Patent Publication Number: US-2007120956-A1

Title: Communication path setting method and communication apparatus

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a communication path setting technique.  
      2. Description of the Related Art  
      A video display device such as a television set which displays various video data obtained by a video input device on its screen generally has no internal means for storing a large amount of video data. To display various video data on the screen, therefore, the video input device as a video data transmission source must transmit video data in the form of streaming to the video display device. The video display device displays the image on the screen in real time while receiving the transmitted video stream.  
      A wireless communication path is one video streaming transmission path. For example, a mechanism proposed for a wireless LAN guarantees a special transmission band for data, such as audio data or video data distributed by streaming, which must be transmitted in real time. For example, a scheme (e.g., IEEE 802.11e) which sets the priority order in accordance with the type of data to be transmitted, and preferentially transmits data having a high priority order is examined and proposed as a means for implementing a QoS technique.  
      This QoS technique can use a wireless communication path formed via a control station such as an access point, and a wireless communication path formed directly between apparatuses. Selective use of these communication paths requires control which selects the optimum communication path.  
      Patent reference 1 (Japanese Patent Laid-Open No. 2004-23613) describes a wireless communication system as an example of the control which selects a communication path. This wireless communication system comprising wireless terminals and a base station transmits a simultaneous broadcast signal under the control of the base station in accordance with, e.g., the communication traffic amount or whether or not the base station is in operation, thereby switching between a wireless communication path which is transmitted via the base station and a wireless communication path which is not. This indicates that the system selects a communication path by regarding all the wireless terminals accommodated in the system as equal, and using only the parameters (the communication traffic and the state of the base station) on wireless communication as communication path selection conditions.  
      Also, patent reference 2 (U.S. Pre-Grant Publication No. 2004/240,405 (Japanese Patent Laid-Open No. 2004-363645)) describes a technique as an example of the communication path selection control. In this technique, a transmission source terminal selects whether to transmit data directly between terminals or via a base station, in accordance with whether the transmission data is real-time data and with the total transmission band amount necessary for the transmission. That is, a transmission device as a transmission source selects a communication path. Also, a communication path is selected in accordance with whether data to be transmitted is real-time data, and whether the communication path can ensure an open transmission band to communicate the data.  
      In each of the inventions described in patent references 1 and 2 described above, the system comprising the base station and terminals selects whether to perform communication between the terminals via the base station or directly under the following conditions. That is, the system selects a communication path in accordance with whether data to be transmitted is real-time data, whether the communication path can ensure an open transmission band to communicate the data, the communication traffic amount, and whether the base station is in operation.  
      This is equivalent to selecting a communication path by regarding all the terminals as equal, and using only the various parameters (the type of transmission data, the use band, the communication traffic, and the operating state of the base station) on wireless communication as communication path selection conditions.  
      Even when communication is performed by selecting a direct communication path between the terminals under the above conditions, a radio wave does not reach a terminal any longer if the terminal moves, and this makes direct communication between the terminals impossible in some places. In this case, the communication may be interrupted. On the other hand, when a communication path transmitted via the base station is selected, the communication is not interrupted as long as the terminals move within the management area of the base station. That is, although an optimum communication path can be selected in accordance with the communication traffic amount, this communication path is not always optimal for the system.  
      In addition, in the invention described in patent reference 2, not the control station but the device as a data transmission source selects a communication path.  
      In this case, the system requires a mechanism which allows each transmission device to detect whether all the transmission devices accommodated in the system are terminals which move during communication, whether each terminal is dedicated to transmit or receive data, and the present status of each terminal in the system. To select the optimum communication path for the system, therefore, each transmission device must detect the conditions of the entire system, increasing the processing load. Also, each transmission device must be equipped with this function.  
     SUMMARY OF THE INVENTION  
      The present invention has been made to solve the above problems, and has as its object to select a communication path connecting wireless terminals via a communication apparatus or a communication path directly connecting the wireless terminals in accordance with the statuses of the wireless terminals, when transmitting data between the wireless terminals.  
      According to an aspect of the present invention, there is provided a communication path setting method of a communication system including a communication apparatus and a plurality of wireless terminals accommodated in the communication apparatus, comprising:  
      a recording step of recording statuses of the plurality of accommodated wireless terminals; and  
      a selecting step of selecting, when transferring data between wireless terminals, one of a first communication path which connects the wireless terminals via the communication apparatus, and a second communication path which directly connects the wireless terminals without via the communication apparatus, in accordance with statuses of the wireless terminals.  
      According to another aspect of the present invention, there is provided a communication apparatus accommodating a plurality of wireless terminals by wireless, comprising:  
      a recording unit adapted to record statuses of the plurality of accommodated wireless terminals; and  
      a selecting unit adapted to, when transferring data between wireless terminals, select one of a first communication path which connects the wireless terminals via the communication apparatus, and a second communication path which directly connects the wireless terminals without via the communication apparatus, in accordance with statuses of the wireless terminals.  
