Communication system, control device, and control method

Abstract

This communication system comprises a first control device that manages a first network, and a second control device that manages a second network that is a higher order network than the first network, wherein: the first control device performs switching control of communication paths and inter-device connections in the first network, which connects a plurality of low-order devices and a plurality of intermediate devices, and notifies the second control device of inter-device connection information indicating a switching control result; and the second control device performs switching control of communication paths and inter-device connections in the second network, which connects the plurality of intermediate devices and a plurality of high-order devices, on the basis of load information obtained from each of the plurality of intermediate devices and the inter-device connection information notified from the first control device.　

Description

Communication system, control device and control method

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

[0002] Conventionally, as shown in FIG. 24, a communication system has been proposed that includes a central control device, a lower NW control device, and a higher NW control device (see, for example, Patent Document 1). FIG. 24 is a diagram showing an example of the configuration of a conventional communication system. The communication system shown in FIG. 24 includes a plurality of lower devices #1 to #3, a plurality of intermediate devices #1 to #2, a plurality of higher devices #1 to #2, a central control device, a lower NW control device, and a higher NW control device. The lower devices and the intermediate devices, and each intermediate device and the higher device are connected via a forwarding device (not shown). The forwarding device is a device that can switch paths, such as a switch or a router.

[0003] Before the path switching, the lower device #2 transfers data to the upper device #2 via the communication path A. The communication path A is a path connecting the lower device #2, the intermediate device #2, and the upper device #2. When congestion occurs in the communication path A, or when congestion is expected to occur, the lower NW control device and the upper NW control device transmit inter-device connection information from the lower NW control device and the upper NW control device to the central control device in order to issue a switching instruction for congestion control.

[0004] The central control device comprehensively determines switching control including the lower device, intermediate device, and upper device based on the inter-device connection information transmitted from the lower NW control device and the upper NW control device. The inter-device connection information is information indicating the connection relationships between the lower device and the intermediate device, and between the intermediate device and the upper device. For example, in the example shown in Figure 24, information is included such as that the lower device #2 and the intermediate device #2 are connected, and that the intermediate device #2 and the upper device #2 are connected.

[0005] The central control device transmits switching control information indicating the determined switching control result to the lower NW control device and the upper NW control device. Based on the switching control information transmitted from the central control device, the lower NW control device outputs switching information including a switching instruction for the communication path and the inter-device connection to the transfer device arranged on the path between the lower device and the intermediate device. Based on the switching control information transmitted from the central control device, the upper NW control device outputs switching information including a switching instruction for the communication path and the inter-device connection to the transfer device arranged on the path between the intermediate device and the upper device.

[0006] A transfer device disposed on a path between a lower device and an intermediate device switches the communication path and the inter-device connection based on switching information transmitted from the lower NW control device. For example, as shown in FIG. 24 , the transfer device switches the inter-device connection so that lower device #2 and intermediate device #1 are connected. As a result, communication path B is established between lower device #2 and intermediate device #1. A transfer device disposed on a path between an intermediate device and an upper device switches the communication path and the inter-device connection based on switching information transmitted from the upper NW control device. For example, as shown in FIG. 24 , the transfer device switches the inter-device connection so that intermediate device #1 and upper device #1 are connected. As a result, communication path B is established between intermediate device #1 and upper device #1.

[0007] Japanese Patent Application Laid-Open No. 2015-156546

[0008] In the conventional communication system described above, a central control device controls switching of the entire network, including the lower-level network control devices and the upper-level network control devices. Therefore, since the central control device also controls switching of communication paths and inter-device connections, delays may occur in switching of communication paths and inter-device connections. As a result, a communication system equipped with multiple control devices has a problem in that it is difficult to control congestion in real time.

[0009] In view of the above circumstances, an object of the present invention is to provide a technique that enables real-time congestion control in a communication system having a plurality of control devices.

[0010] One aspect of the present invention is a communication system comprising a first control device that manages a first network and a second control device that manages a second network that is a higher-level network than the first network, wherein the first control device performs switching control of communication paths and inter-device connections in the first network that connects multiple lower-level devices and multiple intermediate devices, and notifies the second control device of inter-device connection information indicating the switching control results, and the second control device performs switching control of communication paths and inter-device connections in the second network that connects the multiple intermediate devices and multiple higher-level devices based on load information obtained from each of the multiple intermediate devices and the inter-device connection information notified from the first control device.

[0011] One aspect of the present invention is a control device that manages a second network that is a higher-level network than a first network, and that acquires inter-device connection information indicating the results of switching control of communication paths and inter-device connections in the first network that connects multiple lower-level devices and multiple intermediate devices from another control device that manages the first network, and performs switching control of communication paths and inter-device connections in the second network that connects the multiple intermediate devices and multiple higher-level devices based on load information obtained from each of the multiple intermediate devices and the inter-device connection information acquired from the other control device.

[0012] One aspect of the present invention is a control method performed by a communication system that includes a first control device that manages a first network and a second control device that manages a second network that is a higher-level network than the first network, in which the first control device performs switching control of communication paths and inter-device connections in the first network that connects multiple lower-level devices and multiple intermediate devices, and notifies the second control device of inter-device connection information that indicates the switching control results, and the second control device performs switching control of communication paths and inter-device connections in the second network that connects the multiple intermediate devices and multiple higher-level devices based on load information obtained from each of the multiple intermediate devices and the inter-device connection information notified from the first control device.

[0013] According to the present invention, it becomes possible to perform real-time congestion control in a communication system having a plurality of control devices.

[0014] 1 is a diagram illustrating an example of a configuration of a communication system in a first embodiment. FIG. 2 is a diagram illustrating an example of a lower device management table in the first embodiment. FIG. 3 is a diagram illustrating an example of an intermediate device management table in the first embodiment. FIG. 4 is a sequence diagram illustrating a flow of processing performed by a communication system in the first embodiment. FIG. 5 is a flowchart illustrating a flow of congestion determination processing performed by a communication system in the first embodiment. FIG. 6 is a diagram illustrating an example of a configuration of a communication system in a second embodiment. FIG. 7 is a diagram illustrating the processing of a communication system in the second embodiment. FIG. 8 is a diagram illustrating the processing of a communication system in the second embodiment. FIG. 9 is a diagram illustrating the processing of a communication system in the second embodiment. FIG. 10 is a sequence diagram illustrating a flow of processing performed by a communication system in the second embodiment. FIG. 11 is a flowchart illustrating a flow of switching determination processing performed by a communication system in the second embodiment. FIG. 12 is a diagram illustrating the processing of a communication system in a third embodiment. FIG. 13 is a diagram illustrating the processing of a communication system in the third embodiment. FIG. 14 is a diagram illustrating the processing of a communication system in a fourth embodiment. FIG. 15 is a diagram illustrating the processing of a communication system in the fourth embodiment. FIG. 16 is a diagram illustrating the processing of a communication system in the fourth embodiment. FIG. 17 is a diagram illustrating the processing of a communication system in the fourth embodiment. FIG. 18 is a diagram illustrating the processing of a communication system in the fourth embodiment. It is a flowchart which shows the flow of the switching determination process which a lower NW control device performs in the 5th embodiment. It is a figure which shows the configuration example of the communication system in the 6th embodiment. It is a figure which shows the configuration example of the conventional communication system.

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0016] First Embodiment FIG. 1 is a diagram illustrating an example of the configuration of a communication system 100 according to a first embodiment. The communication system 100 is, for example, a fifth-generation mobile communication system (5G). The communication system 100 includes a lower-level device 10, a transfer device 15, an intermediate device 20, a transfer device 25, an upper-level device 30, a lower-level NW control device 40, and an upper-level NW control device 50. In FIG. 1, the communication system 100 includes three lower-level devices 10-1 to 10-3, two intermediate devices 20-1 to 20-2, and two upper-level devices 30-1 to 30-2. However, the number of lower-level devices 10, intermediate devices 20, and upper-level devices 30 is not particularly limited. Furthermore, a plurality of transfer devices 15 and a plurality of transfer devices 25 may be included.

[0017] 1 shows a state in which lower devices 10-1 and 10-2 communicate via intermediate device 20-1, and lower device 10-3 communicates via intermediate device 20-2. Also, the example shown in FIG. 1 shows a state in which intermediate device 20-1 communicates via upper device 30-1, and intermediate device 20-2 communicates via upper device 30-2. Hereinafter, the direction from lower device 10 to upper device 30 will be referred to as "upstream," and the direction from upper device 30 to lower device 10 will be referred to as "downstream."

[0018] The lower device 10 transmits an upstream signal to the connected upper device 30. For example, one or more terminal devices are connected under the lower device 10, and data transmitted from the terminal devices is transmitted as an upstream signal. The upstream signal transmitted from the lower device 10 is transferred to the destination upper device 30 along the communication path between the lower device 10 and the upper device 30. The lower device 10 transmits lower device load information to the lower NW control device 40 at a first timing. The first timing may be a predetermined timing or a timing requested by the lower NW control device 40.

[0019] The lower-level device load information is information relating to the load on the lower-level device 10, such as CTI (Cooperative Transport Interface) information (traffic information), the number of newly connected terminals, the number of terminals for each QoS (Quality of Service), and the usage rate or traffic volume of a CPU (Central Processing Unit). In the following explanation, traffic information will be used as an example of the lower-level device load information. The lower-level device 10 is, for example, a DU (Distributed Unit) of a fifth-generation mobile communication system.

[0020] The transfer device 15 is connected to the lower device 10, the intermediate device 20, and the lower NW control device 40. The transfer device 15 has a switching function that changes the connection relationship between the lower device 10 and the intermediate device 20, and a transfer function that switches (switches) the communication path. The transfer function and the switching function of the transfer device 15 may be realized by separate devices. The transfer device 15 transfers signals along the communication path between the lower device 10 and the intermediate device 20. That is, the transfer device 15 transfers an upstream signal received from the lower device 10 to the destination intermediate device 20 along the communication path. The transfer device 15 also transfers a downstream signal received from the intermediate device 20 to the destination lower device 10 along the communication path. The transfer of signals along the communication path is performed under instructions from the lower NW control device 40.

[0021] The intermediate device 20 aggregates upstream signals received from subordinate lower devices 10 and forwards the aggregated signals to the upper device 30. The intermediate device 20 also receives downstream signals from the upper device 30, in which downstream data addressed to a terminal device is set, and forwards the received downstream signals to the lower device 10 connected to the destination terminal device. The intermediate device 20 transmits intermediate device load information to the upper NW control device 50 at a second timing. The second timing may be a predetermined timing or a timing requested by the upper NW control device 50. The intermediate device load information is information related to the load on the lower NW control device 40, and the specific content is the same as that of the lower device load information. The intermediate device 20 is, for example, a CU (Central Unit) of a fifth-generation mobile communication system.

[0022] The transfer device 25 is connected to the intermediate device 20, the upper device 30, and the upper NW control device 50. The transfer device 25 has a switching function that changes the connection relationship between the intermediate device 20 and the upper device 30, and a transfer function that switches (switches) the communication path. The transfer function and the switching function of the transfer device 25 may be realized by separate devices. The transfer device 25 transfers signals along the communication path between the intermediate device 20 and the upper device 30. That is, the transfer device 25 transfers upstream signals received from the intermediate device 20 to the destination upper device 30 along the communication path. The transfer device 25 also transfers downstream signals received from the upper device 30 to the destination intermediate device 20 along the communication path. The transfer of signals along the communication path is performed under instructions from the upper NW control device 50.

[0023] The upper device 30 processes an upstream signal received from a subordinate intermediate device 20 or forwards the upstream signal to another network. The upper device 30 also forwards a downstream signal received from another network to the destination intermediate device 20. The upper device 30 is, for example, a UPF (User Plane Function) in the 5G communication standard.

[0024] The downstream NW control device 40 is a control device that controls communication paths and inter-device connections in a downstream network (first network). The downstream network is a network that connects the downstream devices 10 and the intermediate device 20. As shown in FIG. 1 , the downstream network is equipped with one or more forwarding devices 15. The downstream NW control device 40 uses load information obtained from each downstream device 10 to predict the traffic volume of some or all communication links (hereinafter simply referred to as "links" or "flows") in the communication path between the downstream device 10 and the intermediate device 20. The downstream NW control device 40 determines congestion in the intermediate device 20 based on the predicted traffic volume for each link.

