Patent Publication Number: US-2011078465-A1

Title: Information processing apparatus, method of controlling information processing apparatus, and storage medium

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus configured to process a job received from a host apparatus. 
     2. Description of the Related Art 
     Some network devices for network communication have a function of saving power consumption by automatically switching into a power saving state when no operation is performed over a predetermined period. 
     In such a network device, when it is in a power saving state, if it is operated by another device via a network, the network device returns to a normal state from the power saving state. 
     In a method, returning to the normal state from the power saving state is performed such that when an input signal is received via a network, a pattern of the received input signal is compared with an input signal pattern registered in advance. If the pattern of the received input signal is identical to the registered input signal pattern, the network device returns to the normal state from the power saving state. 
     It is known to use an input signal pattern called a Magic Packet™, which is a special pattern that does not appear in normal communication, to return a network device from a power saving state into a normal power state (see, for example, Japanese Patent Laid-Open No. 2006-270538). The input signal pattern used here refers to a packet pattern used in Ethernet™. However, not only Ethernet packet patterns but general input signal patterns can be used in the present invention. Therefore, hereinafter, those patterns will be generically referred to as input signal patterns. 
     In the network device having the power saving function, a known signal pattern such as a MAC address of the network device is assigned in advance as the input signal pattern used to return the network device from the power saving state into the normal power state, and thus anybody who knows the assigned input signal pattern can awake the network device from the power saving state. 
     This can cause the network device to exit the power saving state when the network device should remain in the power saving state. That is, the network device cannot remain in the power saving state over a period during which it should remain in the power saving state. 
     In the technique disclosed in Japanese Patent Laid-Open No. 2006-270538, the determination as to whether the network device should exit the power saving state is made simply based on a comparison of a particular bit pattern, and nothing is taken into consideration as to switching into one of a plurality of power saving states. The network device is fully activated into the normal power state in response to even a simple inquiry that can be dealt with out fully activating the network device. For example, even when the inquiry does not request a printing operation, power activation is performed for the whole network device including parts associated with the printing operation. This also makes it difficult to maintain the power saving state for a long period. 
     SUMMARY OF THE INVENTION 
     In view of the above, the present invention provides a technique of controlling the power state such that when a control unit is in a power saving mode, if a job is received from a host apparatus, a NIC unit responds by proxy to the job by using only some particular one or more of devices in the control unit. 
     More specifically, the present invention provides an information processing apparatus comprising a processing unit configured to process data and a storage unit configured to store data, the information processing apparatus being operable in one of power states including a first power state in which the processing unit can process data and can read data from the storage unit, a second power state in which the processing unit cannot process data but the processing unit can read data from the storage unit, and a third power state in which the processing unit cannot process data and the processing unit cannot read data from the storage unit, the information processing apparatus further comprising a receiving unit configured to receive data, and a control unit configured to control the power state of the information processing apparatus such that in a case where the receiving unit receives data when the information processing apparatus is operating in the third power state, the power state of the information processing apparatus is controlled as follows: in a case where the data received by the receiving unit does not need a process by the processing unit but data stored in the storage unit is necessary in processing the data received by the receiving unit, the power state of the information processing apparatus is switched from the third power state into the second power state; and in a case where the data received by the receiving unit does not need a process by the processing unit and data stored in the storage unit is not necessary in processing the data received by the receiving unit, the power state of the information processing apparatus is maintained in the third power state. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram schematically illustrating a configuration of an image input/output system. 
         FIG. 2  is a diagram illustrating a configuration of an image forming apparatus. 
         FIG. 3A  is a diagram illustrating an example of a configuration of a power supply unit in an image forming apparatus, and  FIG. 3B  is a diagram illustrating another example of a configuration of the power supply unit. 
         FIG. 4  is a diagram illustrating a configuration of a power supply control unit according to an embodiment of the invention. 
         FIG. 5  is a table of power states of a power supply circuit. 
         FIG. 6  is a flow chart illustrating a power control process performed in an image forming apparatus. 
         FIG. 7  is a flow chart illustrating a power control process performed in an image forming apparatus. 