      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 view showing an example of the representative configuration of a wireless video transmission system according to the first embodiment;  
       FIG. 2  is a functional block diagram showing an example of the internal arrangement of a QSTA  101  as a video input device;  
       FIG. 3  is a functional block diagram showing an example of the internal arrangement of a QSTA  102  as a video input device;  
       FIG. 4  is a functional block diagram showing an example of the internal arrangement of a QAP  103 ;  
       FIG. 5  is a flowchart showing a process of registering management data at an access point;  
       FIG. 6  is a flowchart showing a process of registering management data at an access point;  
       FIG. 7  is a view showing an example of the arrangement of a management data recording unit  402  according to the first embodiment;  
       FIG. 8  is a flowchart showing a communication path selection process according to the first embodiment;  
       FIG. 9  is a view showing an example of communication path selection in a wireless transmission system;  
       FIG. 10  is a functional block diagram showing an example of the internal arrangement of a QSTA  101  according to the third embodiment;  
       FIG. 11  is a functional block diagram showing an example of the internal arrangement of a QSTA  102  according to the third embodiment; and  
       FIG. 12  is a view showing the configuration of a wireless video transmission system according to the fourth embodiment. 
    
    
     DESCRIPTION OF THE EMBODIMENTS  
      Best modes for carrying out the invention will be explained in detail below with reference to the accompanying drawings. DLS (Direct Link Setup) defined by the IEEE 802.11 standards and by the IEEE 802.11e standards as an extended version of the IEEE 802.11 standards is particularly used for wireless communication. However, the present invention is not limited to DLS, and is of course applicable to a communication control method complying with another communication protocols.  
     First Embodiment  
       FIG. 1  is a view showing an example of the representative configuration of a wireless video transmission system according to the first embodiment. Referring to  FIG. 1 , reference numeral  101  denotes a wireless terminal (QSTA) having a video data transmitting function. For example, the QSTA  101  is a digital video camera capable of transmitting video streams by using a wireless LAN communication function. Reference numeral  102  denotes a wireless terminal (QSTA) having a video data receiving function. For example, the QSTA  102  is a television set capable of receiving video streams by using a wireless LAN communication function. Reference numeral  103  denotes an access point (QAP) accommodating the QSTAs  101  and  102 , e.g., an access point of a wireless LAN. The QSTAs  101  and  102  establish a logical connection relationship (association) with the QAP  103 , thereby forming an infrastructure mode network (BSS) of the QAP  103 .  
      When transmitting an image recorded by the digital video camera  101  to the television set  102  and displaying the image on the television set  102 , two transmission path are possible as video data transmission paths. One is a method of transmitting video data via the access point  103 , and the other is a method of transmitting video data directly between the digital video camera  101  and television set  102 .  
      The method of transmitting video data via the QAP  103  first forms a communication path from the QSTA  101  to the QAP  103 , and a communication path from the QAP  103  to the QSTA  102 . The method then transmits the video data from the QSTA  101  to the QSTA  102  via the QAP  103  by a transmission method which guarantees QoS.  
      On the other hand, the method of directly transmitting video data forms a direct communication path between the QSTAs  101  and  102  by using DLS, and transmits the video data directly from the QSTA  101  to the QSTA  102  by using a transmission method which guarantees QoS.  
      Details of the arrangements of the QSTA  101 , QSTA  102 , and QAP  103  will be explained below with reference to FIGS.  2  to  4 .  
       FIG. 2  is a functional block diagram showing an example of the internal arrangement of the QSTA  101  as a video input device. A controller  201  includes a CPU which controls the whole device in accordance with programs and control data (to be described later), a ROM storing the programs and control data of the CPU, and a RAM which defines a work area used to execute processing by the CPU and various tables. A video input unit  202  comprises a camera and microphone. The video input unit  202  converts an image recorded by the camera into a digital signal, and converts a sound picked up by the microphone into a digital signal. The video input unit  202  transmits the converted video signal and audio signal to a video encoder unit in the next stage.  
      A video encoder unit  203  receives the video signal and audio signal transmitted from the video input unit  202 , and encodes the signals into a video stream containing audio information. An example of this encoding process is a process of generating various video streams different in resolution, frame rate, and transmission rate by using various video formats such as MPEG2, MPEG4, and H.264. The controller  201  instructs the video encoder unit  203  to transmit the video stream to a video data storage unit or wireless communication unit (to be described later). That is, the video encoder unit  203  transmits the video stream to the video data storage unit when storing the video stream inside the device, and transmits the video stream to the wireless communication unit when distributing the video stream as a live image to the QSTA  102  as a video display device.  
      A video data storage unit  204  stores the video stream obtained by recording. The video data storage unit  204  is, e.g., a storage medium such as a DV tape, DVD, or CF card as a removable medium, or a storage medium such as an HDD as a fixed medium. Note that the video stream stored in the video data storage unit  204  is already encoded into a predetermined video format by the video encoder unit  203  during recording.  
      A wireless communication unit  205  has a function of transmitting and receiving radio waves in accordance with the standards (IEEE 802.11) of a wireless LAN, and operates as a wireless terminal connecting to the QAP  103  under the control of the controller  201 . When distributing the recorded image as a live image to the QSTA  102  in the BSS, the wireless communication unit  205  modulates the video stream and transmits it on a radio wave from an antenna  209 . The interior of the radio communication unit  205  is roughly divided into two functional blocks, i.e., a MAC processor  206  and RF unit  207 .  
      The MAC processor  206  processes a MAC (Medium Access Control) layer complying with the wireless LAN standards (IEEE 802.11). That is, the MAC processor  206  internally forms a MAC frame, and exchanges the MAC frame with the REF unit  207 . This MAC frame stores the video stream transmitted from the video encoder unit  203  in the frame body. The MAC processor  206  also stores, in the MAC frame, various kinds of information (e.g., setting information, address information, authentication information, and sequence control information) on a wireless communication channel, and exchanges the information with the RF unit  207  under the control of the controller  201 .  
