Patent Publication Number: US-2023148042-A1

Title: Communication system and communication method

Description:
TECHNICAL FIELD 
     The present invention relates to a technique for enabling continuous communication when a power failure occurs due to disasters or the like. 
     BACKGROUND ART 
     Conventionally, telephone services have been provided via metal cables extending from a communication building to users&#39; homes. The power and the voice communication service can be provided simultaneously to telephones (rotary dial telephones and the like) via the metal cables. 
     In recent years, the metal cables extending in the whole sections from the communication building to users&#39; homes have been replaced with optical fibers to provide a high-speed data communication service to many users&#39; homes. Connecting the whole sections from the communication building to the user&#39;s home via the optical fiber is referred to as Fiber To The Home (FTTH). 
     CITATION LIST 
     Non-Patent Literature 
     
         
         Non-Patent Literature 1: Media Network Technology (NTT Access Network Service Systems Laboratories), https://www.ansl.ntt.co.jp/history/media/index.html, searched on 24 Apr. 2020 
       
    
     SUMMARY OF THE INVENTION 
     Technical Problem 
     In order to connect a PC, a telephone, and the like in a user&#39;s home to a communication network (IP communication network or the like) via an optical fiber, a user&#39;s home side communication device is set in the user&#39;s home. The user&#39;s home side communication device is also referred to as a home gateway (HGW). 
     In order for the user&#39;s home side communication device to operate, it is necessary to supply the power from the commercial power supply. Therefore, if a disaster occurs and a power failure occurs in the user&#39;s home, no power is supplied to the user&#39;s home communication device so that the user&#39;s home side communication device stops working and cannot be connected to the communication network. 
     For dealing with such circumstances, it is considered to feed the power to the user&#39;s home side communication device from the communication building via the optical fiber. With the current technology, however, it is inefficient to feed the power only via the optical fiber and it is difficult to feed the power in a practical manner. 
     The present invention is designed in view of the foregoing, and it is an object thereof to provide a technique for properly operating the user&#39;s home side communication device even when a power failure occurs on the user&#39;s home side due to a disaster. 
     Means for Solving the Problem 
     According to the disclosed technique, provided is a communication system including a communication building side communication device in a communication building and a user&#39;s home side communication device in a user&#39;s home, the communication building side communication device and the user&#39;s home side communication device being connected via an optical fiber and a metal cable, wherein: when a power fed to the user&#39;s home side communication device from a commercial power supply stops, the communication building side communication device feeds the power to the user&#39;s home side communication device via the metal cable to operate the user&#39;s home side communication device; and the user&#39;s home side communication device communicates with the communication building side communication device via the optical fiber. 
     Effects of the Invention 
     According to the technique of the present disclosure, the user&#39;s home side communication device can be properly operated even when a power failure occurs on the user&#39;s home side due to a disaster. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a diagram illustrating an example of an overall configuration of a system according to an embodiment of the present invention. 
         FIG.  2    is a diagram illustrating an example of a configuration of a user&#39;s home side communication device. 
         FIG.  3    is a diagram illustrating an example of a configuration of a communication building side communication device. 
         FIG.  4    is a flowchart illustrating an operation of the communication building side communication device. 
         FIG.  5    is a chart illustrating an example of a sequence between a communication building and a user&#39;s home. 
         FIG.  6    is a chart illustrating an example of a sequence between a communication building and a user&#39;s home. 
         FIG.  7    is a chart illustrating an example of a safety check procedure. 
         FIG.  8    is a diagram illustrating an example of a configuration in a case where SPE is used as a metal cable. 
         FIG.  9    is a diagram illustrating an example of a configuration of a PON. 
         FIG.  10    is a diagram illustrating an example of a configuration inside an optical splitter box. 
         FIG.  11    is a diagram illustrating an example of a hardware configuration of a device. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     Hereinafter, a mode for embodying the present invention (embodiment) will be described with reference to the accompanying drawings. The embodiment described hereinafter is an example only, and embodiments to which the present invention is applied are not limited to the embodiment described hereinafter. 