         FIG. 8  is a pattern table managed by an image forming apparatus. 
         FIG. 9  is a flow chart illustrating a power control process performed in an image forming apparatus. 
         FIG. 10  is a flow chart illustrating a power control process performed in an image forming apparatus. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     The present invention is described in further detail below with reference to embodiments in conjunction with the accompanying drawings. 
     First Embodiment 
       FIG. 1  is a block diagram illustrating a configuration of an image input/output system according to an embodiment of the present invention. In the example shown in  FIG. 1 , the image input/output system includes an image forming apparatus. Although in this example the image forming apparatus is employed as an information processing apparatus, the information processing apparatus may be another apparatus or system configured to process data. 
       FIG. 2  is a diagram illustrating hardware and software configurations of the image forming apparatus  100  shown in  FIG. 1 . In this specific example shown in  FIG. 2 , the image forming apparatus in the image input/output system is assumed to be an MFP (Multi Function Peripheral) configured to communicate, using a particular protocol, with a network device via a network. In the image input/output system, the image forming apparatuses  100  and  111  are capable of communicating with an information processing apparatus (host apparatus)  110  via a network such as a LAN (Local Area Network)  112 . As for the host apparatus  110 , a personal computer (PC) or a workstation may be used. The host apparatus  110  has a printer driver and other utility software installed therein whereby communication with the image forming apparatus  100  or  111  is allowed using the printer driver and information associated with the image forming apparatus  100  or  111  can be acquired and displayed using the utility software. The host apparatus  110  is configured to communicate with the image forming apparatus  100  using different protocols depending on whether a job is associated with the image forming apparatus  100  or with a communication process. 
     Depending on the protocol used, the NIC unit  107  responds to a job received from the host apparatus  110  by proxy for the control unit  109  in the power saving mode. For example, if an echo request of ICMP (Internet Control Message Protocol) is received, the NIC unit  107  responds to it. When a job is received from the host apparatus  110 , the NIC unit  107  detects the type of the received job to determine whether the NIC unit  107  is to respond to it or the control unit  109  or some of devices in the control unit  109  is to respond to the job. More specifically, as shown in  FIG. 2 , the NIC unit  107  has a packet pattern database  127  in which packet patterns corresponding to the respective jobs are registered as will be described in detail later. 
     In the present example, the image input/output system includes two image forming apparatuses. However, there is no particular restriction on the number of image forming apparatuses, as long as there are at least two image forming apparatuses connected to the network. For example, the image input/output system may include three or more image forming apparatuses. 
     The image forming apparatus  100  and the image forming apparatus  111  are similar in configuration and thus the configuration will be described below only for the image forming apparatus  100  and a description of the configuration of the image forming apparatus  111  will be omitted. 
     In  FIG. 1 , the image forming apparatus  100  includes a digital copying unit  101  and an image input/output control unit  105 . The digital copying unit  101  is configured to produce image data of an original document by scanning the original document and print an image of the original document on paper according to the image data. 
     The image input/output control unit  105  is connected to the digital copying unit  101 , the network  112 , and a telephone line  113 , whereby the image input/output control unit  105  controls a process on image data received via the network  112  and the telephone line  113  and transmits resultant image data to the digital copying unit  101  or stores the image data. 
     The image input/output control unit  105  also controls a process performed on scanned image data transmitted from the digital copying unit  101  and transmits resultant data via the network  112  or the telephone line  113  or stores the data. 
     The digital copying unit  101  includes an operation unit  102 , a reader unit  103  and a printer unit  104  which are connected to each other such that image data and other data can be transmitted among them. 
     The operation unit  102  is used to issue an operation command to the digital copying unit  101  or the image input/output control unit  105 . The reader unit  103  is used to read an image of a document and output image data of the image of the document to the printer unit  104  and the image input/output control unit  105 . 
     The printer unit  104  serving as an image output unit is used to form an image on paper in accordance with image data supplied from the reader unit  103  via the image input/output control unit  105 . 
