Patent Publication Number: US-2007104213-A1

Title: Client-server system and server apparatus

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a client-server system in which a client terminal apparatus communicates with a server apparatus via a wireless LAN and a server apparatus constituting the system.  
      2. Description of the Related Art  
      Conventionally, there is known a client-server system that a server apparatus to which an AV device such as a video recorder, a PVR (Personal Video Recorder), a DVD (Digital Versatile Disk) player, an audio apparatus or the like are connected and a client terminal apparatus which includes output apparatus such as television apparatus are connected via a wireless LAN or the like.  
      The client-server system transmits the various types of information of the AV device to the client terminal apparatus from the server apparatus, and outputs it from the output apparatus.  
      For example, in the case of a IEEE802.11a,b,g-type wireless LAN system, when a server apparatus and a client terminal apparatus establish a link via a wireless LAN, the usable channel which is set by the server apparatus is searched among a plurality of channels by the client terminal apparatus after the server apparatus sets one of the channels as the usable channel out of a plurality of channels.  
      Therefore, in setting the usable channels of the system, a wireless LAN system that sets the channels which are detected by searching for not-used channels or channels having the minimum power interference wave among a plurality of channels by the server apparatus as the usable channels is developed (see Patent Publication 1 for example).  
      There has been developed a method for controlling a wireless communication module which enables a stable and efficient wireless communication by measuring the connection status of a link according to the power supply status and by switching the usable channel based on the measurement result (See Patent Publication 2, for example). 
          [Patent Publication 1] Japanese Laid-open Patent Publication No. 2003-249935     [Patent Publication 2] Japanese Laid-open Patent Publication No. 2003-110577        

      However, in the case of Patent Publication 1 and the like, when a link between a server apparatus and a client terminal apparatus is to be established, the server apparatus must set a usable channel among a plurality of channels and the client terminal apparatus must search the usable channel set by the server apparatus. This causes a problem where the link cannot be promptly established after the power source is turned on. This problem causes an inconvenience to a user because the server apparatus and the client terminal apparatus cannot perform transmission and reception of the information until the link is established.  
     SUMMARY OF THE INVENION  
      In view of the above, it is an object of the present invention to provide a client-server system in which the link via a wireless LAN can be established more promptly to consequently provide a more user-friendly system, and a server apparatus constituting the system.  
      In order to solve the above problem, in accordance with a first aspect of the present invention, in a client-server system in which a client terminal apparatus and a server apparatus are connected via one of a plurality of channels of a wireless LAN to have communication therebetween,  
      the server apparatus comprises:  
      a channel usage search unit which searches a usage of the plurality of channels when the server apparatus is in a no-connection status with the client terminal apparatus;  
      a priority level deciding unit which decides priority levels of use of the plurality of channels based on a search result of the channel usage search unit;  
      a server-side usable channel setting unit side which sets the channels as usable channels of the wireless LAN in an order of descending priority levels based on the priority levels decided by the priority level deciding unit when the server apparatus connects to the client terminal apparatus;  
      a server-side priority level information memory unit which stores priority level information regarding the priority level decided by the priority level deciding unit;  
      a server-side priority level information updating unit which updates the priority level information stored in the server-side priority level information memory unit every time when the priority levels of the use of the plurality of channels are decided by the priority level deciding unit;  
      a priority level information transmission unit which transmits the priority level information which is read from the priority level information memory unit to the client terminal apparatus when the server apparatus is in a connection status with the client terminal apparatus; and  
      a search time information acquisition unit which acquires search time information regarding a search time for the usage of the plurality of channels by the channel usage search unit, wherein:  
      the priority level information transmission unit transmits the priority level information including the search time information acquired by the search time information acquisition unit to the client terminal apparatus;  
      the client terminal apparatus comprises:  
      a priority level information receiving unit which receives the priority level information transmitted from the priority level information transmission unit;  
      a client-side priority level information memory unit which stores the priority level information received by the priority level information receiving unit;  
      a client-side priority level information updating unit which updates the priority level information stored in the client-side priority level information memory unit every time when the priority level information is received by the priority level information receiving unit; and  
      a client-side usable channel setting unit which sets the channels as usable channels of the wireless LAN in the order of descending priority levels based on the priority level according to the priority level information stored in the client-side priority level information memory unit when the client terminal apparatus reconnects to the server apparatus.  
