Switching control device and switching method

Abstract

A switching control device comprising: a switching timing determination unit for acquiring period information including information pertaining to a plurality of free periods in which data transmission is not performed for at least first data and second data that are transmitted at different intervals within a specific cycle, and determining, on the basis of the acquired period information, a free period that satisfies a switching condition; and a switching instruction unit that instructs an optical switching device to perform route switching between optical signal transmission sections so that a route is switched within the free period determined by the switching timing determination unit.　

Description

Switching control device and switching method

[0001] The present invention relates to a switching control device and a switching method.

[0002] Conventionally, a system that takes packet loss into consideration has been proposed, as shown in Fig. 9 (see, for example, Non-Patent Document 1). In the system shown in Fig. 9, for example, image data is transmitted from image transmitter #1 to destination image processing device #1 or image processing device #2. At a certain time, when a wireless communication device is connected to communication device #1 via a switching device, the image data transmitted from image transmitter #1 is transferred to image processing device #1 via the wireless communication device and the switching device.

[0003] Image processing device #1 transmits load information indicating the load amount of image processing device #1 to the switching control device. The switching control device grasps the load amount of image processing device #1 based on the load information transmitted from image processing device #1. When the load amount of image processing device #1 exceeds a threshold, the switching control device determines that the image processing device #1 is overloaded, and transmits a switching instruction to the switching device to connect the wireless communication device and communication device #2. As a result, data transmitted from image transmitter #1 is transferred to image processing device #2, which is not overloaded.

[0004] In such a system, if the switching device is an optical switching device that switches the route of an optical path, such as an optical switch, the optical switching device, unlike electrical switching, does not perform buffering. Therefore, image data transmitted to the switching device will be lost from the time the switching device starts to the time the switching device completes. In other words, packet loss occurs when the switching device switches.

[0005] In particular, when the transmitted data is video, short-term packet loss significantly impairs subjective quality. In the case of a single stream, transmission is performed at a fixed cycle, such as 30 fps, so there is a fixed time interval (33.33 ms at 30 fps) between the transmission of an image at time t and the transmission of an image at time t+1. Therefore, frame loss can be avoided by switching immediately after observing the arrival of a group of packets constituting the image at communication device #1. In this way, if the switching device can switch at the image transmission interval, switching can be performed without affecting the video. As described above, this can be achieved because the image transmission interval is known if the transmission is "fixed" at "one flow" like a single stream.

[0006] Mitsuteru Watanabe, Takashi Akama, Yoshitaka Shibata, "Packet Audio-Video System Considering Packet Loss", Information Processing Society of Japan Research Report, Multimedia Communication and Distributed Processing Research Report, 1995-01-26, pp,31-36

[0007] However, in an actual system, it is also assumed that video flows are transmitted from multiple image transmitters. For example, in the diagram shown in Figure 10, it is also assumed that at the same time that image transmitter #1 is transmitting a video flow, image transmitter #2 is also transmitting a different video flow. In this case where video flows transmitted at different cycles are mixed, as shown in Figure 10, if switching is performed immediately after the arrival of a group of packets constituting an image transmitted from image transmitter #1, the timing may overlap with the transmission from image transmitter #2, resulting in frame loss and significant degradation of the video quality. As such, in the past, when multiple video flows transmitted at different cycles are mixed, there was a problem of packet loss occurring due to path switching.

[0008] In view of the above circumstances, an object of the present invention is to provide a technique that can reduce packet loss due to route switching when multiple video flows transmitted at different cycles are mixed together.

[0009] One aspect of the present invention is a switching control device that includes a switching timing determination unit that acquires period information including information on multiple vacant periods during which at least first data and second data are not transmitted at different intervals within a specific cycle, and determines a vacant period that satisfies a switching condition based on the acquired period information, and a switching instruction unit that instructs an optical switching device that switches the path of a transmission section of an optical signal to switch the path within the vacant period determined by the switching timing determination unit.

[0010] One aspect of the present invention is a switching method that acquires period information including information on multiple vacant periods during which at least first data and second data are not transmitted at different intervals within a specific cycle, determines a vacant period that satisfies a switching condition based on the acquired period information, and instructs an optical switching device that switches the path of a transmission section of an optical signal to switch the path within the determined vacant period.

[0011] According to the present invention, it is possible to reduce packet loss due to route switching when multiple video flows transmitted at different cycles are mixed together.

