JP3459737B2 - Network system, communication method in switching device used therein - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to a network system, where a communication method in a switching device used.

[0002]

2. Description of the Related Art Conventionally, as a method of performing data communication between terminals, a packet is transmitted from the terminals and a switching device connecting the terminals detects a destination address of the packet and connects to the destination terminal for communication. Various packet switching networks and communication methods have been studied. FIG. 11 shows the structure of packets exchanged in these packet exchange networks. In FIG.
Reference numeral 101 is an address portion for instructing an output end to output this packet, and reference numeral 1102 is a data portion carried by this packet. FIG. 12 shows a first conventional example of a switching device used in these packet switching networks, and shows a crossbar type switching device having an input terminal number N and an output terminal number N. In FIG. 12, reference numeral 1
A decoder unit 201 reads the address unit of the packet and instructs the control unit which output end should output the packet. Reference numeral 1202 is a FIFO (First In).
First Out), the input packets are temporarily stored and output to the output line in the order of input under the control of the control unit. Reference numeral 1203 is an input line for supplying the packet signal output from the FIFO to the input of the switch. Reference numeral 1204 is a switch, which has a function of switching whether to output the packet signal input to the input line to the output line. Reference numeral 1205 is a control unit,
According to the output from the decoder, the reading control of the FIFO and the opening / closing of each switch are controlled. Reference numeral 1206 is an output line that supplies the packet signal output from the switch to the output end. In this crossbar type switching device, the control unit 1205 performs routing control for changing the output end to be output by controlling the opening / closing of the switch connected to the desired output end. Further, when so-called output competition occurs in which inputs from a plurality of input terminals desire to output to the same output terminal at the same time, the control unit also performs arbitration control of which of the plurality of inputs is to be output. ing. The exchange operation is realized by these controls.

[0003]

However, in the first prior art example, in the case of the input fraction N and the output fraction N, N
Since it requires × N switches, there is a drawback that the scale of the hardware becomes very large. Further, in the first conventional example, N outputs of the switch for connecting the plurality of input lines and the output lines are connected to the same output line. For this reason, the wiring of the connection line becomes long, wiring delay occurs, the stray capacitance of the wiring increases, and the like, and when the number of input terminals N increases, it becomes difficult to increase the operating speed of the switch. Therefore, the first conventional example has a drawback that it is not suitable for high-speed exchange of input packet signals. Furthermore, in the first conventional example, it is necessary to detect the occurrence of output competition for the inputs from all the input terminals and perform the arbitration control for each output terminal. Therefore, this control has a drawback that the hardware scale of the control unit increases. FIG. 13 is a second conventional example made in order to overcome the drawbacks of the first conventional example described above, and by connecting 2 × 2 switches having 2 input terminals and 2 output terminals, which will be described later, in multiple stages, It constitutes a switching device. In FIG. 13, reference numeral 13
Reference numerals 01 to 1312 are 2 × 2 switches each having two input terminals and two output terminals, and have two functions of a straight line that connects the input terminal and the output terminal in a straight line and a crossing that connects and crosses each other. By connecting the 12 2 × 2 switches in a shuffle net shape, an omega type switching device having 8 input terminals and 8 output terminals is realized. FIG. 14 is an internal configuration diagram of the 2 × 2 switch having two inputs and two outputs. In FIG. 14, reference numerals 1401 and 1402 are decoders, which read the address part of an input packet and instruct the control part which output end should output this packet. Reference numeral 1403
And 1404 are FIFO (First In First)
Out), the input packets are temporarily stored and output to the selector in the input order under the control of the control unit. Reference numerals 1405 and 1406 denote selectors, which select the FIFO storing the packet signal to be output to the output destination under the control of the control unit. Selector 14
The state in which 05 selects the FIFO 1403 and the selector 1406 selects the FIFO 1404 is the above-mentioned straight line advance, and the state in which the selector 1405 selects the FIFO 1404 and the selector 1406 selects the FIFO 1403 is the above-described crossing. In the second conventional example, the required number of 2 × 2 switches is NlogN−N / 2.
(The base of log is 2), which is less than the N × N number of the first embodiment, but a decoder, a FIFO, a control unit, and a selector are required for each 2 × 2 switch, so that the hardware as a whole is required. It had the drawback of increasing the scale of clothing. Furthermore, in the second embodiment, even if the different output terminals are not connected to the same output terminal, the desired output destination can be connected depending on the connection status of the other input terminals. There is a problem in that a so-called blocking phenomenon occurs. This is, for example, the input end 5 and the output end 3 of FIG.
2 × 2 switch 1301 is set to the crossing state when is connected, but in order to connect the input terminal 1 to the output terminal 1, the 2 × 2 switch X is set to the straight traveling state. Since it is necessary, blocking will occur and the signal will be discarded. FIG. 15 shows a third conventional example, which includes eight variable wavelength transmitters using tunable laser diodes (TLDs) and eight receivers using photodiodes (PDs). An example of a switching device having eight input terminals and eight output terminals is shown. In FIG. 15, reference numeral 150
Denoted at 1 to 1508 are decoders, which read the address part of an input packet and instruct the control part which output end should output this packet. Reference numerals 1511 to 1518 are FIs.
FO (First In First Out), which temporarily stores the input packets and outputs them to the variable wavelength transmission unit in the order of input under the control of the control unit. Reference numerals 1521 to 1528 are variable wavelength transmitters,
The packet signal output from the FIFO is converted into an optical signal of a predetermined wavelength by the control of the wavelength control unit in the control unit, and the optical signal is output to the star coupler. Reference numeral 1550 is a star coupler, which has a function of combining lights of all wavelengths emitted from the eight variable wavelength transmitters and emitting the combined lights to the eight filters. Reference numerals 1531 to 1538 are filters, each having a function of transmitting only an optical signal of a fixed wavelength and blocking an optical signal of another wavelength. The transmission wavelength of each filter is λ1 for the filter 1531 and λ for the filter 1532.
2, the filter 1533 is λ3, the filter 1534 is λ
4, the filter 1535 is λ5, the filter 1536 is λ
6, the filter 1537 is λ7, the filter 1538 is λ8
Is set to. Reference numerals 1541 to 1548 are reception units, which have a function of converting an optical signal of a predetermined wavelength that has passed through the filter into an electric signal using a photodiode and outputting the electric signal to the output end. Reference numeral 1551 is a control unit that controls the exchange operation of this exchange, and is composed of an arbitration control unit 1552 and a wavelength control unit 1553. The arbitration control unit controls the output contention of the packet input to each input terminal for each output terminal to which the input packet should be output, based on the instruction output from each decoder. The arbitration control unit 1552 instructs the wavelength control unit 1553 on the result of this arbitration. The wavelength control unit controls the transmission wavelength of each variable wavelength transmission unit based on the instruction from the arbitration control unit. In the third conventional example, since the eight filters 1531 to 1538 are set so that the wavelengths of the optical signals that are transmitted are different, the wavelengths of the optical signals that are incident on the respective receiving units are different and unique. is there. Therefore,
By changing the transmission wavelength of each variable wavelength transmission unit, it is possible to realize the routing function of changing the output end to be output. However, in the third conventional example, since it is necessary to collectively control the arbitration of the packets input from all the input terminals, the load on the arbitration control unit becomes large, which impedes the speedup of the switching device. It was. In the wavelength controller,
According to the instruction from the arbitration control unit, it is necessary to control the transmission wavelength to a predetermined wavelength for each packet,
For example, when a packet to be transmitted next has the longest wavelength after the packet having the shortest wavelength is transmitted, the change amount of the transmission wavelength of the variable wavelength transmission unit becomes large. Therefore, high-speed wavelength control is required, the scale of hardware becomes large, or the time required for wavelength change becomes long, which has a drawback that it hinders the speed-up of the switching device.

