Patent Publication Number: US-2005118985-A1

Title: Radio communication system and radio terminal device using faster and slower radio networks cooperatively

Description:
The present application is a divisional of U.S. application Ser. No. 09/541,889, filed Mar. 31, 2000, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a radio terminal device (which is also referred to as a wireless terminal device) having a plurality of communication interfaces and a radio communication system (which is also referred to as a wireless communication system) including such radio terminal devices.  
      2. Description of the Background Art  
      In recent years, the realization of home network is attracting much attention, and in particular, the IEEE 1394 for connecting between digital home electronic devices has been attracting considerable attention. The IEEE 1394 bus is capable of connecting a plurality of terminals in daisy chain or star connection and transferring a wideband data in excess of 100 Mbps. Also, it has a major feature that it is possible to transmit both asynchronous data and isochronous data on the same cable. For this reason, even though the IEEE 1394 bus was originally developed as a next generation version of SCSI, there are increasing trends to use the IEEE 1394 bus as a cable for connecting AV devices.  
      On the other hand, the realization of fast radio network (radio LAN) is also attracting attention. In particular, since the determination of the IEEE 802.11 specification in 1998, many radio LAN products are appearing in the market and there has been a remarkable decrease in the prices of these radio LAN products.  
      In conjunction with this trend for improved performance and reduced cost of the radio technology, there is an active trend to consider applications of the radio technology to the home environment and this trend is expected to grow further in future as can be anticipated by establishment of organizations such as HomeRF and Bluetooth in the U.S.A. Also, from a viewpoint of the home network, the radio system is an easily acceptable system as it does not require any new cable construction. For this reason, the fast radio LAN system is expected to play a central role in the future home network.  
      However, there are some outstanding problems in the application of a radio network to the home environment. One such problem is the realization of a wideband data transfer using radio. Data to be transferred in the home are expected to be mostly video data such as those of TV broadcast or satellite broadcast, so that the realization of a radio system capable of transferring such wideband data is crucial for wider spread of radio systems in the home environment.  
      To this end, a radio system using 5 GHz band is currently proposed. This proposition is aimed at the realization of a radio system capable of realizing the transmission rate of about 20 to 30 Mbps, by which several channels of MPEG2 video data can be transferred. Also, the 5 GHz band radio frequencies are said to be the last frequencies that can penetrate through many walls present in the home environment, so that this is the most promising candidate for the wideband radio system for home use.  
      But the 5 GHz band radio system also has its own problems. Namely, it is currently impossible to realize LSI of the RF function using CMOS. This is a severe drawback in view of a low cost realization of the 5 GHz radio system, and its resolution is imperative since it is expected that wider spread of radio systems in the home environment critically depends on how cheaply this 5 GHz band radio system can be offered to the general users.  
      As described, a radio device for transferring wideband data such as 5 GHz band radio system is expected to be rather expensive, and for this reason it is expected that a cost of the radio terminal itself will be very high in realizing the video data delivery in the home environment. This is a very serious problem for very cost sensitive products such as home electronic devices.  
     SUMMARY OF THE INVENTION  
      It is therefore an object of the present invention to provide a communication system and a terminal device using first and second networks, where the terminal device can receive data transfers as a receiving node in the first network, even when the terminal device has a first network interface through which only reception is possible and a second network interface through which both transmission and reception are possible.  
      More specifically, it is an object of the present invention to provide a radio communication system and a radio terminal device using 2.4 GHz band radio network and 5 GHz band radio network, for example, where the radio terminal device only has a reception function for the 5 GHz band radio network but is still capable of carrying out the authentication/admission processing in the 5 GHz band radio network and/or the AV control protocol processing with respect to a node on the IEEE 1394 bus by utilizing the 2.4 GHz band radio network, while carrying out the actual data transfer using the 5 GHz band radio network.  
