JPH0563722A - Packet relay system - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a packet relay system that suppresses a sudden decrease in performance when the transmission load increases. [Configuration] Packets sent from terminals 411-419 are
Arrives at the lower relay devices 402 to 404. Lower relay device
In 402 to 404, only the packet that arrives earliest among these packets is sent to the upper relay device 401, and the other packets are discarded inside the relay devices 402 to 404. Packets are sent to the upper relay device 401 from the respective lower relay devices 402, 403, 404. In the upper relay device 401, only the packet that arrives earliest is relayed and transmitted to all the lower relay devices 402, 403, 404, and the other packets are relayed.
Abandoned inside 401. Then, the lower relay device 402,4
03 and 404 send the packet from the upper relay apparatus 401 to all the terminals 411 to 419.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a packet relay system in a star network.

[0002]

2. Description of the Related Art Conventionally, IEEE 802.3 10BASE-T is widely known as a standard for star networks. The relay device defined in this standard has the following features.

(1) When a packet arrives at an arbitrary input port of the relay device and the relay device does not relay another packet, the packet that arrives immediately is relayed.

(2) A packet arriving at any input port of the relay device is not relayed to the output port paired with this input port. That is, selective relay is performed so that the packet is not returned to the station that transmitted the packet.

(3) If the relay device has already relayed another packet when the packet arrives at any input port of the relay device, it is considered that a packet collision has occurred and the packet currently being relayed. The relay of the packet that arrives at both fails. In this case, the relay device stops relaying the packet and sends a signal called "jam" to all output ports in order to notify all terminals of the relay failure.

The communication control method defined in the IEEE 802.3 10BASE-T standard has the following features.

(1) The length of the transmission packet is not more than a predetermined length.

(2) When a packet transmission request is generated at an arbitrary terminal, that terminal monitors whether or not the packet is sent from the relay device, and if the packet is not sent from the relay device, the packet is sent. Send,
When a packet is sent, the packet is sent after waiting for a certain period of time after the end of the reception of the packet to stop the packet transmission.

(3) While the above condition (2) is satisfied and the packet is being transmitted, the terminal monitors the state of the signal sent from the relay device.

(4) When a packet is received from the relay device while the terminal is transmitting the packet, it is considered that the packet collided with another packet during the relay of the transmission packet, and a jam signal is transmitted to the packet. ..

(5) When the packet transmission fails, each terminal retransmits after a predetermined time has elapsed.

[0012]

However, the network based on the IEEE802.3 standard, which is characterized as described above, has a problem that the performance thereof is sharply reduced when the load is increased. That is, as the load on the network increases, the number of packets transmitted increases, and the number of packet collisions on the transmission path or the relay device increases. When packet collision occurs, the contents of both the packet transmitted earlier and the packet transmitted later are destroyed. Therefore, both terminals retransmit the packet, and therefore, when the number of packet collisions increases, the packet transmission delay time rapidly increases and the network performance deteriorates.

An object of the present invention is to solve the above-mentioned problems and to provide a packet relay system capable of suppressing a sudden decrease in performance when the transmission load increases.

[0014]

In order to achieve the above object, a packet relay system of the present invention is a network comprising a plurality of terminals and a relay device for relaying signals by connecting the terminals in a star pattern. , When a packet arrives at an arbitrary input port, the relay device relays the arrived packet to the output port when another packet is not relayed, and when the packet has already been relayed, the relay device later A packet that arrives is discarded inside the relay device without being relayed, and the relay devices are connected so as to form a branching hierarchical structure. When a packet arrives, the packet is output to all the lower relay devices, and the relay devices other than the highest relay device
When a packet arrives from a lower relay device or terminal, the packet is output only to the upper relay device, and when a packet arrives from the upper relay device, it is output to all lower relay devices or terminals that are directly connected. A packet is output (Claim 1).

Further, in a network composed of a plurality of terminals and a relay device for relaying signals by connecting the terminals in a star shape, a priority corresponding to the input port of the relay device in a one-to-one correspondence is determined in advance. When packets arrive at the input port from the terminal at the same time, the packet from the input port with the highest priority among these input ports is relayed,
Packets from other input ports are discarded inside the relay device without relaying, and the priority of each input port is changed between the input ports upon completion of packet relay in the relay device. (Claim 2).

When packets arrive at a plurality of input ports from a terminal at the same time as in the above, the packet from the input port with the highest priority among these input ports is relayed, and the relayed packet is input. The priority of the input port is changed to the highest priority of the relay devices (claim 3).

In a network including a plurality of terminals and a relay device that relays signals by connecting the terminals in a star pattern, when packets arrive from a plurality of input ports of the relay device from the terminals at the same time, the packet The packet from the input port having a high arrival frequency is relayed, and the packet from the other input port is discarded inside the relay device without performing the relay (claim 4).

In a network including a plurality of terminals and a relay device that relays signals by connecting the terminals in a star shape, different priorities are set in advance for the respective input ports of the relay device, and within a certain fixed time. When a packet arrives at a plurality of input ports from a terminal, the packet from the input port with the highest priority is relayed, and other packets are discarded inside the relay device without relaying. 5).

In a network including a plurality of terminals and a relay device that relays signals by connecting the terminals in a star pattern, the states of the input ports of the relay device are sequentially monitored, and the input just monitored is input. When a signal from a terminal arrives at a port, the packet from that input port is relayed, and even when packets arrive from multiple terminals at the same time, only the packet from one input port is relayed. (Claim 6). Here, the number of monitoring of the input port in the relay device may be changed between the input ports (claim 7).

In a network including a plurality of terminals and a relay device that relays signals by connecting the terminals in a star shape, after the terminals transmit a transmission request frame,
The packet is transmitted after the transmission request frame transmitted by itself is returned, and the relay device monitors the input ports in order,
When the transmission request frame arrives at any input port, the transmission request frame is relayed, and even when there are transmission requests from multiple terminals, a packet is sent to only one of the terminals that transmitted the transmission request frame. Is transmitted (Claim 8).

Further, in a network composed of a plurality of terminals and a relay device which relays signals by connecting the terminals in a star shape, when packets arrive from the plurality of terminals at the relay device at the same time, these packets are predetermined. The fields are compared and one packet selected according to the comparison result is relayed, and the other packets are discarded inside the relay device without performing the relay (claim 9). Here, the packet relayed by the relay device may be a packet having the largest source address value or a packet having the smallest source address value (claims 10 and 11).

In addition, in a network including a plurality of terminals and a relay device that relays signals by connecting the terminals in a star shape, the terminal transmits a priority determination packet and relays the packet prior to the packet transmission. The device sets the priority for each terminal by the priority determination packet from the terminal, and relays the data packet from the terminal with the highest priority when data packets arrive from multiple terminals at the same time. The packet from the terminal is discarded inside the relay device without being relayed (claim 12).

[0023]

According to the packet relay method of the present invention, when a packet arrives at another input port while the relay device is relaying a packet arriving at an arbitrary input port, the packet arriving later is relayed. Without discarding and relaying only the packets that are already being relayed without discarding,
It is possible to realize a communication system in which the transmission delay time of data does not increase sharply even if the transmission load increases in the star network. Moreover, by connecting the relay devices so as to form a branched hierarchical structure, and by making the operations of these relay devices different between the topmost device and the other devices,
The number of terminals that can be connected can be easily increased.

In the packet relay system according to the second aspect, priorities are given to the input ports of the relay device in advance, and when packets arrive at a plurality of input ports at the same time, the priorities of those input ports are compared to determine the highest priority. Since only packets from input ports with high priority are relayed, even if packets arrive from multiple terminals at the same time to the relay device, only packets from input ports with high priority can be relayed without being discarded. it can. Moreover, by changing the priority of each input port between the input ports upon completion of packet transmission in the relay device, the input ports for which packet relay is prioritized are not biased, and the relay priority for each terminal is equalized. Can be converted.

In the packet relay system of claim 3, when packets arrive at a plurality of input ports from terminals at the same time, only the packet from the input port with the highest priority is relayed, and the relayed packets are input. To change the priority of the input port to the highest priority, then
Even if packets arrive from a plurality of terminals to the relay device at the same time, the packet transmitted from the terminal transmitted last time can be preferentially relayed.

In the packet relay method of the present invention, when packets arrive at a plurality of input ports at the same time, only the packets from the input ports having a high packet arrival frequency are relayed. When the packet arrives, the packet from the terminal with high transmission frequency can be preferentially relayed.

In the packet relay system of claim 5, when a packet arrives at a plurality of input ports within a fixed time,
Since only the packet from the input port with the highest priority is relayed, only the packet from the input port with the highest priority can be relayed even when the first-arrival packet is limited due to the difference in the transmission path length. ..

In the packet relay system according to the sixth aspect, the states of the input ports of the relay device are monitored in order, and when a signal arrives from the terminal at the input port just monitored, only the packet from that port is relayed. Therefore, even when packets arrive from a plurality of terminals at the relay device at the same time, only the packet from the input port that has just been monitored can be relayed without being discarded. Here, if the number of times of monitoring the input port in the relay device is changed between the input ports, the priority is set for each input port, and the packet from the input port having a high priority can be relayed with high probability.

According to another aspect of the packet relay system of the present invention, the terminal transmits a transmission request frame prior to transmitting the packet, transmits the packet after the transmission request frame transmitted by itself is returned, and causes the input port of the relay device to operate. It monitors in order, and when a transmission request frame arrives at the input port just monitored, it relays the transmission request frame, so even if a transmission request occurs at multiple terminals,
The packet can be transmitted only to the terminal that has transmitted the transmission request frame returned from the relay device.