As a technique similar to the third conventional example, "Matthew S. Goodman; Oct.
over 1989-IEEE Communicat
Ion Magazine, p27-35 "to BHYP
A technique called ASS is shown. The configuration is similar to that of FIG. 15, but here, it is preliminarily controlled using the Batcher Banyan algorithm so that packets destined for the same output end are not input to a plurality of wavelength tunable transmitters at the same time. The wavelength of the variable wavelength transmitter is controlled. Also in this configuration, it is necessary to control in advance that packets destined for the same output terminal are not simultaneously input to a plurality of wavelength tunable transmitters, and it is necessary to control the wavelengths of the wavelength tunable transmitters according to the destinations of the packets.

In a switching network for communicating between a plurality of terminals using the switching device as described above,
There is a problem that high speed communication cannot be performed due to the limitation of the operation speed of the exchange. Further, since the hardware of the switching device becomes large, it is difficult to apply it to a small LAN.

[0006]

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to eliminate the need for arbitration control and enable efficient communication.

In order to achieve the above object, the present invention is a network system comprising a switching device and a plurality of terminals connected to each other, wherein the switching device has a plurality of N inputs to which signals from the terminals are input. An end, N output terminals for outputting signals to the terminal, and N input buffer means for temporarily storing signals input from the N input terminals, respectively.
The output terminals to which the N input buffer means are connected are connected in a predetermined order so that the input buffer means are simultaneously connected to different output terminals, and, A signal temporarily stored in the input buffer means is output while the connection means for sequentially switching at a preset timing cycle and the connection relationship between the input buffer means and the output end are being switched by the connection means. And a buffer control means for reading the signal from the input buffer means in synchronism with the connection of the input buffer means to the output end to be provided.

Further, in a network system in which a switching device and a plurality of terminals are connected, the switching device receives a plurality of N input terminals to which a signal from the terminal is input and a signal to the terminal. N output terminals for outputting, N input buffer means for temporarily storing the signals input from the N input terminals, and a signal output from one of the N input buffer means. Corresponding to each input buffer means, and the transmission channels of each of the transmission means are simultaneously transmitted by each of the transmission means. Is a channel control means for controlling to sequentially switch signals in a predetermined order so as to transmit signals on mutually different channels and at a preset timing cycle; and the input buffer means, Buffer control means for reading the signal from the input buffer means in synchronization with the switching of the transmission channel of the corresponding transmission means to the channel to which the signal temporarily stored in the input buffer means should be output; And a signal from the N transmitting means is supplied to each of the N output terminals.

[0009]

Also, in the communication method in the exchange device, the exchange device has a plurality of N input terminals to which a signal from the terminal is input and N output terminals to output a signal to the terminal. , N input buffer means for temporarily storing the signals input from the N input terminals, respectively, and a connection relationship of the output terminals to which the N input buffer means are respectively connected, Connection of the input buffer means and the output end in a predetermined order so that the input buffer means are simultaneously connected to different output ends at the same time and sequentially at a preset timing cycle. While the input buffer means is being switched, the signal is temporarily stored in the input buffer means in synchronization with the input buffer means being connected to the output end to which the signal is to be output. Providing a communication method characterized by communicating the signals read from § means.

According to the present invention, the relationship between input and output is sequentially switched in a preset order so that signals are not transmitted to the same output terminal at the same time, and signals are exchanged accordingly, so that arbitration control can be performed. There is no need.

As a result, the structure of the exchange apparatus can be simplified and efficient communication can be performed.

[0013]

[0014]

[0015]

DETAILED DESCRIPTION OF THE INVENTION

(Embodiment 1) FIG. 1 is a first embodiment of a switching device in a switching network according to the present invention, in which eight variable wavelength transmitters and eight fixed wavelength receivers are used for input 8 and output 8. The structural example of an exchange device is shown. In FIG. 1, 111 to 118 are buffer means for temporarily storing input data, 121 to 128 are wavelength tunable optical transmitters for converting an input signal into an optical signal of an arbitrary wavelength and outputting the optical signal, 131
˜138 are optical filters that transmit optical signals of different specific wavelengths, 141 to 148 and 151 to 158 are optical receivers that convert input optical signals into electrical signals and output the electrical signals, 161
168 is an optical transmitter that converts an input signal into an optical signal of a specific wavelength and outputs the optical signal, 171 is an 8 × 8 star coupler, 17
Reference numeral 2 denotes a buffer control unit for controlling the signals input to the buffers 111 to 118 to be temporarily stored and output at an arbitrary time, and 173 denotes the variable wavelength optical transmitters 121 to 128.
A wavelength control unit 174 for controlling a current injection to each wavelength variable terminal so as to transmit an optical signal of an arbitrary wavelength, 174 is a clock generation circuit, and 175 is a frame generation circuit for determining a wavelength transition time. The optical transmitters 121 to 128 are, for example, wavelength tunable light emitting devices such as DFB lasers and DBR lasers, drive circuits for modulating the light emitting devices, and wavelength stabilizing circuits. The emission wavelength can be changed by injecting a current into the terminal. The optical filters 131 to 138 are filters such as a fiber Fabry-Perot filter and a DFB laser filter, and have wavelengths λ1, λ2, ...
.. transmits only the optical signal of .lambda.8 and blocks the optical signals of other wavelengths. The optical receivers 141 to 148 are Pin-
An optical receiver equipped with a PD or APD, which has photoelectric conversion, equalization amplification, and identification / reproduction functions. Optical receivers 151-158
Is an optical receiver equipped with a Pin-PD or APD, and has photoelectric conversion, equalization amplification, identification reproduction, and retiming functions. The optical transmitters 161 to 168 are optical transmitters equipped with LEDs or Fabry-Perot LDs.