      The MAC processor  206  also has a function of operating as a wireless terminal in the BSS. This function controls wireless communication in accordance with the various kinds of information (e.g., setting information, address information, authentication information, and sequence control information) in the MAC frame controlled by the QAP  103 . For real-time data transmission such as video streaming transmission, the MAC processor  206  supports a band guarantee mechanism defined by IEEE 802.11e, i.e., can reserve a band necessary for the transmission, and preferentially transmit the data by giving it a priority order. That is, the MAC processor  206  performs a process of ensuring QoS in a wireless communication path.  
      Furthermore, the MAC processor  206  supports a DLS function defined by IEEE 802.11e. When instructed to activate DLS by the controller  201 , the MAC processor  206  activates DLS, and forms a direct communication path with respect to a desired wireless terminal in the BSS.  
      The RF unit  207  exchanges radio wave signals via the antenna  209  in the wireless communication unit  205 . The main functions include a function of performing various modulating processes on a bit stream transmitted from the MAC processor  206  and transmitting the bit stream as a radio wave from the antenna  209 , and a function of extracting a bit stream by demodulation from a radio wave received by the antenna  209 .  
      An operation input unit  208  detects a user&#39;s operation, and transmits the detection result to the controller  201 . The operation input unit  208  comprises of a key pad, push switches, slide switches, and the like, and has a function of detecting activation of each key or switch, and transmits the detection result to the controller  201 .  
       FIG. 3  is a functional block diagram showing an example of the internal arrangement of the QSTA  102  as a video display device.  FIG. 3  shows the functions of individual functional blocks by taking a process of receiving a video stream and displaying the received video stream on the screen as an example. A controller  301  includes a CPU which controls the whole device in accordance with programs and control data (to be described later), a ROM storing the programs and control data of the CPU, and a RAM which defines a work area used to execute processing by the CPU and various tables.  
      A wireless communication unit  304  has a function of transmitting and receiving radio waves in accordance with the standards (IEEE 802.11) of a wireless LAN, and operates as a wireless terminal connecting to the QAP  103  under the control of the controller  301 . When receiving video data as a video stream from the QSTA  101  in the BSS, the wireless communication unit  304  demodulates a radio wave signal received from an antenna  308  into the video stream. The interior of the radio communication unit  304  is roughly divided into two functional blocks, i.e., a MAC processor  305  and RF unit  306 .  
      The RF unit  306  exchanges radio wave signals via the antenna  308  in the wireless communication unit  304 . The main functions include a function of performing various modulating processes on a bit stream transmitted from the MAC processor  305  and transmitting the bit stream as a radio wave from the antenna  308 , and a function of extracting a bit stream by demodulation from a radio wave received by the antenna  308 .  
      The MAC processor  305  processes the MAC (Medium Access Control) layer in accordance with wireless LAN standards (IEEE 802.11). That is, the MAC processor  305  internally forms a MAC frame, and exchanges the MAC frame with the REF unit  306 . The MAC processor  305  extracts a video stream from the frame body of this MAC frame, and transmits the extracted video stream to a decoder unit  303 . The MAC processor  305  also stores, in the MAC frame, various kinds of information (e.g., setting information, address information, authentication information, and sequence control information) on a wireless communication channel, and exchanges the information with the RF unit  306  under the control of the controller  301 .  
      The MAC processor  305  also has a function of operating as a wireless terminal in the BSS. This function controls wireless communication in accordance with the various kinds of information (e.g., setting information, address information, authentication information, and sequence control information) in the MAC frame controlled by the QAP  103 . For real-time data transmission such as video streaming transmission, the MAC processor  305  supports a band guarantee mechanism defined by IEEE 802.11e, i.e., can preserve a band necessary for the transmission, and preferentially transmit the data by giving it a priority order. That is, the MAC processor  305  performs a process of ensuring QoS in a wireless communication path.  
      Furthermore, the MAC processor  305  supports a DLS function as defined by IEEE 802.11e. When instructed to activate DLS by the controller  301 , the MAC processor  305  activates DLS, and forms a direct communication path with respect to a desired wireless terminal in the BSS.  
      The decoder unit  303  converts the received video stream into a video signal to be displayed on the screen. The decoder unit  303  transmits the decoded video signal to an image display unit  302 . When requested to display a video stream on the image display unit  302 , the decoder unit  303  decodes the video signal under the control of the controller  301 , thereby generating a video signal converted into an image size corresponding to the image display unit  302 .  
      The image display unit  302  displays a video stream on the screen. That is, the image display unit  302  displays the video signal transmitted from the decoder unit  303  under the control of the controller  301 .  
      A remote control receiver  307  receives control signals transmitted by communication such as infrared radiation from a remote controller (not shown) which remotely controls the QSTA  102 . For example, when receiving a control signal for switching images currently being displayed on the screen from the remote controller, the remote control receiver  307  interprets the contents of the received control signal, and notifies the controller  301  of the contents.  
       FIG. 4  is a functional block diagram showing an example of the internal arrangement of the QAP  103 . Referring to  FIG. 4 , a controller  401  includes a CPU which controls the whole device in accordance with programs (to be described later), a ROM storing the programs of the CPU and control data, and a RAM which defines a work area used to execute processing by the CPU and various tables.  
