Switching device, communication system, and switching method

Abstract

This switching device comprises a demultiplexing unit that has one or more first ports and a plurality of second ports, and demultiplexes signals input from the one or more first ports, and a splitting unit that is connected to a specific second port among the plurality of second ports included in the demultiplexing unit, splits a signal output from the specific second port, and outputs the split signals to at least a communication device to be switched and a communication device to switch to.　

Description

Switching device, communication system, and switching method

[0001] The present invention relates to a switching device, a communication system, and a switching method.

[0002] In an all-photonics network, optical paths are dynamically connected end-to-end. Specifically, a wavelength-tunable transceiver called an APN-T is used at the network endpoints, and a controller issues instructions to the APN-T and APN-G to switch wavelengths, enabling connections between desired locations. The APN-G is a gateway used in the all-photonics network.

[0003] APN-G, like an optical switch or wavelength selective switch, controls whether or not certain wavelengths are allowed to pass, or which port they are output from. By combining these functions, the All-Photonics Network aims to realize a network that can flexibly connect any base station on a wavelength-by-wavelength basis.

[0004] "Open All-Photonics Network Considerations at the IOWN Global Forum," NTT Technical Journal, Vol. 34, No. 3, pp. 12-16, 2022. "Photonic Gateway and Optical Access Technologies Supporting APN," NTT Technical Journal, Vol. 33, No. 2, pp. 36-41, 2021.

[0005] On the other hand, in conventional configurations, when changing the wavelength in the APN-T or the port through which the APN-G passes, it usually takes a certain amount of time for the switch to complete. Therefore, to prevent the main signal to be transferred from being lost, it is necessary to provide a buffer on the transmitting side and control the opening and closing of the buffer in synchronization with the switch. Note that using a buffer increases delays. Therefore, when dynamically changing the destination, it is necessary to provide a buffer mechanism or tolerate the loss of the main signal, which is a problem.

[0006] In view of the above circumstances, an object of the present invention is to provide a technique that can easily switch the transmission destination while reducing loss of the main signal without providing a buffer mechanism.

[0007] One aspect of the present invention is a switching device having one or more first ports and a plurality of second ports, a branching unit that branches a signal input from the one or more first ports, and a branching unit that is connected to a specific second port among the plurality of second ports of the branching unit, and branches a signal output from the specific second port and outputs it to at least a communication device that is the source of switching and a communication device that is the destination of switching.

[0008] One aspect of the present invention is a communication system comprising one or more first communication stations, a plurality of second communication stations, and a switching device that switches connections between the one or more first communication stations and the plurality of second communication stations, wherein the one or more first communication stations comprise a transmitting unit that transmits a signal directed to one or more second communication stations among the plurality of second communication stations during a connection switching operation, and the switching device has one or more first ports and a plurality of second ports, and comprises a branching unit that branches the signal transmitted from the one or more first communication stations via the one or more first ports, and a branching unit that is connected to a specific second port among the plurality of second ports of the branching unit, and branches the signal output from the specific second port and outputs it to at least a switching source communication device and a switching destination communication device.

[0009] One aspect of the present invention is a switching method in which a branching unit has one or more first ports and a plurality of second ports, branches a signal input from the one or more first ports, and a branching unit connected to a specific second port among the multiple second ports of the branching unit branches the signal output from the specific second port and outputs it to at least a communication device from which the signal is to be switched and a communication device to which the signal is to be switched.

[0010] According to the present invention, it is possible to easily switch the transmission destination while reducing loss of the main signal without providing a buffer mechanism.

[0011] FIG. 1 is a diagram illustrating an example of the configuration of a communication system in a first embodiment. FIG. 2 is a sequence diagram illustrating the flow of processing in the communication system in the first embodiment. FIG. 3 is a diagram illustrating an example of the configuration of a communication system in a second embodiment. FIG. 4 is a diagram for explaining the flow of processing in the communication system in the second embodiment. FIG. 5 is a sequence diagram illustrating the flow of processing in the communication system in the second embodiment. FIG. 6 is a diagram illustrating an example of the configuration of a communication system in a third embodiment. FIG. 7 is a sequence diagram illustrating the flow of processing in the communication system in the third embodiment. FIG. 8 is a diagram illustrating an example of the configuration of a communication system in a fourth embodiment. FIG. 9 is a sequence diagram illustrating the flow of processing in the communication system in the fourth embodiment. FIG. 10 is a sequence diagram illustrating the flow of processing in the communication system in the fourth embodiment.

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0013] 1 is a diagram illustrating an example of the configuration of a communication system 100 according to a first embodiment. The communication system 100 includes M (M is an integer equal to or greater than 1) central stations 10, N (N is an integer equal to or greater than 2) aggregation stations 20, a switching device 30, and a wavelength management device 40. The M central stations 10 are connected to the N aggregation stations 20 via the switching device 30.

[0014] The M central offices 10 and the switching device 30, and the switching device 30 and the N aggregation offices 20 are connected via optical transmission paths. The optical transmission paths are optical fibers. The optical transmission paths may be provided with one or more optical amplifiers that amplify optical signals. The M central offices 10 and the wavelength management device 40 are connected via electrical lines.

[0015] The central station 10 transmits an optical signal having a wavelength assigned by the wavelength management device 40 to the aggregation station 20 via the switching device 30. The central station 10 is, for example, a distributed unit (DU) in the 5G communication standard.

[0016] The aggregation station 20 receives the optical signal transmitted from the central station 10 and processes or transmits the received signal to a higher-level device. The aggregation station 20 is, for example, a CU (Central Unit) in the 5G communication standard.

[0017] The switching device 30 switches the connection path between the central station 10 and the aggregation station 20. The switching device 30 outputs an input optical signal of a certain wavelength to the aggregation station 20 as the output destination. The switching device 30 outputs an optical signal of a specific wavelength to multiple aggregation stations 20.