FIG. 2 shows a configuration example of the exchange network of the present invention. In FIG. 2, 201 to 208 are terminals, and 210 is a switching device of the present invention, and each terminal and the switching device are connected by two optical fibers for upstream and for downstream respectively.

FIG. 3 shows a configuration example of a communication control device mounted on a terminal connected to the exchange network of the present invention.
In FIG. 3, 301 is an ATM (Asyncrono).
A packet communication control unit such as usTransfer Mode), 302 is an optical transmitter, and 303 is an optical receiver. It is assumed that the terminal is a computer device, a video device, or the like, and is equipped with the communication control device shown in FIG.

FIG. 4 shows an example of the structure of the wavelength table in the wavelength control unit 173, which is sequentially read by the address from the ROM counter of the wavelength control unit.

FIG. 5 is a block diagram of the wavelength controller.
1 to 508 are wavelength tables shown in FIG. 4, 511 to 518
Is a drive control unit of the variable wavelength transmitter, and 520 is a ROM counter.

FIG. 6 shows a buffer control table in the buffer control unit 172, which is sequentially read by the address from the ROM counter of the wavelength control unit.

First, the wavelength control method of the wavelength controller 173 will be described. Wavelength tunable LD mounted on each optical transmitter
The emission wavelength is set by injecting a control current corresponding to the wavelength read from each wavelength table from the wavelength control terminal. In each wavelength table, the frame pulse generated by the frame generation circuit 175 is the wavelength control unit 1
Every time it is input to the ROM counter 520 of 73, 520
Outputs an address signal and outputs a control signal corresponding to the wavelength shown in FIG. 4 according to the address. The control signal is input to each drive control unit, and the emission wavelength is set by supplying a drive current corresponding to each designated wavelength to the wavelength control terminal of each wavelength tunable LD. Therefore, the emission wavelength of each optical transmitter is λ1, λ3, λ5, λ
7, λ8, λ6, λ4, λ2, λ1 are circulated in this order and transition occurs. The cycle of wavelength transition is determined by the cycle of the frame pulse. For example, if the switching network of the present invention is an ATM switching network, a frame pulse having a cycle of 1 cell (53 bytes) is generated from the clock generated by the clock generation circuit 174, and Every time a frame pulse is input to the wavelength control unit 173, the emission wavelengths of the optical transmitters 121 to 128 are changed at the same timing. In this manner, the light emission wavelengths of the optical transmitters 121 to 128 are changed at a constant cycle regardless of the input signal. The order of wavelength transition is not limited to the order shown in FIG. 4, but the phase of cyclic transition is selected so that the difference in the amount of wavelength transition is as small as possible and transmission at the same wavelength is not performed. Stagger it.

Here, as a cyclic transition pattern, starting from the first wavelength when N wavelengths are arranged in ascending order, odd-numbered wavelengths are selected in ascending order, and after the largest odd-numbered wavelength, the most Select a large even wavelength, select even wavelengths in descending order, select the second shortest wavelength, and then select the shortest wavelength again. I keep it small. Similarly, starting from the second wavelength when N wavelengths are arranged in the shortest order, the even-numbered wavelengths are selected in ascending order, and the largest odd-numbered wavelengths are selected after the largest even-numbered wavelengths. However, an odd numbered wavelength may be sequentially selected in descending order, the shortest wavelength may be selected, and then the second shortest wavelength may be selected again.

Next, the operation of the buffer controller 172 will be described. The buffer control unit 172 includes the buffers 111 to 111.
The read address of the packet input to 118 is generated in the cycle of the frame pulse from the frame generation circuit 175, and the packet is read from each buffer one after another. In each buffer, the input packet is written in the storage area corresponding to the output end to be output, and when the read address corresponding to the storage area is read from the buffer control table of the buffer control unit 172, The stored packet is read out. The buffer control table is configured as shown in FIG. 6, and the ROM of the wavelength controller 173 is provided.
When the address is supplied from the counter 520, the read address of FIG. 6 is supplied to each buffer and the packet is read. As can be seen from FIGS. 4 and 6, if the destination of the packet input to the buffer 111 is the output terminal OUT1, for example, the wavelength of the filter corresponding to the output terminal OUT1 is λ1, so the ROM counter 5
When the address 0 is generated from 20 and the emission wavelength of the optical transmitter 121 is set to λ1, the read address A1 corresponding to the output terminal OUT1 is read from the buffer control unit 172, and the packet is read. . That is, each packet has an output wavelength of the optical transmitter that outputs each packet,
The reading is controlled until the wavelength matches the wavelength corresponding to the output end for outputting each packet.