[0025] When congestion is predicted to occur in any link, the downstream NW control device 40 determines to perform path switching for load balancing. The downstream NW control device 40 instructs the transfer device 15 to switch the communication path (path switching) so that at least a part of the traffic transmitted through the link predicted to be congested is transmitted through a link predicted not to be congested (for example, a link with a lower link utilization rate).

[0026] Furthermore, when the lower NW control device 40 issues a switching instruction to the transfer device 15, it notifies the upper NW control device 50 of device-to-device connection information including at least information about the communication path of the switched lower network. Here, the information about the communication path of the switched lower network includes at least information indicating the intermediate device 20 to be the switching destination (hereinafter referred to as the "switching destination intermediate device") and information indicating the lower device 10 whose device-to-device connection is to be switched so as to connect to the switching destination intermediate device (hereinafter referred to as the "switching target lower device"). Note that the device-to-device connection information notified by the lower NW control device 40 may include not only information about the communication path of the switched lower network but also all information about the communication path of the lower network. The term "all information about the communication path of the lower network" means that it includes information about the communication path of the switched lower network as well as information about the connection relationship between the lower device 10 and the intermediate device 20 that has not been switched. The lower NW control device 40 is one aspect of a first control device.

[0027] The upper NW control device 50 is a control device that controls communication paths and inter-device connections in an upper network (second network). The upper network is a network that connects the intermediate devices 20 and the upper device 30. As shown in FIG. 1 , the upper network is equipped with one or more forwarding devices 25. The upper NW control device 50 uses load information obtained from each intermediate device 20 and inter-device connection information notified by the lower NW control device 40 to predict the traffic volume of some or all links in the communication paths between the intermediate devices 20 and the upper device 30.

[0028] If the upper NW control device 50 does not receive inter-device connection information from the lower NW control device 40, the upper NW control device 50 uses the load information received from each intermediate device 20 to predict the traffic volume of some or all of the links in the communication path between the intermediate device 20 and the upper device 30. The upper NW control device 50 determines congestion in the upper device 30 based on the predicted traffic volume for each link.

[0029] When congestion is predicted to occur in any link, the upper NW control device 50 determines to perform path switching for load balancing. The upper NW control device 50 instructs the transfer device 25 to switch the communication path (path switching) so that at least a part of the traffic transmitted through the link predicted to be congested is transmitted through a link predicted not to be congested (for example, a link with a lower link utilization rate). The upper NW control device 50 is one aspect of the second control device.

[0030] Furthermore, when the upper NW control device 50 issues a switching instruction to the transfer device 25, it notifies the lower NW control device 40 of device-to-device connection information including at least information about the communication path of the upper network for which switching has been performed. Here, the information about the communication path of the upper network for which switching has been performed includes at least information indicating the upper device 30 to which switching is to be performed (hereinafter referred to as the "switching destination upper device") and information indicating the intermediate device 20 whose device-to-device connection is to be switched so as to connect to the switching destination upper device (hereinafter referred to as the "switching target intermediate device"). Note that the device-to-device connection information notified by the upper NW control device 50 may include not only information about the communication path of the upper network for which switching has been performed, but also all information about the communication path of the upper network. The term "all information about the communication path of the upper network" means that it includes information about the communication path of the upper network for which switching has been performed, as well as information indicating the connection relationship between the upper device 30 and the intermediate device 20 for which switching has not been performed.

[0031] Next, a description will be given of specific configurations of the lower NW control device 40 and the upper NW control device 50. First, the configuration of the lower NW control device 40 will be described.

[0032] [Configuration of Lower NW Control Device 40] Lower NW control device 40 includes a collection unit 41, a switching determination unit 42, and a switching instruction unit 43. Collection unit 41 collects lower device load information from each lower device 10. Collection unit 41 saves the collected lower device load information in a lower device management table (not shown). The lower device management table is a table in which information about lower devices 10 is registered. In the lower device management table, traffic information for each lower device 10 is associated with information indicating the intermediate device 20 to which it is connected, as shown in FIG. 2 .

[0033] The lower device management table has multiple records in which information about the lower devices 10 is registered. Each record registers the values ​​of the lower device ID, traffic information, and connected intermediate device. The lower device ID is identification information for identifying the lower device 10. The traffic information is lower device load information obtained from each lower device 10. The connected intermediate device is information indicating the intermediate device 20 to which each lower device 10 is connected.

[0034] The switching determination unit 42 predicts the traffic volume for each link based on the lower-level device load information of each lower-level device 10 collected by the collection unit 41. Then, the switching determination unit 42 determines congestion in each intermediate device 20 based on the predicted traffic volume for each link. If congestion is predicted to occur, the switching determination unit 42 determines that switching of the lower-level network is necessary. If congestion is not predicted to occur, the switching determination unit 42 determines that switching of the lower-level network is not necessary.

[0035] When it is determined that switching of the lower network is necessary, the switching determination unit 42 searches for intermediate devices 20 that are candidates for switching destination. The intermediate devices 20 that are candidates for switching destination are intermediate devices 20 that will not experience congestion even after switching of the communication path. When there are intermediate devices 20 that are candidates for switching destination, the switching determination unit 42 determines one intermediate device 20 as the switching destination intermediate device. For example, when there is one intermediate device 20 that is a candidate for switching destination, the switching determination unit 42 determines that one intermediate device 20 is the switching destination intermediate device. For example, when there are multiple intermediate devices 20 that are candidates for switching destination, the switching determination unit 42 determines one intermediate device 20 from among the multiple intermediate devices as the switching destination intermediate device.

[0036] A method for selecting one intermediate device 20 from among a plurality of devices may be based on, for example, available bandwidth information of the intermediate device 20, the distance to the lower device 10, or the CPU usage rate of the intermediate device 20. By selecting the intermediate device 20 that is closest to the lower device 10 as the switching destination intermediate device, it is possible to reduce delays in the optical path. By selecting the intermediate device 20 with the lowest CPU usage rate as the switching destination intermediate device, it is possible to reduce delays in the hardware resources.

[0037] The switching determination unit 42 notifies the switching instruction unit 43 of information indicating the determined switching destination intermediate device and information indicating the switching target lower device. Furthermore, the switching determination unit 42 refers to the lower device management table and updates the information of the "connection destination intermediate device" of the lower device 10 whose connection destination is to be changed to information indicating the switching destination intermediate device. The switching determination unit 42 notifies the upper NW control device 50 of the inter-device connection information including the information indicating the determined switching destination intermediate device and information indicating the switching target lower device.

[0038] The switching instruction unit 43 transmits to the transfer device 15 a switching instruction including information indicating the switching destination intermediate device notified by the switching determination unit 42 and information indicating the switching target lower device.

[0039] [Configuration of Upper NW Control Device 50] Upper NW control device 50 includes a collection unit 51, an information reflection unit 52, a switching determination unit 53, and a switching instruction unit 54. Collection unit 51 collects intermediate device load information from each intermediate device 20. Furthermore, collection unit 51 collects inter-device connection information notified from lower NW control device 40. Collection unit 51 associates the collected inter-device connection information with time information at which the inter-device connection information was received, and outputs the information reflection unit 52 and the switching determination unit 53.

[0040] Furthermore, collection unit 51 stores the collected intermediate device load information in an intermediate device management table (not shown). The intermediate device management table is a table in which information related to intermediate devices 20 is registered. In the intermediate device management table, traffic information for each intermediate device 20 is associated with information indicating the connected higher-level device 30, as shown in FIG.

[0041] The intermediate device management table has multiple records in which information about intermediate devices 20 is registered. Each record registers values ​​for an intermediate device ID, traffic information, and connected higher-level device. The intermediate device ID is identification information for identifying the intermediate device 20. The traffic information is intermediate device load information obtained from each intermediate device 20. The connected higher-level device is information indicating the higher-level device 30 to which each intermediate device 20 is connected.

[0042] The information reflecting unit 52 notifies the inter-device connection information collected by the collecting unit 51 to the switching determining unit 53. This enables switching determination that reflects the control of the lower network in real time.

[0043] Switching determination unit 53 predicts the traffic volume for each link based on the intermediate device load information of each intermediate device 20 collected by collection unit 51 and the inter-device connection information notified by information reflection unit 52. Then, switching determination unit 53 determines congestion in each upper level device 30 based on the predicted results of the traffic volume for each link. If congestion is predicted to occur, switching determination unit 53 determines that switching of the upper level network is necessary. If congestion is not predicted to occur, switching determination unit 53 determines that switching of the upper level network is not necessary.

[0044] When the switching determination unit 53 determines that switching of the upper network is necessary, it searches for a higher-level device 30 that is a switching destination candidate. The higher-level device 30 that is a switching destination candidate is a higher-level device 30 that will not experience congestion even after switching of the communication path. When there are higher-level devices 30 that are switching destination candidates, the switching determination unit 53 determines one higher-level device 30 as the switching destination higher-level device. For example, when there is one higher-level device 30 that is a switching destination candidate, the switching determination unit 53 determines the one higher-level device 30 as the switching destination higher-level device. For example, when there are multiple higher-level devices 30 that are switching destination candidates, the switching determination unit 53 determines one higher-level device 30 from the multiple higher-level devices 30 as the switching destination higher-level device.

[0045] A method for selecting one host device 30 from among a plurality of devices may be based on, for example, available bandwidth information of the host device 30, the distance from the intermediate device 20, or the CPU usage rate of the host device 30. By selecting the host device 30 that is closest to the intermediate device 20 as the switching destination host device, it is possible to reduce delays in the optical path. By selecting the host device 30 with the lowest CPU usage rate as the switching destination host device, it is possible to reduce delays in the hardware resources.

[0046] Switching determination unit 53 notifies switching instruction unit 54 of information indicating the determined switching destination higher-level device and information indicating intermediate device 20 (hereinafter referred to as "switching target intermediate device") whose inter-device connection is to be switched so as to connect to the switching destination higher-level device. Furthermore, switching determination unit 53 refers to the intermediate device management table and updates the information of "connection destination higher-level device" of intermediate device 20 whose connection destination is to be changed to information indicating the switching destination higher-level device.

[0047] The switching instruction unit 54 transmits to the transfer device 25 a switching instruction including information indicating the switching destination higher-level device notified by the switching determination unit 53 and information indicating the switching target intermediate device.

[0048] [Operation of communication system 100] Fig. 4 is a sequence diagram showing the flow of processing performed by the communication system 100 in the first embodiment. Note that Fig. 4 shows a configuration in which, as an example of processing performed by the communication system 100, the upper NW control device 50 performs processing after the lower NW control device 40 completes processing, but the lower NW control device 40 and the upper NW control device 50 may operate independently.

[0049] Collector 41 of lower NW control device 40 collects lower device load information from each lower device 10 (step S101). Collector 41 outputs the collected lower device load information of each lower device 10 to switching determiner 42. Based on the lower device load information of each lower device 10 output from collector 41, switching determiner 42 determines whether congestion has occurred in any of intermediate devices 20 (step S102).

[0050] Specifically, first, switching determination unit 42 estimates the traffic volume of each intermediate device 20 based on the lower device load information of each lower device 10. In the example shown in FIG. 1 , flows transmitted from lower devices 10-1 and 10-2 arrive at intermediate device 20-1. Therefore, switching determination unit 42 estimates the traffic volume of intermediate device 20-1 based on the lower device load information of each of lower devices 10-1 and 10-2. Similarly, flows transmitted from lower device 10-3 arrive at intermediate device 20-2. Therefore, switching determination unit 42 estimates the traffic volume of intermediate device 20-2 based on the lower device load information of lower device 10-3. For example, switching determination unit 42 predicts the future traffic volume of intermediate device 20-2 based on the lower device load information of lower device 10-3.