     (Overall Configuration) 
       FIG.  1    illustrates an example of an overall configuration of a system according to an embodiment of the present invention. In the example of  FIG.  1   , “city hall”, “fire station”, “ordinary home”, and “public phone” are illustrated as examples of a user&#39;s home. Each user&#39;s home is connected to a communication building via an optical fiber and a metal cable. 
     While  FIG.  1    illustrates a star configuration in which a pair of “optical fiber and metal cable” extends from the communication building to each user&#39;s home, such a configuration is simply an example. Other than the star configuration, a bus configuration and a tree configuration are also possible. 
     A pair of “optical fiber and metal cable” may be a composite cable in which an optical fiber and a metal cable are formed as a single cable, or the optical fiber and the metal cable may be independent from each other. 
     As illustrated in  FIG.  1   , a communication building side communication device  200  is provided in the communication building, and a user&#39;s home side communication device  100  is provided in each user&#39;s home. The communication building side communication device  200  is a device that terminates the optical fiber and the metal cable extending from the user&#39;s home and is connected to a higher communication network. The user&#39;s home side communication device  100  is a device that terminates the optical fiber and the metal cable extending from the communication building and connects the PC, telephones, and the like in the user&#39;s home to a communication network via the optical fiber. 
     In the embodiment, when a power failure occurs in the user&#39;s home under a disaster and the power cannot be fed to the user&#39;s home side communication device  100  from the commercial power supply, the power is fed to the user&#39;s home side communication device  100  from the communication building side communication device  200  via the metal cable to activate the user&#39;s home side communication device  100  so as to continue communication via the optical fiber. 
     In the embodiment, in order to allow the user&#39;s home side communication device  100  of large power consumption to operate normally, the power is fed via the metal cable with a voltage of 380 V that is higher than a voltage (60 V) of Safety Extra-Low Voltage (SELV). Note that “380 V” is an example, and the power may be fed with a voltage that is higher than this voltage or the power may be fed with a voltage lower than this voltage. 
     Furthermore, since the power is fed with a high voltage exceeding the voltage of SELV in the embodiment, the power is fed after checking the normality (safety) of the metal cable, the connection part (connector), and the like in order to secure the safety. As the normality check procedure, it is possible to use the procedure same as the charging procedure under CHAdeMO protocol, for example. 
     (Example of Device Configuration) 
       FIG.  2    illustrates an example of the configuration of the user&#39;s home side communication device  100 . As illustrated in  FIG.  2   , the user&#39;s home side communication device  100  includes a communication unit  110 , a control unit  120 , a metal IF unit  130 , an optical IF unit  140 , a photoelectric conversion unit  150 , a power feed unit  160 , and a power storage unit  170 . Note that either one of or both of the photoelectric conversion unit  150  and the power storage unit  170  may not necessarily be provided. Furthermore, the metal IF unit  130  and the optical IF unit  140  may be referred to as a metal line termination unit and an optical network unit, respectively. 
     The communication unit  110  includes a router, a wireless LAN adapter, a telephone adapter, and the like, and provides a communication service to the PC and the telephone connected to the user&#39;s home side communication device  100  in the user&#39;s home. 
     The control unit  120  controls the user&#39;s home side communication device  100 . In particular, in the embodiment, executed in cooperation with the communication building side communication device  200  under a power failure are the state check, the normality check, and the like. 
     The metal IF unit  130  is physically connected to the metal cable, transmits signals received from the metal cable to the communication unit  110  or the control unit  120 , and sends out signals received from the communication unit  110  or the control unit  120  to the metal cable. Furthermore, the metal IF unit  130  receives the power supplied from the communication building side communication device  200 , and feeds the power to each unit of the user&#39;s home side communication device  100 . 
     The optical IF unit  140  is physically connected to the optical fiber, and converts optical signals received from the optical fiber to electric signals and transmits the electric signals to the communication unit  110  or the control unit  120 . Furthermore, the optical IF unit  140  converts electric signals received from the communication unit  110  or the control unit  120  to optical signals and sends out the optical signals to the optical fiber. 
     The photoelectric conversion unit  150  converts the optical energy received from the optical fiber into the power, and feeds that power to each unit of the user&#39;s home side communication device  100 . The power feed unit  160  receives the power from the commercial power supply via an AC adapter or the like, and feeds the received power to each unit of the user&#39;s home side communication device  100 . The power storage unit  170  receives the power from the power feed unit  160  and the like and stores the power. The power storage unit  170  discharges the power as necessary such as when the power from the commercial power supply is stopped to feed the power to each unit of the user&#39;s home side communication device  100 . 