In the packet relay system according to claims 9 to 11, when packets arrive at the relay device from a plurality of terminals at the same time, predetermined fields of these packets are compared,
Since only one packet selected based on the comparison result is relayed, even when packets arrive from a plurality of terminals at the relay device at the same time, only one packet can be relayed without being discarded.

In the packet relay system according to the twelfth aspect of the present invention, the priority determination packet is transmitted from the terminal prior to the packet transmission, and the relay device sets the priority for each terminal by the priority determination packet from the terminal, When data packets arrive from multiple terminals at the same time, only the data packet from the terminal with the highest priority is relayed. Only packets from the terminal can be relayed without being discarded.

[0032]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows the basic configuration of a system to which the present invention is applied. This system is a central repeater 1
It has two-way links 121, 122, 123, 124 connecting 01 and a plurality of terminals 111, 112, 113, 114, and exchanges data between the terminals. The transmission medium of the bidirectional links 121 to 124 may be a twisted pair wire, a coaxial cable, an optical fiber, or the like. Here, an optical fiber is used as the transmission medium.

FIG. 2 shows an internal configuration example of the relay device 101. The packets transmitted from the terminals 111 to 114 arrive at the input ports 1 to 4 of the relay apparatus 101 via the bidirectional links 121 to 124, respectively. The packets arriving at the input ports 1 to 4 are converted into electric signals by the photoelectric conversion units 201 to 204, and the delay circuits 211 to 214 and the packet detection circuits 221 to
Entered at 224. The packet detection circuits 221 to 224 detect the arrival of the packet and select the selection circuit 2 respectively.
The detection signals 11 to 14 are output to 31. When the detection signals 11 to 14 are input, the selection circuit 231 allows the outputs of the delay circuits 211 to 214 corresponding to the detection signals 11 to 14 to pass through and the electro-optical conversion unit 20.
Send to 5 to 208. The packet thus arrived at the relay device 101 is held by the corresponding delay circuits 211 to 214, and when the switching of the selection circuit 231 is completed, the delay circuit 2
The signals are output from 11 to 214, pass through the selection circuit 231, and are relayed to all the output ports 5 to 8 via the electro-optical conversion units 205 to 208. The selection circuit 231 is connected to one of the terminals 111 to 11
Even if packets arrive from other terminals 111-114 while relaying packets from 4 to all output ports 5-8, they are already in the state of relaying packets. Do not switch to relay.

FIG. 3 shows the structure of the interface circuit inside each of the terminals 111 to 114. When a packet is transmitted from the terminals 111 to 114 to the relay device 101, first, C (not shown)
The PU writes the transmission data and the address of the destination station in the 2-port memory 308. Then, the transmission request is set in the control / status display register 309. The control / status display register 309 includes a transmission request register that is set when writing of transmission data to the 2-port memory 308 is completed, and a reception display register that is set when writing of reception data is completed. It is monitored by the communication control unit 305. If the transmission request register is set and the reception display register is not set, the communication control unit 305 instructs the read control unit 306 to read data. By this instruction, the read controller
The 306 reads the transmission data from the designated address inside the 2-port memory 308 and outputs it to the communication control unit 305. The communication control unit 305 adds the address of the destination station or the address of the own station (source address) to the input transmission data,
Further, an FCS for error detection, a delimiter indicating the start and end of the packet, and the like are added and output to the parallel / serial converter 304. The packet output to the parallel / serial converter 304 is
After the 16-bit or 8-bit parallel data is converted into serial data, it is converted into a code for transmission as an optical signal by the signal modulation unit 302, and finally, the electric signal is converted into an optical signal by the electro-optical conversion unit 310. Transmitted to the relay device 101.

When receiving a packet sent from the relay device 101, the arriving packet is first converted into an electric signal by the photoelectric conversion unit 311. And the signal demodulator
The transmission code is demodulated by 301 into an NRZ code, and the serial / parallel conversion unit 303 converts the packet received as serial data into 16-bit or 8-bit parallel data and outputs the parallel data to the communication control unit 305. The communication control unit 305 compares the destination address of the received packet with its own address, and if they match, continues the receiving process, and if they do not match, interrupts the receiving process. When the destination address of the received packet matches the own station address, the communication processing unit 305 further instructs the write control unit 307 to write the received data, and 2
Write the received data in the port memory 308. afterwards,
Error detection is performed using the FCS of the packet. If no error is detected here, the reception display register in the control / state display register 309 is set when the writing of the reception data is completed. When an error is detected, the error display register in the control / status display register 309 is set. The received data written in the 2-port memory 308 is read by a CPU (not shown) as appropriate.

Next, the operation of this system will be described.

When a transmission request is generated at any of the terminals 111 to 114, the terminal 111 to 114 monitors the state of the signal transmitted from the relay device 101, and when a packet is not transmitted from the relay device 101. Immediately send the packet. That is, each of the terminals 111 to 114 monitors the reception display register in the control / status display register 309 when transmitting a packet, and instructs the read control unit 306 to read data when this is not set. On the other hand, when a packet is sent from the relay device 101, that is, when the reception display register is set, the read control unit
The data reading by the 306 is temporarily suspended, and after the reception of the packet is completed and the signal output is stopped for a certain period of time, the read control unit 306 reads the data and transmits the packet.

When the packets are transmitted from the two terminals 112 and 113 in order, the packet from the terminal 112 first arrives at the input port 2 of the relay device 101, is converted into an electric signal by the photoelectric conversion unit 202, and is then delayed by the delay circuit 212. Held by. At the same time, the arrival of the packet is detected by the packet detection
This is detected by 222, and the detection signal 12 is output from the packet detection circuit 222. The detection signal 12 is input to the selection circuit 231 and the selection circuit 231 is switched to output the signal from the delay circuit 212. This allows the delay circuit 212
The packet output from the packet passes through the selection circuit 231 and is sent to the electro-optical conversion units 205 to 208, where it is converted into optical signals and transmitted to all the terminals 111 to 114. Terminal like this
When a packet from the terminal 113 arrives while relaying the packet from 112, this packet is input from the input port 3 to the photoelectric conversion unit 203, held by the delay circuit 213, and also by the packet detection circuit 223. To be detected.
However, in the selection circuit 231, the packet from the terminal 112 has already been relayed, and switching for newly relaying the packet is not performed. Therefore, although the packet from the terminal 113 is output after being held by the delay circuit 113,
The selection circuit 231 cannot be passed and its selection circuit 2
31 Discarded inside.

On the other hand, the transmitting terminals 112 and 113 compare the transmission source address of the packet transmitted from the relay device 101 with their own address, and if they match, it is judged that the transmission was successful, and if they do not match. Packet is relay device 101
Appropriate retransmission processing is performed after determining that the packet has been discarded internally. In this example, at the terminal 112, the source address of the received packet matches the own station address, and it is determined that the transmission was successful. Also, terminal 113 determines that the transmission has failed, and retransmits the packet.

As described above, when a packet from another terminal 111-114 arrives at the relay apparatus 101 while the packet from the arbitrary terminal 111-114 is being relayed by the relay apparatus 101, it arrives later. It is possible to reduce the number of retransmission packets by discarding stored packets without relaying them and relaying packets that are already being relayed without discarding them. A system that does not increase the data transmission delay time drastically even if the transmission load increases Can be realized.

FIG. 4 shows a modification of the system described above. This system consists of an upper relay device 401,
Subordinate relay device to which multiple terminals 411-419 are directly connected
It has 402, 403, 404 and a bidirectional link 421, and exchanges data between terminals via lower and upper relay devices 401, 402 to 404.

As shown in FIG. 6, the subordinate relay devices 402, 403 and 404 include photoelectric conversion units 601, 602, 603 and 604 and a delay circuit 61.
1,612,613,614, Packet detection circuit 621,622,623,624,
It is composed of a selection circuit 631 and electro-optical conversion units 605, 606, 607, 608. Among them, the photoelectric conversion unit 601, the delay circuit 611,
The packet detection circuit 621 and the electro-optical conversion unit 605 are circuits for performing packet transmission with the upper relay device 401, and the rest are circuits for performing packet transmission with a terminal. In addition, the upper relay device 401 includes the photoelectric converter 601 and the delay circuit 6 from the lower relay devices 402 to 404.
11, the packet detection circuit 621 and the electro-optical conversion unit 605 (circuits that perform transmission with a higher-level relay device) are removed. Further, the terminal has the same configuration as that of the above embodiment.

The packets transmitted from the terminals 411 to 419 are transferred to the photoelectric conversion units 602 to 604 of the lower relay devices 402 to 404.
Arrives at and is converted into an electric signal and input to the delay circuits 612 to 614 and the packet detection circuits 622 to 624. The packet detection circuits 622 to 624 detect arrival of a packet and output detection signals 12 to 14 to the selection circuit 631. When the detection signals 12 to 14 are input, the selection circuit 631 outputs the outputs of the delay circuits 612 to 614 corresponding to the detection signals 12 to 14 to the electro-optical conversion unit 605. As a result, the packets arriving from the terminals 411 to 419 are transmitted to the delay circuits 612 to 612 of the lower relay devices 402 to 404.
It is held by 614, and when the switching of the selection circuit 631 is completed, it is output from the delay circuits 612 to 614 and selected.
Passing through 631, and passing through the electro-optical conversion unit 605, the upper relay device
It is transmitted to 401.

When a packet arrives from the lower relay apparatus 402 to 404 to the electrical conversion section of the upper relay apparatus 401, the packet converted into an electric signal by the electrical conversion section is input to the delay circuit and the packet detection circuit. Then, similarly to the above, after being held by the delay circuit, it passes through the selection circuit,
All subordinate relay devices 402 to 404 via the light / electric converter
Be transmitted to.

