Patent Publication Number: US-2023161396-A1

Title: Power Receiving Device, Power Feeding Device, Method Executed by Power Receiving Device, Method Executed by Power Feeding Device and Communication System

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to Japanese Patent Application No. 2021-190306, filed on Nov. 24, 2021, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The present disclosure relates to a power receiving device, a power feeding device, a method executed by the power receiving device, a method executed by the power feeding device, and a communication system. 
     BACKGROUND 
     Conventionally, as a power supply method for supplying power to a communication device that transmits and receives packet data, a PoE (Power over Ethernet (registered trademark)) technology defined as a standardization technology in IEEE (Institute of Electrical and Electronics Engineers) 802.3af, IEEE802.3at, or the like has been used. For example, Japanese Patent Application Laid-Open Publication No. 2018-019433 discloses a router that communicates with a PoE-capable device and supplies power to the PoE-capable device via a LAN cable. 
     SUMMARY 
     According to an embodiment of the present disclosure, there is provided a power receiving device comprising: a connector configured to be connected to a power feeding device; a power source configured to receive a power supply from the power feeding device via the connector; and a controller configured to perform a predetermined process before a power supply stopping time in response to receiving a preliminary notification of power supply stopping from the power feeding device via the connector. 
     According to an embodiment of the present disclosure, there is provided a power feeding device comprising: one or more connectors configured to be connected to one or more power receiving devices; a power supplier configured to supply power to the one or more power receiving devices via the one or more connectors; a notifier configured to notify a predetermined power receiving device via the one or more connectors of the preliminary notification of power supply stopping; and a controller configured to stop supplying power from the power supplier to the predetermined power receiving device after a predetermined period of time has passed after notifying the predetermined power receiving device of the preliminary notification of power supply stopping by the notifier. 
     According to an embodiment of the present disclosure, there is provided a communication system comprising: one or more power receiving devices; and a power feeding device connected to the one or more power receiving devices, wherein, the one or more power receiving devices comprises: a first connector configured to be connected to the power feeding device; a power source configured to receive a power supply from the power feeding device via the first connector; and a controller configured to perform a predetermined process before a power supply stopping time in response to receiving a preliminary notification of power supply stopping from the power feeding device via the connector, and the power feeding device comprises: one or more second connectors configured to be connected to the one or more power receiving devices; a power supplier configured to supply power to the one or more power receiving devices via the second connector, a notifier configured to notify a predetermined power receiving device via the one or more second connectors of a preliminary notification of power supply stopping; and a controller configured to stop supplying power from the power supplier to the predetermined power receiving device after a predetermined period of time has passed after the notifying the predetermined power receiving device of the preliminary notification of power supply stopping by the notifier. 
     According to an embodiment of the present disclosure, there is provided a method executed by a power receiving device, the power receiving device comprising a connector configured to be connected to a power feeding device, a power source configured to receive a power supply from the power feeding device via the connector and a controller configured to receive a preliminary notification of power supply stopping from the power feeding device via the connector, the method comprising: performing a predetermined process before a power supply stopping time in response to the controller receiving the preliminary notification of power supply stopping. 
     According to an embodiment of the present disclosure, there is provided a method executed by a power feeding device, the power feeding device comprising one or more connectors configured to be connected to one or more power receiving devices, and a power supplier configured to supply power to the one or more power receiving devices via the one or more connectors, the method comprising: notifying a predetermined power receiving device via the one or more connectors of a preliminary notification of power supply stopping; and stopping supplying power from the power supplier to the predetermined power receiving device after a predetermined period of time has passed after notifying the predetermined power receiving device of the preliminary notification of power supply stopping. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram illustrating a configuration example of a communication system according to an embodiment of the present disclosure. 
         FIG.  2    is a block diagram illustrating a configuration example of a power feeding device according to an embodiment of the present disclosure. 
         FIG.  3    is a block diagram illustrating a configuration example of a power receiving device according to an embodiment of the present disclosure. 
         FIG.  4    is a flowchart illustrating an example of a flow of a power supply stopping process executed by a power feeding device according to an embodiment of the present disclosure. 
         FIG.  5    is a flowchart illustrating an example of a flow of a power supply stopping process executed by a power feeding device according to an embodiment of the present disclosure. 
         FIG.  6    is a flowchart illustrating an example of a flow of a power supply stopping process executed by a power receiving device according to an embodiment of the present disclosure. 
         FIG.  7    is a schematic diagram illustrating a configuration example of a communication system according to another embodiment of the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A power feeding device such as a router starts/stops power supply for each port based on a preset power supply schedule, and can control a power source of a power receiving device, which is a PoE-capable device. However, in a case where the power feeding device stops the power supply to the power receiving device at a timing set according to a schedule without notification, there is a possibility that a storage of logs such as system logs that are in operation in the power receiving device is not in time and the unsaved logs disappear. 
     According to the present disclosure, it is possible to provide the power receiving device with the notification of power supply stopping in advance from the power feeding device, and to execute necessary process in the power receiving device before the power supply stops. 
     Hereinafter, embodiments of the present disclosure will be described with reference to drawings and the like. However, the present disclosure can be implemented in many different embodiments, and should not be construed as being limited to the description of the embodiments exemplified below. 
     The drawings may be schematically represented for clarity of explanation, but are merely examples, and do not limit the interpretation of the present invention. Further, the letters “first” and “second” for each element are convenience labels used to distinguish each element, and do not have any further meaning unless otherwise described. In the drawings referred to in the embodiments described below, the same or similar components having the same or similar functions are denoted by the same reference numerals or similar reference numerals (numerals denoted by A, B, 1, 2, or the like on a number XXX), and repeated description thereof may be omitted. In addition, a part of configurations may be omitted from the drawings. In addition, no particular explanation shall be given if the present invention pertains is recognizable for the person ordinarily knowledgeable in the field. 
     First Embodiment 
     &lt;Communication System&gt; 
     A communication system according to a first embodiment of the present disclosure will be described in detail with reference to the drawings. 
       FIG.  1    is a schematic diagram illustrating a configuration example of a communication system  10  according to a first embodiment of the present disclosure. The communication device  10  includes a power feeding device  101  and power receiving devices  103 - 1 ˜ 103 - n  (n is a natural number). In the following description, each of the power receiving devices is simply referred to as a “power receiving device  103 ” when there is no need to distinguish between them. 