[0018] The wavelength management device 40 controls the wavelengths used for communication by each central office 10. For example, when a connection destination is switched, the wavelength management device 40 controls the wavelength of the central office 10 to be switched so that communication is performed at a specific wavelength at least while the connection destination is being switched.

[0019] Next, the functional configuration of each device will be described in detail.

[0020] (Functional Configuration of Central Office 10) The central office 10 includes a control unit 11 and a wavelength-tunable light source 12. The control unit 11 controls the overall functions of the central office 10. The control unit 11 controls the wavelength-tunable light source 12 so that it outputs an optical signal with a wavelength assigned by, for example, a wavelength management device 40. The wavelength-tunable light source 12 is a light source that can output optical signals with multiple wavelengths. The wavelength-tunable light source 12 outputs an optical signal with a wavelength set by the control unit 11.

[0021] (Functional configuration of switching device 30) The switching device 30 includes a wavelength multiplexing / demultiplexing unit 31 and a multiplexer / demultiplexer 32. The wavelength multiplexing / demultiplexing unit 31 has at least one or more first ports and multiple second ports. The wavelength multiplexing / demultiplexing unit 31 multiplexes or demultiplexes optical signals input from a certain port according to their wavelengths. For example, the wavelength multiplexing / demultiplexing unit 31 demultiplexes optical signals input to one or more first ports according to their wavelengths and outputs the demultiplexed signals from any one of multiple second ports. For example, the wavelength multiplexing / demultiplexing unit 31 multiplexes optical signals input to multiple second ports and outputs the multiplexed signals from the first port.

[0022] The wavelength multiplexer / demultiplexer 32 is connected to any one of the plurality of second ports of the wavelength multiplexer / demultiplexer 31. In this specification, it is assumed that the wavelength multiplexer / demultiplexer 32 is connected to the second port that is the output destination of the wavelength λ2, among the plurality of second ports of the wavelength multiplexer / demultiplexer 31.

[0023] The multiplexer / splitter 32 splits the optical signal of a specific wavelength (for example, wavelength λ2) output from the wavelength multiplexer / demultiplexer 31 and outputs the split signal to multiple central stations 20. The split ratios of the multiplexers / splitters 32 may be the same or different.

[0024] (Functional Configuration of Wavelength Management Device 40) The wavelength management device 40 includes a connection wavelength table 41 and a wavelength control unit 42. The connection wavelength table 41 is a table in which information regarding wavelengths for connection to each central station 20 is registered. The connection wavelength table 41 associates at least identification information for identifying each central station 20 with information indicating the wavelength for connection to each central station 20. The wavelength control unit 42 references the connection wavelength table 41 and controls the wavelengths to be assigned to each central station 10. By reference to the connection wavelength table 41, the wavelength control unit 42 can determine the wavelength to be output to the multiplexer / splitter 32, taking into account that the same wavelength is assigned to multiple central stations 20. For example, since the multiplexer / splitter 32 splits an optical signal and outputs it to multiple central stations 20, the same wavelength is assigned to multiple central stations 20. Therefore, the wavelength control unit 42 may determine the wavelength to be output to the multiplexer / splitter 32, taking into account that the same wavelength is assigned to multiple central stations 20.

[0025] 2 is a sequence diagram showing the flow of processing in the communication system 100 according to the first embodiment. Note that the explanation of FIG. 2 will be given for a case where transmission from the central station 10-M is performed to both the aggregate stations 20-1 and 20-N.

[0026] Based on the traffic information of the central station 10-M, the wavelength control unit 42 of the wavelength management device 40 determines that transmission from the central station 10-M is to both the aggregation stations 20-1 and 20-N. For example, the wavelength control unit 42 may obtain the traffic information of the central station 10-M from the central station 10 or from an external device. The wavelength control unit 42 refers to the connection wavelength table 41 and selects wavelength λ2 so that the optical signal transmitted from the central station 10-M is transmitted to both the aggregation stations 20-1 and 20-N. The wavelength control unit 42 transmits a control signal to the central station 10-M instructing it to switch to the selected wavelength λ2 (step S101).

[0027] The control unit 11 of the central office 10-M receives the control signal transmitted from the wavelength management device 40 (step S102). The control unit 11 controls the wavelength-tunable light source 12 to output an optical signal with wavelength λ2 in accordance with the instruction contained in the received control signal. The wavelength-tunable light source 12 generates an optical signal with wavelength λ2 based on the transmission data in accordance with the control of the control unit 11. The wavelength-tunable light source 12 outputs the generated optical signal with wavelength λ2 (step S103).

[0028] The optical signal of wavelength λ2 output from the central office 10-M is input to a first port of the wavelength multiplexing / demultiplexing unit 31 of the switching device 30 via an optical transmission path. The optical signal of wavelength λ2 input to the first port of the wavelength multiplexing / demultiplexing unit 31 is demultiplexed in the wavelength multiplexing / demultiplexing unit 31 and output from a second port corresponding to wavelength λ2 (step S104). A multiplexer / demultiplexer 32 is connected to the second port corresponding to wavelength λ2. Therefore, the optical signal output from the second port corresponding to wavelength λ2 is input to the multiplexer / demultiplexer 32. The optical signal of wavelength λ2 input to the multiplexer / demultiplexer 32 is demultiplexed and output to the aggregation stations 20-1 and 20-N (step S105). As a result, the optical signal of wavelength λ2 is received at the aggregation stations 20-1 and 20-N.