[0051] The switching determination unit 42 compares the estimated traffic volume of each intermediate device 20 with a switching threshold. The switching threshold is a threshold used to determine whether congestion has occurred, which requires switching of the communication path (route switching). For example, the link rate is used as the switching threshold. The link rate is the maximum communication speed of a link. If there is an intermediate device 20 whose traffic volume is equal to or greater than the switching threshold (if there is an intermediate device 20 where congestion will occur in the future), the switching determination unit 42 determines that congestion has occurred in the intermediate device 20 whose traffic volume has become equal to or greater than the switching threshold. On the other hand, if there is no intermediate device 20 whose traffic volume is equal to or greater than the switching threshold (if there is no intermediate device 20 where congestion will occur in the future), the switching determination unit 42 determines that congestion has not occurred.

[0052] If the switching determination unit 42 determines that congestion has not occurred (step S102-NO), the lower-level NW control device 40 ends the processing in Fig. 4. Note that even if congestion has not occurred in the lower-level NW control device 40, the upper-level NW control device 50 performs processing individually, and therefore, the processing from step S106 onwards is executed.

[0053] On the other hand, if the switching determination unit 42 determines that congestion has occurred (step S102—YES), the switching determination unit 42 searches for intermediate devices 20 that are candidates for the switching destination (step S103). The switching determination unit 42 determines whether or not intermediate devices 20 that are candidates for the switching destination exist (step S104). If the switching determination unit 42 determines that intermediate devices 20 that are candidates for the switching destination do not exist (step S104—NO), the lower-level NW control device 40 ends the processing in FIG. 4. Note that even if there are no intermediate devices 20 that are candidates for the switching destination in the lower-level NW control device 40, the upper-level NW control device 50 performs individual processing, and therefore, the processing from step S106 onwards is executed.

[0054] On the other hand, if switching determination unit 42 determines that intermediate device 20 that is a switching destination candidate exists (step S104—YES), switching determination unit 42 determines the existing intermediate device 20 that is a switching destination candidate as the switching destination intermediate device. Switching determination unit 42 notifies switching instruction unit 43 of information indicating the determined switching destination intermediate device and information indicating the switching target lower-level device.

[0055] The switching instruction unit 43 transmits a switching instruction to the transfer device 15, the switching instruction including information indicating the switching destination intermediate device notified by the switching determination unit 42 and information indicating the switching target lower device (step S105). As a result, the transfer device 15 switches the communication path and inter-device connection for the intermediate device 20 where congestion is occurring. Furthermore, in the processing of step S105, the switching determination unit 42 notifies the upper NW control device 50 of the inter-device connection information including information indicating the determined switching destination intermediate device and the switching target lower device (step S105).

[0056] Collection unit 51 of upper NW control device 50 collects intermediate device load information from each intermediate device 20. Furthermore, collection unit 51 collects inter-device connection information when inter-device connection information is notified from lower NW control device 40 (step S106). Collection unit 51 outputs the collected intermediate device load information of each intermediate device 20 to switching determination unit 53, and outputs the collected inter-device connection information to information reflection unit 52.

[0057] 4 at the same time, it is possible that the switching decision has not been made in the lower NW control device 40 at the time of collection by the collection unit 51. In this case, the collection unit 51 collects only the intermediate device load information transmitted from each intermediate device 20.

[0058] Switching determination unit 53 performs congestion determination processing based on at least the intermediate device load information of each intermediate device 20 output from collection unit 51 (step S107). The congestion determination processing is processing for determining whether congestion has occurred. Details of the congestion determination processing will be described later. Note that, when inter-device connection information is obtained from information reflection unit 52, switching determination unit 53 performs congestion determination processing based on the inter-device connection information and the intermediate device load information of each intermediate device 20.

[0059] Here, it is assumed that the switching determination unit 53 determines that congestion has occurred. In this case, the switching determination unit 53 searches for a host device 30 that is a candidate for the switching destination (step S108). The switching determination unit 53 determines whether or not a host device 30 that is a candidate for the switching destination exists (step S109). If the switching determination unit 53 determines that a host device 30 that is a candidate for the switching destination does not exist (step S109-NO), the host NW control device 50 ends the processing in FIG. 4.

[0060] On the other hand, if the switching determination unit 53 determines that there is a higher-level device 30 that is a switching destination candidate (step S109—YES), the switching determination unit 53 determines the existing higher-level device 30 that is a switching destination candidate as the switching destination higher-level device. The switching determination unit 53 notifies the switching instruction unit 54 of information indicating the determined switching destination higher-level device and information indicating the switching target intermediate device.

[0061] The switching instruction unit 54 transmits a switching instruction including information indicating the switching destination higher-level device notified by the switching determination unit 53 and information indicating the switching target intermediate device to the transfer device 25 (step S110). As a result, the transfer device 25 switches the communication path and inter-device connection for the higher-level device 30 where congestion is occurring. Furthermore, in the processing of step S110, the switching determination unit 53 may notify the downstream NW control device 40 of inter-device connection information including information indicating the determined switching destination higher-level device and information indicating the switching target intermediate device.

[0062] 5 is a flowchart showing the flow of congestion determination processing performed by communication system 100 in the first embodiment. Switching determination unit 53 estimates the traffic volume of each upper-level device 30 based on at least the intermediate device load information of each intermediate device 20 (step S201). In the example shown in FIG. 1, intermediate device 20-1 has established communication with upper-level device 30-1, and intermediate device 20-2 has established communication with upper-level device 30-2. Therefore, switching determination unit 53 estimates the traffic volume of upper-level device 30-1 based on the intermediate device load information obtained from intermediate device 20-1. Similarly, switching determination unit 53 estimates the traffic volume of upper-level device 30-2 based on the intermediate device load information obtained from intermediate device 20-2.

[0063] The switching determination unit 53 compares the estimated traffic volume of each host device 30 with the switching threshold. The switching determination unit 53 determines whether congestion has occurred (step S202). Specifically, if there is a host device 30 whose traffic volume is equal to or greater than the switching threshold, the switching determination unit 53 determines that congestion has occurred in the host device 30 whose traffic volume is equal to or greater than the switching threshold. On the other hand, if there is no host device 30 whose traffic volume is equal to or greater than the switching threshold, the switching determination unit 53 determines that congestion has not occurred.

[0064] If the switching determination unit 53 determines that congestion has occurred (step S202-YES), the switching determination unit 53 determines that switching of the upper network is necessary (step S203). Then, the switching determination unit 53 ends the congestion determination process. On the other hand, if the switching determination unit 53 determines that congestion has not occurred (step S202-NO), the switching determination unit 53 determines that switching of the upper network is not necessary (step S204). Then, the switching determination unit 53 ends the congestion determination process.

[0065] According to the communication system 100 configured as described above, the lower NW control device 40 and the upper NW control device 50 each independently perform switching control of the networks they individually manage. This eliminates the need for a central control device that manages the entire network including the lower NW control device 40 and the upper NW control device 50, as in the past. This makes it possible to suppress switching of communication paths and inter-device connections that would occur by going through the central control device. Therefore, real-time congestion control becomes possible in the communication system 100 that includes multiple control devices (the lower NW control device 40 and the upper NW control device 50).

[0066] Furthermore, in the communication system 100, when a switch in the communication path and inter-device connections occurs in the lower network managed by the lower NW control device 40, the upper NW control device 50 is notified of inter-device connection information including information about the communication path of the switched lower network. This allows the upper NW control device 50 to determine whether or not a switch in the communication path and inter-device connections in the upper network is necessary (whether or not congestion has occurred) taking into account the switch made in the lower network. This makes it possible to realize a switch that reflects the control of the lower network in real time. Furthermore, it is possible to suppress unnecessary switch in the upper network.

[0067] Second Embodiment Because the communication environment changes every moment, it is possible that the connection status of the lower network will be updated after a switching decision is made in a higher-level NW control device. Since the higher-level NW control device makes a switching decision in a state before the connection status of the lower network is updated, when the connection status of the lower network is updated, it is necessary to perform switching control of the higher-level network in accordance with the updated connection status of the lower network. Therefore, in the second embodiment, a configuration will be described in which, after a switching decision is made in the higher-level NW control device, it is determined whether inter-device connection information has been received from the lower-level NW control device, and switching control in the higher-level NW control device is performed in accordance with the determination result.

[0068] 6 is a diagram showing an example of the configuration of a communication system 100a in the second embodiment. The communication system 100a is, for example, a fifth-generation mobile communication system (5G). The communication system 100a includes a lower-level device 10, a transfer device 15, an intermediate device 20, a transfer device 25, a higher-level device 30, a lower-level NW control device 40, and a higher-level NW control device 50a. The communication system 100a differs in configuration from the communication system 100 in that the higher-level NW control device 50a is included instead of the higher-level NW control device 50. The other configurations of the communication system 100a are the same as those of the communication system 100. The following description will focus on the differences from the communication system 100.

[0069] The upper NW control device 50a has a different timing for switching the communication path and the inter-device connection from the upper NW control device 50. Other operations of the upper NW control device 50a are the same as those of the upper NW control device 50. For example, after determining to switch the communication path and the inter-device connection, the upper NW control device 50a determines whether or not inter-device connection information has been received from the lower NW control device 40, and switches the communication path and the inter-device connection according to the determination result.

[0070] [Configuration of Upper NW Control Device 50a] Upper NW control device 50a includes a collection unit 51, an information reflection unit 52a, a switching determination unit 53a, and a switching instruction unit 54a. Information reflection unit 52a notifies switching determination unit 53a of inter-device connection information collected by collection unit 51. Information reflection unit 52a also acquires inter-device connection information in the upper network notified by switching determination unit 53a. The inter-device connection information in the upper network is information indicating the connection relationship between devices between intermediate device 20 and upper device 30, and includes, for example, information indicating the switching-destination upper device determined by switching determination unit 53a and information indicating the switching-target intermediate device.

[0071] The information reflecting unit 52a finally determines whether or not switching of the communication path and inter-device connections in the upper network is necessary, based on the inter-device connection information in the lower network and the inter-device connection information in the upper network collected by the collecting unit 51. Specifically, when the information reflecting unit 52a obtains the inter-device connection information in the upper network from the switching determining unit 53a, the information reflecting unit 52a first checks whether or not new inter-device connection information in the lower network has been collected by the collecting unit 51.

[0072] The information reflecting unit 52a determines to switch the communication paths and inter-device connections in the upper network based on the inter-device connection information in the upper network when the inter-device connection information in the lower network has not been newly collected by the collecting unit 51. On the other hand, when the inter-device connection information in the lower network has been newly collected by the collecting unit 51, the information reflecting unit 52a compares the reception time of the inter-device connection information in the upper network with the transmission time of the inter-device connection information in the lower network.

[0073] If the time difference between the reception time of the device-to-device connection information in the upper network and the transmission time of the device-to-device connection information in the lower network is within a predetermined range, the information reflecting unit 52a determines that switching in the lower network will be prioritized and that switching in the upper network will not be performed. The predetermined range is preferably a time period during which it can be considered that the congestion determinations in the lower network and the congestion determinations in the upper network are performed at the same time, such as 1 millisecond.

[0074] When the time difference between the reception time of the device-to-device connection information in the upper network and the transmission time of the device-to-device connection information in the lower network is within a predetermined range, it is highly likely that the congestion determinations in the lower network and the upper network are performed at the same time. In this case, it is expected that the congestion in the upper network will be alleviated by switching the connection status in the lower network.

[0075] Therefore, if the time difference is within a predetermined range, the upper NW control device 50 temporarily waits before switching the communication path and the inter-device connections. If the congestion in the upper network has not improved even after the temporary wait, the communication path and the inter-device connections in the upper network may be switched based on the inter-device connection information in the upper network.

[0076] If the time difference is not within the predetermined range, the information reflecting unit 52a determines to switch the communication path and inter-device connections in the upper network based on the inter-device connection information in the upper network.

[0077] The switching determination unit 53a performs the same processing as the switching determination unit 53. However, when the switching determination unit 53a determines that switching of the communication path and the inter-device connections is necessary, it does not output information indicating the determined switching destination higher-level device or information indicating the switching target intermediate device to the switching instruction unit 54. When the switching determination unit 53a determines that switching of the communication path and the inter-device connections is necessary, it notifies the information reflection unit 52a of inter-device connection information including information indicating the determined switching destination higher-level device and information indicating the switching target intermediate device. In this way, even when the switching determination unit 53a determines that switching of the communication path and the inter-device connections is necessary, it does not instruct switching.