     The image input/output control unit  105  includes a control unit  109 , a facsimile unit  106 , a NIC unit  107 , and a hard disk  108 . The control unit  109  is connected to the reader unit  103  in the digital copying unit  101 , and the facsimile unit  106 , the NIC unit  107 , and the hard disk  108  are connected to the control unit  109 . The facsimile unit  106  is connected to the telephone line  113 , and the NIC unit  107  is connected to the network  112 . 
     If the facsimile unit  106  receives compressed facsimile data via the telephone line  113 , the facsimile unit  106  decompresses the received data and transfers resultant image data to the control unit  109 . 
     When the facsimile unit  106  receives image data from the control unit  109 , the facsimile unit  106  compresses the received image data and transmits resultant compressed image data as facsimile data via the telephone line  113 . The facsimile unit  106  can temporarily store received compressed image data in the hard disk  108  via the control unit  109 . 
     The NIC unit  107  serves as an interface between the network  112  and the control unit  109 , and the NIC unit  107  rasterizes data received from the host apparatus  110  into PDL (Page Description Language) data that is code data indicating an image printable by the printer unit  104 , and transmits the resultant PDL data to the control unit  109 . 
     The control unit  109  controls flowing of data, in particular image data, via the reader unit  103 , the facsimile unit  106 , the NIC unit  107 , and the hard disk  108 . That is, the control unit  109  controls storing and outputting of image data. 
     The control unit  109  includes a CPU  109 A, a ROM  109 B, and a RAM  109 C. In a sleep mode (also referred to as a power saving mode), electric power supplied to the control unit  109  from a power supply is cut off. Depending on the type of a packet received by the NIC unit  107 , a power supply control unit BC controls the power supply such that electric power is supplied to only some particular one or more of devices such as a nonvolatile memory device serving as the RAM  109 C even in the power saving mode. More specifically, the RAM  109 C in the control unit  109  is connected to a power supply circuit  501  including a switch  511 , which will be described later with reference to  FIG. 3B , such that the power supply control unit BC turns on/off the switch  511  under the control of a CPU  121  in the NIC unit  107  to control the electric power to the RAM  109 C. Note that, the power supply control unit BC controls electric power such that when electric power to the image forming apparatus  100  is turned on for the first time, the image forming apparatus  100  first operates in a power state # 1  (in which electric power is supplied to the whole control unit  109 ) and then, while the RAM  109 C is maintained in this state, the power state is switched into a power state # 2  or # 3  (in which electric power is supplied to only some particular one or more of devices in the control unit  109 ). By maintaining the RAM  109 C in the state into which the RAM  109 C is set when the image forming apparatus  100  is started with the power state # 1 , it becomes possible to control an operation such that the NIC unit  107  refers to data, status data, flag data, etc., stored in the RAM  109 C and responds by proxy to the external host apparatus  110 . 
     The NIC unit  107  includes a controller that controls communication performed via a network and also includes a memory. Note that electric power is supplied to the NIC unit  107  from the power supply control unit BC even in the power saving mode so that the NIC unit  107  can receive a request via the network  112 . 
     Depending on the content of an inquiry received from the host apparatus, the power supply control unit BC determines whether the whole control unit  109  is to be maintained in the power saving state or is to be switched to a particular-level power saving state or completely to a normal power state. The control unit  109  includes a plurality of devices such as a CPU, a ROM, a RAM, a hard disk, etc., and the power supply control unit BC controls supplying of power such that electric power is still supplied to some of devices even after the control unit  109  is switched into the power saving mode. 
     More specifically, the power supply control unit BC converts AC electric power supplied from an external AC power supply to DC electric power, and supplies the DC electric power to the hard disk  108 , the NIC unit  107 , the facsimile unit  106 , etc. In the sleep mode, the power supply control unit BC switches the power state into the power saving state by turning off electric power to the control unit  109 , the hard disk  108 , the operation unit  102 , the reader unit  103 , and the printer unit  104 . 
     In processing a job (which will be described in detail later), the power supply control unit BC determines a packet pattern of a received packet and controls the operation including the proxy response process or a WOL (Wake On LAN) process and reactivation of the control unit  109 . 
