JPH11289344A - Data transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a data transmission system that enables transmission and reception of a frame, in accordance with the priority of each frame without changing the structure of a frame format. SOLUTION: The transmission and reception of a frame is enabled in accordance with priority of each frame, without changing the structure of a frame format by structuring so that the priority of the frame is determined by a switching hub 20 on the basis of a frame length, a frame reception frequency, a host protocol, a standard deviation of a frame reception interval and a priority set frame.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of determining a frame priority of a data transmission system in which a plurality of terminals are connected to a switching hub and frames are transmitted and received between the terminals via the switching hub. The present invention relates to a priority determination method suitable for (1).

[0002]

2. Description of the Related Art Conventionally, a data transmission system in which a plurality of terminals are connected to a switching hub and frames are transmitted and received between the terminals via the switching hub has been used as an Ethernet as a LAN (local area network).
A is widely used in various fields such as A.

In such a conventional data transmission system using Ethernet as a LAN, all transmitted and received frames are treated equally.

FIG. 14 is a diagram showing a format structure of a frame transmitted / received in the conventional data transmission system.

In FIG. 14, this frame format includes a destination address DA, a source address SA, a data (DATA) length L, data DATA, and an error detection code FC.
S.

However, in a data transmission apparatus using a frame format as shown in FIG. 14, since all transmitted and received frames are treated equally as described above, a frame with a higher priority is replaced with a frame with a lower priority. Cannot be sent with higher priority.

For this reason, when the FA LAN is constructed by Ethernet, a high-priority frame including control system data (data directly related to control of the production line) and the like is transmitted to information system data (statistical information and the like) of the production line. However, there is a problem in that there is a case where the frame is waited for by a low-priority frame including data which is not directly related to control.

Further, P which is directly related to the control of the production line
In the environment where control terminals such as an LC (programmable logic controller) and information terminals such as a personal computer which are not directly related to control of the production line are mixed, communication of the control terminals is delayed by communication of the information terminals. There is a problem that there is.

In order to solve this problem, a method of providing a field indicating the priority in a frame and transmitting a high-priority frame in preference to a low-priority frame has been studied by IEEE and the like.

FIG. 15 is a diagram showing a format structure of a frame to which a priority field which has been studied in the above-mentioned IEEE and the like is added.

In FIG. 15, this frame format has a priority PR between the data (DATA) length L and the data DATA of the frame format shown in FIG.
It is composed of destination address DA, source address SA, data (DATA) length L, priority PRI, data DATA, and error detection code FCS.
By adopting the frame format having this structure, it becomes possible to control transmission and reception of frames according to the priority of each frame.

[0012]

However, if a data format having the structure shown in FIG. 15 is used, the frame format differs from the conventional frame format, so that communication with the conventional equipment can be performed. The problem of disappearing has arisen.

It is an object of the present invention to provide a data transmission system capable of transmitting and receiving frames according to the priority of each frame without changing the structure of the frame format.

[0014]

According to a first aspect of the present invention, a plurality of terminals are connected to a switching hub, and frames are transmitted and received between the plurality of terminals via the switching hub. In the data transmission system, a priority of the frame is determined based on the attribute of the frame, and transmission and reception of the frame between the terminals are controlled based on the determined priority.

The invention according to claim 2 is characterized in that, in the invention according to claim 1, the priority of the frame is determined to be higher as the frame length of the frame is shorter.

According to a third aspect of the present invention, in the first aspect of the present invention, the priority of the frame is determined to be higher as the frame is received by a port having a higher frame reception frequency. .

According to a fourth aspect of the present invention, in the first aspect of the present invention, the priority of the frame is determined according to an upper layer protocol for transmitting and receiving the frame.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention, if the upper layer protocol for transmitting and receiving the frame is UDP, it is determined that the priority is high.

According to a sixth aspect of the present invention, in the first aspect of the present invention, the priority of the frame is determined to be higher as the frame received at a port having a smaller standard deviation of the frame reception interval of the frame. It is characterized by doing.

According to a seventh aspect of the present invention, in the first aspect of the invention, the priority of the frame is determined based on priority information included in a priority frame transmitted from the terminal. It is characterized by.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a data communication system according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an embodiment of a network configuration employed in a data transmission system according to the present invention.

In FIG. 1, each terminal (terminal 1) 10-
1, terminal (terminal 2) 10-2, terminal (terminal 3) 10-
3. The terminal (terminal 4) 10-4 is connected to the switching hub 20.
, And transmits / receives frames via the switching hub 20.