      A wireless communication unit  403  has a function of transmitting and receiving radio waves in accordance with wireless LAN standards (IEEE 802.11). The wireless communication unit  403  operates as an access point which forms a ESS together with connected wireless terminals under the control of the controller  401 . When receiving video data or control data from a wireless terminal in the BSS, the radio communication unit  403  demodulates the video data or control data received from an antennal  406  via a radio wave. When transmitting video data or control data to a wireless terminal in the BSS, the radio communication unit  403  transmits modulated data as a radio wave from the antenna  406 . The interior of the radio communication unit  403  is roughly divided into two functional blocks, i.e., a MAC processor  404  and RF an unit  405 .  
      The RF unit  405  exchanges radio wave signals via the antenna  406  in the wireless communication unit  403 . The main functions include a function of performing various modulating processes on a bit stream transmitted from the MAC processor  404  and transmitting the bit stream as a radio wave from the antenna  406 , and a function of extracting a bit stream by demodulation from a radio wave received by the antenna  406 .  
      The MAC processor  404  processes the MAC (Medium Access Control) layer in accordance with the wireless LAN standards (IEEE 802.11). That is, the MAC processor  404  internally forms a MAC frame, and exchanges the MAC frame with the RE unit  405 . For example, when transmitting video data from the QSTA  101  to the QSTA  102  via the QAP  103  shown in  FIG. 1 , the MAC processor  404  analyzes a MAC frame received from the QSTA  101 , and changes the MAC header in accordance with a predetermined process and sequence. The MAC processor  404  then forms a MAC frame again, and transmits the MAC frame to the QSTA  102 .  
      Also, when video data is directly transmitted between the QSTAs  101  and  102  using DLS, the MAC processor  404  forms a control MAC frame, and transmits a control signal to the wireless terminals (QSTAs  101  and  102 ) in accordance with a predetermined timing.  
      In addition, when receiving, from a wireless terminal, a request to form a new communication path, a request to form a communication path by DLS, or a request for transferring various data, the MAC processor  404  performs QAP control executed as MAC layer processing.  
      Furthermore, the MAC processor  404  has a function of analyzing various pieces of information (e.g., setting information, address information, authentication information, and sequence control information) in the received MAC frame, and transmitting the obtained information to a management data recording unit  402 .  
      The management data recording unit  402  records management data concerning wireless terminals in the BSS formed by the QAP  103 . The management data recording unit  402  comprises a RAM (Random Access Memory) capable of data write and read, and records not only the MAC layer information obtained by the MAC processor  404  but also information obtained by upper layers. For example, the management data recording unit  402  records not only information regarding the type of wireless terminal obtained by the MAC layer, but also information obtained by a protocol or application as an upper layer of the MAC layer, e.g., information indicating that the wireless terminal is a television set or digital video camera.  
      A process of registering management data in the management data recording unit  402  of the QAP  103  will be explained below with reference to  FIG. 5 .  
       FIG. 5  is a flowchart showing the process of registering management data at an access point. Note that this process is executed when the access point (QAP  103 ) constructs an infrastructure mode network (BESS), and the wireless terminal (QSTA) in the BSS performs association (connection).  
      First, in step S 501 , the QAP  103  determines whether the wireless terminal (QSTA  101  or  102 ) in the BSS at the QAP  103  has issued an association request (connection relationship request). If the wireless terminal (QSTA  101  or  102 ) has issued a connection relationship request, the process advances to step S 502 ; if not, the QAP  103  maintains the present state.  
      In step S 502 , the QAP  103  transmits an association response indicating whether to admit the connection relationship, in response to the association request. The QAP  103  also records information elements (e.g., Capability Information and Listen Interval)  
      defined by IEEE 802.11 into the management data recording unit  402  for each wireless terminal having transmitted the elements. The information elements are wireless terminal information in the MAC layer, and the MAC processor  404  detects and extracts the elements.  
      In step S 503 , the QAP  103  transmits a signal requesting information other than the information elements acquired in step S 502 . Although the wireless terminal information acquired in step S 502  is information in the MAC layer, the above signal requests the wireless terminal (QSTA  101  or  102 ) for wireless terminal information processed in an upper layer (an upper protocol or application layer). An example of the requested wireless terminal information is type information indicating whether the wireless terminal is a digital video camera as a video data transmitter or a television set as a video data receiver.  
      In step S 504 , the QAP  103  determines whether the wireless terminal (QSTA  101  or  102 ) has transmitted a valid response to the transmitted request. If the wireless terminal has transmitted a valid response, the process advances to step S 505 ; if not, the process advances to step S 506 . Whether the response is valid is determined in accordance with whether the wireless terminal information requested in step S 503  is obtained.  
      In step S 505 , the QAP  103  records the wireless terminal information obtained in the response from the wireless terminal into the management data recording unit  402 . Since the obtained wireless terminal information is transmitted as is described in the frame body of the MAC frame, not the MAC processor  404  but the controller  401  capable of analyzing the frame body detects and extracts the information.  
      In step S 506 , the QAP  103  determines whether the wireless terminal (QSTA  101  or  102 ) has newly issued a wireless terminal information update request after the association process is complete. The update request is a request to update the obtained wireless terminal information because the state of the wireless terminal has changed. If the wireless terminal has issued the update request, the process advances to step S 507 ; if not, the process advances to step S 508 .  
      In step S 507 , the QAP  103  additionally records wireless terminal information newly obtained by the update request from the wireless terminal into the management data recording unit  402 , or updates the record. Since the newly obtained wireless terminal information is transmitted as is described in the frame body of the MAC frame, not the MAC processor  404  but the controller  401  capable of analyzing the frame body detects and extracts the information.  