     The control described above makes it possible to process a received job without re-activating unnecessary devices even when the received job is not of a type to which the NIC unit  107  is allowed to directly respond by proxy. That is, the received job is dealt with by supplying electric power only to devices necessary in dealing with the job. This allows a reduction in power consumption to execute a job that needs accessing information that is managed by the control unit  109  and that indicates the status of the image forming apparatus, and thus a reduction in total power consumption of the system is achieved. 
     Referring to  FIG. 2 , main units of the image forming apparatus  100  are the control unit  109  and the NIC unit  107 . 
     The NIC unit  107  includes a network I/F unit  125  configured to transmit/receive a network packet to/from an external LAN  112 , and also includes a NIC control unit  124  configured to activate the NIC unit  107  and communicate with the control unit  109  in the image forming apparatus  100 . The NIC unit  107  also includes a packet pattern DB  127  in which proxy response packet patterns are registered such that in accordance with the proxy response packet pattern, the NIC unit  107  responds to the packet received via the LAN  112  by proxy for the control unit  109  in the image forming apparatus  100 . The NIC control unit  124  includes a CPU  121 , a RAM  123 , and a ROM  122 . 
     The control unit  109  includes an SNMP module unit  508  configured to transmit/receive SNMP (Simple Network Management Protocol) to/from an external apparatus (such as the host PC  150 ) via a network protocol stack  504 . The control unit  109  in the image forming apparatus  100  also includes a port module unit  509  configured to perform printing. 
     The control unit  109  also includes a sleep control unit  507  that controls power saving by switching to/from the sleep mode. The control unit  109  also includes a proxy response registration unit  506  configured to register proxy response packet patterns in the NIC unit  107 . 
     The control unit  109  also includes a user interface (UI) unit  510  used by a user to set functions. The control unit  109  has a function of storing a received packet in a packet storage unit  128 . 
     Next, a description is given below as to a proxy response process performed in the power saving mode by the image forming apparatus configured in the above-described manner. 
     To achieve the power saving mode, it is common to stop supplying electric power to the CPU of the control unit  109 , and only some particular hardware modules are operated during the power saving mode. 
     To realize the proxy response function in the NIC unit  107 , the image forming apparatus has an extension I/F in the NIC unit  107  that makes it possible to communicate with the control unit  109 . 
     Because the NIC unit  107  has the CPU  121 , it is possible to receive a job via the network  112  and perform a process associated with it while keeping functions even in the power saving mode in which the control unit  109  and the printer unit  104  do not operate. 
     The proxy response function refers to a function of responding to a packet by proxy such that in a case where when the control unit  109  is in the power saving mode, a packet addressed to the image forming apparatus  100  is received from the external host PC  110 , if the packet has a pattern identical to a registered packet pattern, then the NIC unit  107  or another server responds to this packet by proxy. 
     The NIC unit  107  in the image forming apparatus is capable of registering an arbitrary number of packet patterns that should be responded to by proxy and corresponding packet patterns that are to be sent in response to the respective received packet patterns. Note that those packet patterns are registering in the network I/F  125  before the operation mode is switched into the power saving mode. 
     Next, controlling of electric power of the image forming apparatus according to the present embodiment is described. 
       FIGS. 3A and 3B  illustrate examples of configurations for the power supply control unit shown in  FIG. 1 .  FIG. 3A  illustrates a conventional configuration of a power supply control unit, while  FIG. 3B  illustrates a configuration of the power supply unit of the image forming apparatus according to the present embodiment of the invention. 
     In  FIG. 3A , a power supply unit  401  includes power supply circuits  411  and  412  that generate different DC voltages that are supplied via different lines, i.e., the power supply circuits  411  and  412  provide different power supply systems. The power supply circuit  411  in the system # 1  provides a power output # 1 , and the power supply circuit  412  in the system # 2  provides a power output # 2  that is different from the power output # 1 . The power output # 1  and the power output # 2  are determined according to potential levels in parts of the image forming apparatus. Note that although the example shown in  FIG. 3A  includes two systems, the image forming apparatus according to the present embodiment may include three or more systems. 