[0012] FIG. 1 is a diagram showing an example of the configuration of a communication system in a first embodiment. FIG. 2 is a diagram showing information related to a plurality of image data transmitted from each image transmitter. FIG. 3 is a diagram showing an example of the configuration of a vacant period table in the first embodiment. FIG. 4 is a flowchart showing the flow of processing performed by a switching control device in the first embodiment. FIG. 5 is a diagram showing an example of the configuration of a communication system in a second embodiment. FIG. 6 is a diagram showing an example of the vacant period table in the second embodiment. FIG. 7 is a diagram showing vacant period information when a plurality of video streams with different frame rates are transmitted in environments with different effective throughputs such as different modulation degrees. FIG. 8 is a diagram showing vacant period information when a plurality of video streams with different frame rates are transmitted. FIG. 9 is a diagram showing an example of the configuration of a conventional system. FIG. 10 is a diagram for explaining conventional problems.

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0014] 1 is a diagram showing an example of the configuration of a communication system 100 according to the first embodiment. The communication system 100 includes an image transmitter 10, a relay device 20, an optical transceiver 30, an optical switching device 40, an image processing device 50, a network device 55, a display device 60, and a switching control device 70.

[0015] 1 shows a configuration in which a communication system 100 includes two image transmitters 10-1 and 10-2, three optical transceivers 30-1 to 30-3, and two image processing devices 50-1 and 50-2. Note that the numbers of the image transmitters 10, relay devices 20, optical transceivers 30, optical switching devices 40, image processing devices 50, network devices 55, and display devices 60 included in the communication system 100 are not particularly limited.

[0016] The image transmitters 10-1 to 10-2 are connected wirelessly to the relay device 20. Control lines that transmit electrical signals are connected between the relay device 20 and the optical transceiver 30-1, between the relay device 20 and the switching control device 70, between the optical transceiver 30-2 and the image processing device 50-1, between the optical transceiver 30-3 and the image processing device 50-2, between the image processing devices 50-1 to 50-2 and the network device 55, and between the network device 55 and the display device 60. The optical transceivers 30-1 to 30-3 and the optical switching device 40 are connected by optical transmission paths. The optical transmission paths are, for example, optical fibers.

[0017] The image transmitter 10 has a function for capturing video. The image transmitter 10 wirelessly transmits a plurality of image data constituting the captured video to the relay device 20. In this embodiment, the image transmitter 10-1 and the image transmitter 10-2 wirelessly transmit image data having different frame rates to the relay device 20. For example, the image transmitter 10-1 transmits a plurality of image data constituting a video captured at a first frame rate (e.g., 30 frames per second (fps)), and the image transmitter 10-2 transmits a plurality of image data constituting a video captured at a second frame rate (e.g., 24 frames per second (fps)). Therefore, within a certain cycle (e.g., a one-second cycle), the plurality of image data transmitted from the image transmitter 10-1 and the plurality of image data transmitted from the image transmitter 10-2 are transmitted at different times. The image transmitter 10 is, for example, a camera-equipped drone.

[0018] The relay device 20 receives image data transmitted at predetermined intervals (frame rate intervals) from each image transmitter 10. The relay device 20 transfers the received image data to the optical transceiver 30-1 in order. There are no particular limitations on the wireless system used for wireless communication between the relay device 20 and each image transmitter 10.

[0019] Furthermore, the relay device 20 identifies vacant periods during which no data is being transmitted based on image data transmitted from each image transmitter 10 at predetermined intervals (frame rate intervals) within a specific cycle (for example, one-second cycles). As described above, the image transmitters 10-1 and 10-2 transmit image data at different intervals because they have different frame rates. However, the image transmitter 10-1 transmits image data at fixed intervals based on the frame rate, and the image transmitter 10-2 also transmits image data at fixed intervals based on the frame rate.

[0020] The relay device 20 can identify multiple vacant periods during which no data transmission is taking place by observing multiple image data acquired from each image transmitter 10 within a specific period. The relay device 20 notifies the switching control device 70 of period information indicating the identified multiple vacant periods for each period. The period information notified by the relay device 20 includes, for each vacant period, vacant period information indicating the start time of the vacant period and the length of the vacant period.

[0021] The optical transceiver 30 transmits and receives image data to and from other devices. The optical transceiver 30-1, for example, receives image data for each image transmitter 10 transferred from the relay device 20. The optical transceiver 30-1 generates an optical signal including the received image data for each image transmitter 10 and transmits the generated optical transmission signal to the optical switching device 40. The optical transceiver 30-2, for example, receives the optical signal transmitted from the optical transceiver 30-1 via the optical switching device 40. The optical transceiver 30-2 converts the received optical signal into image data in an electrical signal and transmits it to the image processing device 50-1. The optical transceiver 30-3, for example, receives the optical signal transmitted from the optical transceiver 30-1 via the optical switching device 40. The optical transceiver 30-3 converts the received optical signal into image data in an electrical signal and transmits it to the image processing device 50-2.