       FIG.  3    illustrates an example of the configuration of the communication building side communication device  200 . Note that the communication building side communication device  200  illustrated in FIG.  3  may be a communication building side communication device  200  that accommodates a single user&#39;s home side communication device  100  or may be a communication building side communication device  200  that accommodates a plurality of user&#39;s home side communication devices  100 . For the sake of simplifying explanations, it is assumed herein that the communication building side communication device  200  illustrated in  FIG.  3    is a communication building side communication device  200  that accommodates a single user&#39;s home side communication device  100 . 
     As illustrated in  FIG.  3   , the station communication device  200  includes a communication unit  210 , a control unit  220 , a metal IF unit  230 , an optical IF unit  240 , and a power feed unit  250 . Furthermore, the metal IF unit  230  and the optical IF unit  240  may be referred to as a metal line termination unit and an optical network unit, respectively. 
     The communication unit  210  is a function unit that includes a router and the like, and enables the higher communication network and the user&#39;s home side communication device  100  to have packet communication. The control unit  220  controls the communication building side communication device  200 . In particular, in the embodiment, executed at the time of a power failure occurring in the user&#39;s home are the state check, the normality check, and the like of the user&#39;s home side communication device  100 . Furthermore, the control unit  220  also has a function of receiving external signals such as J-alert, and comprehending the content thereof. 
     The metal IF unit  230  is physically connected to the metal cable, transmits signals received from the metal cable to the communication unit  210  or the control unit  220 , and sends out signals received from the communication unit  210  or the control unit  220  to the metal cable. Furthermore, the metal IF unit  230  feeds the power from the power feed unit  250  to the user&#39;s home side communication device  100 . 
     The optical IF unit  240  is physically connected to the optical fiber, and converts optical signals received from the optical fiber to electric signals and transmits the electric signals to the communication unit  210  or the control unit  220 . Furthermore, the optical IF unit  240  converts electric signals received from the communication unit  210  or the control unit  220  to optical signals and sends out the optical signals to the optical fiber. The power feed unit  250  receives the power from the commercial power supply via an AC adapter, and feeds the received power to each unit of the communication building side communication device  200 . 
     (Operation Example of Communication Building Side Communication Device  200 ) 
     When a power failure occurs on the user&#39;s home side, the properly operating communication building side communication device  200  executes the normality check and the like of the optical fiber and the metal cable connected to the user&#39;s home side communication device  100  and feeds the power to the user&#39;s home side communication device  100  via the metal cable so as to properly operate the user&#39;s home side communication device  100  even under the power failure. 
       FIG.  4    is a flowchart illustrating an operation example of the communication building side communication device  200 . In S 101 , the user&#39;s home side communication device  100  is in a normal state and communicating with the communication building side communication device  200  via the optical fiber. 
     In S 102 , the control unit  220  of the communication building side communication device  200  determines whether a disaster signal is received. The disaster signal is a J-alert, for example. The disaster signal may be input to the control unit  220  automatically from the system that transmits the disaster signals or may be input manually by those who have detected the disaster signal. 
     Upon receiving the disaster signal (Yes in S 102 ), the control unit  220  determines whether it is possible to communicate via the optical fiber in S 103 . This can be determined based on whether there is a response signal from the user&#39;s home side communication device  100  when the control unit  220  transmits a test signal to the user&#39;s home side communication device  100  from the optical IF unit  240 , for example. 
     When it is possible to communicate via the optical fiber (Yes in S 103 ), the control unit  220  determines whether the power is being fed to the user&#39;s home side communication device  100  in S 104 . It is assumed herein that the control unit  220  is capable of acquiring information regarding whether the power is being fed and information regarding the state (charged amount and the like) of the power storage unit  170  from the user&#39;s home side communication device  100  via the optical fiber, so that it is possible to determine whether the power is being fed based thereupon. 