     Referring to  FIG. 3B , the power supply circuit  501  includes a switch  511  and a voltage conversion circuit  512 . The switch  511  controls transferring of input electric power to the voltage conversion circuit  512 . 
     When the switch  511  is in an ON state, the power output with a voltage converted from an input power voltage is provided. On the other hand, when the switch  511  is in an OFF state, no power output is provided. The power supply control unit BC controls turning-on/off of the power supply circuit  501  such that after the control unit  109  is switched into the power saving mode, only some of or all of devices in the control unit  109  are selectively supplied with electric power to allow the NIC unit  107  to respond by proxy to a job received from the host apparatus  110 . The above-described devices in the control unit  109  include the CPU  109 A, the ROM  109 B, and the RAM  109 C. The determination as to whether electric power is supplied to only some of or all of devices in the control unit  109  is made by the CPU  121  of the NIC unit  107  according to a packet pattern of a received job and a power state specified for the packet pattern registered in advance. 
       FIG. 4  illustrates a configuration of a power supply control unit including a control unit that controls the switch  511  shown in  FIG. 3 . In the example shown in  FIG. 4 , the power supply control unit  650  includes a control unit  614  and a power supply unit  601 . 
     In  FIG. 4 , the power supply unit  601  includes a power supply circuit  611  corresponding to a system # 1  including no switch (corresponding to the switch  511  shown in  FIG. 3B ) that turns on/off electric power. The power supply unit  601  also includes power supply circuits  612  and  613  corresponding to systems # 2  and # 3  including switches S 1  and S 2  that turn on/off electric power. 
     The power supply circuit  612  including the switch S 1  and the power supply circuit  613  including the switch S 2  are connected to the control unit  614  that controls turning-on/off of electric power. 
     The power supply circuit  612  and the power supply circuit  613  each can be in either the ON state or OFF state under the control of the control unit  614 . The power supply unit  601  as a whole has three power states. Note that the control unit  614  is disposed in the power supply control unit BC. 
     If a special power state in which all power supply circuits  611 ,  612 , and  613  are in the OFF state is also counted, the power supply unit  601  has a total of four power states as shown in  FIG. 5 . 
     Note that  FIG. 5  illustrates an example of a state table indicating power states of the power supply circuit shown in  FIG. 4 . That is,  FIG. 5  illustrates power states # 1  to # 4  in which each system is in the ON or OFF state. Note that the power state # 4  is special in that all systems # 1  to # 3  are in the OFF state. The system # 1  corresponds to the power supply circuit  611  having no switch, and thus the system # 1  can be only in the ON state for all power states # 1  to # 3  except for the special power state # 4 . 
       FIG. 6  is a flow chart illustrating an example of a power control procedure performed in the image forming apparatus according to the present embodiment of the invention. That is,  FIG. 6  illustrates a process of periodically determining whether the power state is allowed to be switched into a power saving state. Depending on the determination, the power state is switched into the power state # 2  or # 3  or other power states. In  FIG. 6 , the process includes steps S 801  to S 803  that are performed by the CPU  109 A in the control unit  109  shown in  FIG. 1 . 
     In step S 801 , the CPU  109 A of the control unit  109  determines whether the image forming apparatus is allowed to be switched into a power saving state. If switching into a power saving state is allowed, then a further determination is made as to which power saving state to switch to. 
     For example, in a case where the reader unit  103  is in operation of reading a document or in a case where the printer unit  104  is in operation of printing, the CPU  109 A of the control unit  109  determines that switching into a power saving state is not allowed. Even in a case where switching into a power saving state is allowed, if switching into the power saving state # 3  is prohibited by a user, the CPU  109 A of the control unit  109  determines that switching into the power saving state # 2  is to be performed. 
     If the determination in step S 801  by the CPU  109 A of the control unit  109  is that switching into a power saving state is not to be performed, the process is ended. 
     On the other hand, in a case where the determination in step S 801  by the CPU  109 A of the control unit  109  is that switching into the power saving state # 2  shown in  FIG. 5  is to be performed, the process proceeds to step S 802  to perform switching into the power saving state # 2 . After switching into the power saving state # 2  is completed, the process is ended. In the process of switching into the power saving state # 2 , the CPU  109 A of the control unit  109  sends a command to the control unit  614  to switch the power state into the power state # 2 . In response, the control unit  614  turns off the power to the power supply circuit  613 . 