[0022] The optical switching device 40 switches the connection between the optical transceivers 30 based on the switching timing instructed by the switching control device 70. The optical switching device 40 switches the connection destination of, for example, the optical transceiver 30-1 to either the optical transceiver 30-2 or the optical transceiver 30-3 at the switching timing instructed by the switching control device 70. The optical switching device 40 is, for example, an optical switch. Note that the optical switching device 40 is not limited to an optical switch, and may be any device that can switch the path of the transmission section of the optical signal (for example, between the optical transceivers 30).

[0023] The image processing device 50 performs image processing on the image data captured by the image transmitter 10. There are no particular limitations on the image processing performed by the image processing device 50. For example, the image processing device 50 may perform image processing so as to highlight a part of the image.

[0024] The image processing device 50-1, for example, acquires image data captured by the image transmitter 10 via the relay device 20, the optical transceiver 30-1, the optical switching device 40, and the optical transceiver 30-2. The image processing device 50-1 performs image processing on the acquired image data and transmits the processed image data to the display device 60 via the network device 55. The image processing device 50-2, for example, acquires image data captured by the image transmitter 10 via the relay device 20, the optical transceiver 30-1, the optical switching device 40, and the optical transceiver 30-3. The image processing device 50-3 performs image processing on the acquired image data and transmits the processed image data to the display device 60 via the network device 55.

[0025] Furthermore, the image processing device 50 determines whether or not to send a switching request to the switching control device 70 based on the total processing volume within the device itself. The switching request is a signal requesting that the optical switching device 40 switch the connection path. By sending a switching request from the image processing device 50 to the switching control device 70, the switching control device 70 can switch the connection path of the optical switching device 40.

[0026] When a transmission condition for a switching request is satisfied, the image processing device 50 may transmit a switching request to the switching control device 70. The transmission condition for a switching request is a condition for transmitting a switching request, and may be, for example, when the image processing device 50 is in an overload state (for example, the total processing amount > the threshold), when continuing image processing in the image processing device 50 would result in a large increase in delay (for example, the predicted result of the total processing amount > the threshold), when a failure occurs in the image processing device 50, etc.

[0027] The network device 55 is a device that connects each image processing device 50 and the display device 60. The network device 55 transfers the image data sent from the image processing device 50 after image processing to the display device 60.

[0028] The display device 60 displays the image data after image processing transferred from the network device 55 .

[0029] The switching control device 70 is a device that controls switching of the optical switching device 40. The switching control device 70 controls switching of the optical switching device 40 in response to a request from another device, for example. In this embodiment, a configuration will be described in which the switching control device 70 controls switching of the optical switching device 40 in response to receiving a switching request transmitted from the image processing device 50.

[0030] The switching control device 70 controls the switching of the optical switching device 40 based on the period information notified from the relay device 20. For example, the switching control device 70 instructs the optical switching device 40 to switch paths during an idle period in which no data is being transmitted from each image transmitter 10 and which satisfies the switching time required for switching by the optical switching device 40. The switching time is the time from when the optical switching device 40 receives the switching instruction from the switching control device 70 to when the switching is completed.

[0031] (Device Configuration) Next, specific configurations of the relay device 20 and the switching control device 70 will be described. First, the configuration of the relay device 20 will be described. The relay device 20 includes an interval acquisition unit 21, an interval notification unit 22, and a data communication unit 23. The interval acquisition unit 21 identifies multiple vacant periods for each specific cycle based on multiple image data transmitted from each image transmitter 10. In this case, the interval acquisition unit 21 identifies the start time and length of each vacant period for each vacant period. In this way, the interval acquisition unit 21 acquires period information indicating multiple vacant periods for each cycle.

[0032] The interval notification unit 22 notifies the switching control device 70 of the period information acquired by the interval acquisition unit 21. The interval notification unit 22 may notify the switching control device 70 of the acquired period information every time period information is acquired from the interval acquisition unit 21. The interval notification unit 22 may perform time synchronization with the switching control device 70 and notify the period information at an offset timing separated by a predetermined period (for example, 1 second) (synchronization may be 1 PPS). The data communication unit 23 receives the plurality of image data transmitted from each image transmitter 10. The data communication unit 23 transmits the received plurality of image data to the optical transceiver 30-1.