     The power feeding device  101  is a PoE-capable PSE (Power Sourcing Equipment). The power feeding device  101  is, for example, a power supply switching hub, a power supply adapter, or the like. In the present embodiment, an example in which the power feeding device  101  is a layer 2 (L2) switch is described. 
     The power receiving device  103  is a PoE-capable PD (Powered Device). The power receiving device  103  is, for example, an IP camera, an access point (AP), an IP telephone, a microphone, or the like. In the present embodiment, an example in which the power receiving device  103  is an AP is described. The power receiving device  103  is connected to the power feeding device  101  via a PoE-capable LAN cable. The power receiving device  103  performs data communication with the power feeding device  101 , which is the L2 switch, and receives power from the power feeding device  101 . 
     As the LAN cable for connecting the power feeding device  101  and the power receiving device  103 , the PoE-capable LAN cable can be used. The power feeding method may be either an Alternative A mode, an Alternative B mode, or a four-pair PoE. 
     &lt;Power Feeding Device&gt; 
     Next, the power feeding device  101  according to the present embodiment is described with reference to  FIG.  2   .  FIG.  2    is a block diagram illustrating a configuration example of the power feeding device  101  according to the present embodiment. The power feeding device  101  may include a controller  201 , a communication unit  203 , a storage unit  205 , a power supplier  207 , and a connector(s)  209 . The controller  201 , the communication unit  203 , the storage unit  205 , and the power supplier  207  are connected to each other via a bus  211 . 
     The controller  201  includes an arithmetic process circuit such as a CPU or the like. The controller  201  executes a program stored in the storage unit  205  by the CPU (computer) to realize a communication function and a power supply function for supplying power to the power receiving device  103 . Part or all of the configurations for realizing these functions is not limited to the case where the configuration is realized by software by executing a program, and may be realized by hardware. Note that the function realized by the controller  201  includes a function of controlling each unit constituting the power feeding device  101  in addition to the above-described functions. The controller  201  controls the power supply to the power receiving device  103  connected to the power feeding device  101  based on a power supply schedule described later. 
     The controller  201  includes a notifier  202 . The notifier  202  generates and notifies the power receiving device  103  that receives the power supply from the power feeding device  101  of the preliminary notification of power supply stopping for notifying announcing a power supply stopping. The preliminary notification is generated and notified based on the power supply schedule and a notification schedule, which is described later. The preliminary notification is notified for each of the power receiving devices  103  connected to the power feeding device  101 . 
     The notifier  202  notifies each of the power receiving devices  103  of the preliminary notification of power supply stopping at a predetermined timing before the timing of power supply stopping (power supply stopping time) of each of the power receiving devices  103 . The timing at which the preliminary notification of power supply stopping is notified may be the same for each power receiving device  103  connected to the power feeding device  101  or may be different. For example, the notifier  202  may notify the power receiving devices  103 - 1 ˜ 103 - n  of the preliminary notification of power supply stopping 90 seconds before the power supply stopping time corresponding to each of the power receiving devices  103 - 1 ˜ 103 - n . Further, the notifier  202  may notify the power receiving device  103 - 1  of the preliminary notification of power supply stopping 90 seconds before the power supply stopping time of the power receiving device  103 - 1 , and notify the power receiving device  103 - 2  of the preliminary notification of power supply stopping 60 seconds before the power supply stopping time of the power receiving device  103 - 2 . 
     The preliminary notification may include information indicating a remaining time until the power supply stopping. The controller  201  can calculate the remaining time until the power supply stopping based on the power supply schedule. 
     The notifier  202  may notify each of the power receiving devices  103  of the preliminary notification of power supply stopping a plurality of times. In a case where the preliminary notification of power supply stopping is notified a plurality of times, the notifier  202  may notify the corresponding power receiving device  103  of the preliminary notification at a fixed cycle. In this case, the preliminary notification may be stored in LLDP (Link Layer Discovery Protocol) and notified to the power receiving device  103 . Further, in a case where the preliminary notification of power supply stopping is notified a plurality of times and the preliminary notification includes information indicating the remaining time until the power supply stopping, the remaining time until the power supply stopping is the remaining time from each timing when the preliminary notification is notified to the power supply stopping timing (power supply stopping time). 
     In a case where receiving an update request of the power supply stopping time (power supply stopping timing) from the power receiving device  103 , the controller  201  may update the timing of the power supply stopping to the power receiving device  103 . That is, the controller  201  may extend the power supply stopping time to the power receiving device  103 . The controller  201  may extend the power supply stopping time for a predetermined time set in advance. The notifier  202  generates a new preliminary notification of power supply stopping in response to the update request of the power supply stopping time, and notifies the power receiving device  103  of the preliminary notification. 
     The communication unit  203  is an interface, which is connected to an external device (the power receiving device  103 , the router (not shown), an L3 switch (not shown), or the like) under the control of the controller  201 , and transmits/receives data under the control of the controller  201 . In addition, the communication unit  203  performs process of data to be transmitted to an external device, including packetization of data. 
     The communication unit  203  includes connectors  209 - 1 ˜ 209 - m  (m is a natural number). In the following description, each of the connectors is simply referred to as a “connector  209 ” when there is no need to distinguish between them. The connector  209  is an interface that connects the power supplier  207  and a connector  309  of the power receiving device  103 , which is described later. In the present embodiment, the connector  209  and the power receiving device  103  are connected via the LAN cable. The connector  209  supplies the power supplied from the power supplier  207  to the power receiving device  103 . In addition, the connector  209  transmits the preliminary notification of power supply stopping to the power receiving device  103 . 
     The storage unit  205  is a storage device such as a nonvolatile memory, a hard disk or the like. As the storage unit  205 , in addition to a semiconductor memory such as an SSD (Solid State Drive), a magnetic recording medium (a magnetic tape, a magnetic disk, or the like), an optical recording medium, a magneto-optical recording medium, or elements that can be storage mediums are used. The storage unit  205  has a function as a database for storing an application program for realizing a communication function and a power supply function, various kinds of information, and the like. The application program may be downloaded via a network. Further, the storage unit  205  may be externally present. 
     The storage unit  205  may be connected to the power feeding device  101  and may store a power supply schedule that predetermines a power supply starting/stopping time to the power receiving device  103  that receives the power supply from the power feeding device  101 . The power supply schedule can be set for each power receiving device  103  connected to the power feeding device  101 . Further, the power supply schedule may be appropriately changed by a user. An example of the power supply schedule is shown in Table 1 below. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Power supply 
                 Power supply starting 
               