     In a case where the determination in step S 801  by the CPU  109 A of the control unit  109  is that switching into the power saving state # 3  is to be performed, the process proceeds to step S 803  to perform switching into the power saving state # 3 . 
     In the process of switching into the power saving state # 3 , the CPU  109 A of the control unit  109  sends a command to the control unit  614  to switch the power state into the power state # 3 . In response, the control unit  614  turns off the power to the power supply circuit  612  and the power supply circuit  613 . 
     In the manner described above, the power state of the image forming apparatus  100  is controlled. 
       FIG. 7  is a flow chart illustrating an example of a power control procedure performed in the image forming apparatus according to the present embodiment of the invention. This process is performed when the NIC unit  7  receives a network packet in a situation in which the image forming apparatus  100  is in the power state # 3 . In  FIG. 7 , the process includes steps S 901  to S 905  that are performed by the CPU  121  in the NIC unit  107 . 
     In step S 901 , the CPU  121  in the NIC unit  107  refers to a pattern table that will be described later. Next, in step S 902 , the CPU  121  in the NIC unit  107  determines whether a pattern of a received network packet is equal to one of registered packet patterns. 
     More specifically, in step S 902 , the CPU  121  in the NIC unit  107  compares the packet received via the network with pattern data in the pattern table to determine whether the pattern of the received packet is identical to one of registered patterns. In a case where the CPU  121  in the NIC unit  107  determines that there is no identical pattern, the process proceeds to step S 903 . Note that the patterns subjected to the comparison are registered in advance in the packet pattern database  127  shown in  FIG. 2 . 
     In step S 903 , the CPU  121  in the NIC unit  107  determines whether the comparison is completed for all patterns in the pattern table. In a case where it is determined that the comparison is competed for all patterns in the pattern table, the process proceeds to step S 904 , but otherwise the process returns to step S 901  to determine whether the network pattern is identical to a next pattern in the pattern table. 
     In step S 904 , the CPU  121  in the NIC unit  107  switches the power state into the power state # 1  shown in  FIG. 5  and performs a normal process on the received packet. After step S 904  is completed, the process is ended. This case can occur when the received packet cannot be dealt with only by the NIC unit  7 . A specific example is a case in which the received job includes print data to be printed. 
     On the other hand, in a case where it is determined in step S 902  by the CPU  121  in the NIC unit  107  that the received network packet is identical to one of patterns in the pattern table, the process proceeds to step S 905 . 
     In step S 905 , the CPU  121  in the NIC unit  107  deals with the packet received via the network in a power saving state. After step S 905  is completed, the process is ended. The process in step S 905  will be described in further detail later. 
       FIG. 8  illustrates an example of a pattern table managed by the NIC unit  107  shown in  FIG. 1 . More specifically, this example of the pattern table shown in FIG.  8  is used in step S 902  shown in  FIG. 7  by the CPU  121  in the NIC unit  107  to determine whether the network packet received via the network is identical to one of patterns described in the pattern table. Note that this pattern table is stored in advance in the packet pattern database  127  shown in  FIG. 2 . 
     In the pattern table shown in  FIG. 8 , pattern data  1003  with which to compare a received network packet is described in relation to a target power state  1002  to which to switch if the received network packet is identical to pattern data. In the example shown in  FIG. 8 , there are six target power states. The pattern table makes it possible to select one of power states corresponding to respective power saving states. 
     For example, when an echo request of ICMP (Internet Control Message Protocol) is received, a predetermined response is returned. Because the response is predetermined, the NIC unit  107  can respond to the echo request without changing the power state. 
     In this case, an ICMP echo request is described as a pattern in the pattern data  1003  and a power state # 3  is described as a target power state  1002  corresponding to the ICMP echo request. 
     In the case of SNMP (Simple Network Management Protocol), it has an interface to inquire what internal state the apparatus is in. Note that the apparatus does not necessary remain in the same internal state but can switch into a different internal state. 