     When the power is being fed (Yes in S 104 ), the control unit  220  transmits a control signal to the user&#39;s home side communication device  100  to switch the user&#39;s home side communication device  100  to an energy saving mode in S 105 . The user&#39;s home side communication device  100  continues communication in the energy saving mode. It is assumed herein that the power is being fed by the power storage unit  170 , so that the energy saving mode is selected. After switching to the energy saving mode, the processing is returned to S 103 . 
     When it is not possible to communicate via the optical fiber (No in S 103 ) or the power is not being fed to the user&#39;s home side communication device  100  (No in S 104 ), the control unit  220  determines whether it is possible to communicate via the metal cable in S 106 . This can be determined based on whether there is a response signal from the user&#39;s home side communication device  100  when the control unit  220  transmits minute power necessary for activating the user&#39;s home side communication device  100  and an activation signal from the metal IF unit  230 , for example. For the activation by the metal cable herein, a voltage of 48 V is used, for example. 
     When it is not possible to communicate via the metal cable (No in S 106 ), it is not possible to communicate (S 107 ) and the processing for the user&#39;s home side communication device  100  is ended. In this case, there is a possibility that the metal cable may be disconnected. 
     When it is possible to communicate via the metal cable (Yes in S 106 ), the control unit  220  executes a test for the normality check (safety check) using the metal cable in S 108 . Examples of the test may be an insulation resistance measurement, a leakage current test, a connector lock check, and the like. 
     In the test performed in S 108 , the test such as application of the voltage and current may be performed on the metal cable, and signal transmission/reception for notification and the like of the state (voltage value, current value, resistance value, and the like) may be performed on the optical fiber. It is because the power is fed via the metal cable so that it becomes possible at this point to communicate via the optical fiber. 
     Furthermore, in the test performed in S 108 , both application and the like of the voltage and current and signal transmission/reception may be performed on the metal cable. This is possible since power feeding and communication can be simultaneously performed by using the cable of Single Pair Ethernet (R) to be described later as the metal cable. It is assumed herein that the test is successful. 
     In S 109 , the control unit  220  instructs the metal IF unit  230  to feed the power to the user&#39;s home communication device  100  from the metal IF unit  230  via the metal cable. Herein, the power is fed with a high voltage of 380 V or the like described above, for example. Since the user&#39;s home side communication device  100  operates normally by the power fed via the metal cable, it is possible to perform communication via the optical fiber as with in the communication state of S 101 . 
     In S 110 , the control unit  220  determines whether a disaster recovery signal is received. Note that receiving the disaster recovery signal herein means that the power failure occurred in the user&#39;s home is restored. The disaster recovery signal may be input to the control unit  220  automatically or manually. When no disaster recovery signal is received (No in S 110 ), the processing is returned to S 109  and power feeding via the metal cable is continued. 
     When the disaster recovery signal is received (Yes in S 110 ), power feeding via the metal cable is ended in S 111  and the power feeding is to be shifted to the normal state (S 101 ). 
     Example of Sequence 
     Next, an example of a sequence between the communication building side communication device  200  and the user&#39;s home side communication device  100  will be described by referring to  FIG.  5   . 
     In a normal state (S 201 ), the power is fed to the user&#39;s home communication device  100  from the commercial power supply (AC 100 V), and communication is performed properly between the communication building side communication device  200  and the user&#39;s home side communication device  100  (S 1 , S 2 ). 
     When a disaster occurs (S 202 ), the power fed from the commercial power supply to the user&#39;s home side communication device  100  stops. Therefore, even though the optical signal (S 3 ) from the communication building side communication device  200  reaches the user&#39;s home side communication device  100 , the user&#39;s home side communication device  100  cannot transmit the optical signal. 
     The communication building side communication device  200  upon detecting occurrence of a disaster feeds the power to the user&#39;s home side communication device  100  via the metal cable using a voltage (for example, 48 V) that is equal to or less than SELV (S 4 ) to activate the user&#39;s home side communication device  100  (S 204 , S 205 ). Furthermore, the communication building side communication device  200  performs the normality check (including safety check) of the metal cable in order to check whether it is possible to feed the power with a high voltage (for example, 380 V) (S 5  to S 7 , S 206 ). 
     When the normality is confirmed, the communication building side communication device  200  feeds the power to the user&#39;s home side communication device  100  with a high voltage (for example, 380 V) (S 8 ). Thereby, the user&#39;s home side communication device  100  can operate in a normal state and perform communication via the optical fiber (S 9 , S 10 ). 