      According to the first aspect of the present invention, when the server apparatus is in a no-connection status with the client terminal apparatus, the channel usage search unit searches the usage of the plurality of channels of the wireless LAN. The priority level deciding unit decides the priority levels of the plurality of channels based on the search result. The server-side usable channel setting unit can set the channels as usable channels of the wireless LAN in the order of descending priority levels based on the decided priority levels. Therefore, when the wireless LAN link between the client terminal apparatus and the server apparatus is to be established, the usable channels can be set beforehand by considering the usage of the plurality of channels of the wireless LAN in the server apparatus. Thus, the wireless LAN link can be established more promptly and as a result, a user-friendly client-server system can be provided.  
      When the server apparatus is in a connection status with the client terminal apparatus, the priority level information read from the priority level information memory unit can be transmitted to the client terminal apparatus by the priority level information transmission unit. The client terminal apparatus can set the channels as usable channels in the wireless LAN in the order of descending priority levels by the client-side usable channel setting unit based on the priority levels according to the priority level information received by the priority level information receiving unit. Therefore, when the client terminal apparatus reestablishes the wireless LAN link to the server apparatus after the link is once cut, the client terminal apparatus can set the usable channels by considering the usage of the plurality of channels of the wireless LAN based on the received priority level information at the time of establishment of the wireless LAN link between the client terminal apparatus and the server apparatus.  
      Furthermore, since the server apparatus comprises the server-side priority level information memory unit for storing the priority level information, when the wireless LAN link between the server apparatus and the client terminal apparatus is to be established, the usable channels can be more promptly set based on the stored priority level information. Moreover, when the server apparatus is connected to the client terminal apparatus, the priority level information read from the priority level information memory unit can be transmitted to the client terminal apparatus by the priority level information transmission unit.  
      The client terminal apparatus also comprises the client-side priority level information memory unit for storing the priority level information received by the priority level information receiving unit. Thus, when the wireless LAN link to the server apparatus is reestablished after the link is once cut, the usable channels can be more promptly set based on the stored priority level information.  
      Furthermore, the server apparatus can update the priority level information stored in the server-side priority level information memory unit by the server-side priority level information updating unit every time when the priority levels of the use of the plurality of channels are decided. Thus, the usable channels can be set more properly based on the updated priority level information.  
      The client terminal apparatus can update the priority level information stored in the client-side priority level information memory unit by the client-side priority level information updating unit every time when the priority level information transmitted from the priority level information transmission unit is received by the priority level information receiving unit. Therefore, when the wireless LAN link to the server apparatus is reestablished after the link is once cut, the usable channels can be set more properly based on the updated priority level information.  
      Furthermore, the server apparatus can acquire the search time information regarding the search time of the usage of the plurality of channels according to the channel usage search unit by the search time information acquisition unit. Therefore, the usage of the plurality of channels at a predetermined time can be acquired based on the search time information. Thus, the usable channels can be more properly set in accordance with a time zone.  
      The priority level information transmission unit transmits the priority level information including the search time information acquired by the search time information acquisition unit to the client terminal apparatus. Thus, the client terminal apparatus can set the usable channels more properly based on the acquired search time information in accordance with a time zone when the wireless LAN link to the server apparatus is reestablished after the link is once cut.  
      In accordance with the second aspect of the present invention, in a client-server system in which a client terminal apparatus and a server apparatus are connected via one of a plurality of channels of a wireless LAN to have communication therebetween,  
      the server apparatus comprises:  
      a channel usage search unit which searches a usage of the plurality of channels when the server apparatus is in a no-connection status with the client terminal apparatus;  
      a priority level deciding unit which decides priority levels of use of the plurality of channels based on the search result of a channel usage search unit; and  
      a server-side usable channel setting unit which sets the channels as usable channels of the wireless LAN in an order of descending priority levels based on the priority levels decided by the priority level deciding unit when the server apparatus connects with the client terminal apparatus.  
      According to the second aspect of the present invention, when the server apparatus is in a no-connection status with the client terminal apparatus, the channel usage search unit searches the usage of the plurality of channels of the wireless LAN. The priority level deciding unit decides the priority levels of use of the plurality of channels based on the search result. The server-side usable channel setting unit can set the channels as the usable channels of the wireless LAN in the order of descending priority levels based on the decided priority levels. Therefore, when the wireless LAN link between the client terminal apparatus and the server apparatus is to be established, the usable channels can be set beforehand by considering the usage of the plurality of channels of the wireless LAN in the server apparatus. Thus, the wireless LAN link can be reestablished more promptly and as a result, a user-friendly client-server system can be provided.  
      Preferably, the server apparatus comprises:  
      a priority level information transmission unit which transmits priority information regarding the priority levels decided by the priority level deciding unit to the client terminal apparatus when the server apparatus is in a connection status with the client terminal apparatus; and  
      the client terminal apparatus comprises:  
      a priority level information receiving unit which receives the priority level information transmitted from the priority level information transmission unit; and  
      a client-side usable channel setting unit which sets the channels as usable channels of the wireless LAN in the order of descending priority levels base on the priority level according to the priority level information received by the priority level information receiving unit when the client terminal apparatus reconnects to the server apparatus.  