      In step S 508 , the QAP  103  determines whether interruption to the QAP  103  such as a power OFF has occurred. If interruption such as a power OFF of the QAP  103  has occurred, the QAP  103  terminates the process; if not, the process returns to step S 506 . After the wireless terminal (QSTA  101  or  102 ) has executed and completed the association process with respect to the QAP  103 , the QAP  103  waits for a wireless terminal information update request from a new wireless terminal (QSTA  101  or  102 ).  
      A process of deleting management data recorded in the management data recording unit  402  of the QAP  103  will be explained next with reference to  FIG. 6 .  
       FIG. 6  is a flowchart showing a process of management data registration at the access point. Note that this process is performed when the wireless terminal has executed a disassociation from the access point.  
      First, in step S 601 , the CPU  401  of the QAP  103  determines whether the wireless terminal (QSTA  101  or  102 ) in the BSS has issued a disassociation request for canceling association. If the disassociation request is received from the wireless terminal (QSTA  101  or  102 ), the process advances to step S 602 , and the CPU  401  deletes all information concerning the wireless terminal (QSTA  101  or  102 ) recorded in the management data recording unit  402 . “All information” includes the information elements in the MAC layer, and the wireless terminal information recorded in step S 505  shown in  FIG. 5 .  
      The deleting process can also be performed by a method which additionally records, in the management data recording unit  402 , information indicating that the disassociation process of the wireless terminal (QSTA  101  or  102 ) was executed, as disassociation information.  
      The information recorded in the management data recording unit  402  of the QAP  103  will be explained below with reference to  FIG. 7 .  
       FIG. 7  is a view showing an example of the arrangement of the management data recording unit  402  according to the first embodiment. In  FIG. 7 , reference numeral  701  denotes an accommodated terminal whose field records the names of wireless terminals accommodated under the management of the QAP  103 ; and  702 , an information element whose field records the MAC layer information elements obtained from a wireless terminal when an association request is issued. Note that these information elements are defined by IEEE 802.11, and examples are the MAC address, Capability Information, and Listen Interval.  
      Reference numeral  703  denotes DLS support the field of which records a MAC layer information element obtained from a wireless terminal, e.g., information indicating whether the wireless terminal supports DLS. Note that this information is an information element defined by IEEE 802.11e. Reference numeral  704  denotes machine type information the field of which records information obtained by a protocol or application layer as an upper layer of the MAC layer obtained from a wireless terminal. For example, information indicating whether the wireless terminal has a video data transmitting function or receiving function is recorded. More specifically, when the wireless terminal is a television set, information indicating that the wireless terminal is a video data receiving apparatus is recorded.  
      Reference numeral  705  denotes form information the field of which records information obtained by a protocol or application layer as an upper layer of the MAC layer obtained from a wireless terminal. For example, information indicating the manner of use of the wireless terminal, i.e., whether the wireless terminal is stationary and kept unmoved or moved together with the user who is carrying it is recorded. More specifically, if the wireless terminal is a portable television set, information indicating that the wireless terminal is an apparatus which may move while receiving video data is recorded.  
      Reference numeral  706  denotes state information the field of which records information obtained by a protocol or application layer as an upper layer of the MAC layer obtained from a wireless terminal. For example, information indicating whether the wireless terminal is in a movable state or in a video data-receivable state or transmittable state is recorded. More specifically, if the wireless terminal is a television set and currently being used, e.g., the user is watching television broadcasting on the wireless terminal, information indicating that the wireless terminal is presently incapable of receiving wireless video data is recorded.  
      A process of selecting a communication path by referring to the recorded contents of the management data recording unit  402  of the QAP  103  when transmitting video data from the QSTA  101  to the QSTA  102  in the wireless video transmission system shown in  FIG. 1  will be explained below with reference to  FIG. 8 . For example, this process selects whether to transmit video data using a communication path which goes via the QAP  103 , or by forming a direct communication path between the QSTAs  101  and  102  using the mechanism of DLS. The process then establishes a communication path in accordance with the selection result, and transmits the video data.  
      Also, the QAP  103  performs this process after the wireless terminal (QSTA  101  or  102 ) in the BSS of the QAP  103  has executed the association request.  
       FIG. 8  is a flowchart showing the communication path selection process according to the first embodiment. First, in step S 801 , the QAP  103  determines whether the QSTA  101  has issued a request to transmit video data to the QSTA  102 . More specifically, the QAP  103  determines whether the QAP  103  has received, from the QSTA  101 , information indicating that the user has issued the above request in an application layer as an upper layer of the MAC layer. The user inputs the above request to the operation input unit  208  of the QSTA  101 , and the controller  201  of the QSTA  101  detects the operation. The wireless communication unit  205  of the QSTA  101  describes the request information in the frame body of the MAC frame, and transmits the frame on a radio wave to the QAP  103 .  
      If the QSTA  101  has issued a request for transmission of video data to the QSTA  102 , the process advances to step S 802 , the QAP  103  refers to the information in the management data recording unit  402 , and the controller  401  selects a communication path. More specifically, the controller  401  reads out management data concerning the corresponding wireless terminals (QSTAs  101  and  102 ) from the management data recording unit  402 . If “support” is recorded in the DLS support  703  and “stationary” is recorded in the form  705  of the QSTA  102 , the controller  401  selects a direct communication path to be formed between the QSTAs  101  and  102  by DLS.  