[0029] The communication system 100 configured as described above includes a wavelength multiplexer / demultiplexer 31 having one or more first ports and multiple second ports, which demultiplexes an optical signal input from one or more of the first ports, and a multiplexer / demultiplexer 32 connected to a specific second port among the multiple second ports of the wavelength multiplexer / demultiplexer 31, which demultiplexes the optical signal output from the specific second port and outputs the branched optical signal to at least the central stations 20-1 and 20-N. In this manner, during a switching operation, the communication system 100 temporarily transmits signals to both the source central station 20-1 and the destination central station 20-N. Therefore, a buffer mechanism is not required. Furthermore, because signals are transmitted to both the source and destination central stations, loss of the main signal can be reduced. Therefore, the present invention makes it possible to easily switch the transmission destination while reducing loss of the main signal without a buffer mechanism.

[0030] Second Embodiment In a second embodiment, a configuration will be described in which traffic from a plurality of central stations is aggregated in one aggregation station.

[0031] 3 is a diagram showing an example of the configuration of a communication system 100a according to the second embodiment. The communication system 100a includes M central stations 10a, N aggregation stations 20a, a switching device 30, a wavelength management device 40, a switching management device 50, and an aggregation switch 55. The M central stations 10a are connected to the N aggregation stations 20a via the switching device 30.

[0032] The M central offices 10a and the switching device 30, and the switching device 30 and the N aggregation offices 20a are connected via optical transmission paths. The M central offices 10a and the wavelength management device 40, the M central offices 10a and the switching management device 50, the M central offices 10a and the aggregation switch 55, and the N aggregation offices 20 and the aggregation switch 55 are connected via electric lines.

[0033] The central station 10a transmits an optical signal having a wavelength assigned by the wavelength management device 40 to the aggregation station 20a via the switching device 30. The central station 10a is, for example, a DU in the 5G communication standard.

[0034] The aggregation station 20a receives and processes the optical signal transmitted from the central station 10a. The aggregation station 20a is, for example, a CU in the 5G communication standard.

[0035] The switching management device 50 manages the switching of the transmission destination in each central office 10 a. Specifically, when the switching management device 50 determines that the transmission destination needs to be switched in the central office 10 a, it determines the switching timing of the central office 10 a for which the destination needs to be switched (hereinafter referred to as the “target central office”) and instructs the target central office to switch the transmission destination at the switching timing.

[0036] The aggregation switch 55 collects load information transmitted from each central station 10 a and each aggregation station 20 a, and transmits the collected load information to the switching management device 50.

[0037] Next, the functional configuration of each device will be described in detail. Note that the switching device 30 and wavelength management device 40 are the same as those in the first embodiment, and therefore their description will be omitted.

[0038] (Functional Configuration of the Central Station 10a) The central station 10a includes a control unit 11, a wavelength-tunable light source 12, a load information notification unit 13, and an identifier insertion unit 14. The load information notification unit 13 notifies the load information of the central station 10a at a predetermined timing. The predetermined timing may be periodic or may be a predetermined time. The load information of the central station 10a is transmission traffic information, such as the result of uplink scheduling for a UE (User Element).

[0039] When processing is required in a specific central station 20a, the identifier inserting unit 14 assigns an identifier to the transmission data from the time notified by the switching management device 50. The identifier transmitted by the identifier inserting unit 14 is information that can be identified by the central station 20, and may be, for example, identification information of the central station 20 that is the receiving destination.

[0040] The control unit 11 controls the overall functions of the central office 10. The control unit 11 controls the tunable light source 12 to output an optical signal with a wavelength assigned by, for example, the wavelength management device 40. At this time, the control unit 11 outputs transmission data to which an identifier has been assigned by the identifier insertion unit 14 to the tunable light source 12. The tunable light source 12 is a light source capable of outputting optical signals with multiple wavelengths. The tunable light source 12 generates and outputs an optical signal with a wavelength set by the control unit 11 based on the transmission data output from the control unit 11.

[0041] (Functional Configuration of Aggregation Station 20a) The aggregation station 20a includes a load information notifying unit 21 and an identifying unit 22. The load information notifying unit 21 notifies the aggregation station 20a of load information at a predetermined timing. The load information of the aggregation station 20a is reception traffic information, for example, a utilization rate of the aggregation station 20a relative to the upper link rate.

[0042] The identification unit 22 converts the optical signal transmitted from the central office 10a into an electrical signal and identifies the identifier attached to the transmitted data. The identification unit 22 processes the transmitted data if the identifier indicates the device itself. The identification unit 22 discards the transmitted data if the identifier indicates any device other than the device itself.

[0043] (Functional Configuration of the Switching Management Device 50) The switching management device 50 includes a collection unit 51, a timing determination unit 52, and a switching designation unit 53. The collection unit 51 collects load information transmitted from each central station 10a and each aggregate station 20a. The timing determination unit 52 determines whether switching is necessary based on the collected load information. If the timing determination unit 52 determines that switching of the destination is necessary, it determines the switching timing of the target central station. Specifically, the timing determination unit 52 determines the time at which processing should be started in the destination aggregate station 20a (e.g., aggregate station 20a-1), and determines the switching timing to be the time obtained by subtracting at least the propagation time between the target central station and the destination aggregate station 20a and the propagation time between the switching management device 50 and the target central station from the frame corresponding to that time so that the identifier of the destination aggregate station 20a (e.g., aggregate station 20a-1) can be assigned by the target central station.

[0044] The switching designation unit 53 transmits a switching instruction including information indicating the switching timing determined by the timing determination unit 52 to the target central office.

[0045] 4 is a diagram illustrating the processing flow of the communication system 100a according to the second embodiment. In describing FIG. 4, the central station 20a-1 may be referred to as a communication device to which switching is to be performed, and the central station 20a-N may be referred to as a communication device from which switching is performed.

[0046] The central station 10a-M and the aggregation stations 20a-1 and 20a-N each transmit load information to the switching management device 50 via the aggregation switch 55 at a predetermined timing. The switching management device 50 determines whether or not to switch the destination based on the multiple pieces of load information transmitted from each device. For example, the switching management device 50 may determine whether or not to switch the destination based on information about the amount of traffic that will arrive in the future, such as a scheduling result, or may determine whether or not to switch the destination by predicting future traffic volume using time series prediction.