Next, the communication operation of the exchange network of the present invention will be described. Now, suppose terminal 202 to terminal 208
A case will be described where all communicate with the terminal 201. The terminals 202 to 208 transmit the transmission data to the packet communication control unit 301 of the communication board mounted on the terminal.
Packetize, add information such as destination address to the header of the packet, and output to the optical transmitter 302. The optical transmitter 302 converts the input packet into an optical signal and sends it out from the output port to the upstream optical fiber transmission line. Terminal 2
The packets sent from 02 to 208 pass through the upstream optical fiber transmission line and are input to the switching apparatus 210. The optical signals input from the input terminals IN2 to IN8 of the switching apparatus 210 are received by the optical receivers 152 to 158 and converted into electric signals. A reference numeral 152 equalizes and amplifies the received signal, performs identification reproduction, and inputs it to the buffers 112 to 118. Each buffer detects the destination address of the packet and stores it in the storage area corresponding to the output end of the destination. Here, since all the destinations are the output terminals OUT1, the output terminals OUT1 of the respective buffers are
Is stored in the storage area 1 corresponding to. If the wavelength transition state is a state corresponding to address 0 in FIG. 4 when the packet is stored in the buffer, the emission wavelength of each optical transmitter is the wavelength λ1 for the optical transmitter 121, and the optical transmitter 122.
Is the wavelength λ2, and the following 123, 124, 125, 126, 1
27 and 128 are set to λ4, λ6, λ8, λ7, λ5 and λ3. At this time, the buffer control unit 1
The packet read from each buffer by the read address from 72 is the packet input before the packet is input. When the next timing cycle, that is, a frame pulse from the frame generation circuit 175 is input to the ROM counter 520 of the wavelength control unit, the address counter 520 outputs address 1 and inputs the wavelength tables 501 to 508 and the buffer control 172. Each wavelength table 50
1 to 508 output control signals corresponding to address 1 in FIG. 4 to the drive control units 511 to 518, respectively.
21 to 128 are supplied with a control current to change the emission wavelengths to λ3, λ
1, λ2, λ4, λ6, λ8, λ7, and λ5, respectively. At the same time, the read address corresponding to the address 1 is read from the buffer control table from the buffer control unit 172 and is output to each of the buffers 111 to 118. The read address at this time is A3, A as shown in FIG.
1, A2, A4, A6, A8, A7, A5, which are input to the respective buffers 111 to 118. Since the read address A1 is an address for reading the packet of the storage area 1 corresponding to the output end OUT1, the previously input packet is read from the buffer 112. Since the read addresses of the other buffers are addresses other than the output terminal OUT1, the previously input packet is not read. The packet read from the buffer 112 is input to the optical transmitter 122. Since the light emission wavelength is set to λ1, the optical transmitter 122 converts the packet into an optical signal of wavelength λ1 and outputs it. The optical signal is star coupler 1
The optical filters 131 to 138 are branched at 71 in eight directions.
To enter. Since the transmission wavelength of the optical filter 131 is λ1, the optical signal input to the 131 passes through the 131 and is received by the optical receiver 141. The optical signal of wavelength λ1 input to the optical filters 132 to 138 is blocked there. The optical receiver 141 photoelectrically converts, equalizes, amplifies, identifies and reproduces the received signal and sends it to the optical transmitter 161, and 161 converts the signal into an optical signal and sends it from the output end OUT1 to the downstream optical fiber transmission line. . The signal transmitted through the downlink optical fiber transmission line is input to the optical receiver 303 of the terminal 201, converted into an electric signal, processed by the communication control unit 301, and received. In this way, the packet from the terminal 202 is transmitted to the terminal 201.

In the next timing cycle, the address 2 is output from the ROM counter and the packet is read from the buffer 113, as can be seen from FIGS. 4 and 6. The packet is converted into an optical signal of wavelength λ1 by the optical transmitter 123, passes through the optical filter 131, and is transmitted to the optical receiver 1.
At 41, it is converted into an electric signal. Further, it is converted into an optical signal by the optical transmitter 161, input to the terminal 201 through the downlink optical fiber transmission line, and received.

Similarly, each time a frame pulse is input to the ROM counter 520, the emission wavelength and the read address are changed, and the packets are sequentially read from the buffer 114, the buffer 115, the buffer 116, the buffer 117 and the buffer 118, The data is sequentially output from the output terminal OUT1 and transmitted to the terminal 201. The packets output from the terminals 202 to 208 in this manner are sequentially transmitted to the terminal 2
Received at 01.

In this way, communication is performed between the terminals via the exchange.

In this embodiment, the optical filters 131 to 1 are used.
38 the above-mentioned fiber Fabry-Perot filter and DFB
When a laser filter is used, the control unit is omitted in the figure, but a voltage / current stabilizing circuit and a temperature stabilizing circuit for stabilizing the transmission wavelength are provided as necessary.

Further, the optical receivers 141 to 148 of the present embodiment.
The optical transmitters 161 to 168 are not always necessary, and may be omitted if the transmission output power from the optical filters 131 to 138 is necessary and sufficient. In that case, instead of providing the optical filters 131 to 138 in the switching device 210, one may be arranged in each of the input units of the terminals 201 to 208.

Further, in the present embodiment, the description has been made assuming that the switching device and each terminal are connected by an optical fiber, but an electric wire such as a coaxial cable or a twisted pair cable may be used. In that case, 151-158, 303 and 161-16
The 8302 may be provided with an electric receiver and a transmitter as needed.

(Second Embodiment) A second embodiment of the present invention will be described. FIG. 7 is a diagram showing an embodiment of the second switching device in the switching network of the present invention, and the same parts as those in the first embodiment are designated by the same numbers.

In FIG. 7, reference numerals 721 to 728 denote optical transmitters 731 to 73 for transmitting optical signals having specific wavelengths.
Reference numeral 8 denotes a wavelength tunable filter that transmits an optical signal of an arbitrary wavelength, and the other parts are the same as in the first embodiment. Optical transmitter 7
21 to 728 are optical transmitters equipped with a DFB laser or a DBR laser similarly to the optical transmitters 121 to 128 of the first embodiment, and have emission wavelengths of λ1, λ2, ..., λ8, respectively.
Is set to. Like the optical filters 131 to 138 of the first embodiment, the wavelength tunable filters 731 to 738 can use fiber Fabry-Perot filters, DFB laser filters, or the like, and at least wavelengths λ1 to λ1 can be controlled by voltage or current control.
It can transmit an arbitrary wavelength within λ8. As the buffer control table of the buffer control unit, the table shown in FIG. 8 is used.

In the first embodiment, the transmission wavelength is matched with the wavelength allocated to the receiving side for exchange, whereas in the second embodiment, the reception wavelength is matched with the wavelength allocated to the transmitting side for exchange. Are doing.

First, the wavelength control method of the wavelength controller 173 will be described. As in the first embodiment, the wavelength control unit 173 generates an address from 520 every time a frame pulse from the frame generation circuit 175 is input to the ROM counter 520, and reads the wavelength table of FIG. Control signals from the wavelength control tables 501 to 508 are input to the drive control units 511 to 518, and different voltage or current is supplied from the drive control units to the wavelength control terminals of the wavelength tunable filters 731 to 738, respectively. The drive controller is the first
Although the variable optical transmitter was controlled in the embodiment, the wavelength variable filter is controlled in the present embodiment, so that the drive control unit corresponds to the filter to be used. In the wavelength tunable filter, since the transmission wavelength changes depending on the voltage or current value supplied to the wavelength control terminal, the transmission wavelength of each wavelength tunable filter is set to a different wavelength. The setting of the transmission wavelength is changed, for example, in a cycle of 1 cell (53 bytes) as in the first embodiment. Further, the wavelength transition also repeats in the order shown in FIG. 4, for example, similarly to the first embodiment. In this way, the transmission wavelengths of the wavelength tunable filters 731 to 738 are changed in a constant cycle regardless of the input signal.