When the packet is returned from the upper relay apparatus 401 to all the lower relay apparatuses 402 to 404 in this way, the packet is transmitted to the electrical conversion units of the lower relay apparatuses 402 to 404.
The signal is converted into an electric signal by 601 and is held by the delay circuit 611, then passes through the selection circuit 631, and then the electro-optical conversion unit 606-
It is transmitted to all terminals 411-419 via 608. Here, while the lower relay devices 402 to 404 are transmitting the packets from the terminals 411 to 419 to the upper relay device 401,
When packets arrive from the other terminals 411 to 419, the selection circuits 631 of the relay devices 402 to 404 are already relaying the packets and do not perform new switching. Therefore, the packet that arrives later is discarded inside the selection circuit 631. Further, while the upper relay apparatus 401 is transmitting the packets from any lower relay apparatus 402 to 404 to all the lower relay apparatuses 402 to 404, the packets from other lower relay apparatuses 402 to 404 are transmitted. Even when the packet arrives, the packet that arrives later is discarded by the upper relay device 401. Further, if packets arrive from the terminals 411 to 419 while the lower relay apparatuses 402 to 404 are transmitting the packets from the upper relay apparatus 401 to the terminals 411 to 419, the packets from the terminals 411 to 419 are It is discarded in the selection circuit 631.

FIG. 5 shows an example of a packet flow in this system. In this example, terminals 411,4
Packets are output from 12,415,417,419 at approximately the same time. In this case, when the packet from the terminal 411 arrives at the lower relay apparatus 402 earlier than the packet from the terminal 412, the packet from the terminal 411 is transmitted to the upper relay apparatus 401. At this time, the packet from the terminal 412 is the relay device.
402 Abandoned inside. In addition, the lower relay device 4
Since only packets from terminal 415 arrive at 03,
The packet is directly transmitted to the upper relay device 401. Further, when the packet from the terminal 417 arrives at the lower relay apparatus 404 earlier than the packet from the terminal 419, the packet from the terminal 417 is transmitted to the upper relay apparatus 401, and the packet from the terminal 419 is transferred inside the relay apparatus 404. Be discarded at. In this way, packets are transmitted from the lower relay devices 402, 403, 404 to the upper relay device 401. At this time, if the packet from the relay device 402 (packet from the terminal 411) arrives earliest, this relay device 402
From the other relay devices 403, 404 (terminal 4).
Packets from 15,417) are discarded inside the upper relay device 401. Then, the lower relay devices 402, 403, and 404 relay the packet sent from the upper relay device 401 to all the terminals 411 to 419.

As described above, the upper and lower relay devices
Even in a system equipped with 401, 402 to 404, by changing the operation between the upper relay device 401 and the lower relay devices 402 to 404, it is possible to relay only the first-arriving packet without discarding it, and transmission under high load It is possible to prevent an increase in delay time. Moreover, the upper and lower relay devices 40
The number of connectable terminals can be easily increased by connecting 1,402 to 404 in a branched hierarchical structure.
Although the present system has a two-layer structure including the upper relay device 401 and the lower relay devices 402 to 404, it may have a hierarchical structure of higher layers. In this case, the operation may be changed between the highest level and the other relay devices as described above.

In the above system, when a plurality of packets arrive at the relay device at the same time, there is a problem in which packet is relayed. Therefore, a system capable of relaying a predetermined packet without discarding a predetermined packet even in such a case will be described below.

FIG. 7 shows an example of the internal structure of the relay device applied to the system of FIG. This relay device 700 assigns priorities to the input ports in advance, and when packets arrive at multiple input ports from terminals at the same time, the priorities of the input ports are compared and the packet from the input port with the highest priority is compared. It only relays.

The packets transmitted from the terminals arrive at the input ports 1 to 4, are converted into electric signals by the photoelectric conversion units 701 to 704, and are input to the delay circuits 711 to 714 and the packet detection circuits 721 to 724. It Packet detection circuit
721 to 724 detect the arrival of the packet and output detection signals 11 to 14 to the control circuit 731. Control circuit 731
When the detection signals 11 to 14 are input, which input port 1
Switcher 7 to determine whether to relay the packet from
41 input destinations are the input ports 1 to 4 side (delay circuits 711 to 7
14 side). Here, switching device by control circuit 731
The switching judgment of 741 is performed as follows. (1) When any of the packet detection circuits 721 to 724 detects a packet, switching is performed so as to pass the outputs of the delay circuits 711 to 714 corresponding to the packet detection circuits 721 to 724. (2) When a plurality of packet detection circuits 721 to 724 detect packets at the same time, the priorities assigned to the respective packet detection circuits 721 to 724 are compared in advance, and the highest priority packet detection circuits 721 to 724 are compared. Switch to pass the output of delay circuits 711 to 714 corresponding to. (3) When one switching packet is relayed by the switch 741, each packet detection circuit 721-
Change the priority of 724. Here, every time one packet is relayed, the priority pattern is changed from A to A as shown in FIG.
Change as B → C → D → A → ……. In addition, 7 in the figure
Reference numeral 05 is an electro-optical conversion unit for relaying a packet that has passed through the switch 741 to all output ports.

Next, the system operation using the relay device 700 will be described.

When a transmission request is generated at any terminal, that terminal monitors the state of the signal sent from the relay device 700, as in the above embodiment (FIG. 1), and
If 700 does not send a packet, send the packet immediately. On the other hand, when a packet is sent from the relay device 700, the packet transmission is temporarily suspended, and the packet is transmitted after waiting for the packet reception to end for a certain period of time.

As shown in FIG. 9, when packets arrive from the terminals at the input ports 1, 2, and 4 of the relay device 700 at the same time, these packets are detected by the packet detection circuits 721, 722, 724.
Detected by these packet detection circuits 721,722,724
The detection signals 11, 12, and 14 are output from the control circuit 731. At this time, the priority of each of the packet detection circuits 721 to 724 is shown in FIG.
The pattern B shown in FIG. 6 indicates that the control circuit 731 has the highest priority among the packet detection circuits 721, 722, 724 (“1”).
The packet detection circuit 722 is selected, and the switch 741 is switched to the corresponding input port 2 side. This ensures that only packets that arrive at input port 2 will
After being held by 712, it passes through the switch 741 and passes through the electro-optical conversion unit 7
It is transmitted to all terminals via 05. Then the control circuit 7
In 31, the priority of each of the packet detection circuits 721 to 724 is changed to the pattern C shown in FIG.
Is set to the highest priority.

The transmitting terminal compares the source address of the packet sent from the relay device 700 with its own address. If they match, it is judged that the transmission was successful, and if they do not match, the packet is relayed. Appropriate resend processing is performed by determining that the device 700 has been discarded.

As described above, the input ports 1 to 4, that is, the respective packet detection circuits 721 to 724 are given priorities in advance,
When packets arrive at multiple input ports 1 to 4 at the same time, their priorities are compared, and only packets from the input ports 1 to 4 with the highest priority are relayed, so that packets arrive at the same time from multiple terminals. However, only one packet with high priority can be relayed without being discarded. Moreover, by changing the priority of each of the packet detection circuits 721 to 724 every time one packet is relayed, the input ports 1 to 4 in which the packet relay is prioritized are not biased and the packet is transmitted to each terminal. Can be performed evenly. In the relay device 700, the priority patterns of the packet detection circuits 721 to 724 are changed every time one packet is relayed, but may be changed every time a packet is relayed a plurality of times.

FIG. 10 shows a modification of the control circuit in the relay device. This is to relay only the packet from the input port with the highest priority when the packet arrives from a terminal to multiple input ports, and then to relay the packet arriving at the previously relayed input port with priority. It was done like this.

In the figure, 1001 to 1004 are priority signal generation circuits, and packet detection circuits 721 to 724 (FIG. 7), respectively.
It receives the detection signals 11-14 from the input ports 1 to 14 and generates the priority signals corresponding to the input ports 1-4. Each priority signal generation circuit
The signals output from 1001 to 1004 are input to the arithmetic unit 1011 in order to generate the signal corresponding to the highest priority.
The maximum priority signal from the arithmetic unit 1011 is the comparison circuit 1021 ...
It is sent to one input terminal of 1024. Comparison circuit 1021 to 1024
To the other input terminal of the priority signal generating circuit 10
The output from 01 to 1004 is input. The comparison circuits 1021 to 1024 are
Output of each priority signal generation circuit 1001-1004 and operation circuit 1010
The output of the encoder 1031
Output to. The encoder 1031 includes the comparison circuits 1021 to 1021.
The priority signal generating circuits 1001 to 1004 that have generated the maximum priority signal are determined from the comparison result according to, and the control signal is output to the switch 741 (FIG. 7) based on the determination result.

The maximum priority signal output from the arithmetic unit 1011 is also input to the priority signal generation circuits 1001 to 1004, and the priority of each port 1 to 4 is changed after the packet is relayed. That is, each priority signal generation circuit 1001-10
In 04, the arithmetic circuit 1041 is connected to the output of the arithmetic unit 1011 as shown in the priority signal generating circuit 1001 as an example. The calculation circuit 1041 registers the calculation result by the register 10
42 to change the priority registered in advance. The output of the register 1042 is connected to the gate circuit 1043, and the output of the packet detection circuit 721 is connected to the control input of this gate circuit 1043. Thus, when the detection signal 11 is input from the packet detection circuit 721, the priority signal is output. The priority signal from the register 1042 is also input to the arithmetic circuit 1041 to notify the arithmetic circuit 1041 of the current priority.