[0078] Furthermore, when the switching determination unit 53a switches the communication path and the device-to-device connection, it refers to the intermediate device management table and updates the information on the "connected higher-level device" of the intermediate device 20 whose connection destination is being changed to information indicating the switching destination higher-level device.

[0079] The switching instruction unit 54a transmits to the transfer device 25 a switching instruction including information indicating the switching destination higher-level device notified by the information reflection unit 52a and information indicating the switching target intermediate device.

[0080] The processing of the communication system 100a in the second embodiment will be described using Figures 7 to 9. For simplicity of explanation, the lower-level NW control device 40 and the upper-level NW control device 50a are omitted from Figures 7 to 9. It is also assumed that the upper limit of each link in the lower-level network and the upper-level network is 10G. Before proceeding with the explanation using Figures 7 to 9, it is assumed that the following flows 1 to 3 in the explanation shown in Figure 6 have been performed.

[0081] Flow 1 (4G): Lower device 10-1 → Intermediate device 20-1 → Upper device 30-1 Flow 2 (4G): Lower device 10-2 → Intermediate device 20-1 → Upper device 30-1 Flow 3 (2G): Lower device 10-3 → Intermediate device 20-2 → Upper device 30-2

[0082] Under the above circumstances, it is assumed that congestion will occur in both intermediate device 20-1 and upper device 30-1 when flow 2 increases to 6G. That is, lower NW control device 40 detects that congestion will occur in intermediate device 20-1, and upper NW control device 50a detects that congestion will occur in upper device 30-1.

[0083] Switching determination unit 42 of lower NW control device 40 avoids congestion of (the uplink of) intermediate device 20-1 in response to detecting the occurrence of congestion in intermediate device 20-1. For example, as shown in FIG. 7, switching determination unit 42 determines as the first candidate a switching method in which flow 2 passes through intermediate device 20-2 (and is transmitted to higher-level device 30-1 as in the past). That is, switching determination unit 42 determines intermediate device 20-2 as the connection destination of lower-level device 10-2.

[0084] Switching determination unit 53a of upper NW control device 50a avoids congestion of the link between upper device 30-1 and intermediate device 20-1 in response to detecting the occurrence of congestion in upper device 30-1. For example, as shown in FIG. 8, switching determination unit 53a determines the first candidate switching method for receiving flow 2 coming from intermediate device 20-1 at upper device 30-2. In other words, switching determination unit 53a determines upper device 30-2 as the connection destination of intermediate device 20-1.

[0085] If the lower NW control device 40 and the upper NW control device 50a each independently switch the communication path and the inter-device connection, flow 2 transmitted from the lower device 10-2 cannot be transmitted. Specifically, the lower NW control device 40 instructs the transfer device 15 to switch so that flow 2 passes from the lower device 10-2 to the intermediate device 20-2 in the lower network. Then, the upper NW control device 50a instructs the transfer device 25 to switch so that flow 2 passes from the intermediate device 20-1 to the upper device 30-2 in the upper network. In this case, flow 2 is not forwarded beyond the intermediate device 20-2. As a result, flow 2 cannot be transmitted.

[0086] Therefore, after determining whether to switch the upper network, the upper NW control device 50a checks whether inter-device connection information has been received from the lower NW control device 40 before switching the communication path and inter-device connections of the upper network. If the inter-device connection information has been received from the lower NW control device 40 within a predetermined period, the upper NW control device 50a does not switch the upper network. In this way, when switching the upper network and the lower network is performed, the upper NW control device 50a prioritizes switching the lower network depending on the timing.

[0087] As a result, in the lower network, flow 2 is switched so that it passes through lower device 10-2 → intermediate device 20-2, as shown in FIG. 9 . As a result, the line on the side of intermediate device 20-1 connecting to higher-level device 30-1 becomes 4G, and the line on the side of intermediate device 20-2 connecting to higher-level device 30-1 becomes 6G, thereby avoiding congestion in intermediate device 20. Traffic (e.g., "4G" and "6G") transmitted from intermediate devices 20-1 and 20-2, respectively, is forwarded to higher-level device 30-1. As a result, congestion continues in higher-level device 30-1. Therefore, in such a case, higher-level NW control device 50a switches flow 2 (which had been passing through higher-level device 30-1) to a communication path that passes through higher-level device 30-2. As a result, flow 2 is controlled so that it is forwarded from lower-level device 10-2 → intermediate device 20-2 → higher-level device 30-2. As a result, congestion can be avoided.

[0088] [Operation of communication system 100a] Fig. 10 is a sequence diagram showing the flow of processing performed by communication system 100a in the second embodiment. In Fig. 10, the same processes as those in Fig. 4 are denoted by the same reference numerals as in Fig. 4, and the description thereof will be omitted.

[0089] In the process of step S109, if the switching determination unit 53a determines that there is a higher-level device 30 that is a switching destination candidate (step S109-YES), the switching determination unit 53a determines the existing higher-level device 30 that is a switching destination candidate as the switching destination higher-level device (step S201). The switching determination unit 53a notifies the information reflection unit 52a of inter-device connection information including information indicating the determined switching destination higher-level device and information indicating the switching target intermediate device as inter-device connection information in the higher-level network.

[0090] The information reflecting unit 52a acquires the inter-device connection information in the upper network notified by the switching determining unit 53a. The information reflecting unit 52a executes a switching determination process based on the acquired inter-device connection information in the upper network (step S202). The switching determination process is a process for determining whether or not switching of the communication path and inter-device connections in the upper network is necessary. The switching determination process will be described in detail later.

[0091] 11 is a flowchart showing the flow of switching determination processing performed by the communication system 100a in the second embodiment. The information reflecting unit 52a acquires device-to-device connection information in the upper network as the determination result of the switching determining unit 53a (step S301). The information reflecting unit 52a determines whether device-to-device connection information has been received from the lower NW control device 40 (step S302). If the collecting unit 51 has collected the device-to-device connection information transmitted from the lower NW control device 40, the information reflecting unit 52a determines that the device-to-device connection information has been received from the lower NW control device 40. On the other hand, if the collecting unit 51 has not collected the device-to-device connection information transmitted from the lower NW control device 40, the information reflecting unit 52a determines that the device-to-device connection information has not been received from the lower NW control device 40.

[0092] If the information reflecting unit 52a determines that the inter-device connection information has been received from the downstream NW control device 40 (step S302—YES), the information reflecting unit 52a calculates the time difference between the transmission time of the inter-device connection information collected from the downstream NW control device 40 and the reception time of the inter-device connection information obtained from the switching determining unit 53a. Here, the reception time of the inter-device connection information obtained from the switching determining unit 53a is the time when the information reflecting unit 52a acquired the inter-device connection information from the switching determining unit 53a. The information reflecting unit 52a determines whether the calculated time difference is within a predetermined range (step S303).

[0093] If the information reflecting unit 52a determines that the calculated time difference is within a predetermined range (step S303—YES), the information reflecting unit 52a determines that switching of the upper network is not necessary (step S304), and then ends the switching determination process.

[0094] If the information reflection unit 52a determines in step S302 that device-to-device connection information has not been received from the lower NW control device 40 (step S302-NO), or if the information reflection unit 52a determines in step S303 that the calculated time difference is not within a specified range (step S303-NO), the information reflection unit 52a determines that switching of the upper network is necessary (step S305).

[0095] Thereafter, the information reflecting unit 52a outputs the inter-device connection information obtained from the switching determining unit 53a to the switching instructing unit 54a. The switching instructing unit 54a instructs the transfer device 25 to switch the communication path and the inter-device connections in the upper network by transmitting a switching instruction including information indicating the switching destination upper device and information indicating the switching target intermediate device, which are included in the inter-device connection information output from the information reflecting unit 52 (step S306). Note that the information reflecting unit 52a may notify the lower NW control device 40 of the inter-device connection information obtained from the switching determining unit 53a.

[0096] According to the communication system 100a of the second embodiment configured as above, it is possible to obtain the same effects as those of the first embodiment.

[0097] Furthermore, in the communication system 100a of the second embodiment, if the timing at which the conditions for switching the communication path and inter-device connections are satisfied in the upper NW control device 50a (the timing at which the traffic volume of any upper device 30 becomes equal to or greater than the switching threshold) is close to the timing at which the conditions for switching the communication path and inter-device connections are satisfied in the lower NW control device 40 (within a specified range), the upper NW control device 50a will not switch to the upper network at that timing.

[0098] The upper network accommodates multiple devices that exist in the lower network. Therefore, when the lower network is switched, the number of devices accommodated in each upper network device 30 of the upper network also changes. As a result, congestion in the upper network may be avoided simply by switching the lower network. Therefore, in the communication system 100a of the second embodiment, when the switching timing by the lower NW control device 40 and the switching timing by the upper NW control device 50a are close to each other, the upper NW control device 50a delays the execution of switching control for the upper network. Then, after the lower NW control device 40 switches the lower network, the upper NW control device 50a determines congestion by reflecting the control result in the lower network. This makes it possible to reduce unnecessary switching.

[0099] (Third Embodiment) In the first and second embodiments, the same switching threshold and the same logic were used for determining congestion in the lower network and the upper network. When the same switching threshold and the same logic are used, the number of patterns in which congestion is detected at close timing in the lower network control device and the upper network control device increases. As a result, the lower network control device and the upper network control device switch the communication paths and the inter-device connections at close timing. Furthermore, in the first and second embodiments, a configuration was described in which the lower network control device preferentially switches the communication paths and the inter-device connections.

[0100] In the third embodiment, a configuration will be described in which a lower NW control device and an upper NW control device switch communication paths and inter-device connections at different times. An upper network accommodates more devices than a lower network. Therefore, congestion is more likely to occur in the upper network than in the lower network. Therefore, in the third embodiment, congestion is prevented in advance by preferentially switching communication paths and inter-device connections before congestion occurs in the upper NW control device. The system configuration and the configuration of each device in the third embodiment are the same as those in the second embodiment. Therefore, each device in the second embodiment will be described as an example.

[0101] The third embodiment will be described in detail below. In the third embodiment, in order to switch the communication paths and the inter-device connections at different timings in the lower NW control device 40 and the upper NW control device 50a, switching priorities are set for each of the lower NW control device 40 and the upper NW control device 50a. The switching priority is information for specifying the timing for switching the communication paths and the inter-device connections. Note that the switching priority in the third embodiment differs from an actual switching threshold and is information that is set not for detecting the occurrence of congestion but for switching the communication paths and the inter-device connections in advance before congestion occurs.

[0102] The switching priority is defined in multiple stages. For example, the switching priority is defined in multiple states such as a safe zone (first state), a warning zone (second state), and a dangerous zone (third state). The switching priority decreases in the order of the safe zone, the warning zone, and the dangerous zone. That is, the safe zone has the highest switching priority, and the dangerous zone has the lowest switching priority. Criteria for determining the safe zone, the warning zone, and the dangerous zone may be determined for each resource.

[0103] For example, a safe zone may be defined as a zone where bandwidth or CPU utilization is less than 60%, a warning zone where bandwidth or CPU utilization is between 60% and 80%, and a danger zone where bandwidth or CPU utilization exceeds 80%. Furthermore, a safe zone may be defined as a zone where both the current traffic volume and the predicted traffic volume for the next few minutes are 80% or less, a warning zone may be defined as a zone where the current traffic volume is 80% or less but exceeds 80% in the predicted traffic volume for the next few minutes, and a danger zone may be defined as a zone where the current traffic volume is 80% or less but exceeds 80% in the predicted traffic volume for the next few minutes. Note that this is merely an example, and the criteria for determining the safe zone, warning zone, and danger zone may be determined as appropriate.

[0104] As described above, the safety zone is a state where the probability of congestion occurring is low. The warning zone is a state where the probability of congestion occurring is neither high nor low, but there is a risk of congestion occurring depending on the situation. The danger zone is a state where the probability of congestion occurring is very high or a state where congestion has occurred.

