit, 3 is a frame collision detection circuit, and 4 is a frame collision detection circuit.
5 is an address comparison circuit that compares the self address and the source address in the received frame; 5 is an address storage section that holds the necessary source address based on the result of address comparison between the self address and the address comparison circuit 4; ,6
7 is an address setting unit that sets a self-address; 7 is a control unit that controls the entire device; 8 is a read-only memory (ROM) that stores operating programs to be executed by the control unit 7; 9 is a read-only memory (ROM); Random access memory (RAM) is used by the control unit 7, and 10 is a transmission line forming a bus-type communication medium.

The frame transmission circuit 1 receives a packet for which a transmission request has been generated by the control unit 7 via a line 11, and outputs a transmission frame signal to a line 12. At the same time, the frame transmission circuit 1 also outputs a pseudo transmission frame signal having the same shape as the transmission frame signal to the collision detection circuit 3 via the line 14. The frame receiving circuit 2 reads the frame on the transmission line IO via the line 15 and outputs the received frame signal to the collision detection circuit 3 via the line 16. The collision detection circuit 3 compares the pseudo transmission frame signal on line 14 and the reception frame signal on line 16 to detect whether or not they match.

In other words, if a match is obtained over all frames, it means that there was no collision of transmission frames with other devices. The result of frame collision detection is informed to the control section 7 via line 17. The address comparison circuit 4 compares the destination address in the received frame signal with its own address inputted from the address setting section 6 via the line 18 to determine whether there is a match. When a match is determined, the control unit 7 is informed of this via line 19. Further, since the received frame signal is addressed to itself, necessary information in the received frame signal is taken into the control section 7 via the line 20. Note that the control section 7 reads the preset self-address from the address setting section 6 via the line 21, sends it to the address storage section 5 via the line 13, and stores it as the self-address. This is for the convenience of creating transmission packets and other processing in the control unit 7.

FIG. 2 is a diagram showing the format of an information frame according to this embodiment. In the figure, the information frame l'oo includes a pro-ampule 101, a start delimiter 102, a destination address 103, a source address 104, a 1-kun control 105, an information section 106, a frame check sequence 107, and an end address. It is composed of a delimiter 108.

1 FIG. 3(A) is a diagram showing the format of 1.-kunf 1/-m in the method of this embodiment. In the figure, a token frame 200 includes a preamble 201 and a start delimiter 2.
02, destination address 203, and source address 204
, a 1-kun control 205 , a frame check sequence 207 , and an end delimiter 208 .

Further, FIG. 3(B) is a diagram showing the format of the highest priority token frame in this embodiment system. In FIG. 6, the highest priority token frame 300 has a long preamble 301
, a start delimiter 302 , a destination address 303 , a source address 304 , a token system W 305 , a frame check sequence 307 , and an end delimiter 308 . In the system of this embodiment, the highest priority token frame 300 is used for the purpose of obtaining the transmission right preferentially by forced output of the long preamble 301 under communication control of the C3MA/CD system.

FIG. 4 is a diagram showing the contents stored in the address storage section 5. As shown in FIG. The address storage unit 5 has a self address 501,
and the source address of the device that has previously transmitted to the transmission path 10 under the communication control of the C3MA/CD system, that is, from the perspective of the device of this embodiment, the address in the received frame regardless of whether it is addressed to itself or not. Among the source addresses 104, for example, one that is logically closer to the own address 501 is updated and stored as the source address 502.

The operation of the above configuration will be explained below. FIG. 5 is a flowchart showing process 3 in which the apparatus of this embodiment stores the source address 104 of the information frame 100 in the address storage unit 5 during reception processing under the CSMA/CD system. This program executed by the control unit 7 is stored in the ROM 8 in advance, and is executed when the frame receiving circuit 2 receives a frame. In step 31, the frame receiving circuit 2
Receive the frame signal above. In step S2, the detection result of whether or not a frame collision has occurred on the transmission line 10 is checked using the signal on the line 17. When it is determined that a collision has occurred, there is an error in the received frame, so the process returns to step Sl and the frame is received again. If it is not determined in step S2 that a collision has occurred, the process advances to step S3 to check whether the frame check sequence is normal. If the frame check sequence is abnormal, there is an error in the received frame, so the process returns to step S1 and the frame is received again.