Here, the switching hub 20 relays the frame received at a certain port only to the port to which the destination terminal is connected. For example, terminal (terminal 1) 10-1
Transmits a frame addressed to the terminal (terminal 2) 10-2, the frame is relayed only to the port to which the terminal (terminal 2) 10-2 is connected.

FIG. 2 is a block diagram showing a detailed configuration of the switching hub shown in FIG.

FIG. 2 shows a switching hub 20 having n ports and connectable to n terminals.

In FIG. 2, the switching hub 20
Correspond to the receiving units 21-1 to 21-n,
Reception buffers 22-1 to 22-n, transmission units 23-1 to 23-3
-N, priority 1 transmission buffers 24-1 to 24-n, priority 2 transmission buffers 25-1 to 25-n,..., Priority n transmission buffers 26-1 to 26-n, and an address. It comprises a table 27, a memory 28, and a control unit 29.

Here, the receiving units 21-1 to 21-n receive the frames from the terminals and write the received frames into the receiving buffers 22-1 to 22-n, respectively.

The receiving buffers 22-1 to 22-n
Stores the frames received from the terminals by the receiving units 21-1 to 21-n.
22-n are stored in the order in which they are received from the terminal.

The transmission units 23-1 to 3-n include a priority 1 transmission buffer 24-1 to 24-n and a priority 2 transmission buffer 2
5-1 to 25-n,..., Priority n transmission buffer 26-1
Transmit the frames stored in .about.26-n to the terminal. Here, the transmission of the frames by the transmission units 23-1 to 3-n is performed with priority given to the frames stored in the transmission buffer having the higher priority. In the configuration of FIG. 2, the priority 1 transmission buffers 24-1 to 24-n have the highest priority, and the priority n transmission buffers 26-1 to 26-n have the lowest priority. .

Priority 1 transmission buffers 24-1 to 24-
n, priority 2 transmission buffers 25-1 to 25-n,..., priority n transmission buffers 26-1 to 26-n are buffers for accumulating frames to be transmitted to the terminal for each frame priority. One transmission buffer 24-1 to 24-n has the highest priority, and priority n transmission buffers 26-1 to 26-
n has the lowest priority. Also, priority 1 transmission buffer 2
4-1 to 24-n, priority 2 transmission buffer 25-1 to 2
5-n,..., Priority n transmission buffers 26-1 to 26-n
Are stored in the order of frames transmitted to the terminal.

The address table 27 stores the addresses of the terminals connected to each port.

FIG. 3 is a diagram showing a configuration example of the address table of the switching hub shown in FIG.

In FIG. 3, the terminal address "1" is stored in the port "1", the terminal address "3" is stored in the port "2", and the terminal address "2" is stored in the port "n".
Is stored.

The memory 28 stores programs executed by the control unit 29 and temporary data.

The control unit 29 retrieves the frames stored in the reception buffers 21-1 to 21-n of each port, searches the address table for the port to which the terminal having the destination address of the frame is connected, The frames are written to the priority 1 transmission buffers 24-1 to 24-n, the priority 2 transmission buffers 25-1 to 25-n,..., The priority n transmission buffers 26-1 to 26-n of the port.

Now, in the present invention, the frame length,
By configuring the switching hub 20 to determine the priority of the frame based on the frame reception frequency, the upper protocol, the standard deviation of the frame reception interval, and the priority setting frame, each frame can be determined without changing the frame format structure. Is configured to enable transmission and reception of a frame according to the priority of the frame.

Hereinafter, the detailed operation of the present invention will be described in detail with reference to FIGS.

FIG. 4 is a flowchart showing the processing of the transmission section of the switching hub shown in FIG.

In FIG. 4, when the processing of the transmission units 23-1 to 3-n (hereinafter, referred to as the transmission unit 23) of the switching hub 20 is started (step 101), the priority 1 transmission buffer 24-1. It is checked whether there are any frames in .about.24-n (hereinafter described as priority 1 transmission buffer 24) (step 102). Here, if there is a frame in the priority 1 transmission buffer 24 (YE in step 102).
S), the frame of the priority 1 transmission buffer 24 is transmitted (step 103), and the process returns to step 102.

However, if it is determined in step 102 that there is no frame in the priority 1 transmission buffer 24 (NO in step 102), then the priority 2 transmission buffer 25-1
-25-n (hereinafter described as priority 2 transmission buffer 25) to determine whether there is a frame (step 10).
4). Here, if there is a frame in the priority 2 transmission buffer 25 (YES in step 104), the frame in the priority 2 transmission buffer 25 is transmitted (step 105).
Return to step 102.