      According to one aspect of the present invention there is provided a communication system, comprising: a first terminal device connected to first and second networks, having only a reception function with respect to the first network and transmission and reception functions with respect to the second network, the first network being a radio network according to IEEE 802.11 and the second network being a radio network slower than the first network; and a second terminal device connected to the first and second networks, having at least a transmission function with respect to the first network and transmission and reception functions with respect to the second network; wherein the first terminal device carries out a prescribed procedure required in using the first terminal as a receiving side in the first network, by carrying out communications with the second terminal device through the second network; the second terminal device transmits a prescribed information to the first network on behalf of the first terminal device, the prescribed information being an information required to be transmitted to the first network in order for the first terminal device to receive packets through the first network; and the first terminal device receives the packets through the first network.  
      According to another aspect of the present invention there is provided a terminal device, comprising: a first interface configured to carry out at least a packet transmission with respect to a first network which is a radio network according to IEEE 802.11; a second interface configured to carry out packet transmission and reception with respect to a second network which is a radio network slower than the first network; and a control unit configured to carry out communications with another terminal through the second interface so as to carry out a prescribed procedure required in using the another terminal as a receiving side in the first network, and transmit a prescribed information to the first network on behalf of the another terminal, the prescribed information being an information required to be transmitted to the first network in order for the another terminal to receive packets through the first network, such that the another terminal can receive the packets through the first network.  
      According to another aspect of the present invention there is provided a terminal device, comprising: a first interface configured to carry out at least a packet reception with respect to a first network which is a radio network according to IEEE 802.11; a second interface configured to carry out packet transmission and reception with respect to a second network which is a radio network slower than the first network; and a control unit configured to carry out communications with another terminal through the second interface so as to carry out a prescribed procedure required in using own terminal as a receiving side in the first network, such that the another terminal transmits a prescribed information to the first network on behalf of the own terminal, the prescribed information being an information required to be transmitted to the first network in order for the own terminal to receive packets through the first network, and receive the packets through the first network.  
      According to another aspect of the present invention there is provided a communication system, comprising: a first terminal device connected to first and second networks, having only a reception function with respect to the first network and transmission and reception functions with respect to the second network, the first network being a radio network according to IEEE 802.11 and the second network being a radio network slower than the first network; a second terminal device connected to the first network and a third network different from the first and second networks, having at least a transmission function with respect to the first network and transmission and reception functions with respect to the third network; a third terminal device connected to the second and third networks, having transmission and reception functions with respect to the second and third networks; and a fourth device provided on the third network, having transmission and reception functions with respect to the third networks; wherein the first terminal device carries out a prescribed procedure required in using the first terminal as a receiving side in the first network, by carrying out communications with the third terminal device through the second network; the third terminal device carries out the prescribed procedure by carrying out communications with the second terminal device through the third network; the third terminal device carries out another prescribed procedure required in relaying packets transferred from the fourth device towards the first terminal device at the second terminal device, by transferring a control information received from the first terminal device through the first network, to the second terminal device through the third network; the first terminal device transmits a packet transmission request with respect to the fourth device, to the third terminal device through the second network; the third terminal device transfers the packet transmission request received from the first terminal device, to the fourth device through the third network; the fourth device transmits packets in response to the packet transmission request received from the third terminal device, to the second terminal device through the third network; and the second terminal device transfers the packets received from the fourth device, to the first terminal device through the first network.  
      According to another aspect of the present invention there is provided a terminal device for carrying out a data transfer with respect to a first terminal through a first network, under a control of a second terminal, the first terminal having only a reception function with respect to the first network and transmission and reception functions with respect to a second network, the first network being a radio network according to IEEE 802.11 and the second network being a radio network slower than the first network, the second terminal being connected to the second network and a third network different from the first and second networks and having transmission and reception functions with respect to the second and third networks, the terminal device comprising: a first interface configured to carry out at least a packet transmission with respect to the first network; a second interface configured to carry out packet transmission and reception with respect to the third network; and a control unit configured to receive a control information transferred from the second terminal through the third network, and transfer packets received from a third device provided on the third network, to the first terminal through the first network according to the control information.  