     In a case where when the response varies depending on which internal state the apparatus is in, the power state is returned into the normal state for the whole image forming apparatus  100  including the control unit  109 , and status information is acquired. In accordance with the acquired status information, the response is performed. 
     In this case, various inquiry packet patterns of SNMP are described as patterns in the pattern data  1003 , and the power state # 2  is described as a target power state  1002  assigned to the those patterns. 
       FIG. 9  is a flow chart illustrating an example of a power control procedure performed in the image forming apparatus according to the present embodiment of the invention. More specifically,  FIG. 9  illustrates the details of step S 905  that is performed when it is determined in step S 902  that a pattern identical to a received network packet is found in the pattern table. In  FIG. 9 , the process includes steps S 1101  to S 1105  that are performed by the CPU  121  in the NIC unit  107 . 
     First, in step S 1101 , the CPU  121  in the NIC unit  107  determines based on the pattern table whether the power saving state # 3  is specified as the target power state to which to switch. More specifically, the CPU  121  in the NIC unit  107  refers to data described in the column “target power state”  1002  of the pattern table shown in  FIG. 8  and determines the target power state to which to switch. 
     In a case where the determination by the CPU  121  in the NIC unit  107  is that the power state # 3  is the target power state to which to switch, switching is not necessary because the process is being currently performed in the power state # 3 . In this case, the process proceeds to step S 1102 . 
     In step S 1102 , the NIC unit  107  performs a predetermined process. For example, an ICMP echo reply is returned in response to an ICMP Echo Request. After step S 1102 , the process is ended. Thus, in this case, the power saving state of the control unit  109  is maintained. 
     On the other hand, in a case where the determination in step S 1101  by the CPU  121  in the NIC unit  107  is that the power state # 2  is the target power state to which to switch, the process proceeds to step S 1103 . In step S 1103 , under the control of the CPU  121  of the NIC unit  107 , the power supply control unit BC switches the power state. 
     More specifically, the CPU  121  in the NIC unit  107  sends a command to the control unit  614  shown in  FIG. 5  to switch the power state into the power state # 2 . In response, the control unit  614  turns on the power to the power supply circuit  612  corresponding to the system # 2 . 
     In step S 1103 , after the power supply circuit  612  corresponding to the system # 2  is turned on, the CPU  121  in the NIC unit  107  acquires data from a location (for example, a memory in the control unit  109 ) that has been turned on into an accessible state, and performs a response process. This case occurs, for example, when the NIC unit  107  responds differently depending on a received inquiry such as an SNMP inquiry. 
     After the response process by the NIC unit  107  is completed, the processing flow proceeds to step S 1104 . In step S 1104 , the CPU  121  in the NIC unit  107  returns the power state of the power supply circuit  612  into the power state # 3 . Thereafter, the process is ended. 
     As a result, the electric power in the systems # 2  and # 3  are turned off into the OFF state. Thus, the system # 2  is in the ON state only for a minimum necessary period, and the system # 2  is returned into the previous power state at the end of the minimum necessary period. 
       FIG. 10  is a flow chart illustrating an example of a power control procedure performed in the image forming apparatus according to the present embodiment of the invention. More specifically,  FIG. 10  illustrates an example of a proxy response process performed by the NIC unit  107 . In  FIG. 10 , the process includes steps S 1201  to S 1207  that are performed by the CPU  121  in the NIC control unit  124  by loading a control program from a ROM  122  to a RAM  123  and executing it. More specifically, in this process, the CPU  121  of the NIC unit  107  reads information stored in the RAM  109 C in the control unit  109  and responds to a received job by proxy. 