Now, when the frame is normally received, the process advances to step S4, and control is divided depending on the result of checking the mode flag held as to whether the current communication control mode is token passing mode or C3MA/CD mode. If it is the token mode, the process advances to step S9 to execute reception processing in the token mode. Also, C.S.
If it is the MA/CD mode, the process advances to step S5 and the source address 502 stored in the address storage section 5 is compared with the source address 104 in the frame just received.

In step S6, it is determined which of the source address 502 stored in the address storage section 5 and the received source address 104 is closer to the own address 501. If the received source address 104 is closer to the own address 501, the process advances to step S7 and the source address 502
The content of is replaced with the content of the received source address 104. Generally, devices connected to a network system have unique addresses. The address setting section 6 is a means for setting and holding the value. According to the method of this embodiment, this value does not need to be continuous between devices. The only condition is that there is no duplication between multiple devices. In this respect, a degree of freedom is given to address setting. Specifically speaking, regarding the determination of whether or not the self address 501 is closer to the received source address 104, a smaller value means that the source address 104 is closer than the self address 501. While repeating these comparisons and replacements, the self address 501
The source address 502 that is smaller and closest is obtained. If there is no source address 104 with a value smaller than the self address 501, conversely, the farthest source address 104 with a larger value is set as the closer source address 1, ) 502. There will probably be only one device in the network system that must make such a determination. In this way, the values of the source address 502 held by each device are in a ring relationship, and the 1.-kun destination address is quickly provided when switching to the token passing method later. Of course, it is clear that "closer to the self address 501" means a value larger than the self address 501, and may also be a value closer to the self address 501. Returning to the flow, if the source address 502 is closer to the self address 501 in the above determination, nothing is done and the process proceeds to step S8. In step s8, it is checked whether or not an address match is detected from the address comparison circuit 4. In other words, if the destination address in the received frame and the self address are equal, it means that a frame addressed to the self has been received, so the flow is exited and the reception is received. Day 7 Transfer control to the evening process. Also, if the destination address and the self address do not match, 2. Since the frame has been received, the process returns to step Sl and receives the frame again.

Figure 6 shows that when the device of this embodiment detects a high load state on the transmission path during communication using the CSMA/CD method, communication control is performed using the CSMA/CD method.
This is a flowchart 1 showing the process of switching from the CD method to the token passing method. This program executed by the control unit 7 is stored in the ROMB in advance,
This is executed when the control unit 7 generates a request for sending an information frame. In step Sll, the self address 501 of the address storage unit 5 is set as the source address (, 104) of the information transmission bucket (100), and the address of the transmission destination device is set as the destination address (1.03.). Send information. 8. Assemble the communication frame 100. In step 312, it is checked whether there is a carrier on the transmission path 10, that is, whether another transmission device is transmitting a frame, and while the carrier is being detected, the process repeats step S12 and waits until there is no more carrier. If there is no carrier, the process advances to step S13 to start frame transmission, and during the transmission, it is checked in step S14 whether a frame collision has occurred, and in step S15 it is checked whether frame transmission has ended. In this way, if no frame collision occurs until the end of transmission, the process exits.

Now, if the occurrence of a collision is detected in step 314 during the transmission, the process proceeds to step S16 and a jam frame transmission is performed to stop the frame transmission in progress. A jam frame is a dummy frame prepared for this purpose and containing no information. In step S17, it is checked whether or not a predetermined number of retries has been reached in the retry number register that counts the number of retries of transmission due to such a frame collision. If the predetermined number has not been reached, the process proceeds to step 318. In step 318, the retry count register is incremented by 1 and the process waits for a predetermined waiting time, after which the process returns to step S12. In steps S12 to S15, transmission is retried.

In the C3MA/CD system, the probability of frame collision generally increases as the transmission path load increases. When a frame collision is detected in step S14, Stella 7'316, 31 is displayed again.
Proceed to step 7. Eventually, when it is determined in step S17 that the predetermined number of times has been exceeded, the step S319 switches from the C3MA/CD method to the token passing method.
Proceed to the following process. In step S19, the prepared sender address 502 is read from the address storage unit 5.
jsu. In step S20, this source address 5°2 is set as the destination address 303 of the highest priority token 300, and the own address 501 of the address storage section 5 is set as the source address 304 of the highest priority token 300.