     When the disaster is over and the power is restored (S 207 ), a power restoration signal is transmitted from the user&#39;s home side communication device  100  to the communication building side communication device  200  (S 208 , S 11 ). Thereafter, power feeding via the metal cable is stopped, and communication via the optical fiber is performed as in a normal state (S 12 , S 13 , S 209 ). 
     While the power is fed with 48 V via the metal cable in the example illustrated in  FIG.  5    in order to activate the user&#39;s home side communication device  100  that has stopped due to the power failure, the power may be fed via the optical fiber for this activation.  FIG.  6    illustrates an example of such a case. In the example of  FIG.  6   , the power is fed to the user&#39;s home communication device  100  via the optical fiber in S 4 . 
     In the example of  FIG.  5   , it is necessary for the communication building side communication device  200  to switch the voltage of the power fed to the user&#39;s home communication device  100  via the metal cable from 48 V to 380 V. However, in the example of  FIG.  6   , it is not necessary to do so, and it is possible to use only the power feed unit for feeding the power of 380 V. 
     Example of Normality Check Procedure 
     Referring to  FIG.  7   , an example of the normality check procedure performed on the metal cable will be described. While the test is executed only on the metal cable in the example of  FIG.  7   , power feeding (application and the like of the power and current) may be performed on the metal cable and signal transmission/reception may be performed on the optical fiber. Furthermore, the following processing is a processing that is executed mainly between the control unit  220  of the communication building side communication device  200  and the control unit  120  of the user&#39;s home side communication device  100 . 
     In S 301 , the communication building side communication device  200  transmits a test start signal to the user&#39;s home side communication device  100 . In S 302 , the user&#39;s home side communication device  100  transmits the information (for example, the maximum allowable voltage and the like) on the user&#39;s home side communication device  100  to the communication building side communication device  200 . In S 303 , the communication building side communication device  200  transmits the information on the communication building side communication device  200  to the user&#39;s home side communication device  100 . 
     In S 304 , the user&#39;s home side communication device  100  transmits the information indicating that preparation for receiving the fed power is completed to the communication building side communication device  200 . 
     In S 305 , the communication building side communication device  200  performs an insulation check test by applying the voltage to the metal cable. When no problem is found in the insulation check test, the communication building side communication device  200  starts to feed the power to the user&#39;s home side control device  100  in S 306 . 
     In S 307 , the user&#39;s home side communication device  100  monitors the voltage and the current of the fed power and, when there is any problem, notifies it to the communication building side communication device  200 , and the communication building side communication device  200  stops feeding the power. Furthermore, the communication building side communication device  200  also monitors the voltage and the current of the power to be fed, and stops feeding the power when there is any problem in insulation properties or the like. This makes it possible to secure the safety of the user. 
     When the power fed from the commercial power supply is restored in the user&#39;s home side communication device  100 , the user&#39;s home side communication device  100  transmits a power feeding stop instruction to the communication building side communication device  200  in S 308 . 
     Example of Using Single Pair Ethernet® 
     While any kinds of metal cables may be used as the metal cable according to the embodiment, a cable of Single Pair Ethernet® (referred to as SPE hereinafter) can be used, for example. Since communication and power feeding can be performed simultaneously with the SPE, the safety check of the metal cable (power feeder) can be performed promptly without using the optical fiber. 
       FIG.  8    illustrates an example of an overall configuration of a communication system in a case of using the SPE as the metal cable. The length of the SPE with which communication and power feeding can be simultaneously performed is up to 1 km. Therefore, when the length of the cable from the communication building side communication device  200  to the user&#39;s home side control device  100  exceeds 1 km, a relay point is provided to connect the SPE. In  FIG.  8   , such relay points  300  are illustrated. 
     (Application to PON) 
     The technology that uses the metal cable as an emergency power feeder in a communication network where communication is performed via the optical fiber can also be applied to a Passive Optical Network (PON).  FIG.  9    illustrates an example of the configuration of the PON. With the PON, a splitter as a passive element is used to split an optical signal from the communication building to a plurality of signals and the optical fiber from the communication building to the splitter is shared by a plurality of users&#39; homes to achieve a cost-effective network. The splitter is provided within an optical splitter box  400  illustrated in  FIG.  9   . 