[0033] Next, the configuration of the switching control device 70 will be described. The switching control device 70 includes a switching timing determination unit 71 and a switching instruction unit 72. The switching timing determination unit 71 acquires period information notified from the relay device 20, and determines a vacant period that satisfies the switching condition based on the acquired period information. For example, the switching timing determination unit 71 determines, as the vacant period that satisfies the switching condition, a vacant period identified by vacant period information that satisfies at least the switching time of the optical switching device 40, from among multiple pieces of vacant period information included in the period information.

[0034] The switching timing determination unit 71 may determine, among the multiple vacant period information pieces included in the period information, the period that satisfies the switching time and has the longest vacant period length as the vacant period specified by the vacant period information that satisfies the switching condition, or may determine, as the vacant period that satisfies the switching time and is the first vacant period that satisfies the switching condition and is specified by the vacant period information. Here, the first vacant period that can be switched is the vacant period that has the earliest time after the switching request is received among the multiple vacant period information pieces included in the period information. For example, if the multiple vacant periods included in the period information are t1, t2, t3, ... and the switching request is received at timing t2, t3 is the first vacant period that can be switched.

[0035] In this way, the switching timing determination unit 71 can realize the earliest switching of the optical switching device 40 by selecting, from among the vacant periods notified by the relay device 20, the vacant period that is closest in time to the time when the switching request is received and that is longer than the switching time of the optical switching device 40. Specifically, if the switching time of the optical switching device 40 is 10 ms, the switching timing determination unit 71 determines the switching time so that the switching will be performed in the earliest vacant period of 10 ms or more.

[0036] The switching instruction unit 72 instructs the optical switching device 40 to switch the path within the vacant period determined by the switching timing determination unit 71. For example, when a switching request is transmitted from the image processing device 50-1, the switching instruction unit 72 instructs the optical switching device 40 to switch the path so that image data is transferred to an image processing device 50 other than the image processing device 50-1 (for example, the image processing device 50-2). In this case, the switching instruction unit 72 may instruct the optical switching device 40 to switch the path so as to connect the optical transceiver 30-1 and the optical transceiver 30-3.

[0037] FIG. 2 is a diagram showing information related to multiple image data transmitted from each image transmitter 10. FIGS. 2A and 2B show the period during which packets (image data) constituting video streams with different frame rates arrive at the interval acquisition unit 21 for each cycle. FIG. 2B shows the state one second after FIG. 2A. FIGS. 2A and 2B show video streams with three frame rates: 20 fps (20 frames per second), 24 fps (24 frames per second), and 30 fps (30 frames per second). As shown in FIGS. 2A and 2B, packets arriving at the interval acquisition unit 21 have the same intervals at the same frame rate.

[0038] Fig. 2C is a diagram visually illustrating vacant periods identified based on Fig. 2A. Arrow inf1 in Fig. 2C represents a vacant period. As shown in Fig. 2C, it can be seen that multiple vacant periods exist within one cycle. The interval acquisition unit 21 acquires the start times and lengths of the multiple vacant periods shown in Fig. 2C for each vacant period. For example, the position of the starting point of arrow inf1 represents the start time of the vacant period, and the length of one arrow inf1 represents the length (time) of the vacant period.

[0039] FIG. 3 is a diagram showing an example of the configuration of a vacant period table in the first embodiment. The vacant period table is a table in which information about vacant periods is registered. The vacant period table is stored, for example, by the switching control device 70. As shown in FIG. 3, the vacant period table has multiple records for registering information about each vacant period. Each record includes an ID, a vacant start time, and a vacant period length. The ID represents identification information for identifying the vacant period. The vacant start time represents the time at which the vacant period identified by the ID starts. The vacant period length represents the length (in hours) of the vacant period identified by the ID.

[0040] The vacant period table is updated every time period information is notified from the relay device 20. That is, the vacant period table stores period information for one cycle. In FIG. 3, all of the vacant period information included in the period information notified from the relay device 20 is registered in the vacant period table, but only some of the vacant period information may be registered in the vacant period table. For example, the relay device 20 may notify the switching control device 70 of vacant period information whose vacant period length is equal to or longer than the switching time of the optical switching device 40, out of the vacant period information for one cycle. As a result, only vacant period information that can be switched by the optical switching device 40 is registered in the vacant period table.

[0041] Alternatively, the switching control device 70 may register, in the vacant period table, vacant period information whose vacant period length is equal to or longer than the switching time of the optical switching device 40, from among a plurality of vacant period information pieces included in the period information notified from the relay device 20. In this way, only vacant period information that can be switched by the optical switching device 40 is registered in the vacant period table. By registering some vacant period information in the vacant period table as described above, it is possible to reduce unnecessary vacant period information. As a result, it is possible to reduce the storage capacity and shorten the search time by the switching control device 70.