Next, the operation of the control circuit 1000 will be described with an example.

(1) When a packet is input only to the input port 1 When the packet arrives at the input port 1, the detection signal 11 from the packet detection circuit 721 is input to the control circuit 1000. In the control circuit 1000, the priority signal generation circuit 1001
The gate circuit 1043 receives the detection signal 11 and outputs the priority signal registered in the register 1042 to the calculator 1011.

Suppose now that each of the priority signal generation circuits 1001-10
It is assumed that the register 1042 of 04 has the priorities corresponding to the input port numbers set in advance as follows.

Input port 1 ... 1 (lowest priority) Input port 2 ... 2 Input port 3 ... 3 Input port 4 ... 4 (highest priority) In this case, the priority signal generation circuit 1001 Signals are generated from ~ 1004 as follows.

Priority signal generation circuit 1001 (corresponding to input port 1) ... 1 (minimum priority) Priority signal generation circuit 1002 (corresponding to input port 2) ... 0 (not transmitted) Priority signal generation Circuit 1003 (corresponding to input port 3) ………… 0 (not transmitted) Priority signal generation circuit 1004 (corresponding to input port 4) ………… 0 (not transmitted) Output from priority signal generation circuits 1001 to 1004 The signal is sent to the arithmetic unit 1011, where the signal corresponding to the highest priority is generated. That is, each priority signal generation circuit 1001 ~
The maximum value “1” in the output of 1004 is the comparison circuits 1021 to 1024.
Is output to the arithmetic circuit 1041. As described above, the priority signal generation circuits 1001 to 1004 generate "0" as the priority signal when the detection signals 11 to 14 are not received, and the priority signal becomes higher as the priority becomes higher. When set to, the arithmetic unit 1011 can be configured using a simple OR circuit.

In the comparison circuits 1021 to 1024, the arithmetic unit 10 described above is used.
The output from 11 is compared with the priority signals from priority signal generation circuits 1001-1004. Here, the priority signal generation circuit 10
Since the signal from 01 is "1", the comparison circuits 1021 to 1024
Among them, only the comparison circuit 1021 outputs the signal with the matched comparison input to the decoder 1031. In the decoder 1031, the input port 1 is output based on the output patterns of these comparison circuits 1021 to 1024.
The control signal for selecting the packet from is output to the switch 741. In response to this, the switch 741 in FIG. 7 switches its input destination to the input port 1 side, that is, the delay circuit 711 side,
The packet arriving at the input port 1 is output to each output port via the delay circuit 711, the switch 741 and the electro-optical conversion unit 705.

On the other hand, during this relay, the output from the arithmetic unit 1011 is input to the arithmetic circuit 1041 of each of the priority signal generating circuits 1001 to 1004. As a result, in the arithmetic circuit 1041, the output of the arithmetic unit 1011 is P ₁ and the number of input ports is N (here, N 1
= 4), and when the current priority is P, (N−P ₁ −1 + P) mod N + 1 is calculated, and the calculation result is registered in the register 1042 and the priority corresponding to the input ports 1 to 4 is calculated. Degree signal is changed. Note that a modb in the above mathematical expression indicates the remainder when a is divided by b. The changed priority signal in this example is as follows, and the priority of the input port 1 is set to the highest priority.

Input port 1 ... (4-1-1 + 1) mod4 + 1 = 4 (highest priority) Input port 2 ... (4-1-1 + 2) mod4 + 1 = 1 input port 3 ………… (4-1-1 + 3) mod4 + 1 = 2 Input port 4 ………… (4-1-1 + 4) mod4 + 1 = 3 (2) Packets are simultaneously input to input ports 1 and 2. When input When packets arrive at input ports 1 and 2 at the same time,
The detection signals 11 and 12 are simultaneously input to the control circuit 1000 from the packet detection circuits 721 and 722. In this case, if the priorities of the input ports 1 to 4 are set in advance in the same manner as described above, the following signals are generated from the priority signal generating circuits 1001 to 1004.

Priority signal generating circuit 1001 (corresponding to input port 1) ………… 1 Priority signal generating circuit 1002 (corresponding to input port 2) ……… 2 Priority signal generating circuit 1003 (corresponding to input port 3) ………… 0 (not transmitted) Priority signal generation circuit 1004 (corresponding to input port 4) ……… 0 (not transmitted) As a result, the priority signal generation circuit 1001
The maximum value “2” among the outputs of 1004 to 1004 is that of each comparison circuit 1021.
It is output to ~ 1024. On the other hand, in the comparison circuits 1021 to 1024,
Since the outputs of the priority signal generation circuits 1001 to 1004 are also input, the outputs of the comparison circuits 1021 to 1024 are as follows.

0 (mismatch) Comparison circuit 1022 ...... 1 (match) Comparison circuit 1023 ...... 0 (mismatch) Comparison circuit 1024 ...... 0 (mismatch) Comparing circuits 1021 to 1024 The output is output to the encoder 1031 and a control signal is sent from the encoder 1031 to the switch 741 so as to select the output of the delay circuit 712.
In this way, among the packets arriving at the input ports 1 and 2, only the packet arriving at the input port 2 having the larger input port number is relayed to each output port via the switch 741.

In this case as well, the output of the arithmetic unit 1011 is input to the priority signal generation circuits 1001 to 1004 as well as the comparison circuits 1021 to 1024, and the priority is changed in each of the priority signal generation circuits 1001 to 1004. The priority of the input port 2 is set to the highest priority as follows.

Input port 1 ... (4-2-1 + 1) mod4 + 1 = 3 Input port 2 ... (4-2-1 + 2) mod4 + 1 = 4 (highest priority) Input port 3 ………… (4-2-1 + 3) mod4 + 1 = 1 input port 4 ………… (4-2-1 + 4) mod4 + 1 = 2 In this way, the input ports 1 to 4 have a one-to-one correspondence in advance. When a packet arrives at a plurality of input ports 1 to 4 at the same time, the packet from the input port 1 to 4 having the highest priority is relayed, and the relayed packet arrives at the input. By changing the priority of the ports 1 to 4 to the highest priority, when a plurality of packets arrives from the terminal again, the packets from the input ports 1 to 4 that were relayed previously are preferentially relayed. be able to. By simply relaying based on the priority of the input port, the data length that can be transmitted at one time from the terminal is limited, data transmission becomes intermittent at the time of file transfer, and communication recovery processing becomes necessary. On the other hand, if the packets from the input ports 1 to 4 that were relayed last time can be preferentially relayed as described above, there is no limitation on the data length that can be transmitted from a terminal at one time, and packets from a predetermined terminal can be continuously Can be relayed. Therefore, even during the file transfer, it is possible to avoid the interruption of communication due to the discarding of packets, and it is possible to reduce the load on the terminal due to the recovery of communication.

FIG. 11 shows another modification of the control circuit. This is such that when packets arrive at a plurality of input ports from terminals at the same time, only packets from terminals having a high packet reception frequency are relayed preferentially.

The detection signals 11 to 14 from the packet detection circuits 721 to 724 are input to the transmission number counting circuits 1101 to 1104, respectively. The output of the timer circuit 1105 is also input to each of the transmission number counting circuits 1101 to 1104, and counts the number of transmissions of each terminal for a certain period of time. The number of transmissions counted by the number-of-transmissions counting circuits 1101 to 1104 is input to the arithmetic unit 1111 for the purpose of obtaining the maximum number of transmissions. The maximum number of transmissions from the arithmetic unit 1111 is the comparison circuit 11
It is sent to one of the input terminals of 21 to 1124. Comparison circuit 1121 ~
The other input terminal of the 1124 has a transmission count circuit, respectively.
The outputs of 1101 to 1104 are connected. Comparator circuit 1121 to 11
24 is the output of each transmission number counting circuit 1101-1104 and the arithmetic unit 11
The output of 11 is compared and the result of this comparison is sent to encoder 11
Output to 31. The encoder 1131 includes the comparison circuits 1121 to 1111.
Based on the comparison result of 24, the transmission number counting circuits 1101 to 1104 that have generated the maximum number of transmissions are determined, and a control signal is output to the switch 741 (FIG. 7) based on the determination result.

In each of the transmission number counting circuits 1101 to 1104, the output of the packet detection circuit 721 is connected to the clock input of the counter 1142 via the delay circuit 1141 as shown in the transmission number counting circuit 1101 as an example. .. Counter 1142
A timer circuit 1105 is connected to the reset input of, and this counts the number of transmissions of the terminal within a fixed time. On the other hand, the output of the counter 1142 is connected to the gate circuit 1143. The output of the packet detection circuit 721 is connected to the control input of the gate circuit 1143, and the content of the counter 1142 is output when the detection signal 11 is input from the packet detection circuit 721.

Next, the operation of the control circuit 1100 will be described with an example.

(1) When a packet is input only to the input port 1 When the packet arrives at the input port 1, the detection signal 11 from the packet detection circuit 721 is input to the control circuit 1100. In the control circuit 1100, the gate circuit 1143 of the transmission number counting circuit 1101 receives the detection signal 11 and outputs the content of the counter 1142 to the calculator 1111. The detection signal 11 is also input to the clock input of the counter 1142 via the delay circuit 1141 and adds “1” to the content of the counter 1142.

Now, assume that the content of the counter 1142 is "12".
, The output of the transmission number counting circuit 1101 is “12”, and the outputs of the other transmission number counting circuits 1102, 1103, 1104 are
It becomes "0" because the detection signals 12, 13, 14 are not input.