      In the present invention, the same effect is obtained. Further, when the server apparatus is in a connection status with the client terminal apparatus, the priority level information regarding the decided priority levels can be transmitted to the client terminal apparatus by the priority level information transmission unit. The client terminal apparatus can set the usable channels of the wireless LAN in the order of descending priority levels by the client-side usable channel setting unit based on the priority levels according to the priority level information received by the priority level information receiving unit. Therefore, when the wireless LAN link to the server apparatus is reestablished after the link is once cut, the client terminal apparatus can set the usable channels by considering the usage of the plurality of channels of the wireless LAN based on the received priority level information at the time of the wireless LAN link between the client terminal apparatus and the server apparatus is established.  
      Preferably, the server apparatus comprises:  
      a server-side priority level information memory unit which stores the priority level information; and  
      the priority level information transmission unit transmits the priority level information read from the priority level information memory unit to the client terminal apparatus when the server apparatus is connected to the client terminal apparatus; and  
      the client terminal apparatus comprises:  
      a client-side priority level information memory unit which stores the priority level information which is transmitted by the priority level information transmission unit and is received by the priority level information receiving unit.  
      In the present invention, the same effect is obtained. Further, the server apparatus comprises the server-side priority level information memory unit for storing the priority level information. Therefore, the usable channels can be set more promptly based on the stored priority level information at the time of establishment of the wireless LAN link between the server apparatus and the client terminal apparatus. Furthermore, when the server apparatus is connected to the client terminal apparatus, the priority level information read by the priority level information transmission unit from the priority level information memory unit can be transmitted to the client terminal apparatus.  
      Moreover, the client terminal apparatus includes the client-side priority level information memory unit for storing the priority level information received by the priority level information receiving unit. Therefore, when the wireless LAN link to the server apparatus is reestablished after the link is once cut, the usable channels can be more promptly set based on the stored priority level information.  
      Preferably, the server apparatus comprises:  
      a server-side priority level information updating unit which updates the priority level information stored in the server-side priority level information memory unit every time when the priority levels of the use of the plurality of channels are decided by the priority level deciding unit, and  
      the client terminal apparatus comprises:  
      a client-side priority level information updating unit which updates the priority level information stored in the client-side priority level information memory unit every time when the priority level information which is transmitted from the priority level information transmission unit is received by the priority level information receiving unit.  
      In the present invention, the same effect is obtained. Further, the server apparatus can update the priority level information stored in the server-side priority level information memory unit by the server-side priority level information updating unit every time when the priority levels of use of the plurality of channels are decided. Therefore, the usable channels can be set more properly based on the updated priority level information.  
      Further, the client terminal apparatus updates the priority level information stored in the client-side priority level information memory unit by the client-side priority level information updating unit every time when the priority level information transmitted from the priority level information transmission unit is received by the priority level information receiving unit. Thus, when the wireless LAN link to the server apparatus is reestablished after the link is once cut, the usable channels can be set more properly based on the updated priority level information.  
      Preferably, the server apparatus comprises:  
      a search time information acquisition unit which acquires search time information regarding a search time of the usage of the plurality of channels by the channel usage search unit; and  
      the priority level information transmission unit transmits the priority level information including the search time information acquired by the search time information acquisition unit to the client terminal apparatus.  
      In the present invention, the same effect is obtained. Further, the server apparatus can acquire search time information regarding a search time for searching the usage of the plurality of channels by the search time information acquisition unit. Therefore, the usage of the plurality of channels at a predetermined time can be acquired based on the search time information. Thus, the usable channels can be more properly set in accordance with a time zone.  
      The priority level information transmission unit transmits the priority level information including the search time information acquired by the search time information acquisition unit to the client terminal apparatus. Therefore, the client terminal apparatus can set the usable channels more properly in accordance with a time zone based on the acquired search time information when the wireless LAN link to the server apparatus is reestablished after the link is once cut.  
      In accordance with the third aspect of the present invention, in a server apparatus which is connected to a client terminal apparatus via one of a plurality of channels of a wireless LAN to have communication therebetween, comprises:  
      a channel usage search unit which searches a usage of the plurality of channels when the server apparatus is in a no-connection status with the client terminal apparatus,  
      a priority level deciding unit which decides priority levels of use of the plurality of channels based on a search result by the channel usage search unit, and  
      an usable channel setting unit which sets the channels as usable channels of the wireless LAN in an order of descending priority levels based on the priority levels decided by the priority level deciding unit when the server apparatus connects with the client terminal apparatus.  