However, if it is determined in step 104 that there is no frame in the priority 1 transmission buffer 24 (NO in step 104), then it is checked whether there is a frame in the priority 3 transmission buffer. Continue processing.

Then, the priority n transmission buffers 26-1 to 26-1
It is checked whether or not there is a frame in 26-n (hereinafter described as priority n transmission buffer 26) (step 106).
If there is a frame in the priority n transmission buffer 26 (YES in step 106), the frame in the priority n transmission buffer 26 is transmitted (step 107), and the process returns to step 102. If it is determined that there is no frame (NO in step 106), the process returns to step 102.

FIG. 5 is a flowchart showing the processing of the control unit of the switching hub shown in FIG.

In FIG. 5, the processing of the control unit 29 of the switching hub 20 is performed by sequentially performing the processing from port 1 to port n and repeating the processing.

That is, when the processing of the control unit 29 is started (step 201), the processing of the port 1 is first performed (step 202), and then the processing of the port 2 is performed (step 203). When the port processing is performed and the port n processing is performed (step 204), step 20
Return to 2 and repeat.

The processing of each port is, as shown with respect to the processing of port 1 (step 202), as follows: 1) checking whether there is a frame in the reception buffer 22-1 (step 211) 2) receiving buffer 22-1 If there is a frame (YES in step 211), one frame is extracted from the beginning of the reception buffer 22-1 (step 212). 3) The destination port of the frame extracted from the reception buffer 22-1 (the terminal of the destination address is connected). Port)
In the address table 27 (step 213) 4) Determine the priority of the frame extracted from the reception buffer 22-1 (step 214) 5) Store the frame in the transmission buffer corresponding to the priority determined in step 214 6) If there is no frame in the reception buffer 22-1 (NO in step 211), the process proceeds to step 203 as it is. The processing of the other ports is performed in the same manner as the processing of the port 1.

FIG. 6 is a flowchart showing an example of the priority determination processing shown in FIG.

The priority determination process shown in FIG. 6 is an example of the priority determination process of step 214 in FIG. 5, and the priority determination process determines the priority based on the frame length. That is, it is determined that the shorter the frame length, the higher the priority, and the longer the frame length, the lower the priority.

In general, in the FA, control system data having a higher priority has a shorter frame length than information data having a lower priority. Therefore, it is determined that the shorter the frame length, the higher the priority. As a result, the priority can be determined without changing the frame format.

In this case, with respect to the frame length, the first threshold value <the second threshold value <...
One threshold is set, and the frame length is sequentially compared with the (n-1) thresholds to determine the priority of "1" to "n".

That is, when the priority determination process is started (step 221), it is first checked whether or not the relationship of frame length <first threshold is satisfied (step 222).

Here, if the relationship of frame length <first threshold is satisfied (YES in step 222), the priority of the frame is determined to be "1" (step 223), and this processing is ended (step 222). 229).

However, if it is determined in step 222 that the relationship of frame length <first threshold is not established (NO in step 222), then, regarding the frame length of the frame, frame length <second threshold It is checked whether the relationship is established (step 224).

Here, if the relationship of frame length <second threshold is satisfied (YES in step 224), the priority of the frame is determined to be “2” (step 225), and this processing is terminated (step 225). 229).

However, if it is determined in step 224 that the relationship of frame length <second threshold is not established (NO in step 224), then, regarding the frame length of the frame, frame length <third threshold value Check whether the relationship holds.

In the same manner, the frame length of the frame is compared with the threshold value, and the frame priority is determined.

Then, it is determined whether or not the relationship of frame length <n−1th threshold is satisfied (step 226). If the relationship of frame length <n−1th threshold is satisfied (YES in step 226). , The priority of the frame is set to “n−
1 ”(step 227), and the process is terminated (step 229). However, if it is determined in step 226 that the relationship of frame length <n−1th threshold is not established (NO in step 226). ), The priority of the frame is determined to be “n” (step 228), and this processing ends (step 229).

FIG. 7 is a flowchart showing another example of the priority determination processing shown in FIG.

The priority determination process shown in FIG. 7 is an example of the priority determination process of step 214 shown in FIG. 5, and the priority determination process determines the priority based on the frame reception frequency. . That is, it is determined that a frame received at a port having a high frame reception frequency has a high priority, and a frame received at a port having a low frame reception frequency has a low priority.