Transmission count circuit 1101 ... 12 Transmission count circuit 1102 ... 0 (not transmitted) Transmission count circuit 1103 ... 0 (not transmitted) Transmission count circuit 1104 ... 0 (not transmitted) The number of transmissions thus output from the number-of-transmissions counting circuits 1101 to 1104 is sent to the arithmetic unit 1111, where the maximum number of transmissions is obtained. That is, from the arithmetic unit 1111, the maximum value “12” among the outputs of the transmission number counting circuits 1101 to 1104 is
It is output to the comparison circuits 1121 to 1124. Comparison circuit 1121 to 1124
Then, the output of each computing unit 1111 is the transmission number counting circuit 11
The following signals are output to the encoder 1131 after being compared with the outputs of 01 to 1104.

Comparator circuit 1121 ………… 1 (match) Compare circuit 1122 ………… 0 (mismatch) Compare circuit 1123 ………… 0 (mismatch) Comparator circuit 1124 ………… 0 (mismatch) Encoder 1131 uses this comparator circuit A control signal is output to the switch 741 so as to select a packet from the input port 1 based on the output patterns from 1121 to 1124. In response to this, the switch 741 (Fig. 7) sets its input destination to the input port 1
Side, that is, the delay circuit 711 side, and the packet arriving at the input port 1 is delayed by the delay circuit 711, the switching unit 741, the electro-optical conversion unit.
Output to each output port via 705.

(2) When Packets are Input to Input Ports 1 and 2 at the Same Time When packets arrive at input ports 1 and 2 at the same time,
The detection signals 11 and 12 are simultaneously input to the control circuit 1100 from the packet detection circuits 721 and 722. Assuming that packets are already input to the input ports 1 and 2 12 times and 13 times respectively, the following signals are output from the transmission number counting circuits 1101 to 1104.

Transmission count circuit 1101 ... 12 Transmission count circuit 1102 ... 13 Transmission count circuit 1103 ... 0 (not transmitted) Transmission count circuit 1104 ... 0 (not transmitted) The maximum number of times of transmission "13" is output from the device 1111 to each of the comparison circuits 1121 to 1124, and the outputs of these comparison circuits 1121 to 1124 are as follows.

0 (mismatch) Comparison circuit 1122 ...... 1 (match) Comparison circuit 1123 ...... 0 (mismatch) Comparison circuit 1124 ...... 0 (mismatch) Comparing circuits 1121 to 1124 The output is output to the encoder 1131. From this encoder 1131, a control signal is switched to select the input port 2 having a high packet reception frequency.
It is output to 741. In this way, the input ports 1 and 2
Among the packets arriving at, the packet arriving at the input port 2 having a high reception frequency is relayed to each output port via the switch 741.

As described above, when packets arrive at a plurality of input ports 1 to 4 from a terminal at the same time, only the packet that arrives at the input port having the highest reception frequency among these input ports 1 to 4 is relayed. As a result, packets from terminals with high transmission frequency can be relayed with priority. When the normal transmission load increases, in the case of a terminal having a high transmission frequency, the number of retransmission processes increases, and the processing speed of the terminal extremely decreases. On the other hand, as described above, if packets from terminals with high transmission frequency can be preferentially relayed, it is possible to prevent a decrease in processing speed due to retransmission processing of terminals with high transmission frequency.

FIG. 12 shows another modification of the control circuit. In this method, when a packet arrives at a plurality of input ports from a terminal within a fixed time, only the packet from the input port having the highest priority is relayed.

The detection signals 11 to 14 from the packet detection circuits 721 to 724 are input to the mask circuits 1201 to 1204, respectively. The mask circuits 1201 to 1204 appropriately mask the detection signals 11 to 14 by the mask signal from the mask control circuit 1231.
Detection signals 11 to 14 that have passed through the mask circuits 1201 to 1204 successfully
Is input to the control signal generation circuit 1221 via the selection circuit 1211. The selection circuit 1211 consists of three NOT circuits and an AND circuit, which passes the first detection signals 11 to 14, but thereafter has a high priority (small input port number) detection signal.
Pass only 11-14. The control signal generation circuit 1221 has a predetermined time (ΔT) after the first detection signals 11 to 14 are input.
After waiting for that time, the control signal corresponding to the just input detection signals 11 to 14 is output to the switch 741. This control signal is also input to the mask control circuit 1231. The mask control circuit 1231 appropriately outputs a mask signal to the mask circuits 1201 to 1204 based on this control signal, and masks the detection signals 11 to 14 other than the detection signals 11 to 14 input to the control signal generation circuit 1221. To do.

Next, the operation of the control circuit 1200 will be described. Here, packets 1301, 1302, 13 are input to the input ports 1, 2, 3 of the relay device at the timings shown in FIG. 13, respectively.
The case where 03 arrives is explained.

First, when the packet 1303 arrives at the input port 3, the detection signal 13 is input to the control circuit 1200 from the packet detection circuit 723. In this case, the detection signal 13 passes through the mask circuit 1203 and the selection circuit 1211 and the control signal generation circuit 1221.
Entered in. In response to this, the control signal generation circuit 1221
After the detection signal 13 is input, the control signal output is waited for ΔT time.

When the packet 1302 arrives at the input port 2 within this ΔT time, the control circuit 1200 receives the packet detection circuit.
The detection signal 12 is input from 722. This detection signal 12 is
It is input to the selection circuit 1211 via the mask circuit 1202. Since the selection circuit 1211 is configured such that the detection signal 12 (input port 2) has a higher priority than the detection signal 13 (input port 3), the detection signal 12 is directly output to the selection circuit 1211. After being input to the control signal generation circuit 1221, the detection signal 13 is blocked by the selection circuit 1211. In this way, when the detection signal 12 is input to the generation circuit 1221 after a lapse of ΔT after the first detection signal 13 is input to the control signal generation circuit 1221, the control signal generation circuit 1221 causes the control signal to be switched. It is output to the 741 to notify that the packet has arrived at the input port 2. This allows the switch 741 (Fig. 7).
The input destination is switched to the input port 2 side, and only the packet arriving at the input port 2 is delayed by the delay circuit 712 and the switch.
It is relayed to all output ports via 741 and electro-optical converter 705.

During this relay, the control signal from the control signal generation circuit 1221 is input to the mask control circuit 1231 and, in response to this, the mask control circuit 1231 causes the mask circuits 1201, 1203, 12 to enter.
A mask signal is output to 04 to detect detection signals other than detection signal 12.
Mask 11,13,14. Therefore, after that packet 13
Even when 01 arrives at the input port 1 and the detection signal 11 is input from the packet detection circuit 721, the detection signal 11 is masked by the mask circuit 1201 and is not input to the control signal generation circuit 1221.

As described above, when a packet arrives from a terminal within a certain time (ΔT) at a plurality of input ports 1 to 4, only the packet arriving at the input port 1 to 4 having the highest priority is relayed. By doing so, it is possible to relay packets from high-priority input ports, that is, terminals, even when they arrive at the same time, and it is possible to realize desired priority relay control.

FIG. 14 shows an example of the internal structure of another relay device in the system. This relay device 1400 monitors input ports in order, relays a packet (packet) from a terminal to the input port just monitored, and relays the packet so that packets can be simultaneously sent from a terminal to a plurality of input ports. Even when it arrives, it relays only the packet that has arrived at one valid input port.

Frame transmitted from the terminal (FIG. 15)
Respectively arrive at the input ports 1 to 4 and the photoelectric conversion unit 14
Delay circuit 1411-1414 and frame detector 14 through 01-1404
Entered in 21-1424. The frame detectors 1421 to 1424 are
While the preamble signal in the frame is being input, the arrival notification signal of this preamble signal is sent to the control circuit 14
Continue sending to 31. Further, while a signal other than the preamble signal is being input, the arrival notification signal of the data signal is continuously sent to the control circuit 1431. The control circuit 1431 normally inputs the signals from the frame detectors 1421 to 1424 to 1421 → 1422 → 1423 → 14.
It reads in the order of 24 → 1421 → ……, and monitors whether signals arrive at input ports 1 to 4. Here, the control circuit 1431 monitors the one input port 1 to 4 for a very short time. Further, when the signal from one of the frame detectors 1421 to 1424 is monitored and the arrival notification signal of the preamble signal is monitored, the control circuit 1431 continues the notification signal from the frame detectors 1421 to 1424. Monitor.
Then, when the arrival notification signal of the data signal continues to arrive, the switch 1441 is switched to the delay circuits 1211-1214 corresponding to the monitored frame detectors 1421-1424, and the input ports 1-4 and the output ports where the signals arrive And connect. The transmission frame thus arriving at the relay device 1400 is delayed by the delay circuit.
After being held by 1411 to 1414, they are relayed to all the output ports through the switch 1441 and the electro-optical conversion unit 1451. Here, the delay circuits 1411 to 1414 delay the signals by the minimum time (= t) necessary for recognizing the preamble signal in each terminal, and output the delayed signals to the switch 1441.

Next, the system operation using the relay apparatus 1400 will be described.

When a transmission request is generated at a terminal, the terminal monitors the state of the signal sent from relay apparatus 1400, and when no signal is sent from relay apparatus 1400, the frame shown in FIG. Send 1501. On the other hand, when the signal is transmitted from the relay device 1400, the frame transmission is performed after the signal output is stopped for a certain time or more after the signal reception is completed. This frame 1501 is composed of a preamble part 1511 and a packet part 1521 as shown in the figure. The preamble unit 1511 is a bit string having no meaning as a signal, and it is sufficient that the frame detectors 1421 to 1424 in the relay device 1400 and the terminal itself can detect the preamble signal. Further, the length of the preamble part 1511 is set to the time T required for the control circuit 1431 to complete a round of monitoring of all the input ports 1 to 4 when no signal arrives at the input ports 1 to 4 and each terminal. Is longer than the length of time that flows through the transmission path for a total time (T + t), which is the minimum time t required to recognize the preamble part 1511. By setting the length of the preamble part 1511 of the transmission frame 1501 to be one monitoring period T or more, the control circuit 1431 can always recognize the arrival of the preamble signal.