      If “mobile” is recorded in the form  705  of the QSTA  102 , the controller  401  selects a communication path which connects the QSTAs  101  and  102  via the QAP  103 .  
      In step S 803 , the QAP  103  determines whether the communication path selected in step S 802  goes via the QAP  103 . If the selected communication path goes via the QAP  103 , the process advances to step  5804 . If the selection is made to form a direct communication path between the QSTAs  101  and  102 , the process advances to step S 808 .  
      In step S 804 , the QAP  103  notifies the QSTA  101  that the communication path for transmitting video data to the QSTA  102  goes via the QAP  103 . The QSTA  101  having received this notification forms a communication path to the QSTA  102  via the QAP  103 . In this step, the process, in which the QAP  103  notifies the QSTA  101  that the communication path for transmitting video data to the QSTA  102  goes via the QAP  103 , is performed as follows.  
      In an application layer as an upper layer of the MAC layer, the controller  401  controls the wireless communication unit  403  to describe the notification information in the frame body of the MAC frame, and transmit the frame on a radio wave to the QSTA  101 . The QSTA  101  having received the notification forms a communication path to the QSTA  102  via the QAP  103  in accordance with a communication protocol defined by a wireless LAN complying with IEEE 802.11 and IEEE 802.11e.  
      In step S 805 , the QAP  103  instructs the QSTA  101  to begin transmitting the video data by the communication path established in step S 804 . In step S 806 , the QAP  103  determines whether a user operation or the like has been performed to stop the video data transmission currently being performed. If a user operation or the like has been performed to stop the video data transmission currently being performed, the process advances to step S 807 ; if not, the QAP  103  maintains the present state.  
      In step S 807 , the QAP  103  disconnects the communication path formed from the QSTA  101  to the QSTA  102  via the QAP  103 . Similar to the communication path established process in step S 804 , this process also disconnects the communication path formed via the QAP  103  in accordance with the communication protocol defined by the wireless LAN.  
      Furthermore, in step S 808 , the QAP  103  notifies the QSTA  101  that the communication path for transmitting video data to the QSTA  102  directly connects the QSTAs  101  and  102  using the DLS mechanism. The QSTA  101  having received this notification requests the QAP  103  to form a communication path which directly connects the QSTAs  101  and  102  using the DLS mechanism. In this step, the process in which the QAP  103  notifies the QSTA  101  that the communication path for transmitting the video data to the QSTA  102  directly connects the QSTAs  101  and  102  using the DLS mechanism is performed as follows.  
      In an application layer as an upper layer of the MAC layer, the controller  401  controls the wireless communication unit  403  to describe the notification information in the frame body of the MAC frame, and transmit the frame on a radio wave to the QSTA  101 . The QSTA  101  having received the notification forms a direct communication path from the QSTA  101  to the QSTA  102  in accordance with a procedure defined by IEEE 802.11 and IEEE 802.11e.  
      In step S 809 , the QAP  103  instructs the QSTA  101  to start transmitting the video data through the direct communication path by DLS. In step S 810 , the QAP  103  determines whether a user&#39;s operation or the like has performed control to stop the video data transmission currently being performed. If a user operation or the like has been performed to stop the video data transmission currently being performed, the process advances to step S 811 ; if not, the QAP  103  maintains the present state.  
      In step S 811 , the QAP  103  disconnects the communication path directly connected by DLS. Similar to the direct communication path setting process in step S 808 , this process also disconnects the communication path to the QSTA  102  formed by DLS in accordance with the procedure defined by IEEE 802.11 and IEEE 802.11e.  
      When the disconnecting process in step S 807  or S 811  is complete, the wireless terminals (QSTAs  101  and  102 ) return to the association state with respect to the QAP  103 , and the QAP  103  terminates the process.  
       FIG. 9  is a view showing an example of a communication path selection in the wireless transmission system. The example shown in  FIG. 9  indicates the operation of the flowchart shown in  FIG. 8  from another viewpoint. The configuration shown in  FIG. 9  is the same as that of the wireless transmission system comprising the QAP  103  and QSTAs  101  and  102  shown in  FIG. 1 .  
      In  FIG. 9 , reference numeral  901  denotes a circle indicating an area within which the radio wave from the QAP  103  reaches. When a wireless terminal exists in the circle  901 , this wireless terminal can associate with (connect to) and communicate with the QAP  103  wirelessly.  
      The start state shown in  FIG. 8  is a state in which the QSTAs  101  and  102  connect to the QAP  103  shown in  FIG. 9 . In this state, the distance between the QSTAs  101  and  102  allows them to directly communicate with each other by DLS.  
      If the QSTA  101  issues a request for video data transmission to the QSTA  102 , a communication path connecting the QSTAs  101  and  102  is selected. If the QSTA  102  is a stationary apparatus, i.e., if the QSTA  102  is an apparatus which cannot move while displaying an image, e.g., a television set in a living room, DLS is activated to form a direct communication path between the QSTAs  101  and  102  shown in  FIG. 9 .  
      On the other hand, if the QSTA  102  is a mobile apparatus, i.e., if the QSTA  102  is an apparatus which can move while displaying an image, e.g., a portable television set, a communication path which goes from the QSTA  101  to the QSTA  102  via the QAP  103  is formed without activating DLS.  