In step S21, the highest priority token 300 is transmitted.

In step S12, it is checked whether or not the highest priority token 300 was successfully transmitted. If the highest priority token 300 could not be transmitted normally, the process returns to step 321 and the highest priority token 300 is transmitted again. This is an operation to obtain transmission rights preferentially. For this purpose, a long preamble 301 is provided. When the highest priority token 300 has been successfully transmitted, the process advances to step S23, sets its own communication mode flag to token mode, and exits the process.

The 10 highest priority token 300 transmitted under the communication control of the CSMA/CD method is a control frame that proposes sequential communication method switching to other devices on the network. The highest priority 1-kun 300 will be suddenly output from a certain device when the transmission line 10 becomes under a high load condition. The transmission of the highest priority 1-kun 300 is of course not only when the retransmission attempt of the own information frame exceeds a predetermined number of times, such as when a device that has only been simply receiving the frame receives it. It is also possible to perform this when a disturbance in a frame signal is detected and frame collisions exceeding a predetermined number of times within a predetermined time are counted. The next step is to reconfigure the network address. According to the system of this embodiment, the first communication right is acquired by the transmission device that issued the highest priority token 300. This device sets the source address 502 in the address storage section 5 as the destination address 303 of the highest priority token 3200 and transmits. After receiving the notification, the destination device similarly sends the highest priority token 3.
00 is assembled and further transmitted to the next destination device. The same applies to all other devices. In this way, the highest priority token that signals this is circulated through all the devices in the network. This destination address will not interfere with devices greater than or equal to 2-H. This is because each device updates and stores the source address 502 according to a unified algorithm during communication in the C3MA/CD system. That is, this is because each transmission device stores a transmission device address that is logically closer to its own address. Moreover, since this address 502 is dynamically updated while the network is in operation, the address 502 can be properly registered or deleted for transmission equipment that has stopped operating midway or for new equipment that has started operating. It is. Therefore, even when switching to the token passing method, there is no device that cannot receive the highest priority token 300 at all or a device that is sent the highest priority token 300 even though it is not operating. This is extremely convenient for dynamically operating a network system.

Further, according to a preferable aspect of the method of this embodiment, CSMA
/Highest priority token 3 sent under CD method communication control
00 is a broadcast communication control frame that proposes switching of communication methods to all devices on the network at once. All the other devices that received the circular communication accept the proposal from a certain device, that is, the circular proposal ``Let's communicate using the token passing method'', and the entire network system quickly changes to the token passing method%. It will be easily understood that the expression % is changed.

FIG. 7 is a flowchart showing communication processing in the token passing method and processing when switching this to the C5MA/CD method. This program executed by the control unit 7 is stored in the ROM 8 in advance, and is input to this process when a frame is received during communication using the read-only passing method. Step 7' In S31, it is checked whether the received frame is an information frame 1°O. When the information frame 100 is received, the process advances to step S45 and the specified number of times register is cleared. The specified number of times register is cleared when the transmission line IO is effectively used for information transmission. Step S46
Then, it is determined whether the information frame 100 is addressed to itself by checking its destination address 103. If the information frame 100 is not addressed to itself, the process exits without performing any processing related to the information section 106. Also, information frame 10 addressed to self
If it is 0, the process advances to step 347, where a predetermined reception process is performed for the information frame 100, and the process exits.

Next, if the token 200 is received in step S31, the process advances to step S32 and the token 200 addressed to the self is received.
Find out whether or not. If the token 200 is not addressed to the device itself, the device is not given the right to transmit, so the process exits without doing anything. When the self-addressed token 200 is received, the process advances to step S33 to check whether there is a transmission request within the self-device. When there is a transmission request, the process proceeds to step 342 and an information bucket (100) of data to be transmitted is assembled.

In step S43, the information frame 100 is transmitted,
In step S44, the specified number of times register is cleared to indicate that the transmission line 106 is effectively used for information transmission, and the process exits.