When frames 1501 and 1501 arrive from the terminal at the same time to the input ports 1 and 2 of the relay device 1400, the preamble parts 1511 and 1511 of these frames 1501 and 1501 are detected by the frame detectors 1421 and 1422, respectively, and the frame detection is performed. The arrival notification signal of the preamble signal is output from the devices 1421 and 1422 to the control circuit 1431. At this time, in the control circuit 1431,
Since the signals from the frame detectors 1421 to 1424 are monitored in order, the notification signal from any one of the frame detectors 1421 and 1422 is monitored. Frame detector 1421,1422
If the control circuit 1431 was monitoring the frame detector 1421 when the notification signal from the
1431 continues to monitor the signal from its detector 1421. After that, when the packet detector 1521 is detected by the frame detector 1421 and its arrival notification signal is input, the input destination of the switch 1441 is switched to the input port 1 side. As a result, the input port 1 becomes valid, and only the transmission frame 1501 arriving at this input port 1 is transmitted to all terminals via the delay circuit 1411, the switch 1441, and the electro-optical conversion unit 1451. During this relay, the control circuit 1431 is further operated by the frame detector 1421.
Is monitoring the arrival notification signal of the packet unit 1521 from the next frame, and when the notification signal ends, the next frame detector 14
Switched to monitoring signals from 22. At this time, even if the arrival notification signal of the packet unit 1521 is input from the frame detector 1422 to the control circuit 1431, the control circuit 1431 does not request the switching unit 1441 to switch.

At the terminal that has transmitted, the source address of the frame sent from the relay device 1400 is compared with its own address. If they match, it is judged that the transmission was successful, and if they do not match, the frame is relayed. It is determined that the device 1400 has been discarded, and appropriate retransmission processing is performed.

As described above, the control circuit 1431 sequentially monitors whether or not the frame detectors 1421 to 1424 detect the preamble signal, and the frame detector just monitored.
If the preamble signals are detected in 1421 to 1424, the switching unit 1441 is switched in response to the detection, so that even if the frames arrive at the plurality of input ports 1 to 4 at the same time,
Only one of the input ports is enabled, and only the frame from that port can be relayed without being discarded, and thus increase in transmission delay time under high load can be prevented.

FIG. 16 shows a modification of the relay device. This is to prioritize the data relay from the terminal by changing the number of times the control circuit monitors the frame detector, that is, the input port.

In this example, of the three input ports 1 to 3 of the relay apparatus 1600, the number of times of monitoring the input port 1 is set higher than the number of times of monitoring the other two input ports 2 and 3. That is, the input of the control circuit 1631 is the frame detector.
It is provided one more (4 pieces) than 1621 to 1623.
The signal lines 1661-
The outputs of the frame detectors 1621 to 1623 are connected via 1663, and the remaining inputs have signal lines branched from the signal line 1661.
1664 is connected. The control circuit 1631 outputs the notification signals from the frame detectors 1621 to 1623 to 16 in the same manner as in the above embodiment.
It reads in the order of 21 → 1622 → 1621 → 1623 → 1621 → ..., and monitors the arrival of signals to the input ports 1 to 3.
Therefore, the signals that arrive at the input ports 1 to 3 are
The probability of being monitored by 1631 is 1 /
2, input ports 2 and 3 are each 1/4, and input port 1 has the highest priority.

In this way, by changing the number of times the input ports 1 to 3 are monitored by the control circuit 1631 among the input ports 1 to 3, when a transmission frame arrives at a plurality of input ports 1 to 4 from a terminal at the same time. Can relay frames from the input ports 1 to 3 that have a large number of monitoring times with high probability, and can give priority to relaying data from each terminal. In this control circuit 1300, input port 1
Although the number of times of monitoring of the input port 1 is set higher than that of the other ports 2 and 3, it is not particularly significant that the number of times of monitoring of the input port 1 is high, and the number of times of monitoring of the port 2 or 3 may be increased. Further, the number of transmissions of the input ports 1 to 3 may be different from each other.

FIG. 17 shows still another internal configuration example of the relay device. This relay apparatus 1700 monitors the input ports in order, and when a transmission request frame arrives from the terminal at the input port that was just monitored, relays the transmission request frame and requests transmission from multiple terminals. Even if there is, the packet is transmitted only to the terminal that has transmitted the relayed transmission request frame.

The transmission request frames (FIG. 18) transmitted from the terminals respectively arrive at the input ports 1 to 4, are converted into electric signals by the photoelectric conversion units 1701 to 1704, and are then input to the switch 1711. The input destination of the switch 1711 is shown in FIG.
As shown in FIG. 9, the control circuit 1731 switches the transmission request frame at regular intervals and first outputs the transmission request frame arriving at the input ports 1 to 4 to the subsequent transmission request frame detection circuit 1721. When the transmission request frame is input, the transmission request frame detection circuit 1721 controls the arrival of this frame by the control circuit 1731.
To notify. Upon receiving the notification signal from the transmission request frame detection circuit 1721, the control circuit 1731 switches the switch 1711.
Stop switching and keep it as it is. Further, the transmission request frame detection circuit 1721 detects passage of a packet and notifies the control circuit 1731 of the end of relay. In response to this, the control circuit 1731 restarts the switching of the switch 1711 and monitors whether the transmission request frame has arrived from the terminal to the next input ports 1 to 4. If the arrival of the transmission request frame is not detected after a certain period of time,
The switching unit 1711 is switched to further monitor whether or not a transmission request frame has arrived at the next input ports 1 to 4. Reference numeral 1741 in the drawing is an electro-optical conversion unit that converts the transmission request frame and packets that have passed through the switch 1741 into optical signals and relays them to all output ports.

On the other hand, although not shown, each terminal sends a transmission request frame 1801 shown in FIG. 18 prior to packet transmission.
It transmits (including its own address) and waits for the transmission request frame 1801 to be returned. Then, when the transmission request frame is returned from the relay device 1700, it is determined whether or not the frame is transmitted by the local station, and if it is confirmed that the frame is transmitted by the local station, the packet is transmitted.

Next, the system operation using the relay apparatus 1700 will be described.

When a terminal makes a transmission request, the terminal monitors the state of the signal sent from relay apparatus 1700, and when no packet is sent from relay apparatus 1700, transmission request frame 1801 shown in FIG. When a packet is sent from the relay device 1700, the transmission request frame 1801 is transmitted after waiting for a fixed time or more from the end of reception until there is no packet.

As shown in FIG. 20, it is assumed that transmission request frames 2001 and 2002 arrive at the input ports 2 and 3 at the same time while the input destination of the switch 1711 is being switched to the input port 2 side. In this case, the transmission request frame 2001 arriving at the input port 2 passes through the switch 1711 and is input to the transmission request frame detection circuit 1721. In response to this, the transmission request frame detection circuit 1721 outputs a notification signal to the control circuit 1731 and causes the control circuit 1731 to hold the switch 1711 on the input port 2 side. As a result, the transmission request frame 2001 arriving at the input port 2 passes through the switch 1711 and the transmission request frame detection circuit 1721 and is sent to the electro-optical conversion unit 1741, where it is converted into an optical signal and transmitted to all terminals. It

At the terminal which has transmitted the transmission request frames 2001 and 2002, the address of the transmission request frame returned from the relay device 1700 is compared with its own address, and if they match, it is judged that the transmission is permitted and the packet is transmitted. To do. Also,
If they do not match, it is judged that the transmission is not permitted yet, and the packet transmission is postponed. Here, the terminal connected to the input port 2 determines that the returned transmission request frame 2001 is its own, and starts transmitting the packet 2011 (FIG. 20). This allows packets from this terminal 2011
Only arrives at input port 2 of relay device 1700 and switches 17
11, transmission request frame detection circuit 1721 and electro-optical conversion unit 17
It is transmitted to all terminals via 41.

During this relay, the transmission request frame 2002 is continuously transmitted from the terminal which has postponed the transmission of the packet. Therefore, when the relay is completed and the switch 1711 is switched to the next input port 3 side, the transmission request frame 2002 is input to the transmission request frame detection circuit 1721 and the input destination of the switch 1711 is held on the port 3 side. To be done. As a result, following the relay described above, the packet 2012 whose transmission has been postponed is transmitted and transmitted to all the terminals.

As described above, the transmission request frame is transmitted from the terminal prior to the transmission of the packet, the packet is transmitted after the transmission request frame transmitted by itself is returned, and the input ports of the relay device are monitored in order. , When the transmission request frame arrives at the input port just monitored, by relaying the transmission request frame,
Even if a transmission request is generated at a plurality of terminals, the packet can be transmitted only to the terminal that first transmitted the transmission request frame that arrived at the relay device, and only that packet can be relayed.

Moreover, since the packets are not simultaneously transmitted from a plurality of terminals, the packets are not discarded inside the relay device 1700. Therefore, it is not necessary for each terminal to retransmit the packet, the procedure relating to the retransmission processing can be reduced, and the communication control procedure can be greatly simplified.