In general, in FA, a control system terminal (a terminal transmitting a high-priority frame) has a higher frame transmission frequency than an information terminal (a terminal transmitting a low-priority frame). Therefore, it is determined that a frame received at a port having a higher frame reception frequency (the number of frames received per unit time) has a higher priority. As a result, the priority can be determined without changing the frame format.

In this case, with respect to the frame reception frequency, n-1 threshold values in a relationship of first threshold> second threshold >> ... n-1th threshold are set, and the frame reception frequency is set to this n.
The priority of “1” to “n” is determined by sequentially comparing the threshold with one threshold.

That is, when the priority determination process is started (step 231), first, the frame reception frequency of the port that has received the frame is updated (step 23).
2) Regarding the frame reception frequency, it is checked whether or not the relationship of frame reception frequency> first threshold holds (step 233).

If the relationship of frame reception frequency> first threshold is satisfied (YES in step 233), the priority of the frame is determined to be "1" (step 23).
4), this process ends (step 240).

However, if it is determined in step 233 that the relationship of frame reception frequency> first threshold is not established (NO in step 233), then, regarding the frame reception frequency, frame reception frequency> second threshold It is checked whether or not the relationship is established (step 235).

If the relationship of frame reception frequency> second threshold is satisfied (YES in step 235), the priority of the frame is determined to be "2" (step 23).
6), this process ends (step 240).

However, if it is determined in step 235 that the relationship of frame reception frequency> second threshold is not established (NO in step 235), then, regarding the frame reception frequency, frame reception frequency> third threshold Check whether the relationship is established.

In the same manner, the frame reception frequency is compared with the threshold value, and the frame priority is determined.

Then, regarding the frame reception frequency,
It is checked whether or not the relationship of frame reception frequency> (n-1) th threshold is satisfied (step 237). Here, if the relationship of frame reception frequency> (n-1) th threshold is satisfied (step 237).
YES), the priority of the frame is determined to be “n−1” (step 238), and this process ends (step 240).
If it is determined that the relationship of the (n−1) th threshold is not established (NO in step 237), the priority of the frame is set to “n”.
Is determined (step 239), and this process ends (step 240).

Now, TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are widely used as upper layer protocols of Ethernet. Generally, in the FA, a UDP frame having no connection establishment overhead is used for a control system frame, and a TCP protocol for starting communication after establishing a connection is used for an information system frame.

Here, the type of the upper layer protocol is DATA
It is described in the PROT field of the 10th byte of the IP header in the field.

FIG. 8 shows a frame format PROT.
It is a figure explaining a field.

In FIG. 8, the frame format includes a destination address DA, a source address SA, a data (DATA) length L, data DATA, and an error detection code FC.
S, and the data DATA is composed of an IP header and IP data. Thus, a PROT field is provided in the tenth byte of the IP header. If the PROT field is "6", TCP is used as an upper layer protocol, and if "17", UDP is used as an upper layer protocol. It is shown that.

Therefore, by examining the 10th byte of the PROT field of the IP header, it is determined whether the frame is a low-priority control system using TCP as the upper layer protocol or UDP as the upper layer protocol. It can be determined whether the frame is a control system frame having a high priority.

FIG. 9 is a flowchart showing still another example of the priority determination processing shown in FIG.

The priority determination process shown in FIG. 9 is an example of the priority determination process of step 214 shown in FIG. 5. This priority determination process is performed by setting the PROT field of the 10th byte of the IP header. The frame priority is determined by checking.

That is, when the priority determination process is started (step 241), first, the PROT field of the 10th byte of the IP header of the data DATA of the frame is "17", that is, the upper layer It is checked whether the frame is a high-priority control system using UDP as a protocol (step 242).
If the OT field is "17", the priority of the frame is determined to be the highest priority "1" (step 24).
3), this process ends (step 240).

However, if it is determined in step 242 that the PROT field of the frame is not “17”, the priority of the frame is determined to be the lowest priority “n” (step 244), and this processing is terminated. (Step 240).

FIG. 10 is a view showing a frame transmission interval distribution of the control system / information system terminal.

In general, in FA, a control system terminal (a terminal transmitting a high-priority frame) has a stronger frame transmission periodicity than an information-system terminal (a terminal transmitting a low-priority frame). For this reason, as shown in FIG. 10A, the standard deviation indicating the degree of spread from the average value of the frame interval is small in the control system terminal, and as shown in FIG. The standard deviation indicating the degree of spread from the average value is large.