      According to the third aspect of the present invention, when the server apparatus is in a no-connection status with the client terminal apparatus, the channel usage search unit searches the usages of the plurality of channels of the wireless LAN. The priority level deciding unit decides the priority levels of use of the plurality of channels based on the search result. The server-side usable channel setting unit can set the usable channels in the wireless LAN in the order of descending priority levels based on the decided priority levels. Therefore, when the wireless LAN link between the client terminal apparatus and the server apparatus is established, the server apparatus can set the usable channels beforehand by considering the usages of the plurality of channels of the wireless LAN. Thus, the wireless LAN link can be reestablished more promptly and as a result, a user-friendly client-server system can be provided.  
    
    
     BRIEF DISCRIPTION OF THE DRAWINGS  
      The present invention will become fully understood from the detailed description given hereinafter and the accompanying drawings given by way of illustration only, and thus are not intended as a definition of the limits of the present invention, wherein;  
       FIG. 1  is a schematic diagram showing an entire structure of a client-server system of one preferable embodiment to which the present invention is applied.  
       FIG. 2  is a block diagram showing a principal structure of a server apparatus constituting the client-server system of  FIG. 1 .  
       FIG. 3  is a schematic diagram showing a priority level table stored in an information memory unit of the server apparatus of  FIG. 2 .  
       FIG. 4  is a block diagram showing a principal structure of a client terminal apparatus constituting the client-server system of  FIG. 1 .  
       FIG. 5  is a flowchart showing an example of operations in a link establishment process by the client-server system of  FIG. 1 .  
       FIG. 6  is a flowchart showing an example of operations in a link establishment process by the client-server system of  FIG. 1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERED EMBODIMENT  
      Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples.  
       FIG. 1  is a schematic diagram showing the entire structure of a client-server system  100  according to one preferred embodiment using the present invention.  
      The client-server system  100  of the present embodiment, for example, is a system realized in home. The client-server system  100  comprises, as shown in  FIG. 1 , a server apparatus  2  to which various types of AV devices  1  is connected, and a plurality of client terminal apparatuses  4  (three client terminal apparatuses are shown in  FIG. 1 ) which is connected to the server apparatus  2  via a wireless LAN N so that information communication can be performed and which an output apparatus  3  that outputs various types of information sent from server apparatus  2  is connected to, and the like.  
      The wireless network N, for example, may be a wireless LAN (Local Area Network) which complies with the IEEE (Institute of Electrical and Electronic Engineers) 802.11a,b,g standard.  
      Hereinafter, the server apparatus  2  will be described with reference to  FIG. 2  and  FIG. 3 .  
      Here,  FIG. 2  is a block diagram illustrating the main structure of the server apparatus  2 .  FIG. 3  is a schematic view illustrating a priority level table T stored in an information memory unit  22  of the server apparatus  2 .  
      The server apparatus  2 , for example, as shown in  FIG. 2 , comprises a communication control unit  21  for providing communication with the client terminal apparatus  4  via the wireless network N, an information memory unit  22  for storing the priority level table T regarding the priority levels for the use of the plurality of channels in the wireless LAN, an input unit  23  for inputting various types of information outputted from the AV device  1 , an encoder  24  for encoding various types of information, a timekeeping unit  25 , a CPU  26 , a RAM  27 , a ROM  28 , and the like.  
      The communication control unit  21 , for example, sends and receives various types of information to and from the client terminal apparatus  4  via the wireless network N under the control of the CPU  26 . Specifically, the communication control unit  21  comprises a wireless LAN card  211  or the like in compliance with the IEEE802.11a,b,g standard that includes an antenna  21   a  for the transmission and reception of a wireless signal to and from the client terminal apparatus  4  and a media access controller (MAC)  21   b  for controlling the transmission and reception of an electric wave.  
      The communication control unit  21 , for example, may comprise a signal amplifier (omitted from the drawings) for amplifying a signal transmitted via the antenna  21   a . Further, the communication control unit  21 , for example, may comprise a switch (omitted from the drawings) for providing a switching between a transmission-related function and a reception-related function when the information is transmitted or received.  
      The MAC  21   b , as a channel usage search unit, for example, searches the status of the use (availability) of each of a plurality of channels of a wireless LAN of predetermined standard when the status is at not-connected state where the wireless link is not established between the server apparatus  2  and the client terminal apparatus  4 . Specifically, the MAC  21   b , for example, detects an electrical field intensity and an error rates of each channels and determines whether each of these channels has an electric wave interference with a wireless link of another system or not. And the MAC  21   b  searches the usages of each of the channels based on this determination result.  