[0105] By setting the above-mentioned switching priority in each of the lower NW control device 40 and the upper NW control device 50a, it is possible to execute switching of the communication path and the inter-device connections at different timings. For example, by setting the switching priority to "danger zone" in the lower NW control device 40 and to "warning zone" in the upper NW control device 50a, it is possible to prioritize switching of the communication path and the inter-device connections of the upper network.

[0106] [Configuration of Lower NW Control Device 40] The lower NW control device 40 includes a collection unit 41, a switching determination unit 42, and a switching instruction unit 43. The lower NW control device 40 in the third embodiment differs from the lower NW control device 40 in the first and second embodiments in the processing of the switching determination unit 42.

[0107] The switching determination unit 42 determines that switching of the lower network is necessary when the load (for example, traffic volume, bandwidth usage rate, or CPU usage rate) of each intermediate device 20 obtained based on the lower device load information of each lower device 10 collected by the collection unit 41 reaches the range indicated by the switching priority set in the lower NW control device 40. In this case, the switching determination unit 42 searches for intermediate devices 20 that are switching destination candidates. The search for intermediate devices 20 that are switching destination candidates and the determination of the switching destination intermediate device have been explained in the first embodiment and will not be explained here.

[0108] The switching determination unit 42 notifies the switching instruction unit 43 of information indicating the determined switching destination intermediate device and information indicating the switching target lower device. Furthermore, the switching determination unit 42 refers to the lower device management table and updates the information of the "connection destination intermediate device" of the lower device 10 whose connection destination is to be changed to information indicating the switching destination intermediate device. The switching determination unit 42 notifies the upper NW control device 50a of the inter-device connection information including the information indicating the determined switching destination intermediate device and information indicating the switching target lower device.

[0109] As in the first embodiment, the switching determination unit 42 may determine congestion in each intermediate device 20 based on the predicted traffic volume for each link.

[0110] [Configuration of Upper NW Control Device 50a] The upper NW control device 50a includes a collection unit 51, an information reflection unit 52a, a switching determination unit 53a, and a switching instruction unit 54a. The upper NW control device 50a in the third embodiment differs from the upper NW control device 50a in the second embodiment in the processing of the switching determination unit 53a.

[0111] The switching determination unit 53a determines that switching of the upper network is necessary when the load (e.g., traffic volume, bandwidth usage rate, or CPU usage rate) of each upper device 30 obtained based on the intermediate device load information of each intermediate device 20 collected by the collection unit 51 reaches the range indicated by the switching priority set in the upper NW control device 50a. In this case, the switching determination unit 53a searches for upper devices 30 that are switching destination candidates. The search for upper devices 30 that are switching destination candidates and the determination of the switching destination upper device are similar to those in the first embodiment.

[0112] Switching determination unit 53a notifies information reflecting unit 52a of inter-device connection information including information indicating the determined switching destination higher-level device and information indicating the switching target intermediate device. Furthermore, when switching the communication path and inter-device connection, switching determination unit 53a refers to the intermediate device management table and updates the information of the "connection destination higher-level device" of intermediate device 20 whose connection destination is to be changed to information indicating the switching destination higher-level device.

[0113] The switching determination unit 53a may determine congestion in each higher-level device 30 based on the predicted traffic volume for each link, as in the first embodiment.

[0114] In the following explanation of the third embodiment, it is assumed that the switching priority for the lower NW control device 40 is set to "danger zone (utilization rate 80% or more)" and the switching priority for the upper NW control device 50a is set to "warning zone (utilization rate 60% to 80%)."

[0115] Next, the processing of the communication system 100a in the third embodiment will be described using Figures 12 and 13. For simplicity of explanation, the lower-level NW control device 40 and the upper-level NW control device 50a are omitted in Figures 12 and 13. It is also assumed that the upper limit of each link in the lower-level network and the upper-level network is 10G. In the explanation shown in Figure 12, it is assumed that the following flows 1 to 3 are flowing.

[0116] Flow 1 (3G): Lower device 10-1 → Intermediate device 20-1 → Upper device 30-1 Flow 2 (2G): Lower device 10-2 → Intermediate device 20-1 → Upper device 30-1 Flow 3 (2G): Lower device 10-3 → Intermediate device 20-2 → Upper device 30-2

[0117] In the above situation, the traffic in intermediate device 20-1 is 5G, and the traffic in intermediate device 20-2 is 2G. Also, the traffic in upper device 30-1 is 5G, and the traffic in upper device 30-2 is 2G. In this case, the congestion rate of intermediate device 20-1 is 50% (use of 5G for link 10G), and the congestion rate of intermediate device 20-2 is 20% (use of 2G for link 10G). Therefore, switching determination unit 42 of lower NW control device 40 determines that each intermediate device 20 is in the safe zone. Because the switching priority set in lower NW control device 40 is the "danger zone," switching determination unit 42 determines that switching of the lower network is not necessary.

[0118] Furthermore, the congestion rate of the upper device 30-1 is 50% (5G is being used for the 10G link), and the congestion rate of the upper device 30-2 is 20% (2G is being used for the 10G link). Therefore, the switching determination unit 53a of the upper NW control device 50a determines that each upper device 30 is in the safe zone. Since the switching priority set in the upper NW control device 50a is the "warning zone," the switching determination unit 53a determines that switching of the upper network is not necessary.

[0119] If the traffic of flow 2 increases by 1G to 3G, the traffic will be 6G at intermediate device 20-1 and 6G at upper device 30-1. In this case, the congestion rate of intermediate device 20-1 is 60% (5G used for a 10G link), which means that the congestion rate reaches the warning zone. As a result, switching determination unit 42 of lower NW control device 40 determines that intermediate device 20-1 is in the warning zone. Since the switching priority set in lower NW control device 40 is "danger zone," switching determination unit 42 determines that switching of the lower network is not necessary.

[0120] Furthermore, the congestion rate of the upper device 30-1 is 60% (use of 5G for a 10G link), which means that it has reached the warning zone. As a result, the switching determination unit 53a of the upper NW control device 50a determines that the upper device 30-1 is in the warning zone. Since the switching priority set in the upper NW control device 50a is "warning zone," the switching determination unit 53a determines that switching of the upper network is necessary.

[0121] As described above, the switching priority set in the downstream NW control device 40 is "dangerous area (utilization rate 80% or more)." Therefore, the switching determination unit 42 of the downstream NW control device 40 determines that it is not necessary to switch the communication paths and inter-device connections in the downstream network. As a result, the downstream NW control device 40 does not switch the communication paths and inter-device connections in the downstream network.

[0122] On the other hand, the switching priority set in the upper NW control device 50a is "warning zone (utilization rate 60% to 80%)." Therefore, the switching determination unit 53a of the upper NW control device 50a determines that switching of the communication path and inter-device connections in the upper network is necessary. In this case, the switching determination unit 53a of the upper NW control device 50a avoids congestion in the upper device 30-1, which has reached the "warning zone (utilization rate 60% to 80%)." For example, the switching determination unit 53a determines the upper device 30-2 as the switching destination upper device so that the upper device 30-2 handles flow 2 (a flow transmitted from the lower device 10-2) that had been forwarded to the upper device 30-1. In other words, the switching determination unit 53a determines the upper device 30-2 as the forwarding destination of some of the traffic of the intermediate device 20-1. As a result, the switching determination unit 53a switches the communication path and the inter-device connection so that flow 3 (flow sent from the lower device 10-3) coming from the intermediate device 20-2 is transferred to the higher device 30-2, as shown in Fig. 12. The processing after determining the switching destination higher device (for example, the final switching determination based on the time difference by the information reflection unit 52a) is the same as in the second embodiment.

[0123] As a result, in the upper network, a switch is made so that flow 2 passes through intermediate device 20-1 → upper device 30-2. The traffic of flow 1 (e.g., "3G") transmitted from intermediate device 20-1 is forwarded to upper device 30-1. The traffic of flow 2 (e.g., "3G") transmitted from intermediate device 20-2 and the traffic of flow 3 (e.g., "2G") transmitted from intermediate device 20-3 are forwarded to upper device 30-2. In this way, congestion can be avoided in advance in both upper devices 30-1 and 30-2.

[0124] As in the second embodiment, if the time difference between the reception time of the device-to-device connection information in the upper network and the transmission time of the device-to-device connection information in the lower network is within a predetermined range, the information reflection unit 52a will prioritize switching in the lower network and determine not to switch in the upper network.

[0125] According to the communication system 100a of the third embodiment configured as described above, switching priorities are set in the lower NW control device 40 and the upper NW control device 50a for switching communication paths and inter-device connections at different timings. This allows the lower NW control device 40 and the upper NW control device 50a to switch communication paths and inter-device connections in advance before congestion occurs. Therefore, real-time congestion control becomes possible in the communication system 100a including multiple control devices (lower NW control devices 40 and upper NW control devices 50a).

[0126] (Modification) As in the second embodiment, when the upper NW control device 50a in the third embodiment determines that switching of the communication path and the inter-device connection is necessary, the switching is performed based on whether or not inter-device connection information has been received from the lower NW control device 40. In contrast, when the upper NW control device 50a in the third embodiment determines that switching of the communication path and the inter-device connection is necessary, the switching of the communication path and the inter-device connection may be performed regardless of whether or not inter-device connection information has been received from the lower NW control device 40.

[0127] (Fourth Embodiment) In the first and second embodiments, the same switching threshold and the same logic were used for determining congestion in the lower network and the upper network. When the same switching threshold and the same logic are used, the number of patterns in which congestion is detected at close timing in the lower network control device and the upper network control device increases. As a result, the communication paths and inter-device connections are switched at close timing in the lower network control device and the upper network control device.

[0128] Furthermore, in the second embodiment, even when the upper network control device determines that switching of the communication path and the inter-device connections is necessary, priority is given to switching of the lower network. However, if an abnormal amount of traffic occurs in the upper network, it is desirable to immediately switch in the upper network. Therefore, in the fourth embodiment, if congestion in the lower network and congestion control in the upper network occur closely together, the operation of the upper network is switched depending on the degree of congestion to prevent congestion from occurring in advance. The system configuration and the configuration of each device in the fourth embodiment are the same as those in the second embodiment. Therefore, the devices in the second embodiment will be described as an example.

[0129] Details of the fourth embodiment will be described below. In the fourth embodiment, an operation according to an alert level is set for each of the lower NW control device 40 and the upper NW control device 50a. The lower NW control device 40 and the upper NW control device 50a perform operations according to the multiple alert levels that have been set. The alert level is information for defining the degree of congestion in each of the lower network and the upper network. The alert level may be defined in two stages, for example, a alert area (first alert level) and a danger area (second alert level). Note that the alert level may be defined in three or more stages. The danger area has a higher alert level than the alert area. In other words, the danger area means that the degree of congestion is higher (urgency is required) than the alert area.

[0130] An example of operation according to the alert level of each of the lower NW control device 40 and the upper NW control device 50a is shown in Fig. 15. As shown in Fig. 15, immediate switching is performed regardless of whether the lower network (lower NW in Fig. 15) reaches a alert zone or a danger zone. Therefore, when the load of any intermediate device 20 reaches either a alert zone or a danger zone, the lower NW control device 40 immediately switches the communication path and the inter-device connection.

[0131] On the other hand, as shown in Figure 15, in the upper network (upper NW in Figure 15), switching is delayed when the load reaches a warning zone, and is immediately switched when the load reaches a danger zone. Here, delaying switching means determining whether or not switching of the communication path and the inter-device connections is necessary based on the reception result of the inter-device connection information transmitted from the lower NW control device 40, as shown in the second embodiment. Therefore, the upper NW control device 50a delays switching when the load in any of the upper devices 30 reaches a warning zone, and switches as necessary. Furthermore, the upper NW control device 50a immediately switches the communication path and the inter-device connections when the load in any of the upper devices 30 reaches a danger zone.

[0132] In the following description of the fourth embodiment, as an example, a predicted traffic bandwidth of 100% to 150% is defined as a warning zone, and a predicted traffic bandwidth of more than 150% is defined as a danger zone. In other words, when the predicted traffic bandwidth of any of the higher-level devices 30 reaches the danger zone, the upper-level NW control device 50a immediately switches the communication path and the inter-device connection.