FIG. 21 shows still another internal configuration example of the relay device. This relay device 2100 is for relaying only the packet with the highest priority by comparing the priorities of the packets when the packets arrive from the plurality of terminals at the same time.

The packets transmitted from the terminals are input to the packet relay circuits 2101 to 2103 via the input ports 1 to 3, respectively. The packet relay circuits 2101 to 2103 have the function of relaying the received packet to all the output ports 5 to 7,
It has a function of detecting the reception of a packet and a function of detecting the source address SA (see FIG. 22) of the received packet. That is, the packet relay circuits 2101 to 2103 detect the packets transmitted from the terminals, respectively, and notify the arithmetic control circuit 2121 of the detection signals through the signal lines 2111 to 2113. It also detects the source address SA of the packet and sends it to the local bus.
The data is output to the 2131 and sent to the arithmetic control circuit 2121. Arithmetic control circuit
When the detection signals are input from these packet relay circuits 2101 to 2103, 2121 determines from which terminal the packet is relayed, and the packet relay circuit to which the terminal is connected.
2101 to 2103 are allowed to relay using signal lines 2141 to 2143,
Relay is prohibited for the other packet relay circuits 2101-1103. The determination of packet relay by the arithmetic control circuit 2121 is performed as follows when the packet relay circuits 2101 to 2103 are not relaying. (1) Packet relay circuit 2101-
Of the 2103, the packet relay circuits 2101 to 2103 that first detect the packet are permitted to relay the packet, and the other packet relay circuits 2101 to 2103 are relayed until the relay of the permitted packet is completed. Prohibit (2) When a plurality of packet relay circuits 2101 to 2103 detect packets at the same time, the source addresses SA of these packets are compared, and the packet relay circuits 2101 to 2103 that received the packet with the largest address value are permitted to relay. However, the other packet relay circuits 2101 to 2103 are prohibited from relaying the packets until the relay of the permitted packets is completed.

Next, the system operation using the relay device 2100 will be described with reference to FIGS. Here, FIG.
2 and FIG. 24 show the operation contents on the relay device side.
5 shows the operation contents on the terminal side.

After the power is turned on, the relay device executes a predetermined initial process and enters a waiting state for receiving a packet from each terminal (2301 in FIG. 23). On the other hand, the terminal monitors the state of the transmission line and, if the transmission line is empty, transmits a packet (FIG. 25).
Medium 2501 to 2503). Then, after transmitting the packet, the transmission path is further monitored, and the packet is waited for (2504, 2505). When receiving a packet from a certain terminal, the relay device discards the packet from another terminal if the packet is being relayed (2302, 2305). On the other hand, when packets from other terminals are not being relayed and are not being received from other terminals at the same time, the packets are relayed to all output ports (2303, 2305). After receiving the relayed packet, the terminal that has transmitted determines the source address SA of the packet. At this time, if the address SA matches with its own address, that is, if the transmitted packet is returned, it is determined that the transmission is successful and the packet is relayed to another terminal.
(2506). However, if the source address SA of the received packet does not match the own address, it is determined that the packet transmitted from the own terminal has been discarded, and after waiting for a certain period of time, the packet is retransmitted (2507).

When packets from a plurality of terminals arrive at the relay device at the same time, the relay device performs the simultaneous reception process.
(2306). That is, the source address SA of the received packet is compared (2401 in FIG. 24), only the packet having the largest value of the address SA is relayed, and the other packets are discarded (2402, 2403).

As described above, when packets arrive at the relay device from a plurality of terminals at the same time, the source addresses SA of these packets are compared, and only the packet having the largest address value is relayed to determine the address value. It is possible to realize a system in which only packets from large terminals can be relayed without being discarded, and the transmission delay time does not increase even under heavy load.

In the above example, the source address SA of the received packet is compared, and only the packet having the largest address value is relayed. However, the source address SA is not significant, and the priority of the packet is It suffices if they can be uniquely distinguished. Therefore, the packet having the smallest source address SA may be relayed preferentially, or the packet having the largest number of "1" s in SA may be relayed. Furthermore, not only SA but other fields of the packet may be compared.

Further, in the above example, the address of each terminal
The (source address SA) may be changed at regular intervals. According to this, the terminals that perform packet transmission are not biased,
It is possible to make each terminal evenly transmit packets. From the same reason, it is also possible to change the packet comparison method by the relay device at every fixed timing.

26 to 32 show a modification of the above embodiment. 26 to 28 show operation contents on the relay device side, and FIG. 29 shows operation contents on the terminal side.

After the power is turned on, the relay device executes a predetermined initial process and enters a waiting state for receiving a packet from each terminal (2601 in FIG. 26). On the other hand, each terminal writes the desired priority 3004 in the priority determination packet shown in FIG. 30 and transmits it to the relay device as soon as the relay device is in the reception waiting state (2901 in FIG. 29). When the relay device receives the priority determination packet, the relay device enters the priority determination processing (2606). In the priority determination process, as shown in FIG. 27, each terminal is associated with the priority in accordance with the priority order requested by each terminal. That is, the table shown in FIG. 32 is searched according to the priority requested by the terminal (2701), and if the terminal corresponding to the requested priority is not registered, the terminal address is written corresponding to the priority. (2702,270
Four). If the terminal corresponding to the requested priority is already registered, the priority that is the closest to the priority and the table is empty is searched, and the address of the terminal is written corresponding to the priority. (2703, 2708). In this way, the optimum priority is determined for each terminal, and when the contents of the table are updated, the determined priority is written in the response packet shown in FIG. 31 and returned to the source terminal (2710).

When the response packet is returned from the relay device, the terminal monitors the state of the transmission line and, if the transmission line is empty, transmits the data packet (2902 to 2905). Then, after transmitting the data packet, the transmission path is further monitored and the reception of the data packet is waited (2906, 2907). The relay device, when receiving the data packet, discards the packet if the data packet from another terminal is being relayed (26
03, 2607). On the other hand, when a data packet from another terminal is not being relayed and is not being received from another terminal at the same time, the packet is relayed to all output ports (2604, 2605). After receiving the relayed data packet, the terminal that has transmitted determines the source address. At this time, if the source address matches its own address, that is, if the transmitted data packet is returned, it is determined that the transmission was successful and the data packet was relayed to another terminal (2908). However, if the source address of the received packet does not match its own address, it is determined that the data packet sent from the own terminal has been discarded, and after a certain period of time, the data packet is retransmitted (2909).

When packets from a plurality of terminals arrive at the relay device at the same time, the relay device performs the simultaneous reception process.
(2608). That is, the table of FIG. 32 is searched according to the source address SA of the received packet (28 in FIG. 28).
01), and compare the priority set for each terminal (2
802). Then, only the packet from the terminal having the highest priority among these priorities is relayed, and the other packets are discarded (2803, 2404).

As described above, the priority determining packet is transmitted from each terminal prior to the packet transmission, and the relay device sets the priority for each terminal by the priority determining packet from the terminal, When data packets arrive at the same time, the data packet from the terminal having a high priority is relayed, so that only the packet from any terminal can be relayed without being discarded. Moreover, since the priority of each terminal is determined by the priority determination packet from the terminal, the terminal can determine the desired priority.

In the above embodiment, the number of times relaying can be performed with the once set priority is determined so that the highest priority is not semipermanently set for one terminal, and when that number is reached, the priority is changed. It is also possible to add processing.

[0125]

In summary, according to the present invention, the following excellent effects are exhibited.

According to the first aspect of the present invention, it is possible to realize a system in which the transmission delay time of data does not increase sharply even if the transmission load increases in the star type network and the number of connected terminals can be easily increased. it can.

According to the second aspect of the present invention, priorities corresponding to the input ports of the relay device are set in advance in a one-to-one correspondence, and when packets arrive at a plurality of input ports at the same time, the input having the highest priority among these input ports Since only the packet from the port is relayed, even if the packets arrive at the relay device from multiple terminals at the same time, only one packet can be relayed without being discarded, further reducing the increase in transmission delay time under heavy load. can do. Moreover, since the priority of each input port is changed among the input ports upon completion of packet relay in the relay device, packets from each terminal can be relayed evenly.

According to the present invention, when packets arrive at a plurality of input ports from terminals at the same time, only the packet from the input port having the highest priority is relayed, and the input port to which the relayed packet is input is relayed. Since the priority is changed to the highest priority, even if packets arrive from multiple terminals at the same time to the relay device, the packets from the last relayed terminal can be relayed again, and the packets can be continuously transmitted from the predetermined terminal. Can be sent. Therefore, even during file transfer or the like, the load caused by the recovery process of the terminal can be reduced without the packet being discarded and the communication being interrupted.

In claim 4, when packets arrive at a plurality of input ports at the same time, only packets from the input ports having a high packet arrival frequency are relayed. Therefore, when packets arrive at a relay device from a plurality of terminals at the same time. It is possible to relay only packets from a terminal that has a high transmission frequency, and it is possible to prevent a decrease in processing speed due to retransmission processing of that terminal.

According to the fifth aspect, when packets arrive at a plurality of input ports within a fixed time, only the packet from the input port having the highest priority is relayed, so that desired priority relay can be realized.

According to the sixth aspect, the states of the input ports of the relay device are monitored in order, and when a signal arrives from the terminal at the input port that was just monitored, the packet from that port is relayed. Even when packets arrive from the terminal to the relay device at the same time, only the packet from the input port just monitored can be relayed without being discarded.

In claim 7, since the number of times the relay device monitors the input port is changed between the input ports, the data relay from each terminal can be prioritized.