      The MAC  21   b  also functions as a priority level deciding unit to decide the priority levels for the use of the plurality of channels based on the search result for the usages of a plurality of channels.  
      Here, the decision of the priority made by the MAC  21   b  is preferably performed at predetermined time interval. That is, for example, the MAC  21   b  preferably searches the usages of a plurality of channels every time when the timekeeping unit  25  measures a substantially one hour and decides the priority levels of the channels because the channel usage may be different depending on a time zone of a day.  
      The decided priority level is transmitted to the information memory unit  22  under the control of the CPU  26  to be stored as the priority level table T (after-mentioned).  
      Further, the MAC  21   b , as a usable channel setting unit of server side, sets the channels as usable channels of the wireless LAN in the order of descending priority levels based on the order of priority which is decided when connecting to the client terminal apparatus  4 . Specifically, the MAC  21   b  sets the channel which has the highest priority level in the priority level table T as the usable channel when the power source of the server apparatus  2  is turned on or when the wireless link is established, and transmits the predetermined synchronization establishment signal (beacon signal) via the set channel at a substantially fixed interval. At this time, when the MAC  21   b  determines that the channel having the highest priority level is being used in another wireless link, then the MAC  21   b  sets a channel having the next highest priority level as the usable channel based on the priority level table T and performs the setting of the channel in this order sequentially.  
      The communication control unit  21  functions as a priority level information transmission unit to transmit the priority level table T regarding the priority levels for the use of a plurality of channels determined under the control of the CPU  26  to the client terminal apparatus  4 , when the wireless link between the server apparatus  2  and the client terminal apparatus  4  is established and is in connection status, for example.  
      Further, the communication control unit  21 , for example, transmits various types of image information and audio information which are inputted from the AV device  1  via the input unit  23  and encoded by the encoder  24  to transmit to the client terminal apparatus  4 .  
      As for the information memory unit  22 , for example, a recording medium such as a rewritable memory card or HDD or the like can be used. Further, the information memory unit  22  functions as the priority level information memory unit of server side to store the priority level table T (see  FIG. 3 ) that shows the correspondence among priority levels (PRIORITY), a channel (a toe), and a received signal strength (RSSI; dB).  
      Here,  FIG. 3  shows the priority level table T for a time zone from 10:00 to 11:00. However, the priority level tables of other time zones may be stored in the information memory unit  22 .  
      The information memory unit  22  may be incorporated in the main unit of the apparatus or may be connected to outside via a wireless or a wired link.  
      The encoder  24 , for example, encodes various types of information which are inputted from the AV device  1  and transmitted to the client terminal apparatus  4  to an image information having a predetermined file format (e.g., Joint Photographic Experts Group (JPEG), Moving Picture Experts Group phase 2 (MPEG-2)).  
      As for the AV device  1 , for example, a video recorder, a PVR (Personal Video Recorder), a DVD (Digital Versatile Disk) player, an audio apparatus, a BS (Broadcasting Satellite) tuner, a CS (Communication Satellite) tuner, a STB (Set Top Box) or the like can be used.  
      As for the timekeeping unit  25 , for example, a real-time clock can be used. And the timekeeping unit  25  keeps the execution time of various processes, such as a processing time for deciding priority levels for the use of channels, for example.  
      The CPU (Central Processing Unit)  26  controls each unit of the server apparatus  2  integrally, reads out various programs stored in the ROM  28  and expands the programs on a work area of the RAM  27 , and executes various processes based on these programs.  
      As for the RAM (Random Access Memory)  27 , for example, a rewritable memory can be used. And the RAM  27  constitutes a storage area and a work area for programs and various types of data or the like read from the ROM  28  under the control of the CPU  26 .  
      As for the ROM (Read Only Memory)  28 , for example, a read-only memory is used. And the ROM  28  stores various programs executed under the control of the CPU  26  and data and the like regarding the processing of these programs. Specifically, the priority level table updating program  28   a  is stored in the ROM  28 . This priority level table updating program  28   a  makes the CPU  26 , as the order of the server-side priority information updating unit, to realize the function according to the process of updating the information of the priority level table T stored in the information memory unit  22  every time when the order of priority for the use of the plurality of channels is decided by the MAC  21   b.    
      That is, when the wireless link between the server apparatus  2  and the client terminal apparatus  4  is cut and is in a no-connection status, the MAC  21   b  searches the usages of the plurality of channels in the wireless LAN at a predetermined timing and decides the priority levels of the channels. Thereafter, the CPU  26  updates the information of the priority level table T to be the latest information by executing the priority level table update program  28   a.    