[0133] [Configuration of Lower NW Control Device 40] The lower NW control device 40 includes a collection unit 41, a switching determination unit 42, and a switching instruction unit 43. The lower NW control device 40 in the fourth embodiment differs from the lower NW control devices 40 in the first to third embodiments in the processing of the switching determination unit 42.

[0134] The switching determination unit 42 performs the same processing as the switching determination unit 42 in the first embodiment. When the switching determination unit 42 determines that switching of the lower network is necessary, it operates in accordance with the load of each intermediate device 20 (e.g., traffic volume, bandwidth usage rate, or CPU usage rate) obtained based on the lower device load information of each lower device 10 collected by the collection unit 41. For example, the switching determination unit 42 operates in accordance with the alert level reached by the load of each intermediate device 20. Since the lower NW control device 40 defines that immediate switching is to be performed regardless of the alert level, immediate switching of the lower network is performed. In this case, the switching determination unit 42 searches for intermediate devices 20 that are candidates for switching destination. The search for intermediate devices 20 that are candidates for switching destination and the determination of the switching destination intermediate device have been described in the first embodiment and are therefore omitted here.

[0135] The switching determination unit 42 notifies the switching instruction unit 43 of information indicating the determined switching destination intermediate device and information indicating the switching target lower device. Furthermore, the switching determination unit 42 refers to the lower device management table and updates the information of the "connection destination intermediate device" of the lower device 10 whose connection destination is to be changed to information indicating the switching destination intermediate device. The switching determination unit 42 notifies the upper NW control device 50a of the inter-device connection information including the information indicating the determined switching destination intermediate device and information indicating the switching target lower device.

[0136] [Configuration of Upper NW Control Device 50a] The upper NW control device 50a includes a collection unit 51, an information reflection unit 52a, a switching determination unit 53a, and a switching instruction unit 54a. The upper NW control device 50a in the fourth embodiment differs from the upper NW control device 50a in the second embodiment in the switching determination unit 53a and the processing of the switching determination unit 53a.

[0137] The switching determination unit 53a performs the same processing as the switching determination unit 53a in the second embodiment. When the switching determination unit 53a determines that switching of the communication path and the inter-device connection is necessary, the switching determination unit 53a notifies the information reflection unit 52a of inter-device connection information including information indicating the determined switching destination higher-level device, information indicating the switching target intermediate device, and information indicating the alert level of the higher-level device 30 in which congestion is occurring. In this way, the processing of the switching determination unit 53a differs from that of the switching determination unit 53a in the second embodiment in that the inter-device connection information includes information indicating the alert level of the higher-level device 30 in which congestion is expected to occur.

[0138] When the switching determination unit 53a determines that switching of the upper network is necessary, it determines the alert level of the upper device 30 where congestion is expected to occur, based on the load of each upper device 30 (e.g., traffic volume, bandwidth usage rate, CPU usage rate, etc.) obtained based on the intermediate device load information of each intermediate device 20 collected by the collection unit 51.

[0139] The information reflecting unit 52a performs the same processing as the information reflecting unit 52a in the second embodiment. Here, when the information reflecting unit 52a acquires the inter-device connection information in the upper network notified from the switching determining unit 53a, the information reflecting unit 52a performs an operation according to the alert level of the upper device 30 in which congestion is occurring, which is included in the acquired inter-device connection information in the upper network. Note that, since different operations are defined depending on the alert level in the upper NW control device 50a, the information reflecting unit 52a performs an operation according to the alert level that has been reached.

[0140] For example, if the alert level reached by any of the higher-level devices 30 is in the alert zone, the information reflecting unit 52a performs processing similar to that of the second embodiment. For example, if the alert level reached by any of the higher-level devices 30 is in the danger zone, the information reflecting unit 52a immediately switches the higher-level network. In this case, the information reflecting unit 52a outputs information indicating the switching destination higher-level device and information indicating the switching target intermediate device, which are included in the inter-device connection information in the higher-level network, to the switching instructing unit 54a. As a result, the information reflecting unit 52a immediately switches the communication paths and inter-device connections in the higher-level network.

[0141] Next, the processing of the communication system 100a in the fourth embodiment will be described using Figures 14 to 19. For simplicity of explanation, the lower-level NW control device 40 and the upper-level NW control device 50a are omitted from Figures 14 to 19. Furthermore, Figures 14 to 19 show an example in which there are six lower-level devices 10 and three intermediate devices 20. The upper limit of each link in the lower-level network and the upper-level network is 10G, and a predicted traffic bandwidth of 10G to 15G (100% to 150%) is considered a warning zone, and anything over 15G (150%) is considered a danger zone. In the explanations shown in Figures 14 to 19, it is assumed that the following flows 1 to 6 are flowing.

[0142] Flow 1 (2G): lower device 10-1 → intermediate device 20-1 → upper device 30-1 Flow 2 (1G): lower device 10-2 → intermediate device 20-1 → upper device 30-1 Flow 3 (1G): lower device 10-3 → intermediate device 20-2 → upper device 30-1 Flow 4 (2G): lower device 10-4 → intermediate device 20-2 → upper device 30-1 Flow 5 (1G): lower device 10-5 → intermediate device 20-3 → upper device 30-2 Flow 6 (1G): lower device 10-6 → intermediate device 20-3 → upper device 30-2

[0143] Under the above circumstances, the traffic in intermediate device 20-1 is 3G, the traffic in intermediate device 20-2 is 3G, and the traffic in intermediate device 20-3 is 2G. Furthermore, the traffic in upper device 30-1 is 6G, and the traffic in upper device 30-2 is 2G. In this case, the congestion rate of intermediate device 20-1 and 20-2 is 50% (use of 5G for link 10G), and the congestion rate of intermediate device 20-3 is 20% (use of 2G for link 10G), so congestion does not occur. Similarly, the congestion rate of upper device 30-1 is 60% (use of 6G for link 10G), and the congestion rate of upper device 30-2 is 20% (use of 2G for link 10G), so congestion does not occur. Therefore, congestion is not detected in either the lower network or the upper network.

[0144] However, assume a situation in which the traffic of flow 1 (flow transmitted from lower device 10-1) increases by a new 3G to 5G, the traffic of flow 3 (flow transmitted from lower device 10-3) increases by a new 3G to 4G, and the traffic of flow 4 (flow transmitted from lower device 10-4) increases by a new 4G to 6G. In this case, the traffic at intermediate device 20-1 becomes 6G, the traffic at intermediate device 20-2 becomes 10G, and the traffic at upper device 30-1 becomes 16G. Therefore, the predicted traffic bandwidth at intermediate device 20-2 becomes 10G (100%), and the predicted traffic bandwidth at upper device 30-1 becomes 16G (160%).

[0145] As a result, it is assumed that congestion will occur in both intermediate device 20-2 and upper device 30-1. In this case, lower-level NW control device 40 detects that congestion will occur in intermediate device 20-2, and upper-level NW control device 50a detects that congestion will occur in upper device 30-1. Here, the congestion rate of intermediate device 20-2 is 100% (use of 10G for the 10G link), which means that it has reached the warning zone, and the congestion rate of upper device 30-1 is 160% (use of 16G for the 10G link), which means that it has reached the danger zone.

[0146] In response to detecting the occurrence of congestion in intermediate device 20-2, switching determination unit 42 of lower NW control device 40 avoids congestion in intermediate device 20-2 (on its uplink). For example, as shown in FIG. 16, switching determination unit 42 determines as the first candidate a switching method in which flow 4 passes through intermediate device 20-3 (and is transmitted to higher-level device 30-1 as before). That is, switching determination unit 42 determines intermediate device 20-3 as the connection destination of lower-level device 10-4. Then, because the load on intermediate device 20-2 has reached the warning zone, switching determination unit 42 immediately switches the communication path and the inter-device connection.

[0147] In response to detecting the occurrence of congestion in the upper device 30-1, the switching determination unit 53a of the upper NW control device 50a avoids congestion in the links between the upper device 30-1 and the intermediate device 20-1 and between the upper device 30-1 and the intermediate device 20-2. For example, as shown in FIG. 17, the switching determination unit 53a determines the first candidate switching method for receiving flow 2 (flow transmitted from the lower device 10-2) coming from the intermediate device 20-1 at the upper device 30-2. That is, the switching determination unit 53a determines the upper device 30-2 as the forwarding destination of some of the traffic of the intermediate device 20-1. Then, because the load on the upper device 30-1 has reached a dangerous level, the upper NW control device 50a immediately switches the communication path and the inter-device connection.

[0148] 18 shows the result of switching the communication paths and inter-device connections in the lower network in the lower NW control device 40 and switching the communication paths and inter-device connections in the upper network in the upper NW control device 50a. When switching the communication paths and inter-device connections in the lower NW control device 40, the lower NW control device 40 notifies the upper NW control device 50a of inter-device connection information in the lower network. As a result, the upper NW control device 50a takes into account the inter-device connection information in the lower network and switches the connection relationship between the intermediate device 20-3 and the upper device 30-1 so that flow 4 transmitted from the lower device 10-4 reaches the upper device 30-1 via the intermediate device 20-3.

[0149] 18, due to switching in the lower network and upper network, the line between upper device 30-1 and intermediate device 20-1 becomes 5G, the line between upper device 30-1 and intermediate device 20-2 becomes 4G, and the line between upper device 30-1 and intermediate device 20-3 becomes 6G. This avoids congestion in the lower network. However, the traffic of upper device 30-1 is 15G, and congestion continues.

[0150] The upper NW control device 50a determines that flow 4 (flow transmitted from the lower device 10-4) coming from the intermediate device 20-3 should be received by the upper device 30-2. That is, the upper NW control device 50a determines the upper device 30-2 as the forwarding destination of part of the traffic of the intermediate device 20-3. As a result, the upper NW control device 50a switches the communication path and the inter-device connection so that flow 4 (flow transmitted from the lower device 10-4) coming from the intermediate device 20-3 is forwarded to the upper device 30-2, as shown in FIG. 19. Because the load on the upper device 30-1 has reached a dangerous level, the upper NW control device 50a immediately switches the communication path and the inter-device connection. This also makes it possible to avoid congestion in the upper device 30-1.

[0151] [Operation of communication system 100a] Fig. 20 is a flowchart showing the flow of switching determination processing performed by communication system 100a in the fourth embodiment. In Fig. 20, the same processes as those in Fig. 11 are assigned the same reference numerals as in Fig. 11, and descriptions thereof will be omitted.

[0152] In the process of step S303, if the information reflecting unit 52a determines that the calculated time difference is within a predetermined range (step S303—YES), the information reflecting unit 52a determines whether switching of the upper network is necessary (step S401). For example, the information reflecting unit 52a may make this determination based on information indicating the alert level included in the inter-device connection information notified by the switching determining unit 53a.

[0153] Specifically, the information reflecting unit 52a determines that switching of the upper network is necessary when the inter-device connection information includes information indicating that the alert level is "dangerous area." On the other hand, the information reflecting unit 52a determines that switching of the upper network is not necessary when the inter-device connection information does not include information indicating that the alert level is "dangerous area."

[0154] Here, the information reflecting unit 52a determines whether or not switching of the upper network is necessary depending on whether or not the inter-device connection information notified from the switching determining unit 53a includes information indicating that the alert level is “dangerous area.” In contrast, the information reflecting unit 52a may determine that switching of the upper network is necessary when the inter-device connection information includes information indicating immediate switching as an operation according to the alert level.

[0155] If the information reflecting unit 52a determines that switching of the upper network is not necessary (step S401-NO), the information reflecting unit 52a determines that switching of the upper network is not necessary (step S304), and then ends the switching determination process.

[0156] If the information reflecting unit 52a determines in step S302 that device-to-device connection information has not been received from the lower NW control device 40 (step S302-NO), if the information reflecting unit 52a determines in step S303 that the calculated time difference is not within a specified range (step S303-NO), or if the information reflecting unit 52a determines that switching of the upper network is not necessary (step S401-YES), the information reflecting unit 52a determines that switching of the upper network is necessary (step S402).