[0042] 4 is a flowchart showing the flow of processing performed by the switching control device 70 in the first embodiment. The switching timing determination unit 71 acquires period information notified from the relay device 20 (step S101). The switching timing determination unit 71 registers vacant period information included in the acquired period information in a vacant period table (step S102). Thereafter, the switching timing determination unit 71 determines whether a switching request has been received (step S103). Here, the switching request is a request for path switching due to the processing load of the image processing device 50-1.

[0043] If the switching timing determination unit 71 determines that a switching request has not been received (step S103—NO), the switching control device 70 terminates the processing of FIG. 4. On the other hand, if the switching timing determination unit 71 determines that a switching request has been received (step S103—YES), the switching timing determination unit 71 determines an available period for performing path switching by the optical switching device 40 (step S104). Specifically, the switching timing determination unit 71 refers to the available period table and, based on the time when the switching request was received, determines the available period that is closest in time to the time when the switching request was received and that satisfies the switching time as the available period for performing path switching. Note that, as described above, the method by which the switching timing determination unit 71 determines an available period for performing path switching is not limited to this, and the longest period may be selected.

[0044] The switching timing determination unit 71 notifies the switching instruction unit 72 of information about the determined vacant period (e.g., vacant start time and vacant period length). The switching instruction unit 72 instructs the optical switching device 40 to switch paths based on the vacant period information notified by the switching timing determination unit 71 (step S105). For example, the switching instruction unit 72 may instruct the optical switching device 40 to switch paths at any timing within the vacant period specified by the vacant period information notified by the switching timing determination unit 71, as long as the timing is within the vacant period and the optical switching device 40 can perform switching. By the switching instruction unit 72 instructing the path switching at the start time of the vacant period specified by the vacant period information, the optical switching device 40 can perform path switching early. Furthermore, by the switching instruction unit 72 instructing the path switching at a time midway within the vacant period specified by the vacant period information, path switching can be performed taking into account an error that may occur when the switch instruction arrives before or after the vacant period.

[0045] Through the above processing, the optical switching device 40 switches the connection destination. For example, the optical switching device 40 switches the optical path so that the optical transceiver 30-1 is connected to the optical transceiver 30-3. After completing the switching, the optical switching device 40 transfers the image data transmitted from the optical transceiver 30-1 to the optical transceiver 30-3. The optical transceiver 30-3 transmits the image data received via the optical switching device 40 to the image processing device 50-2. As a result, the image data that has undergone image processing in the image processing device 50-2 is transferred to the display device 60 via the network device 55. As a result, the processing load on the image processing device 50-1 can be reduced.

[0046] In Fig. 4, for convenience of explanation, the processing of the switching control device 70 is described as a series of flows, but the processing from step S101 to step S102 shown in Fig. 4 and the processing from step S103 to step S105 shown in Fig. 4 may be executed as separate flowcharts. The processing from step S101 to step S102 is an update processing related to updating the vacant period table held by the switching control device 70. The processing from step S103 to step S105 is a switching processing related to route switching.

[0047] According to the communication system 100 configured as described above, the switching control device 70 is equipped with a switching timing determination unit 71 that acquires period information including information on multiple vacant periods during which data transmission is not performed for multiple image data transmitted from the image transmitter 10-1 and multiple image data transmitted from the image transmitter 10-2 at different intervals within a specific period, and determines a vacant period that satisfies a switching condition based on the acquired period information, and a switching instruction unit 72 that instructs an optical switching device that switches the path of the transmission section of the optical signal to switch the path within the vacant period determined by the switching timing determination unit 71.

[0048] As a result, the optical switching device 40 performs path switching during the vacant period. By performing switching by the optical switching device 40 during the vacant period in this manner, it is possible to avoid a collision between the time when image data arrives and the switching timing. Therefore, when multiple video flows transmitted at different cycles are mixed, it is possible to reduce packet loss due to path switching.

[0049] Second Embodiment It is assumed that the radio wave conditions in the wireless section between the image transmitter and the relay device change significantly depending on the environmental changes. Therefore, in the second embodiment, a configuration will be described in which optical path switching is performed without packet loss even when the vacant period fluctuates due to changes in the radio wave conditions.

[0050] 5 is a diagram showing an example of the configuration of a communication system 100a according to the second embodiment. The communication system 100a includes an image transmitter 10, a relay device 20, an optical transceiver 30, an optical switching device 40, an image processing device 50, a network device 55, a display device 60, a switching control device 70a, and a radio wave condition observation device 80.