               
                   
                   
                 stopping time 
                 time 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Power receiving 
                 10:00 
                 PM 
                 5:00 AM 
               
               
                   
                 device 103-1 
               
               
                   
                 Power receiving 
                 0:00 
                 AM 
                 6:00 AM 
               
               
                   
                 device 103-2 
               
            
           
           
               
               
               
               
            
               
                   
                 . . . 
                 . . . 
                 . . . 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Power receiving 
                 2:00 
                 AM 
                 8:00 AM 
               
               
                   
                 device 103-n 
               
               
                   
                   
               
            
           
         
       
     
     As shown in Table 1, the power receiving device  103 - 1  may be scheduled so that the power supply from the power feeding device  101  is stopped at 10:00 PM and the power supply is started (resumed) at 5 AM. Similarly, the power receiving device  103 - 2  may be scheduled so that the power supply from the power feeding device  101  is stopped at 0:00 AM and the power supply is started (resumed) at 6:00 AM, and the power receiving device  103 - n  may be scheduled so that the power supply from the power feeding device  101  is stopped at 2:00 AM and the power supply is started (resumed) at 8:00 AM. The power supply schedule is not limited to the data table shown in Table 1. For example, the power supply starting time may be set after a predetermined time has elapsed from the power supply stopping time. 
     In addition, the storage unit  205  may store a notification schedule that predetermines a timing for notifying the power receiving device  103  of the preliminary notification of power supply stopping and the number of times of notification. The notification schedule can be set for each power receiving device  103  connected to the power feeding device  101 . The notification schedule may be changed as appropriate by a user. An example of the notification schedule is shown below. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                 Number of 
               
               
                   
                 Notification timing 
                 notifications 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Power receiving 
                 10 minutes before the 
                 30 times (per 20 
               
               
                   
                 device 103-1 
                 power supply 
                 seconds) 
               
               
                   
                   
                 stopping 
               
               
                   
                 Power receiving 
                 10 minutes before the 
                 once 
               
               
                   
                 device 103-2 
                 power supply 
               
               
                   
                   
                 stopping 
               
               
                   
                 . . . 
                 . . . 
                 . . . 
               