      If the QSTA  102  is a stationary apparatus, it cannot move to an area  902  shown in  FIG. 9  as indicated by a moving  903 . If the QSTA  102  is a mobile apparatus, however, it can move to the area  902  shown in  FIG. 9  as indicated by the moving  903 . Although a wireless terminal in the area  902  can communicate with the QAP  103 , the radio wave from the QSTA  101  may not directly reach the area  902 . Accordingly, if a direct communication path is formed by activating DLS upon path selection and the QSTA  102  moves to the area  902 , no radio wave reaches the QSTA  102  any longer, so video data transmission is interrupted.  
      The first embodiment can prevent the above problem by selecting a communication path in accordance with whether the QSTA  102  is a stationary device or mobile device in step S 802  shown in  FIG. 8 , and transmitting video data by a communication path established in step S 804  or S 808  shown in  FIG. 8 .  
     Second Embodiment  
      The second embodiment according to the present invention will be explained in detail below with reference to the accompanying drawings. The second embodiment will be explained by taking as an example a case in which a QSTA  101  transmits video data to a QSTA  102  while moving in the configuration shown in  FIG. 1 . An example is a case in which the QSTA  101  is a digital video camera which performs recording and transmits video data to the QSTA  102  in real time while moving in an area  901  shown in  FIG. 9 .  
      First, in the management data registration process shown in  FIG. 5 , to notify a QAP  103  that the QSTA  101  is a mobile device, information indicating that a form  705  of the QSTA  101  is mobile is recorded in a management data recording unit  402  of the QAP  103 . If a video data transmission request as shown in  FIG. 8  is issued after that, a communication path which goes via the QAP  103  is selected by referring to the recorded contents of the form  705 . After the communication path is formed, video data transmission is started.  
      This makes it possible to maintain the video data transmission even when the QSTA  101  shown in  FIG. 9  moves to an area  902  from which no radio wave can directly reach the QSTA  102 .  
     Third Embodiment  
      The third embodiment according to the present invention will be explained in detail below with reference to the accompanying drawings. QSTAs  101  and  102  shown in  FIG. 1  are sometimes used as stationary devices or mobile devices in accordance with user&#39;s forms of use. For example, when the QSTA  101  is a digital video camera, it is sometimes used in an immovable state because it is connected to an AC plug socket by a power cable to receive power when playing back internally recorded video data. On the other hand, the QSTA  101  is sometimes used as it is moved while receiving power from a built-in battery in order to perform recording.  
      In another example, the user sets, in the QSTA  101 , information indicating whether to move the QSTA  101  while using it.  
      A method of selecting a communication path in accordance with the use state, i.e., in accordance with whether to use the QSTA  101  as a stationary device or mobile device will be explained below.  
       FIG. 10  is a functional block diagram showing an example of the internal arrangement of the QSTA  101  according to the third embodiment. Referring to  FIG. 10 , a power detecting function is added to the functions shown in  FIG. 2 . A power detector  1001  is a functional block for the power detecting function. The power detector  1001  has a function of detecting whether a power cable is supplying power such as AC 100 V to the QSTA  101 , or a built-in battery is supplying power to the QSTA  101 . Whenever detecting a change in power supply path, the power detector  1001  notifies a controller  201  of the change.  
      When notified by the power detector  1001  that the power supply path has changed, the controller  201  controls the QSTA  101  to notify a QAP  103  of the change. This notification is performed in accordance with the flowchart shown in  FIG. 5 . A management data recording unit  402  of the QAP  103  records, e.g., “mobile” in a form  705  and “installed state” in a state  706  of the QSTA  101 . In this case, the power cable is supplying power to the QSTA  101 .  
      When a video data transmission request as shown in  FIG. 8  is issued after that, a communication path using DLS is selected by referring to the recorded contents of the form  705  and state  706  of the QSTA  101 . After the communication path is formed, video data transmission is started.  
      In this example, it is unnecessary to assume that the QSTA  101  moves to an area  902  shown in  FIG. 9  to which no radio wave directly comes from the QSTA  102 . Therefore, video data transmission can be maintained even when the communication path using DLS is set.  
      On the other hand, if “mobile” is recorded in the form  705  of the QSTA  101  and “movable state” is recorded in the state  706  of the QSTA  101 , the battery is supplying power to the QSTA  101 . When a video data transmission request as shown in  FIG. 8  is issued after that, a communication path going via the QAP  103  is selected by referring to the recorded contents of the form  705  and state  706  of the QSTA  101 . After the communication path is formed, video data transmission is started.  
      In this example, the QSTA  101  may move to the area  902  shown in  FIG. 9  to which no radio wave directly comes from the QSTA  102 . Accordingly, video data transmission can be maintained by setting the communication path going via the QAP  103 .  
      A method of selecting a communication path in accordance with the use state of the QSTA  102 , i.e., in accordance with whether the QSTA  102  is used as a stationary device or mobile device will be explained below in the same manner as for the QSTA  101 .  
       FIG. 11  is a functional block diagram showing an example of the internal arrangement of the QSTA  102  according to the third embodiment. Referring to  FIG. 11 , a predetermined function is added to the functions shown in  FIG. 3 . The added functional block is a power detector  1101 . The power detector  1101  has a function of detecting whether a power cable is supplying power such as AC 100 V to the QSTA  102 , or a built-in battery is supplying power to the QSTA  102 . Whenever detecting a change in power supply channel, the power detector  1101  notifies a controller  301  of the change.  
      When notified by the power detector  1101  that the power supply path has changed, the controller  301  controls the QSTA  102  to notify the QAP  103  of the change. This notification is performed in accordance with the flowchart shown in  FIG. 5 . The management data recording unit  402  of the QAP  103  records, e.g., “mobile” in the form  705  and “installed state” in the state  706  of the QSTA  102 . In this case, the power cable is supplying power to the QSTA  102 .  