[0051] 5 shows a configuration in which a communication system 100a includes two image transmitters 10-1 and 10-2, three optical transceivers 30-1 to 30-3, and two image processing devices 50-1 and 50-2. Note that the numbers of the image transmitters 10, relay devices 20, optical transceivers 30, optical switching devices 40, image processing devices 50, network devices 55, and display devices 60 included in the communication system 100a are not particularly limited.

[0052] The image transmitters 10-1 to 10-2 are connected wirelessly to the relay device 20. Control lines that transmit electrical signals are connected between the relay device 20 and the optical transceiver 30-1, between the relay device 20 and the switching control device 70a, between the optical transceiver 30-2 and the image processing device 50-1, between the optical transceiver 30-3 and the image processing device 50-2, between the image processing devices 50-1 to 50-2 and the network device 55, between the network device 55 and the display device 60, and between the switching control device 70a and the radio wave condition observation device 80. The optical transceivers 30-1 to 30-3 and the optical switching device 40 are connected by optical transmission paths.

[0053] The communication system 100a differs in configuration from the communication system 100 in that it includes a switching control device 70a instead of the switching control device 70, and in that it newly includes a radio wave condition observation device 80. The following description will focus on the differences from the communication system 100.

[0054] The radio wave condition monitoring device 80 acquires a control signal for the wireless section between each image transmitter 10 and the relay device 20. Based on the acquired control signal, the radio wave condition monitoring device 80 acquires an MCS (Modulation and coding scheme) index value that indicates the modulation currently being used. The radio wave condition monitoring device 80 notifies the switching control device 70a of the acquired MCS index value. The radio wave condition monitoring device 80 executes this process at a predetermined timing.

[0055] In Wi-Fi (registered trademark), the modulation level of data transmitted and received between the image transmitter 10 and the relay device 20 is dynamically changed depending on the radio wave conditions. For example, when the radio wave conditions are poor, the reliability of the data can be improved by changing the modulation to a simpler one, and when the radio wave conditions are good, the throughput can be improved by using a more complex modulation. Therefore, the switching control device 70a controls the switching of the optical switching device 40, taking into account the radio wave conditions in the wireless section.

[0056] Therefore, the switching control device 70a holds a vacant period table for each MCS index as shown in Fig. 6 so that it can identify each MCS index notified from the radio wave condition observation device 80. Fig. 6 is a diagram showing an example of a vacant period table in the second embodiment. The configuration of the vacant period table is the same as that in the first embodiment. The difference from the first embodiment is that vacant period information for each MCS index is registered.

[0057] The switching control device 70a includes a switching timing determination unit 71a and a switching instruction unit 72. When the switching timing determination unit 71a receives period information notified from the relay device 20, if the switching timing determination unit 71a has acquired an MCS index value from the radio wave condition observation device 80, the switching timing determination unit 71a registers the period information notified from the relay device 20 in the vacant period table corresponding to the most recent acquired MCS index value. This allows period information according to the network condition of the current wireless section to be registered in the appropriate vacant period table.

[0058] It is also possible that the value of the MCS index is notified from the radio wave condition observation device 80 immediately after receiving the period information notified from the relay device 20. Therefore, the switching timing determiner 71a may provide a predetermined buffer period, and if the value of the MCS index is notified from the radio wave condition observation device 80 before the predetermined buffer period has elapsed since the timing of receiving the period information notified from the relay device 20, the switching timing determiner 71a may register the period information notified from the relay device 20 in the vacant period table corresponding to the notified MCS index value.

[0059] On the other hand, if the switching timing determination unit 71a does not receive the MCS index value from the radio wave condition observation device 80 within a predetermined buffer period from the time when the switching timing determination unit 71a receives the period information notified from the relay device 20, the switching timing determination unit 71a may register the period information notified from the relay device 20 in the vacant period table corresponding to the latest MCS index value that has already been notified.

[0060] Note that, like the first embodiment, some vacant period information may be registered in the vacant period table for each MCS index.

[0061] The process performed by the switching timing determination unit 71a is the same as that in the first embodiment, except that the vacant period table corresponding to the value of the MCS index is referenced.

[0062] Fig. 7 is a diagram showing vacant period information when multiple video streams with different frame rates are transmitted in environments with different effective throughputs, such as different modulation indices. Fig. 7 shows vacant period information for MCS index = 3 and vacant period information for MCS index = 7. For example, the dot "+" in Fig. 7 indicates vacant period information for MCS index = 7, and the dot "x" in Fig. 7 indicates vacant period information for MCS index = 3.