               
                   
                 Power receiving 
                 20 minutes before the 
                 40 times (per 30 
               
               
                   
                 device 103-n 
                 power supply 
                 seconds) 
               
               
                   
                   
                 stopping 
               
               
                   
                   
               
            
           
         
       
     
     The power supplier  207  supplies power to the power receiving device  103  via the connector  209  under the control of the controller  201 . The power supplier  207  supplies power to the power receiving device  103  for each port. 
     The power supplier  207  may be an IC that controls on/off of the PoE power supply in accordance with a rule defined in the PoE standard. The power supplier  207  controls starting/stopping of the power supply to the power receiving device  103  based on control by the controller  201 . The power supplied to the power supplier  207  is supplied from the outside. The source of the power supplied to the power feeding device  101  is not particularly limited, and may be an input from a DC power supply, an input from an AC power supply, or an input from another power feeding device. The controller  201  stops the power supply from the power supplier  207  to the power receiving device  103  after a predetermined time has elapsed since the preliminary notification of power supply stopping is notified to the power receiving device  103 . 
     In the power supply schedule, in a case where the resume of the power supply from the power feeding device  101  to the predetermined power receiving device  103  is set after a predetermined time has elapsed from the power supply stopping, the controller  201  may resume the power supply from the power supplier  207  to the predetermined power receiving device  103  via a connector  209  corresponding to the predetermined power supply device  103  at the set time based on the power supply schedule. 
     The power feeding device  101  may further include an operation unit (not shown) and a display unit (not shown). The operation unit outputs a signal corresponding to an operation input by the user by an operation button or the like to the controller  201 . The operation button includes, for example, a power switch, a cursor key, and the like, and is an operator that receives an instruction from the user. The display unit is a display device such as a liquid crystal display, an OLED display and the like, and displays a screen based on the control of the controller  201 . 
     &lt;Power Receiving Device&gt; 
     The power receiving device  103  according to the present embodiment is described with reference to  FIG.  3   . As described above, in the present embodiment, the power receiving device  103  is an access point (AP). In the present embodiment, the power receiving device  103  is a network device which is wired or wirelessly connected via a network to the power feeding device  101  that is the L2 switch and a communication terminal (not shown) connected to the power receiving device  103 . The power receiving device  103  has a function of relaying the communication terminal (not shown) and a power feeding device  101 , which is the L2 switch. 
       FIG.  3    is a block diagram illustrating a configuration example of the power receiving device according to the present embodiment. The power receiving device  103  may include a controller  301 , a communication unit  303 , a storage unit  305 , and a power source  307 . The controller  301 , the communication unit  303 , the storage unit  305 , and the power source  307  are connected to each other via a bus  311 . 
     The controller  301  includes an arithmetic process circuit such as a CPU. The controller  301  executes a program stored in the storage unit  305  by a CPU (computer) to realize various functions executed by the power receiving device  103 , such as a communication function and the like. In addition, the controller  301  is not limited to a case where a part or all of a configuration for realizing these functions is realized by software by executing a program, and may be realized by hardware. Note that the function realized by the controller  301  includes a function of controlling each unit constituting the power receiving device  103  in addition to the above-described functions. 
     The controller  301  acquires the preliminary notification of power supply stopping announcing the power supply stopping from the power feeding device  101  via the connector  309 , which is described later. The controller  301  executes a predetermined process based on the preliminary notification by the power supply stopping timing (power supply stopping time). The power supply stopping time at which the power supply from the power feeding device  101  is stopped is specified based on the preliminary notification. 
     In a case where the preliminary notification includes information indicating the remaining time until the power supply stopping, the controller  301  can specify the power supply stopping time based on the timing at which the preliminary notification is notified and the remaining time until the power supply stopping. In a case where the preliminary notification does not include the information indicating the remaining time until the power supply stopping, the controller  301  may specify the power supply stopping time based on the identification information such as the IP address of the power feeding device  101  that has notified the preliminary notification. For example, the power receiving device  103  may store a data table associating identification information of the power feeding device  101  and the remaining time from the timing at which the preliminary notification is notified from the power feeding device  101  to the timing of the power supply stopping in the storage unit  305  in advance. The power receiving device  103  may store identification information and the remaining time from the timing at which the preliminary notification is notified to the timing of the power supply stopping for each of one or more power feeding devices  101 . In addition, in the case where the preliminary notification does not include information indicating the remaining time until the power supply stopping, the controller  301  may inquire of the power feeding device  101  that has notified the preliminary notification about power supply stopping time. 