      Next, the client terminal apparatus  4  will be described with reference to  FIG. 4 .  FIG. 4  is a block diagram illustrating the main structure of the client terminal apparatus  4 .  
      The client terminal apparatus  4 , as shown in  FIG. 4 , for example, comprises a communication control unit  41  for providing the communication with the server apparatus  2  via the wireless network N, an information memory unit  42  for storing the priority level table T received via this communication control unit  41 , a decoder  43  for decoding various types of encoded information received by the communication control unit  41 , an output unit  44  for outputting various types of information to the output apparatus  3 , a CPU  45 , a RAM  46 , a ROM  47 , and the like.  
      The communication control unit  41 , for example, as same as the communication control unit  21  included in the server apparatus  2 , includes a wireless LAN card  411  including an antenna  41   a  and a MAC  41   b  and the like, and sends and receives various types of information to and from the server apparatus  2  via the wireless network N.  
      Specifically, the communication control unit  41 , for example, as a priority level information receiving unit, receives the priority level table T transmitted from the communication control unit  21  of the server apparatus  2 .  
      The received priority level table T is transmitted to the information memory unit  42  to be stored therein.  
      The MAC  41   b , as a client-side usable channel setting unit, for example, as same as the MAC  21   b  of the server  2 , sets the usable channels of the wireless LAN in the order of descending priority levels based on the priority levels of channels prescribed in the priority level table T received via the communication control unit  41  when reconnecting to the server  2 .  
      The information memory unit  42 , for example, has substantially the same structure as that of the information memory unit  22  included in the server apparatus  2 . The information memory unit  42  functions as a client-side priority level information memory unit to store the priority level table T received via the communication control unit  41 .  
      The decoder  43 , for example, performs a process according to the file format of each of various types of encoded information which are received from the communication control unit  41  and decode the encrypted information to the predetermined information.  
      The output unit  44 , for example, includes an output terminal (omitted from the drawings) connected to an input terminal of the output apparatus  3  such as television apparatus or the like (omitted from the drawings), and outputs image information and audio information decrypted by the decoder  43  to the output apparatus  3 .  
      The output apparatus  3  is a general apparatus such as a television apparatus and thus will not be described in detail.  
      The CPU  45  controls each of the components of the client terminal apparatus  4  integrally. The CPU  45  reads various programs stored in the ROM  47  and expands the programs on a work area of the RAM  46  and executes various types of processes based on these programs.  
      As for the RAM  46 , for example, a rewritable memory can be used. And the RAM  46  constitutes a storage area and a work area and the like for programs and various types of data or the like read from the ROM  47  under the control of the CPU  45 .  
      The ROM  47 , for example, is a read-only memory and stores various programs executed under the control of the CPU  45  and data or the like regarding the processing of these programs. Specifically, the priority level table updating program  47   a  is stored in the ROM  28 . This priority level table updating program  47   a  makes the CPU  45 , as the client-side priority level information updating unit, to realize the function according to the process which updates the information priority level T stored in the information memory unit  42  every time when the priority level table T transmitted from the communication control unit  21  of the server apparatus  2  is received via the communication control unit  41 .  
      That is, after the priority level table T is updated by the MAC  21   b  of the server apparatus  2 , due to the wireless link between the server apparatus  2  and the client terminal apparatus become not connected, the CPU  45  updates the information of the priority level table T stored in the information memory unit  42  beforehand based on the execution of the priority level table updating program  47   a  every time when the priority level table T sent from the communication control unit  21  of the server apparatus  2  is received via the communication control unit  41  of the client terminal apparatus  4   
      Next, a link establishment process by the client-server system  100  will be described with reference to  FIGS. 5 and 6 .  
       FIGS. 5 and 6  are flowcharts showing an example of operations in the link establishment process. Specifically,  FIG. 5  shows the first link establishment process in which a wireless link between the server apparatus  2  and the client terminal apparatus  4  is established for the first time.  FIG. 6  shows a link establishment process after the first establishment onwards for reestablishing the wireless link and for updating the priority level table T.  
      The server apparatus  2  and the client terminal apparatus  4  are provided with an identical ID so that the system can be differentiated from other systems.  
      First, with reference to  FIG. 5 , the first link establishment process will be described.  
      In a status where the wireless link between the server apparatus  2  and the client terminal apparatus  4  is not yet established after the power source of the server apparatus  2  is turned on, the MAC  21   b  of the communication control unit  21  searches the usage (availabilities) of the plurality of channels of the wireless LAN (Step S 1 ).  
      Next, based on the search result of the usage of the plurality of channels, the MAC  21   b  decides priority levels of the use of the plurality of channels (Step S 2 ).  
      When the priority levels are decided, then the priority levels are stored as the priority level table T in the information memory unit  22  under the control of the CPU  26  (Step S 3 ).  