[0157] Thereafter, the information reflecting unit 52a outputs the inter-device connection information obtained from the switching determining unit 53a to the switching instructing unit 54a. The switching instructing unit 54a instructs the transfer device 25 to switch the communication path and the inter-device connections in the upper network by transmitting a switching instruction including information indicating the switching destination upper device and information indicating the switching target intermediate device, which are included in the inter-device connection information output from the information reflecting unit 52 (step S306). Note that the information reflecting unit 52a may notify the lower NW control device 40 of the inter-device connection information obtained from the switching determining unit 53a.

[0158] According to the communication system 100a of the fourth embodiment configured as above, it is possible to obtain the same effects as those of the second embodiment.

[0159] Furthermore, in the communication system 100a according to the fourth embodiment, operations are set for the lower NW control device 40 and the upper NW control device 50a according to the alert level. As a result, for example, in a situation where the upper NW control device 50a needs to immediately switch the communication path and the inter-device connection (for example, a situation where traffic flowing to the upper device 30 greatly exceeds the link upper limit), the communication path and the inter-device connection can be immediately switched. Then, the upper NW control device 50a switches the communication path and the inter-device connection as needed, taking into account the inter-device connection information notified from the lower NW control device 40. Therefore, real-time congestion control can be performed in the communication system 100a including multiple control devices (the lower NW control device 40 and the upper NW control device 50a).

[0160] Fifth Embodiment In the first to fourth embodiments, an example of upstream communication from a lower device to a higher device has been described. In actual communication, upstream communication and downstream communication are mixed. Therefore, in the fifth embodiment, a configuration will be described in which switching control is performed by determining whether to prioritize switching control for upstream communication or switching control for downstream communication.

[0161] FIG. 21 is a diagram illustrating an example of the configuration of a communication system 100b according to the fifth embodiment. The communication system 100b is, for example, a fifth-generation mobile communication system (5G). The communication system 100b includes a lower-level device 10, a transfer device 15, an intermediate device 20, a transfer device 25, an upper-level device 30, a lower-level NW control device 40b, and an upper-level NW control device 50b. In FIG. 21, the communication system 100b includes three lower-level devices 10-1 to 10-3, two intermediate devices 20-1 to 20-2, and two upper-level devices 30-1 to 30-2. However, the number of lower-level devices 10, intermediate devices 20, and upper-level devices 30 is not particularly limited. Furthermore, a plurality of transfer devices 15 and a plurality of transfer devices 25 may be included.

[0162] The lower-level NW control device 40b is a control device that controls communication paths and inter-device connections in the lower-level network. Specifically, the lower-level NW control device 40b controls communication paths and inter-device connections in the upstream section of the lower-level network, and communication paths and inter-device connections in the downstream section of the lower-level network. The lower-level NW control device 40b determines which control of the upstream section or the downstream section should be prioritized, using the amount of congestion or delay requirements in the lower-level network. The lower-level NW control device 40b notifies the upper-level NW control device 50b of priority information indicating the determined prioritized section and inter-device connection information including information about the communication paths in the lower-level network.

[0163] The upper NW control device 50b is a control device that controls communication paths and inter-device connections in the upper network. The upper NW control device 50b performs switching control based on priority information included in inter-device connection information obtained from the lower NW control device 40b and information on communication paths in the lower network.

[0164] Next, the specific configurations of the lower NW control device 40b and the upper NW control device 50b will be described. First, the configuration of the lower NW control device 40b will be described.

[0165] [Configuration of the downstream NW control device 40b] The downstream NW control device 40b includes an upstream section switching determination unit 44b, a downstream section switching determination unit 45b, and an upstream / downstream switching determination unit 46b. The upstream section switching determination unit 44b collects downstream device load information for the upstream section in the downstream network from each downstream device 10, and determines whether switching of the communication path for the upstream section and the inter-device connection is necessary. The upstream section switching determination unit 44b includes a collection unit 41b, a switching determination unit 42b, and a switching instruction unit 43b.

[0166] The collection unit 41b collects lower-level device load information for the upstream section from each lower-level device 10. The collection unit 41b stores the collected lower-level device load information for the upstream section in a lower-level device management table (not shown). The switching determination unit 42b predicts the traffic volume for each link based on the lower-level device load information for the upstream section of each lower-level device 10 collected by the collection unit 41b. The switching determination unit 42b then determines congestion in the upstream section of each intermediate device 20 based on the predicted traffic volume for each link. If congestion is predicted to occur in the upstream section, the switching determination unit 42b determines that switching of the lower-level network in the upstream section is necessary. If congestion is not predicted to occur in the upstream section, the switching determination unit 42b determines that switching of the lower-level network in the upstream section is not necessary.

[0167] When the switching determination unit 42b determines that switching of the lower network in the uplink section is necessary, it searches for intermediate devices 20 that are candidates for switching destinations in the uplink section. The search for intermediate devices 20 that are candidates for switching destinations and the determination of the switching destination intermediate device have been described in the first embodiment, so a description thereof will be omitted. Furthermore, the switching determination unit 42b determines the priority of switching for the uplink section based on the amount of congestion or delay requirements. The priority in the fifth embodiment is determined by 5QI (5G Quality of Service Identifier) ​​or the required delay of an application. The switching determination unit 42b notifies the uplink / downlink switching determination unit 46b of inter-device connection information for the uplink section, including information indicating the determined switching destination intermediate device, information indicating the switching target lower device, and information indicating the priority.

[0168] The downstream section switching determination unit 45b collects downstream section load information of the downstream section in the downstream network from each downstream device 10, and determines whether or not switching of the communication path and inter-device connection of the downstream section is necessary. The downstream section switching determination unit 45b includes a collection unit 47b, a switching determination unit 48b, and a switching instruction unit 49.

[0169] The collection unit 47b collects downstream section lower device load information from each lower device 10. The collection unit 47b stores the collected downstream section lower device load information in a lower device management table (not shown). The switching determination unit 48b predicts the traffic volume for each link based on the downstream section lower device load information for each lower device 10 collected by the collection unit 47b. The switching determination unit 48b then determines congestion in the downstream section of each intermediate device 20 based on the predicted results of the traffic volume for each link. If congestion is predicted to occur in the upstream section, the switching determination unit 48b determines that switching of the downstream section of the lower network is necessary. If congestion is not predicted to occur in the downstream section, the switching determination unit 48b determines that switching of the lower network in the downstream section is not necessary.

[0170] When the switching determination unit 48b determines that switching of the lower network in the downlink section is necessary, it searches for intermediate devices 20 that are candidate switching destinations for the downlink section. The search for intermediate devices 20 that are candidate switching destinations and the determination of the switching destination intermediate device have been explained in the first embodiment, so a description thereof will be omitted. Furthermore, the switching determination unit 48b determines the priority of switching for the downlink section based on the amount of congestion or delay requirements. The switching determination unit 48b notifies the uplink / downlink switching determination unit 46b of inter-device connection information for the downlink section, including information indicating the determined switching destination intermediate device, information indicating the switching target lower device, and information indicating the priority.

[0171] The switching instruction unit 49 transmits to the transfer device 15 a switching instruction including information indicating the switching destination intermediate device notified by the switching determination unit 48b and information indicating the switching target lower device.

[0172] The uplink / downlink switching determination unit 46b determines whether to prioritize control of the uplink section or the downlink section based on the inter-device connection information for the uplink section output from the uplink section switching determination unit 44b and the inter-device connection information for the downlink section output from the downlink section switching determination unit 45b. The uplink / downlink switching determination unit 46b determines, for example, the section with the highest priority included in the inter-device connection information as the priority section. Note that if the priorities are the same, the uplink / downlink switching determination unit 46b determines the downlink section as the priority section.

[0173] On the other hand, when the uplink / downlink switching determination unit 46b acquires inter-device connection information only from either the uplink segment switching determination unit 44b or the downlink segment switching determination unit 45b, it determines the segment corresponding to the acquired inter-device connection information as the priority segment. The uplink / downlink switching determination unit 46b includes information indicating the determined priority segment in the inter-device connection information corresponding to the priority segment and transmits the information to the upper NW control device 50b. The uplink / downlink switching determination unit 46b also causes the uplink segment switching determination unit 44b or the downlink segment switching determination unit 45b corresponding to the priority segment to perform route switching.

[0174] [Configuration of Upper NW control device 50b] Upper NW control device 50b includes a collection unit 51b, a switching determination unit 53b, and a switching instruction unit 54. Collection unit 51b collects intermediate device load information from each intermediate device 20. Furthermore, collection unit 51b collects inter-device connection information notified from lower NW control device 40b. Collection unit 51b associates the collected inter-device connection information with time information at which the inter-device connection information was received, and outputs the information to switching determination unit 53b. Furthermore, collection unit 51b saves the collected intermediate device load information in an intermediate device management table (not shown).

[0175] Switching determination unit 53b predicts the traffic volume for each link based on the intermediate device load information and device-to-device connection information of each intermediate device 20 collected by collection unit 51b. For example, switching determination unit 53b predicts the traffic volume for each link when switching is performed to a path specified by information indicating the switching destination intermediate device and information indicating the switching target lower device, which are included in the device-to-device connection information.

[0176] The switching determination unit 53b determines congestion in each upper level device 30 based on the predicted traffic volume for each link. If congestion is predicted to occur, the switching determination unit 53b determines that switching of the upper level network is necessary. If congestion is not predicted to occur, the switching determination unit 53b determines that switching of the upper level network is not necessary.

[0177] When the switching determination unit 53b determines that switching of the upper network is necessary, it searches for a candidate upper device 30. The search for a candidate upper device 30 and the determination of the upper device 30 are explained in the first embodiment, and therefore will not be explained here.

[0178] Switching determination unit 53b notifies switching instruction unit 54 of information indicating the determined switching destination higher-level device and information indicating the switching target intermediate device. Furthermore, switching determination unit 53b refers to the intermediate device management table and updates the information of the "connection destination higher-level device" of intermediate device 20 whose connection destination is to be changed to information indicating the switching destination higher-level device.

[0179] [Operation of the downstream NW control device 40b] Fig. 22 is a flowchart showing the flow of the switching determination process performed by the downstream NW control device 40b in the fifth embodiment. In Fig. 22, the process of the uplink / downlink switching determination unit 46b will be mainly explained.

[0180] The uplink / downlink switching determination unit 46b collects inter-device connection information from either or both of the uplink segment switching determination unit 44b and the downlink segment switching determination unit 45b (step S501). The uplink / downlink switching determination unit 46b determines whether it has received inter-device connection information from each of the uplink segment switching determination unit 44b and the downlink segment switching determination unit 45b (step S502). If the uplink / downlink switching determination unit 46b determines that it has received inter-device connection information from only one of the uplink segment switching determination unit 44b and the downlink segment switching determination unit 45b (step S502-NO), the uplink / downlink switching determination unit 46b executes switching based on the acquired inter-device connection information (step S503).

[0181] For example, when the uplink / downlink switching determiner 46b receives inter-device connection information from the uplink segment switching determiner 44b, it instructs the uplink segment switching determiner 44b to switch the communication path and the inter-device connection. The switching instruction unit 43 of the uplink segment switching determiner 44b switches the communication path and the inter-device connection in the lower network based on the inter-device connection information obtained from the switching determiner 42b. Thereafter, the uplink / downlink switching determiner 46b includes information indicating the determined priority segment in the inter-device connection information corresponding to the priority segment and transmits the information to the upper NW control device 50b.

[0182] On the other hand, if the uplink / downlink switching determination unit 46b determines that it has received inter-device connection information from both the uplink segment switching determination unit 44b and the downlink segment switching determination unit 45b (step S502—YES), the uplink / downlink switching determination unit 46b calculates the time difference between the reception time of the inter-device connection information for the uplink segment received from the uplink segment switching determination unit 44b and the reception time of the inter-device connection information for the downlink segment received from the downlink segment switching determination unit 45b. The uplink / downlink switching determination unit 46b determines whether the calculated time difference is within a predetermined range (step S504).