Next, the operation of the buffer controller 172 will be described. Similar to the first embodiment, the buffer control unit 172 reads the read address from the buffer control table according to the address from the ROM counter, and reads the packet input to the buffer. However, the buffer control table shown in FIG. 8 is used.

Next, the communication operation of the exchange network of the present invention will be described. Similar to the first embodiment, a case where all of the terminals 202 to 208 communicate with the terminal 201 will be described. Similar to the first embodiment, the packet sent from each terminal is transmitted to the switching device 210 and input to each of the buffers 112 to 118. In each buffer, the destination address of the packet is detected and stored in the storage area 1 corresponding to the output terminal OUT1. If the wavelength transition state is the state corresponding to address 0 in FIG. 4 when the packet is stored in the buffer, the transmission wavelength of each optical filter is as follows: the optical filter 731 has a wavelength λ1 and the variable wavelength optical filter 732 has a wavelength λ1.
Is the wavelength λ2, and the following 733, 734, 735, 736, 7
37 and 738 are set to λ4, λ6, λ8, λ7, λ5, and λ3. At this time, the packet read from each buffer by the read address from the buffer control unit 172 is the packet input before the packet is input. The next timing cycle, that is, the frame pulse from the frame generation circuit 175 is transmitted to the ROM of the wavelength controller.
When input to the counter 520, 520 is the address 1
Is output and is input to each of the wavelength tables 501 to 508 and the buffer control unit 172. Each wavelength table 501-50
8 outputs a control signal corresponding to the address 1 in FIG. 4 to the drive control units 511 to 518, and the optical filters 721 to 518.
A control current is supplied to 728 to set the transmission wavelengths to λ3, λ1, λ
2, λ4, λ6, λ8, λ7 and λ5 are set. At the same time, the read address corresponding to the address 1 is read from the buffer control table from the buffer control unit 172 and is output to each of the buffers 111 to 118. The read addresses at this time are A2, A3, A1, A4, as shown in FIG.
A8, A5, A7, A6, and the buffers 111 to 1
18 is input. The read address A1 is output terminal O
Since the address is an address for reading a packet in the storage area 1 corresponding to UT1, the buffer 113 is first transferred to the buffer 1
The packet input to 13 is read out. Since the read addresses of the other buffers are addresses other than the output end OUT1, the previously input packet is not read.
The packet read from the buffer 113 is input to the optical transmitter 723. The optical transmitter 723 has an emission wavelength of λ3.
, The packet is converted into an optical signal of wavelength λ3 and output. The optical signal is branched into eight directions by the star coupler 171, and is input to each of the optical filters 731 to 738. Since the transmission wavelength of the optical filter 731 is λ3 at this time, the optical signal input to the 731 passes through the 731 and is received by the optical receiver 141. At this time, the transmission wavelengths of the optical filters 732 to 738 are set to those other than λ3.
The optical signal of wavelength λ3 input to 2-738 is blocked there. The optical receiver 141 photoelectrically converts, equalizes, amplifies, identifies and reproduces the received signal and sends it to the optical transmitter 161, and 161 converts the signal into an optical signal and sends it from the output end OUT1 to the downstream optical fiber transmission line. . The signal transmitted through the downlink optical fiber transmission line is input to the optical receiver 303 of the terminal 201, converted into an electric signal, processed by the communication control unit 301, and received. In this way, the packet from the terminal 203 is transmitted to the terminal 201.

In the next timing cycle, the address 2 is output from the ROM counter and the packet is read from the buffer 115, as can be seen from FIGS. 4 and 8. The packet is converted into an optical signal of wavelength λ5 by the optical transmitter 125, passes through the optical filter 731 whose transmission wavelength is set to the wavelength λ5 at this time, and is converted into an electric signal by the optical receiver 141. Further, it is converted into an optical signal by the optical transmitter 161, input to the terminal 201 through the downlink optical fiber transmission line, and received.

Similarly, the transmission wavelength and the read address are changed each time a frame pulse is input to the ROM counter 520, and the packets are sequentially read from the buffer 117, the buffer 118, the buffer 116, the buffer 114 and the buffer 112. The signals are sequentially output from the output terminal 1 and transmitted to the terminal 201. In this way, the terminal 202
The packets output from ˜208 are sequentially received by the terminal 201.

In this embodiment, the optical receivers 141 to 14 are used.
8 and the optical transmitters 161 to 168 are not always necessary and may be omitted if the transmission output power from the wavelength tunable filters 731 to 738 is sufficient.

The optical transmitters 731 to 738 of this embodiment are also provided.
In the case of using the optical transmitter equipped with the above-mentioned DFB laser or DBR laser, although the control unit is omitted in the figure, a current stabilizing circuit and a temperature stabilizing circuit for stabilizing the emission wavelength are required. Provide accordingly.

Further, in the present embodiment, the description has been made assuming that the switching device and each terminal are connected by an optical fiber, but an electric wire such as a coaxial cable or a twisted pair cable may be used. In that case, 151-158, 303 and 161-16
8, 302 may be provided with electrical receivers and transmitters as needed.

In addition, the optical transmitters (121 to 128, 721 to 728) and the optical filter (1) of the switching device are added.
If both 31 to 138 and 731 to 738 are variable in wavelength (121 to 128 and 731 to 738), both of the exchange methods described in the first and second embodiments can be implemented.
When the transmitter side is variable as in the first embodiment, the transmission wavelength of the wavelength tunable filter is controlled to be fixed, and when the optical filter side is variable as in the second embodiment, the optical The wavelength controller may control so that the emission wavelength of the transmitter is fixed.

(Third Embodiment) FIG. 9 shows an embodiment of a third switching device in the switching network of the present invention. 91
Numerals 1 to 918 are buffers for storing the input packet in the storage area corresponding to the output end of the destination and storing it in another empty storage area when the storage area is saturated. 92
1 to 928 are output without storing unless the destination of the input packet corresponds to the output end to be connected,
If it corresponds to the output end to be connected, a storage area is provided for each packet output from the same terminal and stored,
This is a buffer for sending packets in the order in which they are sent from the terminal. The other part has the same configuration as the first or second embodiment, but in the description, it will be described as being the same as the first embodiment.

The network configuration is that of FIG.

The terminal has the configuration shown in FIG. However, when the packet communication control unit 301 of the terminal continuously sends a plurality of packets, the packets are sent with numbers indicating the sending order. In addition, the destination address of the input packet signal is detected, the packet addressed to the own terminal is processed by the packet communication control unit 301 and the data is output to a computer, etc., and the packet addressed to other terminals is relayed as it is and the optical transmitter. A device having a function of sending out to the optical fiber transmission line from 302 is used.