     The RAM  109 C of the control unit  109  is realized using a DRAM, and the RAM  109 C can be in one of switchable power states: a non-powered state; a power state in which the RAM  109 C is self-refreshed and it is not allowed to read information from the RAM  109 C; and a normal power state in which the RAM  109 C is operable in a normal manner. The RAM  109 C is controlled such that self-refreshing in a power saving state does not cause information to be lost. In an operation mode (self-refresh mode) in which self-refreshing is performed, the RAM  109 C is in a power state in which the RAM  109 C is supplied with a lower power supply voltage than that in the normal state. Therefore, to make it possible for the CPU  121  of the NIC unit  107  to read information from the RAM  109 C, the power supply voltage level supplied to the RAM  109 C is increased to a normal level. After reading of information from the RAM  109 C by the CPU  121  of the NIC unit  107  is completed, the power supply voltage is returned to the voltage optimum for the self-refreshing operation (steps S 1205  to S 1207 ). 
     First, in step S 1201 , the CPU  121  of the NIC unit  107  determines whether a received packet is identical to a packet registered in the packet pattern database  127 . In a case where the CPU  121  in the NIC unit  107  determines that the packet is not registered, the process proceeds to step S 1202  to awake the control unit  109  from the sleep and transfer the packet to the control unit  109 . In step S 1202 , under the control of the CPU  121 , the power supply control unit BC returns the power state into the power state # 1 . After step S 1202  is completed, the process is ended. Thereafter, the received packet is transferred from the NIC unit  171  to the control unit  109 , and a response process is performed for the packet. 
     On the other hand, in a case where the determination in step S 1201  by the CPU  121  is that the packet received by the NIC unit  107  is identical to a packet registered in the packet pattern database  127 , the process proceeds to step S 1203 . 
     In step S 1203 , the CPU  121  determines whether, to deal with the received packet, it is necessary to access the memory in the control unit  109  that is in the power saving mode. In a case where the CPU  121  determines that it is not necessary to access the memory in the control unit  109  but it is possible to respond to the packet by accessing the memory in the NIC unit  107 , the process proceeds to step S 1204 . 
     In step S 1204 , the CPU  121  performs the proxy response process described above with reference to  FIG. 9 . After step S 1204  is completed, the process is ended. 
     On the other hand, in a case where the CPU  121  determines in step S 1203  that it is not possible to respond to the packet by only accessing the memory in the NIC unit  107  without accessing the memory in the control unit  109 , the process proceeds to step S 1205 . 
     In step S 1205 , under the control of the CPU  121 , the power supply control unit BC re-activates only the RAM  109 C in the control unit  109 . In step S 1206 , the CPU  121  accesses the RAM  109 C in the control unit  109  to acquire information necessary in the response process. Next, in step S 1207 , under the control of the CPU  121 , the power supply control unit BC switches the power state into the power saving state by again turning off the electric power to the RAM  109 C in the control unit  109 . After step S 1207  is completed, the process is ended. 
     Thus, depending on the content of the inquiry, the control unit  109  is maintained in the power saving state or is switched to another particular-level power saving state or fully switched into the normal power state. Thus, when the NIC unit  107  receives a packet, even if proxy response by the NIC unit  107  is not allowed for this received packet, it is not necessary to return the power state into the normal power state for all devices in the control unit  109 , but it is sufficient to supply electric power to, for example, the memory necessary in responding to the packet. That is, the reactivation is performed only for particular devices. The devices include memory resources such as the memory or the hard disk disposed in the control unit  109 . 
     In the embodiments described above, it is assumed that the image forming apparatus is an electrophotographic image forming apparatus. However, the present invention is also applicable to other types of image forming apparatuses such as an ink-jet image forming apparatus. 
     The image forming apparatus is not limited to the MFP (Multi Function Peripheral), but the image forming apparatus may be a single-function apparatus such as a printer. 
     Other Embodiments 
     Aspects of the present invention can also be realized by a computer of a system or apparatus (or devices such as a CPU or MPU) that reads out and executes a program recorded on a memory device to perform the functions of the above-described embodiment(s), and by a method, the steps of which are performed by a computer of a system or apparatus by, for example, reading out and executing a program recorded on a memory device to perform the functions of the above-described embodiment(s). For this purpose, the program is provided to the computer for example via a network or from a recording medium of various types serving as the memory device (e.g., computer-readable medium). 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2009-221340, filed Sep. 25, 2009, which is hereby incorporated by reference herein in its entirety.