Therefore, the frame priority can be determined using the frame transmission interval distribution of the control / information terminal.

FIG. 11 is a flowchart showing still another example of the priority determination processing shown in FIG.

The priority determination process shown in FIG. 11 is an example of the priority determination process of step 214 shown in FIG. 5, and the priority determination process is based on the frame transmission interval of the control / information terminal. The frame priority is determined using the distribution, that is, the standard deviation indicating the degree of spread from the average value of the frame interval.

Here, the standard deviation can be obtained from the time intervals (T1 to T.) of the frames received n times in the past. Then, it is determined that the smaller the standard deviation, the higher the priority. As a result, the priority can be determined without changing the frame format.

In this case, regarding the standard deviation, n-1 having a relationship of first threshold value <second threshold value <... <n-1th threshold value
Thresholds are set, and the standard deviation is sequentially compared with the (n-1) thresholds to determine the priority of "1" to "n".

That is, when the priority determination process is started (step 251), first, the standard deviation of the frame reception interval of the port that has received the frame is updated (step 252). Then, with respect to the standard deviation, it is checked whether or not the relationship of standard deviation <first threshold is satisfied (step 253).

Here, if the relationship of standard deviation <first threshold is satisfied (YES in step 253), the priority of the frame is determined to be “1” (step 254), and this processing is ended (step 254). 260).

However, at step 253, the standard deviation <the first
If it is determined that the relationship of the threshold values does not hold (step 2
Next, it is checked whether or not the relationship of standard deviation <second threshold value is satisfied with respect to the standard deviation (step 2).
55).

Here, if the relationship of standard deviation <second threshold is satisfied (YES in step 255), the priority of the frame is determined to be “2” (step 256), and this processing is terminated (step 256). 260).

However, at step 255, the standard deviation <second
If it is determined that the relationship of the threshold values does not hold (step 2
Next, it is checked whether or not the relationship of standard deviation <third threshold is satisfied with respect to the standard deviation.

Hereinafter, similarly, the standard deviation is compared with the threshold value, and the frame priority is determined.

Then, with respect to the standard deviation, it is checked whether or not the relationship of standard deviation <n−1th threshold is satisfied (step 257). Here, if the relationship of standard deviation <n−1th threshold is satisfied (step 257) (YES in step 257), the priority of the frame is determined to be “n−1” (step 258),
This processing ends (step 260), but step 2
If it is determined at 57 that the relationship of the standard deviation <the (n−1) th threshold is not established (NO at step 257), the priority of the frame is determined to be “n” (step 259), and this processing is performed. The process ends (step 260).

Note that the terminal may transmit the priority setting frame to the switching hub 20 to set the priority of the frame transmitted by the terminal. In this case, the same address as the terminal is assigned to the switching hub 20. FIG. 12 is a diagram showing a format of the priority setting frame.

In FIG. 12, the priority setting frame format includes a destination address DA and a source address S
A, data (DATA) length L, data DATA, and error detection code FCS. The address of the switching hub 20 is described in the destination address DA, and the priority of the frame of the terminal is described in the data DATA. Is described.

FIG. 13 is a flowchart showing the processing of the control unit of the switching hub shown in FIG. 2 when the priority setting frame is used.

In this case, the control unit 29 of the switching hub 20 stores the priority for each port, and determines that the priority of the frame received at each port is the priority currently set for that port. judge. The port priority can be changed by a priority setting frame transmitted by the terminal. As a result, the priority can be determined without changing the frame format.

In FIG. 13A, the processing of the control unit 29 of the switching hub 20 is performed by sequentially performing the processing from port 1 to port n and repeating the processing.

That is, when the processing of the control unit 29 is started (step 261), the processing of the port 1 is first performed (step 262), and then the processing of the port 2 is performed (step 263). When the processing of the port is performed and the processing of the port n is performed (step 264), the step 26 is performed.
Return to 2 and repeat.