In the first and second embodiments, the following operation is performed when consecutive packets having the same destination are input to the buffers 111 to 118. For example, when the size of the storage area of the buffer is one packet, when a packet of the same destination is input before the previously input packet is read, the packet that is input later is discarded. If the size of the storage area is sufficiently large, it takes a cycle of wavelength transition, that is, 8 packets, from the time when one packet is read to the time when the next packet is read. , There was a delay.

In the present embodiment, the buffers 911-9 are provided.
When a continuous packet of the same destination is input to 18, the packet is stored in the storage area corresponding to the destination while the storage area corresponding to the destination is free, and is stored in another empty storage area when the storage area is saturated. The packet stored in the other storage area is transmitted to a terminal different from the destination, is relayed there, is input to the switching device 210, and is stored there if the destination storage area is free. By doing so, the packet is transmitted without being discarded, and the delay time is also reduced on average. However, since the order of the packets is changed, the buffers 921 to 928 change the order of the packets.

Next, a communication operation when eight packets are continuously transmitted from the terminal 202 to the terminal 201 will be described. The packet communication control unit 301 of the terminal 202
The data from the computer device is packetized, the destination address and the numbers 1 to 8 indicating the sending order of the packets are added, and the packets are sequentially sent from the optical transmitter 302. The packet is input from the input terminal IN2 of the switching device 210 through the optical fiber transmission line and stored in the storage area of the buffer 912 corresponding to the destination. The first input packet 1 is the storage area 1 corresponding to the output terminal OUT1.
Memorized in. At this time, the emission wavelength of each optical transmitter is assumed to be in a state corresponding to address 7 in FIG. That is, the emission wavelength of the optical transmitter 121 is λ2, the emission wavelength of the optical transmitter 122 is λ4, and the following 123, 124, 125, 126, 1
27 and 128 are λ6, λ8, λ7, λ5, λ3 and λ1. When the second packet 2 is input next, the destination of this packet 2 is the output terminal OUT1, so it should be stored in the storage area 1, but the packet 1 previously input is still read out. Since it is not stored, it is stored in the vacant storage area 2. At this time, the wavelength transition corresponds to the address 0, the packet previously stored in the storage area 2 is read from the buffer 912, and the packet 2 is stored in the empty storage area 2. Next, when the third packet 3 is input, the address 1 is supplied from the buffer control unit 172 to each buffer, and the first input packet 1 stored in the storage area 1 is read from the buffer 912. It Packet 3 is written in storage area 1 because packet 1 has been read out. Packet 1 is the optical transmitter 122
Is converted into an optical signal of wavelength λ1 and output, and is branched by the star coupler 171 and input to each of the optical filters 131 to 138. The optical signal of wavelength λ1 passes through the optical filter 131, is converted into an electrical signal by the optical receiver 141, and is converted into the buffer 9
It is temporarily stored at 11. The optical signal of wavelength λ1 input to another optical filter is lost there. Next, when the fourth packet 4 is input, the packet 4 is stored in the empty storage area 3. Similarly, packet 5, packet 6, packet 7, and packet 8 are stored in storage area 4, storage area 5, and storage area 5, respectively.
The data is sequentially stored in the storage area 6 and the storage area 7. Packet 8
When is input, the address corresponds to 6, and the packet 7 previously stored in the storage area 6 is read out.
Then, when the address 7 is supplied, the packet 5 stored in the storage area 4 is read out. Similarly, when the addresses are sequentially supplied as 0, 1, 2, 3, and 4, the packets 2 stored in the storage areas 2, 1, 3, 5, and 7 are
3, 4, 6, and 8 are read out in order. The packet 7 is converted into an optical signal of wavelength λ6 by the optical transmitter 122, branched by the star coupler 171, and input to each of the optical filters 131 to 138. The optical signal having the wavelength λ6 passes through the optical filter 136, is converted into an electric signal by the optical receiver 146, and the buffer 9
26. The optical signal of wavelength λ6 input to another optical filter is lost there. The buffer 926 detects the destination address of the input packet 7. Since the destination of the packet 7 is the output end OUT1 and not the output end OUT6, the buffer 926 does not store the packet 7 and outputs it as it is. The packet 7 is converted into an optical signal by the optical transmitter 166 and sent from the output end OUT6 to the downstream optical fiber transmission line. The packet 7 transmitted through the optical fiber transmission line is input to the terminal 206, converted into an electric signal by the optical receiver 303, and the destination address is detected by the packet communication control unit 301. Since the destination of the packet 7 is the terminal 201 and not the terminal 206, the packet 7 is sent to the optical transmitter 302 as it is, converted into an optical signal, and sent to the upstream optical fiber transmission line. The packet 7 transmitted through the optical fiber is input from the input terminal IN6 of the switching device 210, converted into an electric signal by the optical receiver 156, and stored in the buffer 916. The buffer 916 detects the destination address of the packet 7 and stores it in the storage area 1 corresponding to the output terminal OUT1 which is the destination. Packet 7 has address 1
Is supplied and is stored in the buffer 911 by the same operation as described above. Similarly, packets 5, 2,
4, 6, 8 are output terminals OUT4, 2,
Output from terminals 3, 5 and 7, respectively, and terminals 204 and 20
2, 203, 205, 207 are relayed to exchange device 2
10 buffers 914, 912, 913, 915, 91
7 is stored in each of the storage areas 1. Since the packet 3 was stored in the storage area 1, it is stored in the buffer 911 similarly to the packet 1. Packets 5, 2, 4,
6 and 8 are read out when the emission wavelength of the optical transmitter connected to each stored buffer is set to λ1 and converted into an optical signal of wavelength λ1 by each optical transmitter. , Are sequentially stored in the buffer 921 as described above. In this way, the eight packets input from the input terminal IN1 are stored in the buffer 921. Packet 1
8 to 8 relay the terminals as described above, and therefore the order is changed. Therefore, the buffer 921 detects the numbers indicating the transmission order of the input packets, and reads the packets in the order of the numbers. Each packet is buffer 9
The data is read out from 21 in the order of transmission from the terminal 202, converted into an optical signal by the optical transmitter 161, and transmitted to the optical fiber transmission line. Each packet transmitted through the optical fiber transmission line is input to the terminal 201 and received.

Communication is performed in this manner.

In the embodiment described so far, FIG.
Although the description has been made assuming that a plurality of terminals are connected to one switching device as shown in, the present invention is not limited to this, and a plurality of terminals may be connected to a plurality of switching devices.