In claim 8, the terminal transmits the transmission request frame before transmitting the packet, the relay device sequentially monitors the input ports, and when the transmission request frame arrives at the input port just monitored, Since the transmission request frame is relayed, even when the transmission requests are simultaneously generated by a plurality of terminals, it is possible to relay the packet only from the terminal which has transmitted the relayed transmission request frame. Moreover, since packets are not transmitted from a plurality of terminals at the same time, packet retransmission processing is not required at each terminal, and the communication control procedure can be significantly reduced.

According to the ninth to eleventh aspects, when packets arrive at the relay device from a plurality of terminals at the same time, predetermined fields of these packets are compared, and only one packet selected by the comparison result is relayed. Even if packets arrive from a plurality of terminals at the relay device at the same time, only one packet can be relayed without being discarded.

According to the twelfth aspect, the priority for each terminal is set in the relay device by the priority determining packet transmitted from the terminal, and when the data packets arrive from a plurality of terminals at the same time, the priority is high. Since only the data packet from the terminal is relayed, even if data packets arrive at the relay device from a plurality of terminals at the same time, only one data packet can be relayed without being discarded. Moreover, since the priority of each terminal is determined by the priority determination packet from the terminal, the relay priority can be determined on the terminal side.

[Brief description of drawings]

FIG. 1 is a block diagram showing a star network in which the present invention is used.

FIG. 2 is a diagram illustrating an internal configuration example of a relay device in a star network.

FIG. 3 is a configuration diagram showing an interface circuit inside a terminal in a star network.

FIG. 4 is another configuration diagram of a star network.

5 is a diagram showing an example of a packet flow in the network of FIG.

6 is a diagram showing an internal configuration of a lower relay device in the network of FIG.

FIG. 7 is a diagram illustrating another internal configuration example of a relay device.

8 is a diagram showing an example of a priority pattern of a packet detection circuit in the relay device of FIG.

9 is a diagram illustrating an example of packet input / output in the relay device in FIG.

10 is a configuration diagram showing a modification of the control circuit in the relay device in FIG.

FIG. 11 is a configuration diagram showing another modification of the control circuit.

FIG. 12 is a configuration diagram showing still another modified example of the control circuit.

FIG. 13 is a diagram showing an example of the timing of arrival of packets at an input port.

FIG. 14 is a configuration diagram showing still another internal configuration example of the relay device.

15 is a diagram showing a configuration of a transmission frame transmitted to the relay device in FIG.

16 is a diagram showing a modification of the relay device in FIG.

FIG. 17 is a configuration diagram showing still another internal configuration example of the relay device.

18 is a diagram showing a configuration of a transmission request frame transmitted to the relay device in FIG.

19 is a diagram showing a switching timing of a switch in the relay device of FIG.

20 is a diagram showing an example of the relationship between the switching timing of the switch and the input / output of packets in the relay device of FIG.

FIG. 21 is a diagram showing still another internal configuration example of the relay device.

22 is a diagram showing a configuration of a packet transmitted to the relay device in FIG.

FIG. 23 is a flowchart showing the operation contents on the relay device side.

24 is a flowchart showing the processing contents of the simultaneous reception processing of FIG. 23.

FIG. 25 is a flowchart showing operation contents on the terminal side used together with the relay device.

FIG. 26 is a flowchart showing the operation contents of still another relay device.

27 is a flowchart showing the processing contents of the priority determination processing of FIG.

28 is a flowchart showing the processing contents of the simultaneous reception processing of FIG.

FIG. 29 is a flowchart showing operation contents on the terminal side.

[Fig. 30] Fig. 30 is a diagram illustrating a configuration example of a priority order determination packet transmitted from a terminal.

FIG. 31 is a diagram showing a configuration example of a response packet transmitted from a relay device.

FIG. 32 is a diagram showing a configuration example of a table for associating each terminal with a priority.

[Explanation of symbols]

 101 Relay device 111 to 114 Terminal 121 to 124 Bidirectional link 201 to 204 Photoelectric conversion unit 205 to 208 Lightning conversion unit 211 to 214 Delay circuit 221 to 224 Packet detection circuit 231 Selection circuit 401 Upper relay device 403 to 404 Lower relay Device 411 to 419 Terminal 731 Control circuit 741 Switching device 1001 to 1004 Priority signal generation circuit 1011 Arithmetic unit 1021 to 1024 Comparison circuit 1031 Encoder 1101 to 1104 Transmission count circuit 1105 Timer circuit 1201 to 1204 Mask circuit 1311 Selection circuit 1321 Control signal Generation circuit 1231 Mask control circuit 1421 to 1422 Frame detector 1721 Transmission request frame detection circuit 2101 to 2104 Packet relay circuit 2121 Operation control circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuhiro Kasai 5-1-1 Hidaka-cho, Hitachi-shi, Ibaraki Hitachi Cable Company, Ltd., Optro System Laboratories (72) Inventor Taisho Onuki Hidaka-cho, Hitachi-shi, Ibaraki 5-1 1-1 Hitachi Cable Co., Ltd., Optro System Laboratory (72) Inventor Michio Futani 5-1-1 Hidakacho, Hitachi City, Ibaraki Hitachi Cable Co., Ltd. (72) Inventor Kuriyama Masaru 5-1-1, Hidaka-cho, Hitachi, Ibaraki Hitachi Cable Company, Ltd., Optro System Research Center (72) Inventor Yasumasa Imai 5-1-1, Hidaka-cho, Hitachi, Ibaraki Hitachi Cable, Ltd. Hidaka in the factory

Claims (12)

[Claims] 1. In a network comprising a plurality of terminals and a relay device for relaying a signal by connecting the terminals in a star pattern, the relay device is configured so that when a packet arrives at an arbitrary input port, the other packet When the relay has not been performed, the arrived packet is relayed to the output port, and when the packet has already been relayed, the later arrived packet is discarded without being relayed inside the relay device. The relay devices are connected so as to form a branched hierarchical structure, and when the packet arrives from the lower relay device, the uppermost relay device outputs the packet to all the lower relay devices, and the other than the highest one. The relay device outputs the packet only to the upper relay device when the packet arrives from the lower relay device or the terminal, and directly outputs the packet when the packet arrives from the upper relay device. A packet relay method characterized in that a packet is output to all the lower relay devices or terminals that are connected. 2. In a network comprising a plurality of terminals and a relay device for relaying a signal by connecting the terminals in a star shape, a priority corresponding to the input port of the relay device in a one-to-one correspondence is determined in advance, and a plurality of terminals are provided. When packets arrive at the input port from the terminal at the same time, the packet from the input port with the highest priority among those input ports is relayed, and the packets from other input ports are not relayed inside the relay device. A packet relay method characterized by discarding and changing the priority of each input port between input ports upon completion of packet relay in a relay device. 3. In a network including a plurality of terminals and a relay device for relaying signals by connecting the terminals in a star shape, a priority corresponding to an input port of the relay device is determined in advance, and a plurality of terminals are provided. When packets arrive at the input port from the terminal at the same time, the packet from the input port with the highest priority among those input ports is relayed, and the packets from other input ports are not relayed inside the relay device. A packet relay method characterized in that the priority of the input port to which the discarded and further relayed packet is input is changed to the highest priority among the relay devices. 4. In a network composed of a plurality of terminals and a relay device that relays signals by connecting the terminals in a star pattern, when packets arrive from the terminals at a plurality of input ports of the relay device at the same time, A packet relay method in which a packet from an input port with a high packet arrival frequency is relayed, and a packet from another input port is discarded inside the relay device without being relayed. 5. In a network including a plurality of terminals and a relay device that relays signals by connecting the terminals in a star pattern, different priorities are set in advance for each input port of the relay device, and within a certain fixed time. When a packet arrives at a plurality of input ports from a terminal, the packet from the input port with the highest priority is relayed, and other packets are discarded inside the relay device without relaying. Relay system. 6. In a network comprising a plurality of terminals and a relay device that relays signals by connecting the terminals in a star shape, the states of the input ports of the relay device are sequentially monitored and just monitored. When a signal from a terminal arrives at an input port, the packet from that input port is relayed, and even when packets arrive from multiple terminals at the same time, only the packet from one input port is relayed. A packet relay method characterized in that 7. The number of monitoring of the input port in the relay device is changed between the input ports.
The packet relay method described. 8. In a network comprising a plurality of terminals and a relay device for relaying a signal by connecting the terminals in a star shape, the terminal transmits a transmission request frame, and then the transmission request frame transmitted by itself. , The packet is transmitted, the relay device monitors the input ports in order, and when the transmission request frame arrives at any input port, the transmission request frame is relayed, and the plurality of terminals A packet relay method characterized in that even when a transmission request is made, only one of the terminals that has transmitted the transmission request frame is made to transmit the packet. 9. In a network comprising a plurality of terminals and a relay device for relaying a signal by connecting the terminals in a star pattern, when packets arrive at the relay device from the plurality of terminals at the same time, these packets are A packet relay method in which predetermined fields are compared and one packet selected based on the comparison result is relayed, and other packets are discarded inside the relay device without relaying. 10. The packet relay method according to claim 9, wherein the packet relayed by the relay device is a packet having a largest value of a source address. 11. The packet relay method according to claim 9, wherein the packet relayed by the relay device is a packet having a smallest value of a source address. 12. In a network comprising a plurality of terminals and a relay device for relaying a signal by connecting the terminals in a star pattern, the terminal transmits a priority determination packet prior to packet transmission, The relay device sets the priority for each terminal by the priority determination packet from the terminal, and when data packets arrive from a plurality of terminals at the same time, relays the data packet from the terminal with the highest priority, A packet relay method characterized in that packets from other terminals are discarded inside the relay device without being relayed.