     When the controller  301  acquires the preliminary notification of power supply stopping announcing the power supply stopping from the power feeding device  101 , the controller  301  may measure the remaining time until the power supply stopping time at which the power supply from the power feeding device  101  is stopped. In other words, the controller  301  may count down the remaining time until the power supply stopping time. 
     The predetermined process executed by the controller  301  until the power supply stopping time from the power feeding device  101  includes at least one from among saving of the system log inside the power receiving device  103  and saving of a configuration file. 
     In a case where the power receiving device  103  functioning as an access point is connected to an external device such as a communication terminal (not shown), the controller  301  transmits a connection destination change request requesting the connected external device to change the connection destination via the communication unit  303  before the timing when the power supply from the power feeding device  101  is stopped. In addition, the controller  301  stops acceptance of new access from the external device. 
     Additionally, in a case where the power receiving device  103  notified of the preliminary notification of power supply stopping from the power feeding device  101  is the controller access point (controller AP), the power receiving device  103  notified of the preliminary notification executes at least one from among notifying the other power receiving device  103  connected to the same power feeding device  101  of the power supply stopping and transferring its controller authority to the other power receiving device  103  before the power supply stopping. Here, the controller AP means an access point that can collectively set and manage other member access points (member APs) connected to the same power feeding device  101 . That is, the controller AP provides a virtual controller function to other member APs. 
     For example, it is assumed that the power receiving device  103 - 1  in  FIG.  1    is a controller AP, and other power receiving devices  103 - 2 ˜ 103 - n  connected to the same power feeding device  101  are member APs. When the power receiving device  103 - 1  is notified of the preliminary notification of power supply stopping from the power feeding device  101 , the power receiving device  103 - 1  may notify the other power receiving devices  103 - 2 ˜ 103 - n  that the power supply will stop to the power receiving device  103 - 1  from the power feeding device  101 . Upon receiving the notification, the power receiving devices  103 - 2 ˜ 103 - n  may select a next controller AP. For example, in a case where the power receiving device  103 - 2  is selected as the next controller AP, the power receiving device  103 - 2  functions as the controller AP after the power supply from the power feeding device  101  to the power receiving device  103 - 1  is stopped. 
     In addition, when the power receiving device  103 - 1 , which is the controller AP, is notified of the preliminary notification of power supply stopping from the power feeding device  101 , the power receiving device  103 - 1  may transfer the controller authority to any one of the other power receiving devices  103 - 2 ˜ 103 - n . The power receiving device  103  to which the controller authority has been transferred from the power receiving device  103 - 1  functions as the controller AP after the power supply from the power feeding device  101  to the power receiving device  103 - 1  is stopped. In this case, the power receiving device  103  to which the controller authority is transferred may be selected in advance from the power receiving devices  103 - 2 ˜ 103 - n . For example, priorities of the power receiving devices  103  functioning as the next controller AP may be determined among the power receiving devices  103 - 2 ˜ 103 - n.    
     The notification of stopping the power supply from the power receiving device  103 - 1  to the other power receiving devices  103 - 2 ˜ 103 - n  and the transfer of the controller authority may be performed by radio communication between the power receiving devices  103  via the communication unit  303  described later, or may be performed by wire communication via the power feeding device  101 . In addition, the power feeding device  101  may notify the power receiving devices  103 - 2 ˜ 103 - n  of the power supply stopping to the power receiving device  103 - 1  or transfer the control authority based on the power supply schedule. 
     In a case where the predetermined process is not completed by the power supply stopping time, the controller  301  can request the power feeding device  101  to update the power supply stopping time one or more times. When a new preliminary notification of the power supply stopping is notified from the power feeding device  101  based on the update request of the power supply stopping time, the controller  301  completes the predetermined process by the power supply stopping time specified on the basis of the new preliminary notification. 
     The communication section  303  is wired or wirelessly connected to external devices (such as the power feeding device  101 , a communication terminal (not shown), etc.). The communication unit  303  is an interface for transmitting and receiving data under the control of the controller  301 . 
     The communication unit  303  includes the connector  309 . The connector  309  is an interface connecting the power source  307  and the connector  209  of the power feeding device  101 . In the present embodiment, the connector  309  and the power feeding device  101  are connected via the LAN cable. The connector  309  supplies power supplied from the power feeding device  101  to the power source  307  described later. In addition, the connector  309  receives the preliminary notification announcing the stop of the power supply from the power feeding device  101 , and transmits the preliminary notification to the controller  301 . 