[0183] If the uplink / downlink switching determination unit 46b determines that the calculated time difference is not within a predetermined range (step S504—NO), the uplink / downlink switching determination unit 46b executes switching based on the acquired inter-device connection information (step S503). On the other hand, if the uplink / downlink switching determination unit 46b determines that the calculated time difference is within a predetermined range (step S504—YES), the uplink / downlink switching determination unit 46b determines whether the priority of the uplink section is higher than the priority of the downlink section (step S506). That is, the uplink / downlink switching determination unit 46b determines whether the condition of uplink priority > downlink priority is met.

[0184] If the uplink / downlink switching determination unit 46b determines that the priority of the uplink section is higher than the priority of the downlink section (step S506—YES), the uplink / downlink switching determination unit 46b instructs the uplink section switching determination unit 44b to switch the communication path and the inter-device connection. The switching instruction unit 43 of the uplink section switching determination unit 44b switches the communication path and the inter-device connection in the lower network based on the inter-device connection information obtained from the switching determination unit 42b (step S507). Thereafter, the uplink / downlink switching determination unit 46b includes information indicating the determined priority section in the inter-device connection information corresponding to the priority section and transmits this information to the upper NW control device 50b (step S504).

[0185] If the uplink / downlink switching determination unit 46b determines that the priority of the uplink section is not higher than the priority of the downlink section (step S506—NO), the uplink / downlink switching determination unit 46b instructs the downlink section switching determination unit 45b to switch the communication path and the inter-device connections. The switching instruction unit 49 of the downlink section switching determination unit 45b switches the communication path and the inter-device connections in the lower network based on the inter-device connection information obtained from the switching determination unit 48b (step S508). Thereafter, the uplink / downlink switching determination unit 46b includes information indicating the determined priority section in the inter-device connection information corresponding to the priority section and transmits this information to the upper NW control device 50b (step S504).

[0186] The communication system 100b configured as described above can achieve the same effects as those of the first embodiment. Furthermore, the communication system 100b can prioritize control of the section with the highest priority even when congestion occurs in both the uplink section and the downlink section. Therefore, the communication system 100b including multiple control devices (the lower NW control device 40b and the upper NW control device 50b) can perform real-time congestion control.

[0187] (Sixth embodiment) In the sixth embodiment, a configuration is described in which a switching preparation period is set in the upper NW control device for upstream traffic, and if the lower NW control device does not switch the communication path and inter-device connections in the lower network during the switching preparation period, the upper NW control device switches the communication path and inter-device connections in the upper network in advance.

[0188] FIG. 23 is a diagram illustrating a configuration example of a communication system 100c according to the sixth embodiment. The communication system 100c is, for example, a fifth-generation mobile communication system (5G). The communication system 100c includes a lower-level device 10, a transfer device 15, an intermediate device 20, a transfer device 25, an upper-level device 30, a lower-level NW control device 40c, and an upper-level NW control device 50c. In FIG. 23, the communication system 100c includes three lower-level devices 10-1 to 10-3, two intermediate devices 20-1 to 20-2, and two upper-level devices 30-1 to 30-2. However, the number of lower-level devices 10, intermediate devices 20, and upper-level devices 30 is not particularly limited. Furthermore, a plurality of transfer devices 15 and a plurality of transfer devices 25 may be included.

[0189] The lower NW control device 40c performs the same processing as the lower NW control device 40 in the first embodiment. Furthermore, the lower NW control device 40c operates according to status information indicating the status of the upper NW control device 50c, which is included in the inter-device connection information acquired from the upper NW control device 50c. The status information indicating the status of the upper NW control device 50c represents the status related to switching of the upper NW control device 50c to the upper network. For example, the status information indicating the status of the upper NW control device 50c includes any of no switching, preparing to switch, and switched.

[0190] "No switching" indicates that the upper NW control device 50c has no plans to switch the upper network. "Preparing to switch" indicates that the upper NW control device 50c has plans to switch the upper network and is in a state of preparation for switching. "Switching" indicates that the upper NW control device 50c has switched the upper network.

[0191] The lower NW control device 40c can grasp the state of the upper network by acquiring state information indicating the state of the upper NW control device 50c.

[0192] The upper NW control device 50c performs the same processing as the upper NW control device 50a in the second embodiment. Furthermore, the upper NW control device 50c transmits inter-device connection information including status information indicating the status of the upper NW control device 50c to the lower NW control device 40c. The upper NW control device 50c waits for a predetermined preparation period from the time when the upper NW control device 50c transmits the inter-device connection information to the lower NW control device 40c. If the communication path and inter-device connections in the lower network have not been switched in the lower NW control device 40c after the preparation period has elapsed, the upper NW control device 50c switches the upper network.

[0193] [Configuration of Lower NW Control Device 40c] The lower NW control device 40c includes a collection unit 41c, a switching determination unit 42c, and a switching instruction unit 43. The collection unit 41c collects lower device load information from each lower device 10. Furthermore, the collection unit 41c collects inter-device connection information transmitted from the upper NW control device 50c.

[0194] The switching determination unit 42c performs the same processing as the switching determination unit 42 in the first embodiment. Furthermore, the switching determination unit 42c acquires the inter-device connection information collected by the collection unit 41c. The switching determination unit 42c switches the communication path and the inter-device connection in the lower network as necessary based on the status information included in the inter-device connection information.

[0195] [Configuration of Upper-Level NW Control Device 50c] The upper-level NW control device 50c includes a collection unit 51, an information reflection unit 52c, a switching determination unit 53a, and a switching instruction unit 54a. The information reflection unit 52c performs the same processing as the information reflection unit 52a in the second embodiment. Furthermore, the information reflection unit 52c acquires the predicted traffic volume and link rate used when the switching determination unit 53a made a congestion determination. The information reflection unit 52c determines the current state of the upper-level NW control device 50c based on the acquired predicted traffic volume and link rate. Specifically, the information reflection unit 52c determines whether the current state of the upper-level NW control device 50c is no switching, switching preparation, or switching based on the following conditions:

[0196] Without switching: traffic volume < link rate x 0.8 Switching preparation: link rate x 0.8 < traffic volume < link rate switching: traffic volume > link rate

[0197] The information reflecting unit 52c includes state information indicating the determined current state of the upper NW control device 50c in the inter-device connection information in the form of "state." The information reflecting unit 52c notifies the lower NW control device 40c of the inter-device connection information including the state information. Note that, when the current state of the upper NW control device 50c is "preparing for switching," the information reflecting unit 52c waits for a preparation period based on the timing of transmitting the inter-device connection information.

[0198] If the information reflecting unit 52c obtains inter-device connection information from the lower NW control device 40c during the preparation period, the information reflecting unit 52c determines whether or not switching of the communication path and the inter-device connection is necessary in accordance with the obtained inter-device connection information. On the other hand, if the information reflecting unit 52c does not obtain inter-device connection information from the lower NW control device 40c during the preparation period, the information reflecting unit 52c performs switching of the upper network in accordance with the inter-device connection information obtained from the switching determining unit 53a. The fact that inter-device connection information has not been obtained from the lower NW control device 40c means that switching of the communication path and the inter-device connection has not been performed in the lower NW control device 40.

[0199] In the communication system 100c configured as described above, the upper NW control device 50c notifies the lower NW control device 40c of its own state. Then, if the lower NW control device 40c has not performed switching, the upper NW control device 50c switches the communication paths and inter-device connections in the upper network first. This makes it possible to perform switching to avoid congestion in the upper network without switching the communication paths and inter-device connections in the lower network.

[0200] Some of the functional units of the lower NW control devices 40, 40b, and 40c and the upper NW control devices 50, 50a, 50b, and 50c in the above-described embodiment may be implemented by a computer. In this case, a program for implementing this function may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be read into a computer system and executed. Note that the term "computer system" here includes hardware such as an OS (Operating System) and peripheral devices.

[0201] 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 realize some of the aforementioned functions, or may be capable of realizing the aforementioned functions in combination with programs already stored in the computer system, or may be realized using programmable logic devices such as FPGAs (Field Programmable Gate Arrays).

[0202] 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.

[0203] The present invention can be applied to a communication system having a plurality of control devices that manage different networks.

[0204] 10, 10-1 to 10-3... lower devices, 15, 25... transfer devices, 20, 20-1 to 20-2... intermediate devices, 30, 30-1 to 30-2... upper devices, 40, 40b, 40c... lower NW control devices, 50, 50a, 50b... upper NW control devices, 41, 41b, 41c, 47b, 51, 51b... collection units, 42, 42b, 42c, 48b, 53, 53a, 53b... switching determination units, 43, 54, 54a... switching instruction units, 44b... upstream section switching determination units, 45b... downstream section switching determination units, 46b... upstream / downstream switching determination units, 52, 52a, 52c... information reflection units, 100, 100a, 100b, 100c... communication systems

Claims

1. A communication system comprising a first control device that manages a first network and a second control device that manages a second network that is a higher-level network than the first network, wherein the first control device performs switching control of communication paths and inter-device connections in the first network that connects a plurality of lower-level devices and a plurality of intermediate devices, and notifies the second control device of inter-device connection information indicating the switching control results, and the second control device performs switching control of communication paths and inter-device connections in the second network that connects the plurality of intermediate devices and a plurality of higher-level devices, based on load information obtained from each of the plurality of intermediate devices and the inter-device connection information notified from the first control device.

2. The communication system of claim 1, wherein the second control device comprises: an information reflection unit that acquires the inter-device connection information notified from the first control device; and a switching determination unit that determines whether or not switching of the communication path and inter-device connection in the second network is necessary, taking into account the inter-device connection information acquired by the information reflection unit.

3. The communication system of claim 2, wherein the switching determination unit, when determining that switching of the communication path and inter-device connections in the second network is necessary, notifies the information reflection unit of information indicating that switching is necessary, and the information reflection unit further decides not to switch the communication path and inter-device connections in the second network if the timing at which the notification from the switching determination unit is obtained and the timing at which the inter-device connection information notified from the first control device is transmitted are within a predetermined range.

4. The communication system described in claim 3, wherein the information reflection unit decides to switch the communication path and inter-device connection in the second network if the timing at which the notification is received from the switching determination unit and the timing at which the inter-device connection information notified from the first control device is transmitted are not within a predetermined range.

5. A communication system as claimed in any one of claims 1 to 4, wherein the first control device and the second control device are set with one of the states as a switching priority defined by multiple stages of states for specifying the timing for executing switching of the communication path and inter-device connections, the first control device determines that switching of the communication path and inter-device connections in the first network is necessary when the load of any of the plurality of intermediate devices reaches the set state, and the second control device determines that switching of the communication path and inter-device connections in the second network is necessary when the load of any of the plurality of upper devices reaches the set state.

6. A communication system as claimed in any one of claims 1 to 4, wherein the first control device and the second control device are set with operations to be performed for at least a first alert level and a second alert level that requires more urgency than the first alert level, the first control device switches the communication paths and inter-device connections in the first network when the load of any of the plurality of intermediate devices reaches the first alert level or the second alert level, and the second control device performs operations based on the results of the first control device's switching of the communication paths and inter-device connections in the first network when the load of any of the plurality of upper level devices reaches the first alert level, and switches the communication paths and inter-device connections in the first network when the second alert level is reached.

7. A control device that manages a second network that is a higher-level network than a first network, which acquires inter-device connection information indicating the results of switching control of communication paths and inter-device connections in the first network that connects multiple lower-level devices and multiple intermediate devices from another control device that manages the first network, and performs switching control of communication paths and inter-device connections in the second network that connects the multiple intermediate devices and multiple higher-level devices based on load information obtained from each of the multiple intermediate devices and the inter-device connection information acquired from the other control device.

8. A control method performed by a communication system comprising a first control device that manages a first network and a second control device that manages a second network that is a higher-level network than the first network, wherein the first control device performs switching control of communication paths and inter-device connections in the first network that connects multiple lower-level devices and multiple intermediate devices, and notifies the second control device of inter-device connection information indicating the switching control results, and the second control device performs switching control of communication paths and inter-device connections in the second network that connects the multiple intermediate devices and multiple higher-level devices, based on load information obtained from each of the multiple intermediate devices and the inter-device connection information notified from the first control device.

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