      According to another aspect of the present invention there is provided a terminal device for controlling a data transfer with respect to a first terminal through a first network from a second terminal, the first terminal having only a reception function with respect to the first network and transmission and reception functions with respect to a second network, the first network being a radio network according to IEEE 802.11 and the second network being a radio network slower than the first network, the second terminal being connected to the first network and a third network different from the first and second networks and having at least a transmission function with respect to the first network and transmission and reception functions with respect to the third network, the terminal device comprising: a first interface configured to carry out packet transmission and reception with respect to the second network; a second interface configured to carry out packet transmission and reception with respect to the third network; and a control unit configured to carry out communications with the first terminal through the first interface and communications with the second terminal through the second interface, so as to carry out a prescribed procedure required in using the first terminal as a receiving side in the first network, carry out another prescribed procedure required in relaying packets transferred from a third device provided on the third network towards the first terminal at the second terminal by transferring a control information received from the first terminal through the first network to the second terminal through the third network, and transfer the packet transmission request received from the first terminal through the second network to the third device through the third network.  
      According to another aspect of the present invention there is provided a terminal device for receiving a data transfer through a first network from a first terminal by utilizing a second terminal through a second network, the first network being a radio network according to IEEE 802.11 and the second network being a radio network slower than the first network, the first terminal being connected to the first network and a third network different from the first and second networks and having at least a transmission function with respect to the first network and transmission and reception functions with respect to the third network, and the second terminal being connected to the second network and the third network and having transmission and reception functions with respect to the second and third networks, the terminal device comprising: a first interface configured to carry out at least a packet reception with respect to a first network which is a radio network according to IEEE 802.11; a second interface configured to carry out packet transmission and reception with respect to a second network which is a radio network slower than the first network; and a control unit configured to carry out communications with the second terminal through the second interface so as to carry out a prescribed procedure required in using own terminal as a receiving side in the first network, transmit a packet transmission request with respect to a third device provided on the third network to the second terminal through the second network, and receive packets transmitted from the third device in response to the packet transmission request and relayed by the first terminal through the first network.  
      According to another aspect of the present invention there is provided a method of packet transfer in a communication system including a first terminal device connected to first and second networks, having only a reception function with respect to the first network and transmission and reception functions with respect to the second network, the first network being a radio network according to IEEE. 802.11 and the second network being a radio network slower than the first network, and a second terminal device connected to the first and second networks, having at least a transmission function with respect to the first network and transmission and reception functions with respect to the second network, the method comprising the steps of: carrying out a prescribed procedure required in using the first terminal as a receiving side in the first network, by carrying out communications between the first terminal device and the second terminal device through the second network; transmitting a prescribed information from the second terminal device to the first network on behalf of the first terminal device, the prescribed information being an information required to be transmitted to the first network in order for the first terminal device to receive packets through the first network; and receiving the packets at the first terminal device through the first network.  
      According to another aspect of the present invention there is provided a method of packet transfer in a communication system including a first terminal device connected to first and second networks, having only a reception function with respect to the first network and transmission and reception functions with respect to the second network, the first network being a radio network according to IEEE 802.11 and the second network being a radio network slower than the first network, a second terminal device connected to the first network and a third network different from the first and second networks, having at least a transmission function with respect to the first network and transmission and reception functions with respect to the third network, a third terminal device connected to the second and third networks, having transmission and reception functions with respect to the second and third networks, and a fourth device provided on the third network., having transmission and reception functions with respect to the third networks, the method comprising the steps of: carrying out a prescribed procedure required in using the first terminal as a receiving side in the first network, by carrying out communications between the first terminal device and the third terminal device through the second network; carrying out the prescribed procedure by carrying out communications between the third terminal device and the second terminal device through the third network; carrying out another prescribed procedure required in relaying packets transferred from the fourth device towards the first terminal device at the second terminal device, by transferring a control information received from the first terminal device through the first network, from the third terminal device to the second terminal device through the third network; transmitting a packet transmission request with respect to the fourth device, from the first terminal device to the third terminal device through the second network; transferring the packet transmission request received from the first terminal device, from the third terminal device to the fourth device through the third network; transmitting packets in response to the packet transmission request received from the third terminal device, from the fourth device to the second terminal device through the third network; and transferring the packets received from the fourth device, from the second terminal device to the first terminal device through the first network.  
      Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic diagram showing a configuration of a network system according to the first embodiment of the present invention.  
       FIG. 2  is a diagram showing a protocol stack for a control packet transfer protocol used in the network system of  FIG. 1 .  