[0063] As shown in Figure 7, it can be seen that the vacant period length is longer for MCS index = 7 than for MCS index = 3. This information is registered in the vacant period table corresponding to MCS index = 3 and the vacant period table corresponding to MCS index = 7.

[0064] Next, the processing flow of the switching control device 70a in the second embodiment will be described. When the switching timing determination unit 71a receives a switching request from the image processing device 50-1, it reads out the vacant period table corresponding to the MCS index value most recently notified by the radio wave condition observation device 80. For example, if the MCS index value most recently notified by the radio wave condition observation device 80 is "3," the switching timing determination unit 71a reads out the vacant period table corresponding to the MCS index value "3."

[0065] The switching timing determination unit 71a refers to the vacant period table corresponding to the read MCS index value "3" and determines the vacant period for performing path switching by the optical switching device 40. The subsequent processes, including the process for determining the vacant period for performing path switching by the optical switching device 40, are the same as those in the first embodiment, and therefore description thereof will be omitted.

[0066] In the communication system 100a configured as described above, the switching control device 70a determines the vacant period for executing the route switching, taking into account the radio wave conditions in the wireless section. Even when the radio wave conditions deteriorate and the MCS index value drops, resulting in a change in the vacant period compared to when the radio wave conditions are good, it is possible to determine the timing for switching the optical route so that it does not collide with the arrival of video. Therefore, when multiple video flows transmitted at different intervals coexist, it is possible to reduce packet loss associated with the route switching.

[0067] Furthermore, by constantly updating the vacant period table held by the switching control device 70a, when the number of video streams, frame rate, radio wave conditions, or number of terminals changes, it is possible to determine a vacant period that is more in line with the latest conditions.

[0068] (Modification 1) In the example shown in FIG. 6, a configuration is shown in which the vacant period table is divided for each MCS index, but a plurality of vacant period tables may be prepared by dividing into classes according to received radio wave strength.

[0069] (Variation 2) The interval acquisition unit 21 may be configured not to acquire a vacant period when a condition that the radio wave conditions in the wireless section are poor is met. When the radio wave conditions are poor (for example, when the effective throughput in the wireless section is less than the video rate), the original transmission cycle deviates, and it is assumed that the packet interval based on the frame rate cannot be acquired. In this case, even if a vacant period is determined, it is likely to be inaccurate. In this case, the time when the image data arrives may conflict with the switching timing. To avoid such problems, the interval acquisition unit 21 does not acquire a vacant period when a condition that the radio wave conditions in the wireless section are poor is met.

[0070] (Third embodiment) In the second embodiment, a configuration was shown in which the switching control device holds a vacant period table for each MCS index. In contrast, in the third embodiment, a configuration will be described in which, instead of separating the vacant period tables for each MCS index, the switching control device holds and updates a vacant period table corresponding to the maximum MCS index value observed by a radio wave condition observation device, and in the case of an MCS index different from the maximum MCS index value (when the radio wave condition is worse and the MCS index is smaller), the vacant period is determined based on the longest vacant period.

[0071] The system configuration and device configuration of the third embodiment are the same as those of the second embodiment, and the following description will focus on the differences from the second embodiment.

[0072] The switching control device 70a holds a vacant period table corresponding to the maximum MCS index value observed by the radio wave condition observation device 80. When a switching request is received, a switching timing determination unit 71a included in the switching control device 70a determines whether the MCS index value most recently notified from the radio wave condition observation device 80 matches the MCS index value in the vacant period table it holds. If the MCS index value most recently notified from the radio wave condition observation device 80 matches the MCS index value in the vacant period table it holds, the switching timing determination unit 71a references the vacant period table it holds and determines a vacant period for performing path switching by the optical switching device 40, using the method described in the first embodiment.

[0073] On the other hand, if the value of the MCS index most recently notified by the radio wave condition observation device 80 does not match the value of the MCS index in the vacant period table held, it is assumed that the radio wave conditions in the wireless section are poor. Therefore, the switching timing determination unit 71a refers to the vacant period table held, and determines the longest vacant period length as the vacant period for causing the optical switching device 40 to perform path switching.

[0074] Fig. 8 is a diagram showing vacant period information when multiple video streams with different frame rates are streamed. Fig. 8 shows vacant period information for MCS index = 3 and vacant period information for MCS index = 7. For example, the dot "+" in Fig. 8 indicates vacant period information for MCS index = 7, and the dot "x" in Fig. 8 indicates vacant period information for MCS index = 3.