[0047] For example, when the switching management device 50 determines that the upstream link of the aggregation station 20a-2 is likely to be overflowed after Ams due to upstream traffic from the central station 10a-M, it determines that a destination switch is necessary. On the other hand, when the upstream link of the aggregation station 20a-2 is not likely to be overflowed after Ams due to upstream traffic from the central station 10a-M, it determines that a destination switch is not necessary. Here, it is assumed that the switching management device 50 determines that a destination switch is necessary when it determines that the upstream link of the aggregation station 20a-2 is likely to be overflowed after Ams. In this case, at the timing when it determines that a destination switch is necessary, the switching management device 50 decides that the aggregation station 20a-N will not process the signal transmitted from 10a-M.

[0048] The switching management device 50 then determines the time at which processing should be initiated in the central station 20a-1. For example, the switching management device 50 may determine time t1, which is a timing after Ams, as the time at which processing should be initiated in the central station 20a-1. The switching management device 50 determines the switching timing so that the central station 10a-M can assign an identifier that identifies the central station 20a-1 to the signal corresponding to the determined time t1. Specifically, the switching management device 50 determines the switching timing based on a propagation time d1 between the switching management device 50 and the central station 10a-M, a propagation time d2 between the central station 10a-M and the destination central station 20a-1, and a time d3 from the time it is determined that switching of the destination is necessary until time t1. For example, the switching management device 50 determines the switching timing to be the time obtained by subtracting the propagation time d1 and the propagation time d2 from time d3. The switching management device 50 transmits a switching instruction including information indicating the determined switching timing and information indicating the destination to the central office 10a-M.

[0049] The central station 10a-M receives the switching instruction transmitted from the switching management device 50, and transmits the transmitted data with an identifier (for example, "B") indicating the aggregate station 20a-N attached thereto until the timing included in the switching instruction arrives. The signal transmitted from the central station 10a-M is output to both the aggregate stations 20a-1 and 20a-N by the switching device 30. However, the aggregate station 20a-1 discards the received signal because it is not addressed to itself. The aggregate station 20a-M processes the received signal because it is addressed to itself.

[0050] When the timing included in the switching instruction arrives, the central station 10a-M adds an identifier (for example, "A") indicating the aggregate station 20a-1 to the transmission data and transmits it thereafter. The signal transmitted from the central station 10a-M is output to both the aggregate stations 20a-1 and 20a-N by the switching device 30. The aggregate station 20a-1 processes the received signal because it is addressed to itself. However, the aggregate station 20a-M discards the received signal because it is not addressed to itself.

[0051] 5 and 6 are sequence diagrams showing the flow of processing in the communication system 100a according to the second embodiment. It is assumed that, before the processing in FIGS. 5 and 6 starts, an optical signal with wavelength λ2 is transmitted from the central station 10a-M, with an identifier indicating the aggregation station 20a-N attached to the transmission data. In this case, the central station 10a-1 discards the transmission data based on the optical signal with wavelength λ2, and the central station 10a-M processes or forwards the transmission data based on the optical signal with wavelength λ2.

[0052] The load information notification unit 13 of the central station 10a-M transmits load information at a predetermined timing (step S201). The load information transmitted from the load information notification unit 13 is output to the switching management device 50 via the aggregation switch 55. The load information notification unit 21-1 of the aggregation station 20a-1 transmits load information at a predetermined timing (step S202). The load information transmitted from the load information notification unit 21-1 is output to the switching management device 50 via the aggregation switch 55. The load information notification unit 21-N of the aggregation station 20a-N transmits load information at a predetermined timing (step S203). The load information transmitted from the load information notification unit 21-N is output to the switching management device 50 via the aggregation switch 55.

[0053] The collector 51 of the switching management device 50 collects load information transmitted from the central station 10a-M, the aggregation station 20a-1, and the aggregation station 20a-N (step S204). The collector 51 outputs the collected load information to the timing determiner 52. The timing determiner 52 determines whether or not the destination of the central station 10a-M needs to be switched based on the multiple pieces of load information output from the collector 51 (step S205). It is assumed here that it is determined that the destination of the central station 10a-M needs to be switched. For example, it is assumed that it is determined that the destination of the central station 10a-M needs to be switched to the aggregation station 20a-1 instead of the aggregation station 20a-N. The central station 10a-M is the target central station.

[0054] In this case, the timing determiner 52 determines the switch timing to be the time obtained by subtracting the propagation time between the target central station and the destination central station 20 a-1 and the propagation time between the switching management device 50 and the target central station from the time when processing should start in the destination central station 20 a-1 (step S206). The timing determiner 52 outputs information indicating the determined switch timing to the switch designator 53. The switch designator 53 transmits a switch instruction including the information indicating the switch timing output from the timing determiner 52 to the target central station (step S207).

[0055] The control unit 11 of the central station 10a-M receives the switching instruction transmitted from the switching management device 50 (step S208). The central station 10a-M transmits an optical signal of wavelength λ2 based on the transmission data to which an identifier indicating the aggregation station 20a-N has been assigned until the switching timing included in the received switching instruction arrives (step S209). Thereafter, when the switching timing included in the switching instruction arrives, the identifier insertion unit 14 assigns an identifier indicating the aggregation station 20a-1 to the transmission data to be transmitted from the time of the switching timing. The identifier insertion unit 14 outputs the transmission data to which the identifier has been assigned to the control unit 11. The control unit 11 outputs the transmission data to which the identifier has been assigned by the identifier insertion unit 14 to the wavelength-tunable light source 12. The wavelength-tunable light source 12 generates and outputs an optical signal of wavelength λ2 based on the transmission data output from the control unit 11 (step S210).