      Thereafter, the MAC  21   b  sets the channels as usable channels of the wireless LAN in the order of descending priority levels based on the priority levels of the priority level table T. Then, the MAC  21   b  transmits a predetermined synchronization establishment signal at a substantially fixed interval on the set channel (Step S 4 ).  
      After the power source of the client terminal apparatus  4  is turned on, the MAC  41   b  of the communication control unit  41  sequentially searches the plurality of channels. When a synchronization establishment signal sent from the communication control unit  21  of the server apparatus  2  is received (Step S 5 ), the MAC  41   b  identifies a channel related to the synchronization establishment signal and set the channel as a usable channel (Step S 6 ).  
      Next, when the wireless link between the server apparatus  2  and the client terminal apparatus  4  is established via the usable channel (Step S 7 ), the communication control unit  21  of the server apparatus  2  sends the priority level table T to the client terminal apparatus  4  under the control of the CPU  26 , (Step S 8 ).  
      In the client terminal apparatus  4 , when the client terminal apparatus  4  receives the priority level table T transmitted from the server apparatus  2  via the communication control unit  41  (Step S 9 ), the CPU  45  transmits the priority level table T to the information memory unit  42  and the priority level table T is stored in the information memory unit  42  (Step S 10 ).  
      When the wireless link is not established even when the synchronization establishment signal is transmitted, the MAC  21   b  of the server apparatus  2  searches the usage of a plurality of channels every one hour elapsed time (Step S 11 ; YES) to decide the priority levels of the channels (Step S 12 ).  
      Next, a link establishment process after the first establishment onward will be described with reference to  FIG. 6 .  
      In the following description, it is assumed that the information of priority levels at a predetermined time is previously stored in the priority level table T.  
      In a status where the wireless link between the server apparatus  2  and the client terminal apparatus  4  is not yet established after the power source of the server apparatus  2  is turned on, the MAC  21   b  of the communication control unit  21  sets the channels as usable channels in the order of descending priority levels of the wireless LAN based on the priority levels in the priority level table T stored in the information memory unit  22 . Then, the MAC  21   b  transmits a predetermined synchronization establishment signal on the set channel at a substantially fixed interval (Step S 21 ).  
      At this time when the power source of the client terminal apparatus  4  is turned on and the establishment of the wireless link is instructed, the MAC  41   b  of the communication control unit  41  searches the plurality of channels according to the priority levels of the priority level table T stored in the information memory unit  42  (Step S 22 ). When the synchronization establishment signal of the predetermined channel sent from the communication control unit  21  of the server apparatus  2  is received via communication control unit  41  (Step S 23 ), the MAC  41   b  sets the channel related to the synchronization establishment signal as the usable channel (Step S 24 ). Next, the wireless link between the server apparatus  2  and the client terminal apparatus  4  is established on this usable channel (Step S 25 ).  
      When the wireless link is not established even when the synchronization establishment signal is transmitted, the MAC  21   b  of the server apparatus  2  re-searches the usage of the plurality of channels of the wireless LAN (Step S 27 ) every one hour elapsed time (Step S 26 ; Yes). Then, the MAC  21   b  decides the priority levels for the use of the plurality of channels based on the search result of the usage of the plurality of channels (Step S 28 ).  
      When the priority levels are decided, the CPU  26  executes the priority level table update program  28   a  to update the information for the priority level table T stored in the information memory unit  22  to the latest information (Step S 29 ).  
      Thereafter, the MAC  21   b  sets the channels as the usable channels in the order of descending priority levels of the wireless LAN based on the priority levels of the updated priority level table T. Then, the MAC  21   b  transmits a predetermined synchronization establishment signal on the set channel at a substantially fixed interval (Step S 30 ).  
      When the establishment of the wireless link is instructed at the client terminal apparatus  4  and when the wireless link between the server apparatus  2  and the client terminal apparatus  4  is established (Step S 31  to Step S 33 ) in the same process as step S 23  through step S 25  by the MAC  41   b  of the communication control unit  41 , the communication control  21  of the server apparatus  2  transmits the updated priority level table T to the client terminal apparatus  4  under the control of the CPU  26  (Step S 34 ).  
      When the client terminal apparatus  4  receives the priority level table T sent from the server apparatus  2  via the communication control unit  41  (Step S 35 ), the CPU  45  executes the priority level table update program  28   a  to update the information for the priority level table T stored in the information memory unit  22  to the latest information (Step S 36 ).  