     The communication unit  303  may wirelessly communicate with the power feeding device  101 , the other power receiving device  103 , or an external communication terminal (not shown). In this case, as the communication unit  303 , for example, a communication module capable of performing communication using a radio LAN, a Bluetooth (registered trademark), or the like is used. 
     The storage unit  305  is a storage device such as the nonvolatile memory, the hard disk, and the like. As the storage unit  305 , in addition to the semiconductor memory such as an SSD (Solid State Drive), the magnetic recording medium (a magnetic tape, a magnetic disk, or the like), the optical recording medium, the magneto-optical recording medium, or elements that can be storage mediums are used. The storage unit  305  has a function as a database that stores application programs for realizing various functions executed by the power receiving device  103 , such as a communication function, and various kinds of information. The application program may be downloaded via a network. 
     The power source  307  receives power from the power feeding device  101  connected via the connector  309 , and functions as a power source for the power receiving device  103 . The connector  309  is the interface that connects the power source  307  and the power feeding device  101 . 
     The power receiving device  103  may acquire the preliminary notification of power supply stopping from the power feeding device  101  a plurality of times from the power feeding device  101 . The preliminary notification of power supply stopping may include information indicating the remaining time until the power supply stopping. In the case where information indicating the remaining time until the power supply stopping is included in the preliminary notification of power supply stopping, the controller  301  does not need to measure the remaining time until the power supply stopping time (power supply stopping timing). 
     In the communication system  10  according to the present embodiment, the power feeding device  101  notifies the power receiving device  103  that receives the power supply from the power feeding device  101  of the preliminary notification of power supply stopping based on the preset power supply schedule. When the power receiving device  103  acquires the preliminary notification of power supply stopping from the power feeding device  101  via the connector  309 , the power receiving device  103  can specify the power supply stopping time (power supply stopping timing) at which the power supply from the power feeding device  101  is stopped based on the preliminary notification. The power receiving device  103  executes process such as saving of an unsaved log or data file, a request for changing the connection destination to an external device, and a stopping of acceptance of a new access from the external device by the power supply stopping time. 
     Since the power receiving device  103  can execute process necessary before shutdown, it is possible to prevent a trouble that may occur when power supply from the power feeding device  101  is resumed and the power receiving device  103  is restarted. In a case where an external device such as a communication terminal is connected to the power receiving device  103 , it is possible to prevent a communication trouble by changing the connection destination to other access point in advance before the power receiving device  103  is shut down in response to a request for changing the connection destination. Further, since the power receiving device  103  stops accepting the new access from the external device before shutdown, the external device can avoid connection with the power receiving device  103  in which the shutdown time (power supply stopping time) is approaching in advance. In addition, in the case the power receiving device  103  that is scheduled to stop the power supply functions as the controller AP, by transferring the controller authority to the other power receiving device  103  in advance, the other power receiving device  103  can quickly function as the controller AP after the power supply stopping. 
     &lt;Power Supply Stopping Process&gt; 
     A process of stopping the power supply from the power feeding device  101  to the power receiving device  103  based on the power supply schedule is described. 
       FIG.  4    and  FIG.  5    are flow diagrams illustrating an example of a flow of process executed by the power feeding device  101  according to the embodiment of the present invention. 
     First, in the power feeding device  101 , the controller  201  determines whether or not the power supply to the power receiving device  103  is scheduled to be stopped based on the power supply schedule (S 401 ). If not scheduled (S 401 ; No), the controller  201  repeats S 401  process. 
     In a case where the power supply stopping is scheduled (S 401 ; Yes), the controller  201  determines whether or not the notification timing of a preliminary notification has been reached based on the notification schedule (S 403 ). In a case where the notification timing has not been reached (S 403 ; No), the controller  201  repeats S 403  process. In a case where the notification timing is reached (S 403 ; Yes), the notifier  202  generates the preliminary notification (S 405 ). The controller  201  notifies (transmits) the power receiving device  103  via the connector  209  the generated preliminary notification (S 407 ). 
     The controller  201  determines whether or not the update request of the power supply stopping time has been received from the power receiving device  103  (S 409 ). In a case where the update request of the power supply stopping time is received from the power receiving device  103  (S 409 ; Yes), the controller  201  updates the power supply stopping time for the power receiving device  103  (the power supply stopping timing to the power receiving device  103 ) (S 411 ). When the power supply stopping time is updated, the controller  201  returns to S 405  process, and generates a preliminary notification of power supply stopping based on an updated power supply stopping time. 
     In a case where the update request of the power supply stopping time has not been received from the power receiving device  103  (S 409 ; No), the controller  201  determines whether or not the preliminary notification notified (transmitted) to the power receiving device  103  is the last notification based on the notification schedule (S 413 ). In a case where the preliminary notification notified (transmitted) to the power receiving device  103  is not the last notification (S 413 ; No), the controller  201  returns to S 403  process. 