[0075] As shown in Figure 8, it can be seen that the length of vacant periods is shorter when MCS index = 3 than when MCS index = 7. Furthermore, when MCS index = 3, the frequency with which vacant periods of 4 ms or more appear is also reduced. As mentioned above, vacant periods become shorter as the MCS decreases or the radio wave conditions deteriorate, but considering that the timing at which they occur is roughly the same, packet loss can be avoided by switching at the determined optical path switching timing even when the MCS decreases.

[0076] In cases where the switching control device 70a places more importance on avoiding packet loss due to switching than on switching the path of the optical switching device 40 immediately after receiving a switching request, it is desirable to determine an empty period with the longest empty period. If it is desired to switch the path of the optical switching device 40 as soon as possible after receiving a switching request, the switching control device 70a can switch to the nearest empty period from a certain number of candidates (for example, four) arranged in order of the length of the empty period, thereby avoiding packet loss due to switching and shortening the time until switching is completed.

[0077] According to the communication system 100a of the third embodiment configured as above, it is possible to obtain the same effects as those of the second embodiment.

[0078] Since the effective throughput of the wireless section fluctuates, the timing at which switching is possible also fluctuates. However, this does not change randomly, and unless the timing at the source changes, the change basically shortens the vacant period. Therefore, when the wireless environment is expected to deteriorate, it is possible to achieve switching with reduced packet loss by adjusting to a timing with a longer vacant period.

[0079] (Modification) The interval acquisition unit 21 may be configured not to perform the operation of acquiring the vacant period when the condition that the radio wave condition in the wireless section is poor is satisfied.

[0080] (Modification common to the first to third embodiments) In each of the above-described embodiments, a configuration has been shown in which the switching control device 70, 70a controls the optical switching device 40 to switch the path of the transmission section of the optical signal in accordance with the load state of the image processing device 50. The trigger for the switching control device 70, 70a to control the optical switching device 40 to switch the path of the transmission section of the optical signal is not limited to this. For example, the switching control device 70, 70a may control the optical switching device 40 to switch the path of the transmission section of the optical signal in accordance with a change in the network status of a specific section.

[0081] Although an embodiment of the present invention has been described above in detail 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.

[0082] The present invention can be applied to a technique for switching transmission sections of optical signals.

[0083] DESCRIPTION OF SYMBOLS 10, 10-1 to 10-2...image transmitter, 20...relay device, 21...interval acquisition unit, 22...interval notification unit, 23...data communication unit, 30, 30-1 to 30-3...optical transceiver, 40...optical switching device, 50, 50-1 to 50-2...image processing device, 55...network device, 60...display device, 70, 70a...switching control device, 71, 71a...switching timing determination unit, 72...switching instruction unit, 80...radio wave condition observation device, 100, 100a...communication system

Claims

1. A switching control device comprising: a switching timing determination unit that acquires period information including information on multiple vacant periods during which at least first data and second data are not transmitted at different intervals within a specific cycle, and determines vacant periods that satisfy switching conditions based on the acquired period information; and a switching instruction unit that instructs an optical switching device that switches the path of a transmission section of an optical signal to switch the path within the vacant period determined by the switching timing determination unit.

2. The switching control device according to claim 1, wherein the switching timing determination unit determines, from among the plurality of vacant periods included in the period information, a vacant period that satisfies at least the switching time required for switching of the optical switching device as a vacant period that satisfies the switching condition.

3. The switching control device according to claim 2, wherein the switching timing determination unit determines the longest period among a plurality of vacant periods included in the period information that satisfies the switching time as the vacant period that satisfies the switching condition.

4. The switching control device according to claim 2, wherein the switching timing determination unit determines the first vacant period among the plurality of vacant periods included in the period information that satisfies the switching time and is switchable as the vacant period that satisfies the switching condition.

5. A switching control device according to any one of claims 1 to 4, wherein the switching timing determination unit acquires radio wave information relating to radio wave conditions in the wireless section and determines an available period that satisfies the switching condition, taking the acquired radio wave information into consideration.

6. The switching control device according to claim 5, wherein the radio wave information is information for identifying a modulation method used in wireless communication, and the switching timing determination unit acquires the period information for each modulation method and determines an empty period that satisfies the switching condition based on the period information corresponding to the modulation method identified in the radio wave information.

7. A switching control device according to any one of claims 1 to 4, wherein the switching timing determination unit retains only information on vacant periods that meet the switching time required for switching the optical switching device, from among information on multiple vacant periods included in the acquired period information.

8. A switching method comprising: acquiring period information including information on a plurality of vacant periods during which at least first data and second data transmitted at different intervals within a specific cycle are not being transmitted; determining a vacant period that satisfies a switching condition based on the acquired period information; and instructing an optical switching device that switches the path of an optical signal transmission section to switch the path within the determined vacant period.

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