       FIG.  10    illustrates an example of an internal configuration of the optical splitter box according to the embodiment that uses the optical fiber and the metal cable. In the example illustrated in  FIG.  10   , the optical fiber and the metal cable are formed into a single cable as a composite cable. The optical fiber and the metal cable are separated within a composite cable branch box  410  inside the optical splitter box  400 , and the optical fiber is branched for a plurality of users&#39; homes by the splitter. 
     The metal cable is also branched for the plurality of users&#39; homes, and switches  411 ,  412 , and  413  are provided to each of the branched metal cables. The switches are semiconductor switches, for example, and the control unit  220  of the communication building side communication device  200  can control ON/OFF thereof. 
     For example, provided that there are a user&#39;s home A, a user&#39;s home B, and a user&#39;s home C as illustrated in  FIG.  10   , it is assumed that there are a user&#39;s home side communication device  100 A, a user&#39;s home side communication device  100 B, and a user&#39;s home side communication device  100 C provided in the respective homes. 
     It is assumed that a disaster occurs and a power failure occurs in the user&#39;s home A, the user&#39;s home B, and the user&#39;s home C. In that case, basically, a flow illustrated in  FIG.  4    is executed for each of the user&#39;s home side communication device  100 A, the user&#39;s home side communication device  100 B, and the user&#39;s home side communication device  100 C. 
     In particular, S 106  (check whether it is possible to communicate via the metal cable, activation of the user&#39;s home side communication device  100 ) and S 108  (normality check test of the metal cable) are performed by turning ON only the switch for the target user&#39;s home. For example, when the communication building side communication device  200  checks the metal cable for the user&#39;s home side communication device  100 A, the communication building side communication device  200  turns ON the switch  411  (turns OFF the switches  412  and  413 ) to perform the normality check of the metal cable for the user&#39;s home side communication device  100 A. Then, the communication building side communication device  200  turns ON the switch  412  (turns OFF the switches  411  and  413 ) to perform the normality check of the metal cable for the user&#39;s home side communication device  100 B. At last, the communication building side communication device  200  turns ON the switch  413  (turns OFF the switches  411  and  412 ) to perform the normality check of the metal cable for the user&#39;s home side communication device  100 C. 
     When the normality check of the entire metal cables for the user&#39;s home side communication device  100 A, the user&#39;s home side communication device  100 B, and the user&#39;s home side communication device  100 C is OK, all switches are turned ON to start to feed the power to the user&#39;s home side communication device  100 A, the user&#39;s home side communication device  100 B, and the user&#39;s home side communication device  100 C. Thereby, even during a disaster, the user&#39;s home side communication device  100 A, the user&#39;s home side communication device  100 B, and the user&#39;s home side communication device  100 C can perform optical fiber communication by the PON as with in a normal state. 
     In a case where the normality check of the metal cables for the user&#39;s home side communication device  100 A and the user&#39;s home side communication device  100 B is OK but the normality check of the metal cable for the user&#39;s home side communication device  100 C is NG, for example, the switch  411  and the switch  412  are turned ON and the switch  413  is turned OFF to start to feed the power. 
     (Example of Hardware Configuration) 
     Each of the user&#39;s home side communication device  100  and the station home side communication device  200  may not necessarily be a single device physically but may be configured by connecting a plurality of devices in a network. For example, each of the control unit  120  of the user&#39;s home side communication device  100  and the control unit  220  of the station home side communication device  200  may be implemented by causing a computer, for example, to execute a program in which the processing content described in the embodiment is written. 
     The above-described program can be recorded on a computer-readable recording medium (portable memory or the like) to be saved and distributed. Furthermore, the above-described program can be provided through a network such as the Internet or an e-mail. 
       FIG.  11    is a diagram illustrating an example of the hardware configuration of the above-described computer. The computer of  FIG.  11    includes a drive device  1000 , an auxiliary storage device  1002 , a memory device  1003 , a CPU  1004 , an interface device  1005 , a display device  1006 , an input device  1007 , an output device  1008 , and the like, which are mutually connected via a bus BS. 