The processing of each port is, as shown with respect to the processing of port 1 (step 262), 1) checking whether there is a frame in the reception buffer 22-1 (step 271) 2) receiving buffer 22-1 If there is a frame (YES in step 271), one frame is extracted from the head of the reception buffer 22-1 (step 272) 3) It is checked whether the destination address is the address of the switching hub 20 (step 273) 4) The destination address Is not the address of the switching hub 20 (NO in step 273),
The destination table (port to which the terminal of the destination address is connected) of the frame extracted from 2-1 is searched in the address table 27 (step 274). 5) The priority of the frame extracted from the reception buffer 22-1 is determined. (Step 275) 6) Write a frame to the transmission buffer corresponding to the priority determined in Step 275 (Step 276) 7) If there is no frame in the reception buffer 22-1 (NO in Step 271), go to Step 8) If it is determined in step 273 that the destination address is the address of the switching hub 20 (step 2)
If YES in step 73, the priority information is extracted from the received frame (step 277), and the priority setting is updated (step 278). The processing of the other ports is performed in the same manner as the processing of the port 1.

The priority determination process in step 275 in this case is as shown in FIG.

That is, when the priority determination process is started (step 281), the priority currently set for the receiving port is determined as the priority of the frame (step 282), and the priority determination process is performed. finish.

As described above, according to the present invention, the frame length,
The switching hub 20 determines the priority of the frame based on the frame reception frequency, the upper protocol, the standard deviation of the frame reception interval, and the priority setting frame, so that the priority of each frame can be changed without changing the structure of the frame format. Transmission and reception of the corresponding frame can be performed.

[0103]

As described above, according to the present invention,
Since the switching hub 20 determines the priority of the frame based on the frame length, the frame reception frequency, the upper protocol, the standard deviation of the frame reception interval, and the priority setting frame, the structure of the frame format is not changed. There is an effect that frames can be transmitted and received according to the priority of each frame.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a network configuration employed in a data transmission system according to the present invention.

FIG. 2 is a block diagram showing a detailed configuration of the switching hub shown in FIG.

FIG. 3 is a diagram showing a configuration example of an address table of the switching hub shown in FIG. 2;

FIG. 4 is a flowchart showing a process of a transmission unit of the switching hub shown in FIG. 2;

FIG. 5 is a flowchart showing a process of a control unit of the switching hub shown in FIG. 2;

FIG. 6 is a flowchart illustrating an example of a priority determination process illustrated in FIG. 5;

7 is a flowchart showing another example of the priority determination process shown in FIG.

FIG. 8 is a view for explaining a PROT field of a frame format.

FIG. 9 is a flowchart illustrating still another example of the priority determination process illustrated in FIG. 5;

FIG. 10 is a diagram illustrating a frame transmission interval distribution of a control system / information system terminal.

11 is a flowchart showing still another example of the priority determination process shown in FIG.

FIG. 12 is a diagram showing a format of a priority setting frame.

FIG. 13 is a flowchart showing the processing of the control unit of the switching hub shown in FIG. 2 when the priority setting frame shown in FIG. 12 is used.

FIG. 14 is a diagram showing a format structure of a frame transmitted and received in a conventional data transmission system.

FIG. 15 is a diagram showing a format structure of a frame to which a priority field which has been studied in IEEE or the like is added.

[Explanation of symbols]

 10-1 Terminal (Terminal 1) 10-2 Terminal (Terminal 2) 10-2 Terminal (Terminal 3) 10-4 Terminal (Terminal 4) 20 Switching Hubs 21-1 to 21-n Receiving Units 22-1 to 22- n reception buffer 23-1 to 3-n transmission unit 24-1 to 24-n priority 1 transmission buffer 25-1 to 25-n priority 2 transmission buffer 26-1 to 26-n priority n transmission buffer 27 address Table 28 Memory 29 Control unit

Claims (7)

[Claims] 1. A data transmission system for connecting a plurality of terminals to a switching hub and transmitting and receiving frames between the plurality of terminals via the switching hub, wherein a priority of the frame is determined based on an attribute of the frame. A data transmission system for controlling transmission and reception of frames between the terminals based on the determined priority. 2. The data transmission system according to claim 1, wherein the priority of the frame is determined to be higher as the frame length of the frame is shorter. 3. The data transmission system according to claim 1, wherein the priority of the frame is determined to be higher as the frame is received by a port having a higher frame reception frequency. 4. The data transmission system according to claim 1, wherein the priority of the frame is determined according to a higher-level protocol for transmitting and receiving the frame. 5. The data transmission system according to claim 4, wherein if the upper layer protocol for transmitting and receiving the frame is UDP, the priority is determined to be high. 6. The data transmission system according to claim 1, wherein the priority of the frame is determined to be higher as the standard deviation of the frame reception interval of the frame is smaller at the port. 7. The data transmission system according to claim 1, wherein the priority of the frame is determined based on priority information included in a priority frame transmitted from the terminal.