     In a case where the preliminary notification notified (transmitted) to the power receiving device  103  is the last notification (S 413 ; Yes), the controller  201  determines again whether or not the update request of the power supply stopping time has been received from the power receiving device  103  (S 415 ). In a case where the update request of the power supply stopping time has been received from the power receiving device  103  (S 415 ; Yes), the process proceeds to S 411  process. In a case where the update request of the power supply stopping time has not been received from the power receiving device  103  (S 415 ; No), the controller  201  determine whether or not the power supply stopping time of the power receiving device  103  has been reached (S 417 ). In a case where the power supply stopping time of the power receiving device  103  is reached (S 417 ; Yes), the controller  201  stops the power supply to the power receiving device  103  via the power supplier  207  (S 419 ), and ends the series of processes. On the other hand, in a case where the power supply stopping time of the power receiving device  103  has not been reached (S 417 : No), the controller  201  returns to S 415  process. 
       FIG.  6    is a flowchart illustrating an example of a flow of process executed by a power receiving device  103  according to an embodiment of the present invention. 
     The controller  301  of the power receiving device  103  determines whether or not the preliminary notification for announcing a stoppage of the power supply from the power feeding device  101  has been acquired via the connector  309  (S 501 ). In a case where the preliminary notification has not been acquired (S 501 ; No), the controller  301  repeats S 501  process. In a case where the preliminary notification is acquired (S 501 ; Yes), the controller  301  specifies the power supply stopping time (power supply stopping timing) at which the power supply from the power feeding device  101  is stopped based on the preliminary notification (S 503 ), and executes a predetermined process (S 505 ). Here, the start of the execution of the predetermined process (S 505 ) may be concurrent with the identification of the power supply stopping time (S 503 ), or may be prior to the identification of the power supply stopping time (S 503 ). 
     The controller  301  determines whether or not the predetermined process being executed can be completed before the power supply stopping time (S 507 ). In a case where it is determined that the predetermined process can be completed before the power supply stopping time (S 507 ; Yes), the controller  301  continues to execute the predetermined process and completes the predetermined process (S 511 ). After completion of the predetermined process, the controller  301  performs a shutdown process of the power receiving device  103  (S 513 ), and ends the series of processes. 
     On the other hand, in a case where it is determined that the predetermined process cannot be completed before the power supply stopping time (S 507 ; No), the controller  301  generates an update request for requesting the power feeding device  101  to update the power supply stopping time, and transmits the generated update request to the power feeding device  101  (S 509 ). The update request is transmitted to the power feeding device  101  via the connector  309 . After the updating request is transmitted, the controller  301  returns to S 501  process. 
     Second Embodiment 
     A communication system according to a second embodiment of the present disclosure is described in detail with reference to the drawings. 
       FIG.  7    is a schematic diagram illustrating a configuration example of a communication system  60  according to the second embodiment of the present disclosure. The communication system  60  includes a first power feeding device  101 A, first power receiving devices  103 A- 1 ˜ 103 A-n (n is a natural number), a second power feeding device  101 B, and second power receiving devices  103 B- 1 ˜ 103 B-m (m is a natural number). 
     The first power feeding device  101 A and the second power feeding device  101 B are PoE-capable PSEs, similarly to the power feeding device  101  in the first embodiment. In the present embodiment, the first power feeding device  101 A and the second power feeding device  101 B are both layer 2 (L2) switches. Since configurations of the first power feeding device  101 A and the second power feeding device  101 B are the same as the configuration of the power feeding device  101  in the first embodiment, detailed explanation thereof is omitted. 
     The first power feeding device  101 A and the second power feeding device  101 B are connected to each other via an external device (such as a router (not shown), an L3 switch (not shown), a server (not shown), and the like). In this embodiment, the first power feeding device  101 A and the second power feeding device  101 B are connected to each other via a router  601 . 
     The first power receiving devices  103 A- 1 ˜ 103 A-n (n is a natural number) and the second power receiving devices  103 B- 1 ˜ 103 B-m (m is a natural number) are PoE-capable PDs (Powered Device) as in the power receiving device  103  of the first embodiment. In the present embodiment, the first power receiving devices  103 A- 1 ˜ 103 A-n and the second power receiving devices  103 B- 1 ˜ 103 B-m are access points (APs). 
     The first power receiving devices  103 A- 1 ˜ 103 A-n (n is a natural number) are connected to the first power feeding device  101 A via the PoE-capable LAN-cable. Each of the first power receiving devices  103 A- 1 ˜ 103 A-n performs data communication with the first power feeding device  101 A and receives power from the first power feeding device  101 A. Each of the first power receiving devices  103 A- 1 ˜ 103 A-n are simply referred to as a “first power receiving device  103 A” when there is no need to distinguish between them. 
     The second power receiving devices  103 B- 1 ˜ 103 B-m are connected to the second power feeding device  101 B via the PoE-capable LAN-cable. Each of the second power receiving devices  103 B- 1 ˜ 103 B-m performs data communication with the second power feeding device  101 B and receives power from the second power feeding device  101 B. Each of the second power receiving devices  103 B- 1 ˜ 103 B-m are simply referred to as a “second power receiving device  103 B” when there is no need to distinguish between them. 