FIG. 10 shows an example of the configuration when the network is expanded by using a plurality of switching devices. In the figure, reference numerals 1001 to 1008 are the exchange devices described in the first, second or third embodiment, and they may be mixed.
However, when the exchange apparatus of the third embodiment is used, the terminal 1
011 to 1077 use the terminal described in the third embodiment.

The communication operation is similar to that of the above embodiment. For example, when communication is performed from the terminal 1011 to the terminal 1075, the packet sent from the terminal 1011 is exchanged by the switching device 1001 by the exchange operation described in the above embodiment. The switching device 1 is connected to an output terminal connected to the switching device 1008.
Similarly, in 008, the switching device 1007 is connected to the terminal 1075, and the terminal 1075 receives the same. When the switching device described in the third embodiment is used as the switching device 1001, for example, a packet from the terminal 1011 is relayed to the terminal 1017 and then the switching devices 1001, 100.
8, 1007 and is sent to the terminal 1075.

In this embodiment, the structure for expanding the network has been described as the tree structure shown in FIG. 10. However, the present invention is not limited to this, and the mesh, bus type, loop type and the like in the above embodiments. Communication can be performed by arbitrarily connecting a plurality of the exchange devices described above.

(Fourth Embodiment) A fourth embodiment of the present invention will be described. FIG. 16 is a diagram showing an embodiment of a fourth switching device in the switching network of the present invention, and the same parts as those in the first embodiment are designated by the same numbers. FIG. 17 is a switch control table used in this embodiment and shows the input / output connection relationship of the switches. In the first, second and third embodiments, the wavelength division multiplexing optical switch using the optical signal is used, but in the present embodiment, an example using the space division type switch using the electric signal is shown.

In FIG. 16, reference numeral 1601 denotes an 8-input / 8-output switch, and the same parts as those in the first embodiment are designated by the same reference numerals. The switch 1601 is a ROM counter 520.
Receives addresses from the input terminals I1 to I8 and output terminal Q
The connection relationships 1 to Q8 are set as in the control table of FIG. The ROM counter 520 is the frame generation circuit 1
An address is generated every time a frame pulse from the switch 75 is input, and the input / output connection relationship of the switch 1601 is shown in FIG.
The switch 1601 is controlled so as to correspond to the control table of. Addresses from the ROM counter 520 are, for example, addresses 0, 1, 2, ...
・ ··············································· The buffer control unit 172 receives the address from the ROM counter, outputs the read address from the buffer control table of FIG. 6, and reads the packet input to the buffer. In this way, the same operation as in the first embodiment is performed.

Next, the communication operation of this embodiment will be described. Similar to the first embodiment, a case where all of the terminals 202 to 208 communicate with the terminal 201 will be described. Terminal 2
The packets transmitted from 02 to 208 are transmitted to the switching device 210 through the upstream optical fiber transmission path, converted into electric signals by the optical receivers 152 to 158, and then converted into the respective buffers 1.
Enter 12 to 118. In each buffer, the destination address of the packet is detected and stored in the storage area 1 corresponding to the output terminal OUT1. If the packet is stored in the buffer, the address from the ROM counter 520 will be as shown in FIG.
, The input terminal I1 of the switch 1601 is connected to the output terminal Q1, the input terminal I2 is connected to the output terminal Q2, and I3 is connected to Q4, and I4 is connected to I4.
To Q6, I5 to Q8, I6 to Q7, I7 to Q5
In addition, I8 is connected to Q3. At this time, the packet read from each buffer by the read address from the buffer control unit 172 is the packet input before the packet is input. The next timing cycle, that is, the frame pulse from the frame generation circuit 175 becomes R
When input to the OM counter 520, the address 520 supplies the address 1 to the switch 1601 and the buffer control unit 172. At address 1, the input end I1 of the switch 1601 is connected to the output end Q3, the input end I2 is connected to the output end Q1, and hereinafter I3 is Q2, I4 is Q4, and I5 is Q6.
I6 is connected to Q8, I7 is connected to Q7, and I8 is connected to Q5. At the same time, the read address corresponding to the address 1 is read from the buffer control table of the buffer control unit 172 and input to each of the buffers 111 to 118. The read address at this time is A3, A1, A as shown in FIG.
2, A4, A6, A8, A7, A5, which are input to the respective buffers 111 to 118. Read address A1
Is an address for reading the packet of the storage area 1 corresponding to the output terminal OUT1, and therefore the packet input to the buffer 112 first is read from the buffer 112. Since the read addresses of the other buffers are addresses other than the output end OUT1, the previously input packet is not read. The packet read from the buffer 112 is input to the input end I2 of the switch 1601. At this time, since the input end I2 of the switch 1601 is connected to the output end Q1, the packet is output from the output end Q1. The output packet is input to the optical transmitter 161, converted into an optical signal, and output from the output end OUT1 to the downstream optical fiber transmission line.
The signal transmitted through the downlink optical fiber transmission line is input to the optical receiver 303 of the terminal 201, converted into an electric signal, processed by the communication control unit 301, and received. In this way, the packet from the terminal 203 is transmitted to the terminal 201.

In the next timing cycle, the address 2 is output from the ROM counter 520 and the packet is read from the buffer 3 as can be seen from FIGS. The packet is input from the input end I3 of the switch 1601 and output to the output end Q1. The output packet is converted into an optical signal by the optical transmitter 161, input into the terminal 201 through the downstream optical fiber transmission line, and received.

Similarly, each time a frame pulse is input to the ROM counter 520, the input / output connection relationship of the switch 1601 and the read address of each buffer are changed, and the packet is buffer 4, buffer 5, buffer 6 and buffer 7. And sequentially read from the buffer 8 and output terminal O
It is sequentially output from the UT 1 and transmitted to the terminal 201. The packets output from the terminals 202 to 208 in this manner are sequentially received by the terminal 201.

Communication is performed in this manner.

The switch control table and buffer control table used in this embodiment are not limited to these.

[0061]

According to the present invention, the relationship of input and output is sequentially switched in such an order that no signal is transmitted to the same output terminal at the same time, and signals are exchanged accordingly, so that arbitration control is required. Lost.

As a result, the structure of the exchange apparatus can be simplified and efficient communication can be performed.

[0063]

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of a switching device in a switching network of the present invention.

FIG. 2 is a diagram showing a configuration example of a switching network of the present invention.

FIG. 3 is a diagram showing a configuration example of a communication control unit of a terminal connected to the exchange network of the present invention.

FIG. 4 is a diagram showing a configuration example of a wavelength table.

FIG. 5 is a configuration diagram of a wavelength control unit.