      As described above, according to the client-server system  100  of the present embodiment, the server apparatus  2  having no connection with the client terminal apparatus  4  searches the usages of the plurality of channels in the wireless LAN to decide the priority levels of use of the plurality of channels based on the search result. The channels are set as the usable channels in the order of descending priority levels of the wireless LAN based on the decided priority levels. Therefore, the usable channel can be set beforehand by considering the usage of plurality of the channels of the wireless LAN in the server apparatus  2 , at the time of the establishment of the wireless LAN link between the client terminal apparatus  4  and the server apparatus  2 . Thus, the wireless LAN link can be established more promptly and as a result, the client-server system  100  which is user-friendly can be provided.  
      The server apparatus  2 , in a status being connected with the client terminal apparatus  4  can send the priority level table T to the client terminal apparatus  4  by the communication control unit  21 . Furthermore, the client terminal apparatus  4  can set channels in the order of descending priority levels as usable channels in the wireless LAN by the MAC  41   b  based on the priority levels according to the priority level table received by the communication control unit  41 . Thus, when the wireless LAN link between the server apparatus  2  and the client terminal apparatus  4  is re-established after the link is once cut, the client terminal apparatus  4  can set the usable channels by considering the usage of plurality of the channels of the wireless LAN based on the priority level table T which is received at the time of the establishment of the wireless LAN link between the client terminal apparatus  4  and the server apparatus  2 .  
      Furthermore, when the wireless LAN link between the server apparatus  2  and the client terminal apparatus  4  is to be established, the server apparatus  2  can more swiftly set the usable channels based on the priority level table T stored in the information memory unit  22 . When the server apparatus  2  is to be connected to the client terminal apparatus  4 , the server apparatus  2  can use the communication control unit  21  to transmit the priority level table T to the client terminal apparatus  4 .  
      When the wireless LAN link between the client terminal apparatus  4  and the server apparatus  2  is to be reestablished after the link is once cut, the client terminal apparatus  4  can more swiftly set the usable channels based on the priority level table T that is received via the communication control unit  41  and stored in the information memory unit  42 .  
      Furthermore, the server apparatus  2  can update the priority level table T stored in the information memory unit  22  every time when the priority levels for use of the plurality of channels are decided. Thus, the usable channels can be set more properly based on the updated priority level table T.  
      The client terminal apparatus  4  can update the priority level table T stored in the information memory unit  42  every time when the priority level table T sent from the server apparatus  2  is received by the communication control unit  41 . Thus, when the wireless LAN link between server apparatus  2  and the client terminal apparatus  4  is to be reestablished after the link is once cut, the usable channels can be set more properly based on the updated priority level table T.  
      Furthermore, the server apparatus  2  can acquire search time information regarding a search time for usage of the plurality of channels. Thus, usages of the plurality of channels at a predetermined time can be obtained based on the search time information, and the usable channels can be more properly set depending on a time zone.  
      Further, the priority level table T including the search time information is sent to the client terminal apparatus  4 . Thus, when the wireless LAN link between the client terminal apparatus  4  and the server apparatus  2  is to be reestablished after the link is once cut, the client terminal apparatus  4  can set the usable channels more properly based on the obtained search time information according to the time zone.  
      The present invention is not limited to the above embodiments and may be subjected to various modifications and design changes within the scope of the present invention.  
      For example, although the server apparatus  2  is structured to send the generated priority level table T to the client terminal apparatus  4  so that the client terminal apparatus  4  can use the priority level table T to set the usable channels, the present invention is not limited to this. Whether the priority level table T is to be sent from the server apparatus  2  to the client terminal apparatus  4  or not may be changed appropriately.  
      Although it is stated that the server apparatus  2  and the client terminal apparatus  4  include the information memory units  22  and  42  for storing the priority level table T, respectively, the present invention is not limited to this. Whether the server apparatus  2  and the client terminal apparatus  4  respectively include the information memory units  22  and  42  or not also may be changed individually.  
      Furthermore, although the above embodiment generates the priority level table T several times per day at a predetermined times, the present invention is not limited to this. The priority level table T may be generated once in a day at one predetermined time.  
      Although the priority level table T was updated as needed, the present invention is not limited to this. Another configuration also may be used where, once the priority level table T is prepared, the priority level table T may be continuously used without update. That is, when the client-server system  100  is used under an environment in which the line is not busy, there is a case where it is only required to set a predetermined channel once and the second setting is not required.  
      Although the above embodiment uses the wireless LAN cards  211  and  411  for the connection to the wireless network N, the present invention is not limited to this. Any configuration may be used as long as the configuration allows the wireless LAN to be established.  
      The entire disclosure of Japanese Patent Application No. Tokugan 2005-326264 filed on Nov. 10, 2005 including specification, claims, drawings and summary are incorporated herein by reference in its entirety.