      When a video data transmission request as shown in  FIG. 8  is issued after that, a communication path using DLS is selected by referring to the recorded contents of the form  705  and state  706  of the QSTA  102 . After the communication path is formed, video data transmission is started.  
      In this example, it is unnecessary to assume that the QSTA  102  moves to the area  902  shown in  FIG. 9  to which no radio wave directly comes from the QSTA  101 . Therefore, video data transmission can be maintained even when the communication path using DLS is set.  
      On the other hand, if “mobile” is recorded in the form  705  of the QSTA  102  and “movable state” is recorded in the state  706  of the QSTA  102 , the battery is supplying power to the QSTA  102 . When a video data transmission request as shown in  FIG. 8  is issued after that, a communication path going via the QAP  103  is selected by referring to the recorded contents of the form  705  and state  706  of the QSTA  102 . After the communication path is formed, video data transmission is started.  
      In this example, the QSTA  102  may move to the area  902  shown in  FIG. 9  to which no radio wave directly comes from the QSTA  101 . Accordingly, video data transmission can be maintained by setting the communication path going via the QAP  103 .  
     Fourth Embodiment  
      The fourth embodiment according to the present invention will be explained in detail below with reference to the accompanying drawings. In the fourth embodiment, one wireless terminal which transmits video data and a plurality of wireless terminals which receive the video data exist in the BSS of an access point.  
       FIG. 12  is a view showing the configuration of a wireless video transmission system according to the fourth embodiment. As shown in  FIG. 12 , QSTAs  1201  and  1202  are added to an area  901  of a QAP  103 . Each wireless terminal can associate with and communicate with the QAP  103  by wireless.  
      In this system configuration shown in  FIG. 12 , a management data recording unit  402  of the QAP  103  records one wireless terminal for which a machine type  704  is “video transmitter”, and three wireless terminals for each of which the machine type  704  is “video receiver”. If a QSTA  101  issues a video data transmission request as shown in  FIG. 8  in this state, a communication path going via the QAP  103  is selected without using DLS, since there is no other wireless terminal which transmits video data.  
      As described above, the QAP  103  can detect by the process shown in  FIG. 5  whether a wireless terminal associating with the QAP  103  is a video transmitter or video receiver. The QAP  103  can also select a communication path optimum for the system configuration by referring to the contents.  
      A basis for selecting a communication path going via the QAP  103  without using DLS will be explained below. In the system configuration shown in  FIG. 12 , the QSTA  1201  or  1202  sometimes issues a video data receiving request while the QSTA  101  is transmitting video data to a QSTA  102 , regardless of a communication path.  
      If the QSTA  101  is directly transmitting the video data to the QSTA  102  by using DLS, the QSTA  101  must disconnect the communication path using DLS once in order to execute the request. After that, the QSTA  101  forms communication paths for the QSTA  102  and QSTA  1201  (QSTA  1202 ) again by using a multicast address via the QAP  103 . This interrupts the reception of the video data by the QSTA  102 .  
      To prevent this video data interruption, a communication path which goes from the QSTA  101  to the QSTA  102  via the QAP  103  is preselected. If the QSTA  1201  (QSTA  1202 ) in the area  901  of the QAP  103  issues a video data receiving request after that, the destination address transmitted from the QSTA  101  is changed to the multicast address. Consequently, the video data can be transmitted to the QSTA  102  and QSTA  1201  (QSTA  1202 ).  
      As described above, the QSTA  102  can receive the video data without any interruption, and the QSTA  1201  can also receive the video data.  
      Note that the present invention can be applied to a system constituted by a plurality of devices (e.g., a host computer, interface, reader, and printer) or to an apparatus (e.g., a copying machine or facsimile apparatus) comprising a single device.  
      It is of course also possible to achieve the object of the present invention by supplying a recording medium recording the program code of software for implementing the functions of the above embodiments to a system or apparatus, and reading out and executing the program code stored in the recording medium by a computer (or a CPU or MPU) of the system or apparatus.  
      In this case, the program code read out from the recording medium implements the functions of the above embodiments, and the recording medium storing this program code constitutes the invention.  
      As this recording medium for supplying the program code, it is possible to use, e.g., a flexible disk, hard disk, optical disk, magnetooptical disk, CD-ROM, CD-R, magnetic tape, nonvolatile memory card, or ROM.  
      Also, besides the functions of the above embodiments are implemented by executing the readout program code by the computer, the present invention naturally includes a case where an OS (Operating System) or the like running on the computer performs part or the whole of actual processing in accordance with designations by the program code, thereby implementing the functions of the embodiments.  
      Furthermore, the present invention of course also includes a case where the program code read out from the recording medium is written in a memory of a function expansion board inserted into the computer or of a function expansion unit connected to the computer, and a CPU or the like of the function expansion board or function expansion unit performs part or the whole of actual processing in accordance with designations by the program code, thereby implementing the functions of the above embodiments.  
      In the embodiments described above, when transferring data between wireless terminals, it is possible to automatically set an effective communication path from a communication path connecting the wireless terminals via a communication device, and a communication path directly connecting the wireless terminals without going via the communication device, in accordance with the statuses of the individual wireless terminals.  
      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. 2005-342842, filed on Nov. 28, 2005, which is hereby incorporated by reference herein in its entirety.