[0056] The optical signal of wavelength λ2 output from the central office 10a-M is input to a first port of the wavelength multiplexing / demultiplexing unit 31 of the switching device 30 via an optical transmission path. The optical signal of wavelength λ2 input to the first port of the wavelength multiplexing / demultiplexing unit 31 is demultiplexed in the wavelength multiplexing / demultiplexing unit 31 and output from a second port corresponding to wavelength λ2 (step S211). A multiplexer / demultiplexer 32 is connected to the second port corresponding to wavelength λ2. Therefore, the optical signal output from the second port corresponding to wavelength λ2 is input to the multiplexer / demultiplexer 32. The optical signal of wavelength λ2 input to the multiplexer / demultiplexer 32 is demultiplexed and output to the aggregation stations 20a-1 and 20a-M (step S212).

[0057] The central station 20a-1 receives the optical signal with wavelength λ2 output from the multiplexer / splitter 32 (step S213). The identification unit 22-1 converts the received optical signal with wavelength λ2 into an electrical signal and identifies the identifier attached to the transmission data. Specifically, the identification unit 22-1 identifies whether the identifier attached to the transmission data indicates the central station 20a-1. In this example, the identifier attached to the transmission data indicates the central station 20a-1. Therefore, the identification unit 22-1 determines that the identifier attached to the transmission data indicates the central station 20a-1. In this case, the central station 20a-1 processes the transmission data (step S214). Note that if the transmission data needs to be transferred to a higher-level device, the central station 20a-1 transfers the transmission data to the higher-level device.

[0058] The central station 20a-N receives the optical signal with wavelength λ2 output from the multiplexer / splitter 32 (step S215). The identification unit 22-N converts the received optical signal with wavelength λ2 into an electrical signal and identifies the identifier attached to the transmission data. Specifically, the identification unit 22-N identifies whether the identifier attached to the transmission data indicates the central station 20a-N. In this example, the identifier attached to the transmission data indicates the central station 20a-1. Therefore, the identification unit 22-N determines that the identifier attached to the transmission data does not indicate the central station 20a-N. In this case, the central station 20a-N discards the transmission data (step S216).

[0059] In the communication system 100 configured as described above, the target central station 10a assigns a specified identifier to a transmission frame and transmits it based on the time specified in the switching instruction sent from the switching management device 50. As a result, the destination central station 20a processes or forwards only frames addressed to itself and discards frames addressed to other central stations 20a. This makes it possible to achieve switching without frame loss.

[0060] Furthermore, compared to the first embodiment in which post-reception processing is always performed by a plurality of central stations 20, redundancy can be achieved with fewer processing resources (power consumption, CPU load, etc.).

[0061] Third Embodiment In the first embodiment, switching between a central station and an aggregation station has been described as an example. In the third embodiment, switching between a wireless station and a central station will be described.

[0062] 7 is a diagram showing an example of the configuration of a communication system 100b according to the third embodiment. The communication system 100b includes L (L is an integer equal to or greater than 1) wireless stations 60, M central stations 10, a switching device 30, and a wavelength management device 40. The L wireless stations 60 are connected to the M central stations 10 via the switching device 30. Note that in this embodiment, multiple central stations 10 are included.

[0063] The L radio stations 60 are connected to the switching device 30, and the switching device 30 is connected to the M central stations 10 via optical transmission paths. The optical transmission paths are optical fibers. The L radio stations 60 are connected to the wavelength management device 40 via electrical lines.

[0064] The radio station 60 transmits an optical signal having a wavelength assigned by the wavelength management device 40 to the central station 10 via the switching device 30. The radio station 60 is, for example, a radio unit (RU) in the 5G communication standard.

[0065] The central station 10 receives the optical signal transmitted from the wireless station 60 and processes it or transmits it to a higher-level device.

[0066] The switching device 30 switches the connection path between the central office 10 and the radio station 60. The switching device 30 outputs an input optical signal of a certain wavelength to the destination central office 10. The switching device 30 outputs an optical signal of a specific wavelength to multiple central offices 10.

[0067] The wavelength management device 40 controls the wavelengths used for communication by each wireless station 60. For example, when a connection destination is switched, the wavelength management device 40 controls the wavelengths of each wireless station 60 whose connection destination is to be switched so that communication is performed at a specific wavelength at least while the connection destination is being switched.

[0068] Next, the functional configuration of each device will be described in detail.

[0069] (Functional configuration of radio station 60) The radio station 60 includes a control unit 61 and a wavelength-tunable light source 62. The control unit 61 controls the overall functions of the radio station 60. The control unit 61 controls the wavelength-tunable light source 62 so that it outputs an optical signal with a wavelength assigned by, for example, the wavelength management device 40. The wavelength-tunable light source 62 is a light source that can output optical signals with multiple wavelengths. The wavelength-tunable light source 62 outputs an optical signal with a wavelength set by the control unit 61.

[0070] (Functional Configuration of Wavelength Management Device 40) The wavelength management device 40 includes a connection wavelength table 41 and a wavelength control unit 42. The connection wavelength table 41 is a table in which information about wavelengths for connection to each central station 10 is registered. The connection wavelength table 41 associates identification information for identifying each central station 10 with information indicating wavelengths for connection to each central station 10. The wavelength control unit 42 refers to the connection wavelength table 41 and controls the wavelengths to be assigned to each wireless station 60.

[0071] 8 is a sequence diagram showing the flow of processing in the communication system 100b according to the third embodiment. Note that the explanation of FIG. 8 will be given for a case where transmission from the wireless station 60-L is performed to both the central stations 10-1 and 10-N.