     In the present embodiment, the first power receiving device  103 A connected to the first power feeding device  101 A and the second power receiving device  103 B connected to the second power feeding device  101 B are connected via the router  601 . One of the first power receiving device(s)  103 A and the second power receiving device(s)  103 B functions as the controller AP, and the other power receiving devices serving as the member AP, are collectively set and managed by the controller AP. 
     In the first embodiment, it has been described that, in the case where the predetermined power receiving device  103 , which is the controller AP, of the power receiving devices  103  that receive power supply from the power feeding device  101  receives the preliminary notification announcing the power supply stopping, the power receiving device  103  that has received the preliminary notification executes at least one from among the notifying the power supply stopping to other power receiving devices (member APs) that are connected to the same power feeding device  101  and transferring its controller authority to another power receiving device  103 . 
     However, in a case where a predetermined power receiving device, which is the controller AP, receives the preliminary notification announcing the power supply stopping, the notification of power supply stopping to other power receiving devices (member APs) and the transfer of the controller authority to another power receiving device (member AP) are not limited to the power receiving device(s) connected to the same power feeding device  101 . 
     In the present embodiment, in a case where the first power receiving device  103 A, which is the controller AP, receives the preliminary notification announcing the stoppage of the power supply from the first power feeding device  101 A, the first power receiving device  103 A that has received the preliminary notification may execute at least one from among the notification of power supply stopping and its own controller authority to the second power receiving devices  103 B- 1 ˜ 103 B-m that receives the power supply from the second power feeding device  101 B. 
     Upon receiving the notification, the second power receiving devices  103 B- 1  ˜ 1038 - m  may select the following controller AP. For example, in a case where the second power receiving device  103 B- 1  is selected as the following controller AP, the second power receiving device  103 B- 1  functions as the controller AP after the power supply from the first power feeding device  101 A to the first power receiving device  103 A- 1  is stopped. 
     The first power receiving device  103 A- 1  may transfer the controller authority to any one of the second power receiving devices  103 B- 1 ˜ 103 B-m when the first power receiving device  103 A- 1 , which is the controller AP, is notified from the first power feeding device  101 A of the preliminary notification of power supply stopping. The second power receiving device  103 B to which the controller authority has been transferred from the first power receiving device  103 A- 1  functions as the controller AP after the power supply from the first power feeding device  101 A to the first power receiving device  103 A- 1  is stopped. In this case, the second power receiving device  103 B to which the controller authority is transferred may be selected in advance from the second power receiving devices  103 B- 1 ˜ 103 B-m. 
     As described above, by transferring the controller authority to the other power receiving device  103  in advance before the power supply to the power receiving device  103  functioning as the controller AP is stopped, the other power receiving device  103  can quickly function as the controller AP after the power supply stopping. 
     The notification of power supply stopping and the transfer of the controller authority from the first power receiving device  103 A- 1  to the second power receiving devices  103 B- 1  ˜ 1038 - m  may be performed by the radio communication, or may be performed by communication via the first power feeding device  101 A, the router  601 , and the second power feeding device  101 B. 
     [Modifications] 
     In each of the embodiments described above, the case where the power receiving device  103  is the access point (AP) has been described as an example, but the power receiving device  103  is not limited to the access point. The power receiving device  103  may be the IP camera, the IP telephone, a PoE-capable microphone, a PoE-capable speaker, or the like. 
     In a case where the power receiving device  103  is the IP camera, the predetermined process executed before the power supply stopping time includes storage of an unsaved log, storage of unsaved image data, and the like. In a case where the power receiving device  103  is the IP telephone, the predetermined process executed before the power supply stopping time may include the notification of power supply stopping to the user, or the like. 
     Further, in each of the embodiments described above, the case where the power receiving device  103  is the access point (AP) has been described as an example, but in a case where a plurality of power receiving devices  103  are provided, all the power receiving devices  103  may be the same type of device or may be different types of devices. 
     Each of the embodiments described above as an embodiment of the present disclosure can be appropriately combined and implemented as long as they do not conflict with each other. Further, based on the configuration shown in the embodiments, any addition, deletion, or design change of components, or any addition, omission, or change of conditions of the process, as appropriate by people skilled in the art, is also included in the scope of the invention, as long as it has the gist of the present disclosure. 
     It is understood that other effects which are different from the effects brought about by each of the above-described embodiments, but which are obvious from the description of this embodiment, or which can be easily predicted by people skilled in the art, are naturally brought about by an embodiment of this disclosure.