If it is determined in step S33 that there is no transmission request, the process advances to step S34 and the predetermined number of times register is incremented by one. Since the transmission line 10 is not used even though the transmission M()-kun 200) has been sent to the self, the public transmission line 10
Add 1 to the specified number of registers to mean that the load is light.
I'll keep it that way. In step S35, it is checked whether the contents of the specified number of times register have exceeded the specified number of times. If it is not over, proceed to step S39 and receive 2 tokens.
Performs processing to pass 0 to the next device. In other words, step S39
The source address 502 is read from the address storage unit 5, and in step S40, the source address 502 is set to the destination address 203 of the token 200, and the self address 501 is set to the source address 204 of the token 200, and the next device is sent. Assemble the token 200 to, step S'41
Send 1-kun 200. 1.-This is normal transmission right transfer processing in the Kunpassing method. If it is determined in step S35 that the specified number of times has been exceeded, the process advances to step S336 and the communication mode is changed to C3MA/CD.
Assemble the highest priority token 300 for the proposal to switch to the scheme. This is because it has been determined that the transmission line 10 is in a low load state. In step 536, the address storage unit 5
The source address 502 of
is set in the source address 304 of the highest priority token 300 to assemble the i priority token 300 for the next device.

In step S37, the highest priority token 300 is transmitted, and in step 3388, the communication mode flag of the own device is set to CSMA/CD mode, and from this point on, the own device switches to the C3MA/CD mode and exits the process. Processing within the next device that receives the highest priority 1-kun 300 is similar. In this way, we will inform you of this in turn. Since the preamble 301 of the highest priority token 300 is long, there is no problem in quickly transmitting the highest priority token 300 even if there is already a device that communicates using the C3MA/CD method. In this way, all devices in the network system are sequentially and quickly switched to the C3MA/CD system. Of course, as described above, it is possible to switch the entire system all at once using the broadcast communication control. This point is also a unique benefit obtained by a network system using a bus-type communication medium. Note that it may be determined that the load on the transmission path is low by detecting that there is no transmission frame within a predetermined time.

[Effects] As described above, according to the present invention, in a data communication system using a path type communication medium, when the transmission path is low load, the CSM
When communication is performed using the A/CD method and a high load state of the transmission path is detected under the communication control, a token frame with a preamble longer than other transmission frames is issued as a token frame to switch the communication control to the token passing method. By outputting , it is possible to provide a data communication system and device that enables quick switching and allows the most efficient data communication both during low load and high load.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the main configuration of a transmission device used to implement a data communication system according to an embodiment of the present invention, and FIG. 2 shows the format of an information frame in this embodiment system. Figure 3 (A) is a diagram showing the format of the token frame in this embodiment method, Figure 3 (B) is a diagram showing the format of the highest priority token frame in this embodiment method, and Figure 4 is an address storage diagram. FIG. 5 is a diagram showing the contents stored in the storage unit 5. FIG. The flowchart shown in FIG. 6 shows the C3MA communication control when the device of this embodiment detects a high load state of the transmission path during communication using the C3MA/CD method.
Figure 7 is a flowchart showing the process of switching from the /CD system to the token passing system.
3 is a flowchart showing a process when switching to a 3MA/CD system. Here, l...frame transmitting circuit, 2...frame receiving circuit, 3...collision detection circuit, 4...address comparison circuit, 5...address storage section, 6...address setting section , 7... Control unit, 8... ROM, 9... RA
M, 10...transmission line. 2

Claims (2)

[Claims] (1) In a data communication method for a network system in which multiple data communication devices are connected to a bus-type communication medium, a distributed control token passing method is used for a network system operating under communication control using a random access C3MA/CD method. 2. A data communication method, wherein the data communication device outputs a preamble token frame that is longer than other transmission frames when switching to communication control according to the present invention. (2) In a data communication device connected to a network system using a bus-type communication medium, the data communication device includes communication control means using a random access CSMA/CD method, communication control means using a distributed control token passing method, and the like. The communication control means based on the random access type C3MA/CD system operates under the communication control based on the random access type C3MA/CD system. 1. A data communication device, wherein the preamble generating means outputs a token frame with a long preamble added thereto when switching a network system using a distributed control type token passing method to communication control.