[0072] The wavelength control unit 42 of the wavelength management device 40 determines, based on the traffic information of the radio station 60-L, that transmission from the radio station 60-L is to both the central stations 10-1 and 10-N. For example, the wavelength control unit 42 may obtain the traffic information of the radio station 60-L from the radio station 60-L itself, or from an external device. The wavelength control unit 42 refers to the connection wavelength table 41 and selects wavelength λ2 so that the optical signal transmitted from the radio station 60-L is transmitted to both the central stations 10-1 and 10-N. The wavelength control unit 42 transmits a control signal to the radio station 60-L instructing it to switch to the selected wavelength λ2 (step S301).

[0073] The control unit 61 of the wireless station 60-L receives the control signal transmitted from the wavelength management device 40 (step S302). The control unit 61 controls the tunable light source 62 to output an optical signal with wavelength λ2 in accordance with the instruction contained in the received control signal. The tunable light source 62 generates an optical signal with wavelength λ2 based on the transmission data in accordance with the control of the control unit 61. The tunable light source 62 outputs the generated optical signal with wavelength λ2 (step S303).

[0074] The optical signal of wavelength λ2 output from the radio station 60-L is input to a first port of the wavelength multiplexing / demultiplexing unit 31 of the switching device 30 via the optical transmission path. The optical signal of wavelength λ2 input to the first port of the wavelength multiplexing / demultiplexing unit 31 is demultiplexed in the wavelength multiplexing / demultiplexing unit 31 and output from a second port corresponding to wavelength λ2 (step S304). A multiplexer / demultiplexer 32 is connected to the second port corresponding to wavelength λ2. Therefore, the optical signal output from the second port corresponding to wavelength λ2 is input to the multiplexer / demultiplexer 32. The optical signal of wavelength λ2 input to the multiplexer / demultiplexer 32 is demultiplexed and output to the central offices 10-1 and 10-N (step S305). As a result, the optical signal of wavelength λ2 is received at the central offices 10-1 and 10-N.

[0075] According to the communication system 100b configured as above, the same effects as those of the first embodiment can be obtained even in the connection configuration between the radio stations 60 and the central station 10.

[0076] Fourth Embodiment In a fourth embodiment, a configuration will be described in which traffic from a plurality of wireless stations is aggregated in one central station.

[0077] 9 is a diagram showing an example of the configuration of a communication system 100c according to the fourth embodiment. The communication system 100c includes M central stations 10c, a switching device 30, a wavelength management device 40, a switching management device 50, an aggregation switch 55, and L radio stations 60c. The L radio stations 60c are connected to the M central stations 10c via the switching device 30. Note that in this embodiment, multiple central stations 10c are included.

[0078] The L radio stations 60c and the switching device 30, and the switching device 30 and the M central stations 10c are connected via optical transmission paths. The L radio stations 60c and the wavelength management device 40, the L radio stations 60c and the switching management device 50, the L radio stations 60c and the aggregation switch 55, and the M central stations 10c and the aggregation switch 55 are connected via electric lines.

[0079] The radio station 60c transmits an optical signal having a wavelength assigned by the wavelength management device 40 to the central station 10c via the switching device 30. The radio station 60c is, for example, a DU in the 5G communication standard.

[0080] The central station 10c receives the optical signal transmitted from the wireless station 60c and processes it or transmits it to a higher-level device. The central station 10c is, for example, a DU in the 5G communication standard.

[0081] The switching management device 50 manages switching of the transmission destination in each wireless station 60 c. Specifically, when the switching management device 50 determines that switching of the transmission destination in the wireless station 60 c is necessary, the switching management device 50 determines the switching timing of the wireless station 60 c that requires switching of the transmission destination (hereinafter referred to as the “target wireless station”) and instructs the target wireless station to switch the transmission destination at the switching timing.

[0082] The aggregation switch 55 collects load information transmitted from each wireless station 60c and each central station 10. The aggregation switch 55 transmits the collected load information to the switching management device 50.

[0083] Next, the functional configuration of each device will be described in detail. Note that the switching device 30 and wavelength management device 40 are the same as those in the third embodiment, and therefore descriptions thereof will be omitted.

[0084] (Functional configuration of radio station 60c) The radio station 60c includes a control unit 61, a wavelength-tunable light source 62, a load information notification unit 63, and an identifier insertion unit 64. The load information notification unit 63 notifies the load information of the radio station 60c at a predetermined timing. The load information of the radio station 60c is transmission traffic information, such as the result of uplink scheduling for the UE.

[0085] When processing is required in a specific central office 10, the identifier inserting unit 64 assigns an identifier to the transmitted data from the time notified by the switching management device 50. The identifier transmitted by the identifier inserting unit 64 is information that can be identified by the central office 10, and may be, for example, identification information of the central office 10 that is the destination.

[0086] The control unit 61 controls the overall functions of the radio station 60c. The control unit 61 controls the tunable light source 62 to output an optical signal with a wavelength assigned by, for example, the wavelength management device 40. At this time, the control unit 61 outputs transmission data to which an identifier has been assigned by the identifier insertion unit 64 to the tunable light source 62. The tunable light source 62 is a light source that can output optical signals with multiple wavelengths. The tunable light source 62 generates and outputs an optical signal with a wavelength set by the control unit 61 based on the transmission data output from the control unit 61.

[0087] (Functional Configuration of Central Station 10c) The central station 10c includes a load information notifying unit 13 and an identifying unit 15. The load information notifying unit 13 notifies the load information of the central station 10c at a predetermined timing. The load information of the central station 10c is reception traffic information, such as the utilization rate of the central station 10c relative to the upper link rate. Alternatively, the load information may be an effective reception rate obtained as performance monitoring information, or the load may be obtained from the difference in the number of received bytes obtained multiple times from the SNMP MIB (Simple Network Management Protocol Management Information Base) for the interface in question as the reception rate of the central station 10c.

[0088] The identification unit 15 converts the optical signal transmitted from the wireless station 60c into an electrical signal and identifies the identifier attached to the transmitted data. The identification unit 15 processes the transmitted data if the identifier indicates the wireless station itself. The identification unit 15 discards the transmitted data if the identifier indicates any device other than the wireless station itself.