FIG. 6 is a diagram showing a configuration example of a buffer control table.

FIG. 7 is a diagram showing a second embodiment of a switching device in the switching network of the present invention.

FIG. 8 is a diagram showing a configuration example of a buffer control table in the second embodiment.

FIG. 9 is a diagram showing a third embodiment of a switching device in the switching network of the present invention.

FIG. 10 is a diagram showing another configuration example of the exchange network of the present invention.

FIG. 11 is a diagram showing the structure of a packet.

FIG. 12 is a diagram showing a first configuration example of a conventional exchange device.

FIG. 13 is a diagram showing a second configuration example of a conventional exchange device.

FIG. 14 is a diagram showing an internal configuration of the switch of FIG.

FIG. 15 is a diagram showing a third configuration example of a conventional exchange device.

FIG. 16 is a diagram showing a fourth embodiment of the exchange device in the network system of the present invention.

FIG. 17 is a diagram showing a configuration example of a switch control table.

[Explanation of symbols]

111-118 Input buffers 121-128, 1521-1528 Optical transmitter (variable wavelength) 131-138, 1531-1538 Optical filter (fixed wavelength) 141-148, 1541-1548 Optical receiver 151-158 Optical receiver 161- 168 Optical receiver (fixed wavelength) 171, 1550 Star coupler 172 Buffer controller 173, 1553 Wavelength controller 174 Clock generator 175 Frame generator 201-208 Terminal 210 Switching device 301 Packet communication controller 302 Optical transmitter (fixed wavelength) ) 303 optical receivers 501 to 508 wavelength control tables 511 to 518 drive control unit 520 ROM counters 721 to 728 optical transmitters (fixed wavelength) 731 to 738 optical filters (variable wavelength) 911 to 918 input buffers 921 to 928 output buffer 10 1-1008 changer from 1011 to 1077 terminal 1101 address 1102 data unit 1201,1401,1402,1501～1508
Decoders 1202, 1403, 1404, 1511-1518
FIFO 1203 input line 1204 switches 1205, 1407, 1551 control unit 1206 output lines 1301 to 1312 switches 1405, 1406 selector 1552 arbitration control unit

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-8-237698 (JP, A) JP-A-4-369143 (JP, A) JP-A-5-3493 (JP, A) JP-A-7- 79238 (JP, A) JP 8-237306 (JP, A) JP 4-167634 (JP, A) JP 63-272132 (JP, A) JP 6-350563 (JP, A) JP-A-60-233959 (JP, A) JP-A-63-275292 (JP, A) JP-A-59-182638 (JP, A) JP-A-56-91544 (JP, A) 1994 IEEJ Autumn Meeting, SB-8-8 1996 SICC, B-1077 (58) Fields investigated (Int.Cl. ⁷ , DB name) H04L 12/50 H04L 12/28-12/46 H04B 10/02 H04Q 3/52 H04Q 11/04

Claims (8)

(57) [Claims] 1. A network system comprising a switching device and a plurality of terminals connected to each other, wherein the switching device receives a plurality of N input terminals to which signals from the terminals are input and signals to the terminals. N output terminals for outputting, N input buffer means for temporarily storing signals input from the N input terminals, and connection of the output terminals to which the N input buffer means are respectively connected Connection means for sequentially switching the relationships in a predetermined order so that the respective input buffer means are simultaneously connected to different output terminals, and at a preset timing cycle; and the connection means. While the connection relationship between the input buffer means and the output terminal is being switched, the input buffer is output to the output terminal to which the signal temporarily stored in the input buffer means is to be output. A network control system for reading the signal from the input buffer means in synchronization with the connection of the buffer means. 2. The transmitting means converts the signal output from one of the N input buffer means into a signal of any one of the N channels and outputs the signal. N corresponding to each input buffer means, and N
And N receiving means for receiving each of the respective channels and outputting the received signals to the corresponding N output end sides, and each of the transmitting means transmits a signal to the channel. 2. The network system according to claim 1, wherein the connection relationship of the output terminals to which each of the N input buffer means is connected is switched by sequentially switching in the predetermined order. 3. The transmitting means includes a transmitting means for converting a signal output from one of the N input buffer means into a signal of any one of the N channels and outputting the signal. N corresponding to each input buffer means, and N
And N receiving means for receiving each of the respective channels and outputting the received signals to the corresponding N output end sides, each of the receiving means being the channel for receiving the signal. 2. The network system according to claim 1, wherein the connection relationship of the output terminals to which the N input buffer means are respectively connected is switched by sequentially switching the output terminals in the predetermined order. 4. The connection means has a switch for switching the relationship between the input from the N input buffer means and the output to the N output terminals, and by the switching control of the switch, the N switch is provided. 2. The network system according to claim 1, wherein the connection relationship of the output terminals to which each of the input buffer means is connected is switched. 5. The network system according to claim 1, wherein the switching device has N output buffer units for temporarily storing the signals passed through the connection unit. 6. A network system comprising a switching device and a plurality of terminals connected to each other, wherein the switching device receives a plurality of N input terminals to which signals from the terminals are input and signals to the terminals. N output terminals for output, N input buffer means for temporarily storing the signals input from the N input terminals, and a signal output from one of the N input buffer means Corresponding to each input buffer means, and N transmitting means for converting the signal of any one of N channels to output, and the transmitting channels of each transmitting means are simultaneously transmitted by each transmitting means. Is a channel control means for controlling to sequentially switch signals in a predetermined order so as to transmit signals on mutually different channels and at a preset timing cycle; and the channel control means. While the channel switching control is being performed, the transmission channel of the transmission means corresponding to each of the input buffer means is synchronized with the channel to which the signal temporarily stored in the input buffer means should be output. And a buffer control means for reading the signal from the input buffer means, and the signals from the N transmitting means are supplied to the N output terminals, respectively. . 7. The network system according to claim 2, wherein the N channels are lights having wavelengths different from each other. 8. A communication method in a switching device, wherein the switching device has a plurality of N input terminals to which a signal from the terminal is input and N output terminals to output a signal to the terminal. , N input buffer means for temporarily storing signals input from the N input terminals, respectively, and a connection relationship of the output terminals to which the N input buffer means are respectively connected, Of the input buffer means are simultaneously switched to different output terminals in a predetermined order and at a preset timing cycle, the input buffer means and the output terminal are connected. While the input buffer means is being switched, the signal is temporarily stored in the input buffer means in synchronization with the connection of the input buffer means to the output terminal to which the signal is to be output. A communication method, characterized in that the communication is performed by reading the signal from the means.