     The program implementing the processing by the above-mentioned computer is provided by a recording medium  1001  such as a CD-ROM or a memory card, for example. When the recording medium  1001  to which the program is stored is set to the drive device  1000 , the program is installed to the auxiliary storage device  1002  from the recording medium  1001  via the drive device  1000 . Note that, however, the program may not necessarily be installed via the recording medium  1001  but may be downloaded from another computer via a network. The auxiliary storage device  1002  stores the installed program and also stores necessary files, data, and the like. 
     The memory device  1003  reads out and stores the program from the auxiliary storage device  1002 , when there is an instruction to start the program. The CPU  1004  implements a function related to the control units ( 120 ,  220 ) according to the program stored in the memory device  1003 . The interface device  1005  is used as an interface for being connected to the network. The display device  1006  displays Graphical User Interface (GUI) and the like by the program. The input device  1007  is configured with a keyboard, a mouse, buttons, a touch panel, or the like, and used to input various operation instructions. The output device  1008  outputs the results of arithmetic operations. 
     Effects of Embodiment 
     According to the technique related to the embodiment, it is possible to properly operate the user&#39;s home side communication device and continue communication via the optical fiber even when a power failure occurs on the user&#39;s home side due to a disaster. 
     Summary of Embodiment 
     The communication system and the communication method described at least in each of the following supplementary items are described in the present Description. 
     (Item 1) 
     A communication system including a communication building side communication device in a communication building and a user&#39;s home side communication device in a user&#39;s home, the communication building side communication device and the user&#39;s home side communication device being connected via an optical fiber and a metal cable, wherein: when a power fed to the user&#39;s home side communication device from a commercial power supply stops, the communication building side communication device feeds the power to the user&#39;s home side communication device via the metal cable to operate the user&#39;s home side communication device; and the user&#39;s home side communication device communicates with the communication building side communication device via the optical fiber. 
     (Item 2) 
     The communication system according to item 1, wherein the communication building side communication device performs safety check of the metal cable before feeding the power to the user&#39;s home side communication device. 
     (Item 3) 
     The communication system according to item 1 or 2, wherein, upon receiving a disaster signal, the communication building side communication device feeds the power to the user&#39;s home side communication device. 
     (Item 4) 
     The communication system according to any one of items 1 to 3, wherein the communication building side communication device feeds the power to the user&#39;s home side communication device with a voltage exceeding a voltage of SELV. 
     (Item 5) 
     The communication system according to any one of items 1 to 4, wherein: a PON is configured with the optical fiber; the optical fiber is branched to a plurality of optical fibers and the metal cable is branched to a plurality of metal cables by an optical splitter box in the PON; and a switch is provided to each of the branched metal cables. 
     (Item 6) 
     A communication method for a communication system including a communication building side communication device in a communication building and a user&#39;s home side communication device in a user&#39;s home, the communication building side communication device and the user&#39;s home side communication device being connected via an optical fiber and a metal cable, the communication method including: when a power fed to the user&#39;s home side communication device from a commercial power supply stops, feeding the power to the user&#39;s home side communication device from the communication building side communication device via the metal cable to operate the user&#39;s home side communication device for allowing the user&#39;s home side communication device to communicate with the communication building side communication device via the optical fiber. 
     While the embodiment has been described heretofore, the present invention is not limited to the specific embodiment but various modifications and changes are possible within the scope of the present invention described in the claims. 
     REFERENCE SIGNS LIST 
     
         
         
           
               100  User&#39;s home side communication device 
               110  Communication unit 
               120  Control unit 
               130  Metal IF unit 
               140  Optical IF unit 
               150  Photoelectric conversion unit 
               160  Power feed unit 
               170  Power storage unit 
               200  Communication building side communication 
             device 
               210  Communication unit 
               220  Control unit 
               230  Metal IF unit 
               240  Optical IF unit 
               250  Power feed unit 
               300  Relay point 
               400  Optical splitter box 
               410  Composite cable branch box 
               411  to  413  Switch 
               1000  Drive device 
               1001  Recording medium 
               1002  Auxiliary storage device 
               1003  Memory device 
               1004  CPU 
               1005  Interface device 
               1006  Display device 
               1007  Input device 
               1008  Output device