[0089] (Functional Configuration of the Switching Management Device 50) The switching management device 50 includes a collection unit 51, a timing determination unit 52, and a switching designation unit 53. The collection unit 51 collects load information transmitted from each wireless station 60c and each central station 10. The timing determination unit 52 determines whether switching is necessary based on the collected load information. If the timing determination unit 52 determines that switching of the transmission destination is necessary, it determines the switching timing of the target wireless station. Specifically, the timing determination unit 52 determines the time at which processing should be started in the destination central station 10c (e.g., the central station 10c-1), and determines the switching timing to be the time obtained by subtracting at least the propagation time between the target wireless station and the destination central station 10c and the propagation time between the switching management device 50 and the target wireless station from the frame corresponding to that time so that the identifier of the destination central station 10c (e.g., the central station 10c-1) can be assigned by the target wireless station.

[0090] The switching designation unit 53 transmits a switching instruction including information indicating the switching timing determined by the timing determination unit 52 to the target wireless station.

[0091] 10 and 11 are sequence diagrams showing the flow of processing in the communication system 100c according to the fourth embodiment. It is assumed that, before the processing in FIGS. 10 and 11 starts, an optical signal with wavelength λ2 is transmitted from the wireless station 60c-L, with an identifier indicating the central station 10c-M attached to the transmission data. In this case, the central station 10c-1 discards the transmission data based on the optical signal with wavelength λ2, and the central station 10c-M processes or forwards the transmission data based on the optical signal with wavelength λ2.

[0092] The load information notification unit 63 of the wireless station 60c-L transmits load information at a predetermined timing (step S401). The load information transmitted from the load information notification unit 63 is output to the switching management device 50 via the aggregation switch 55. The load information notification unit 13-1 of the central station 10c-1 transmits load information at a predetermined timing (step S402). The load information transmitted from the load information notification unit 13-1 is output to the switching management device 50 via the aggregation switch 55. The load information notification unit 13-M of the central station 10c-M transmits load information at a predetermined timing (step S403). The load information transmitted from the load information notification unit 13-M is output to the switching management device 50 via the aggregation switch 55.

[0093] The collection unit 51 of the switching management device 50 collects load information transmitted from the wireless station 60-M, the central station 10c-1, and the central station 10c-M (step S404). The collection unit 51 outputs the collected load information to the timing determination unit 52. The timing determination unit 52 determines whether or not it is necessary to switch the transmission destination of the wireless station 60c-L based on the multiple pieces of load information output from the collection unit 51 (step S405). Here, it is assumed that it is determined that it is necessary to switch the transmission destination of the wireless station 60c-L. For example, it is assumed that it is determined that it is necessary to switch the transmission destination of the wireless station 60c-L to the central station 10c-1 instead of the central station 10c-N. The wireless station 60c-L is the target wireless station.

[0094] In this case, the timing determiner 52 determines the switching timing to be the time obtained by subtracting the propagation time between the target wireless station and the destination central station 10c-1 and the propagation time between the switching management device 50 and the target wireless station from the time when processing should be started at the destination central station 10c-1 (step S406). The timing determiner 52 outputs information indicating the determined switching timing to the switching designator 53. The switching designator 53 transmits a switching instruction including the information indicating the switching timing output from the timing determiner 52 to the target wireless station (step S407).

[0095] The control unit 61 of the radio station 60c-L receives the switching instruction transmitted from the switching management device 50 (step S408). The radio station 60c-L transmits an optical signal with wavelength λ2 based on the transmission data to which an identifier indicating the central station 10c-M has been assigned until the switching timing included in the received switching instruction arrives (step S409). Thereafter, when the switching timing included in the switching instruction arrives, the identifier insertion unit 64 assigns an identifier indicating the central station 10c-1 to the transmission data to be transmitted from the time the switching timing arrives. The identifier insertion unit 64 outputs the transmission data to which the identifier has been assigned to the control unit 61. The control unit 61 outputs the transmission data to which the identifier has been assigned by the identifier insertion unit 64 to the wavelength-tunable light source 62. The wavelength-tunable light source 62 generates and outputs an optical signal with wavelength λ2 based on the transmission data output from the control unit 61 (step S410).

[0096] The optical signal of wavelength λ2 output from the wireless station 60c-L is input to a first port of the wavelength multiplexing / demultiplexing unit 31 of the switching device 30 via an optical transmission path. The optical signal of wavelength λ2 input to the first port of the wavelength multiplexing / demultiplexing unit 31 is demultiplexed in the wavelength multiplexing / demultiplexing unit 31 and output from a second port corresponding to wavelength λ2 (step S411). A multiplexer / demultiplexer 32 is connected to the second port corresponding to wavelength λ2. Therefore, the optical signal output from the second port corresponding to wavelength λ2 is input to the multiplexer / demultiplexer 32. The optical signal of wavelength λ2 input to the multiplexer / demultiplexer 32 is demultiplexed and output to the central offices 10c-1 and 10c-M (step S412).

[0097] The central office 10c-1 receives the optical signal with wavelength λ2 output from the multiplexer / splitter 32 (step S413). The identification unit 15-1 converts the received optical signal with wavelength λ2 into an electrical signal and identifies the identifier attached to the transmission data. Specifically, the identification unit 15-1 identifies whether the identifier attached to the transmission data indicates the central office 10c-1. In this example, the identifier attached to the transmission data indicates the central office 10c-1. Therefore, the identification unit 15-1 determines that the identifier attached to the transmission data indicates the central office 10c-1. In this case, the central office 10c-1 processes the transmission data (step S414). If the transmission data needs to be transferred to a higher-level device, the central office 10c-1 transfers the transmission data to the higher-level device.

[0098] The central office 10c-M receives the optical signal with wavelength λ2 output from the multiplexer / splitter 32 (step S415). The decision unit 15-M converts the received optical signal with wavelength λ2 into an electrical signal and identifies the identifier attached to the transmitted data. Specifically, the decision unit 15-M determines whether the identifier attached to the transmitted data indicates the central office 10c-M. In this example, the identifier attached to the transmitted data indicates the central office 10c-1. Therefore, the decision unit 15-M determines that the identifier attached to the transmitted data does not indicate the central office 10c-M. In this case, the central office 10c-M discards the transmitted data (step S416).

[0099] According to the communication system 100c configured as above, the same effects as those of the second embodiment can be obtained also in the connection configuration between the wireless station 60c and the central station 10c.

[0100] Some of the functional units of the central stations 10, 10a, and 10c, the aggregation stations 20 and 20a, the wavelength management device 40, the switching management device 50, and the radio stations 60 and 60c in the above-described embodiments may be implemented by a computer. In this case, a program for implementing the functions may be recorded on a computer-readable recording medium, and the program may be read into and executed by a computer system. Note that the term "computer system" here includes an operating system (OS) and hardware such as peripheral devices.

[0101] Furthermore, "computer-readable recording media" refers to portable media such as flexible disks, optical magnetic disks, ROMs (Read Only Memory), and CD-ROMs, as well as storage devices such as hard disks built into computer systems. Furthermore, "computer-readable recording media" may also include devices that dynamically store programs for a short period of time, such as communication lines used when transmitting programs over networks like the Internet or communication lines like telephone lines, or devices that store programs for a fixed period of time, such as volatile memory within the computer systems that serve as servers or clients. Furthermore, the programs may be designed to implement some of the aforementioned functions, or may be capable of implementing the aforementioned functions in combination with programs already stored in the computer system, or may be implemented using programmable logic devices such as FPGAs (Field-Programmable Gate Arrays).

[0102] Although an embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention.

[0103] The present invention can be applied to a communication system that performs switching without using a buffer mechanism or the like.

[0104] 10, 10-1 to 10-M, 10a-1 to 10a-M, 10c-1 to 10c-M... central station, 11, 61... control unit, 12, 62... wavelength-tunable light source, 13, 21, 63... load information notification unit, 14, 64... identifier insertion unit, 15, 22... identification unit, 20, 20-1 to 20-N, 20a-1 to 20a-N... aggregation station, 30... switching device, 31... wavelength multiplexing / demultiplexing unit, 32... multiplexer / demultiplexer, 40... wavelength management device, 41... connection wavelength table, 42... wavelength control unit, 50... switching management device, 51... collection unit, 52... timing determination unit, 53... switching designation unit, 55... aggregation switch, 60, 60-1 to 60-L, 60c-1 to 60c-L... radio station, 100, 100a, 100b, 100c...communication systems

Claims

1. A switching device comprising: one or more first ports and a plurality of second ports; a wavelength division multiplexing unit that demultiplexes a signal input from the one or more first ports; and a branching unit that is connected to a specific second port among the plurality of second ports of the wavelength division multiplexing unit, branches a signal output from the specific second port, and outputs the signal to at least a communication device at a switching source and a communication device at a switching destination.

2. The switching device according to claim 1, wherein the wavelength division multiplexing unit demultiplexes the input signal according to wavelength, and the branching unit branches the signal output from the specific second port at a predetermined branching ratio and outputs the signal to at least a communication device at a switching source and a communication device at a switching destination.

3. A communication system comprising one or more first communication stations, a plurality of second communication stations, and a switching device that switches connections between the one or more first communication stations and the plurality of second communication stations, wherein the one or more first communication stations include a transmission unit that transmits a signal to one or more of the plurality of second communication stations during a connection switching operation, and the switching device includes one or more first ports and a plurality of second ports, a wavelength division multiplexing unit that demultiplexes the signal transmitted from the one or more first communication stations via the one or more first ports, and a branching unit that is connected to a specific second port among the plurality of second ports of the wavelength division multiplexing unit, branches a signal output from the specific second port, and outputs the signal to at least a communication device at a switching source and a communication device at a switching destination.

4. The communication system according to claim 3, wherein the wavelength division multiplexing unit demultiplexes the input signal according to wavelength, the transmission unit of the one or more first communication stations transmits a signal having a wavelength output from the specific second port so as to be transferred to the one or more second communication stations, and the branching unit branches the signal output from the specific second port at a predetermined branching ratio and outputs the signal to at least a communication device at a switching source and a communication device at a switching destination.

5. The transmission unit of the one or more first communication stations further includes an identifier insertion unit that assigns an identifier for identifying the signal destination. The identifier insertion unit assigns an identifier representing the communication device before switching during a period until a predetermined timing notified from the outside, and assigns an identifier representing the communication device after switching during a period after the predetermined timing. The communication system according to claim 3 or 4.

6. The communication system according to claim 5, further comprising a management device that determines the predetermined timing. The management device collects load information from each of the one or more first communication stations and the plurality of second communication stations, and when it is necessary to switch the transmission destination based on the collected load information, determines the predetermined timing based on the time when processing should start at the second communication station that is the switching destination.

7. The communication system according to claim 6, wherein the management device determines the time obtained by subtracting the propagation time between the first communication station that is the switching target of the transmission destination and the second communication station that is the switching destination and the propagation time between the management device and the first communication station that is the switching target of the transmission destination from the time when processing should start at the second communication station that is the switching destination as the predetermined timing.

8. A switching method in a demultiplexing unit having one or more first ports and a plurality of second ports, demultiplexing a signal input from the one or more first ports, and a branching unit connected to a specific second port among the plurality of second ports of the demultiplexing unit branches the signal output from the specific second port and outputs it to at least the communication device before switching and the communication device after switching.