       FIG. 3  is a diagram showing a protocol stack for a data packet transfer protocol used in the network system of  FIG. 1 .  
       FIG. 4  is a block diagram for explaining one exemplary processing for packet transfer among radio terminals in the network system of  FIG. 1 .  
       FIG. 5  is a block diagram for explaining another exemplary processing for packet transfer among radio terminals in the network system of  FIG. 1 .  
       FIG. 6  is a diagram showing a processing sequence for communications among radio terminals in the network system of  FIG. 1 .  
       FIG. 7  is a diagram showing a MAC address correspondence table that can be used in the network system of  FIG. 1 .  
       FIG. 8  is a schematic diagram showing a configuration of a network system according to the second embodiment of the present invention.  
       FIG. 9  is a diagram showing a processing sequence for communications among radio terminals in the network system of  FIG. 8 , in the case of direct packet transfer.  
       FIG. 10  is a diagram showing a processing sequence for communications among radio terminals in the network system of  FIG. 8 , in the case of packet transfer relaying.  
       FIG. 11  is a schematic diagram showing a configuration of a network system according to the third embodiment of the present invention.  
       FIG. 12  is a diagram showing a protocol stack for a AV/C protocol execution used in the network system of  FIG. 11 .  
       FIG. 13  is a diagram showing a protocol stack for a MPEG2 data transfer protocol used in the network system of  FIG. 11 .  
       FIG. 14  is a diagram showing a network configuration as recognized by a radio terminal and a node on IEEE  1394  bus, and exemplary communication resources reserved in the network system of  FIG. 11 .  
       FIG. 15  is a diagram showing a processing sequence for communications among radio terminals in the network system of  FIG. 11 .  
       FIG. 16  is a schematic diagram showing a configuration of a network system according to the fourth embodiment of the present invention.  
       FIG. 17  is a diagram showing a first half of a processing sequence for communications among radio terminals in the network system of  FIG. 16 .  
       FIG. 18  is a diagram showing a second half of a processing sequence for communications among radio terminals in the network system of  FIG. 16 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      In the following, the preferred embodiments of the present invention will be described with references to the drawings. In the first to fourth embodiments described below, an exemplary case of a radio system in a home network of a home will be described, where this radio system can use a faster (assumed to be 5 GHz band) radio LAN as a first network and a slower (assumed to be 2.4 GHz band) radio LAN, and define a unidirectional downlink on the faster radio LAN. Among these, the third and fourth embodiments are specifically directed to the case where the IEEE 1394 bus can be used as a third network in addition.  
      Referring now to  FIG. 1  to  FIG. 7 , the first embodiment of a radio communication system and a radio terminal device according to the present invention will be described in detail.  
      This first embodiment is directed to a scheme by which a radio terminal having only a reception function with respect to the 5 GHz band radio LAN (or capable of utilizing only a reception function with respect to the 5 GHz band radio LAN) carries out a processing (such as authentication/admission processing, for example) with respect to the 5 GHz band radio LAN, via the 2.4 GHz band radio LAN.  
       FIG. 1  shows an exemplary configuration of a network system in which the 5 GHz band radio LAN and the 2.4 GHz band radio LAN are used cooperatively. These radio LANs are both operated according to the IEEE 802.11 protocol, but uses different radio frequencies so that there is no interference between them.  
      The network system of  FIG. 1  includes a radio terminal  101  which provides a P.C. (Point Coordinator) function in the 5 GHz band radio LAN  121 , a radio terminal  103  which has transmission and reception functions with respect to the 5 GHz band radio LAN, and a radio terminal  102  which has only a reception function with respect to the 5 GHz band radio LAN. In addition, the radio terminal  101  and the radio terminal  102  have transmission and reception functions with respect to the 2.4 GHz band radio LAN by which they can communicate with each other.  
      Note that the following description is directed to an exemplary case in which each of the radio terminal  101  and the radio terminal  102  has a MAC address on the 2.4 GHz band radio LAN and a MAC address on the 5 GHz band radio LAN separately, but it is also possible to use the same MAC address for the MAC address on the 2.4 GHz band radio LAN and the MAC address on the 5 GHz band radio LAN. In the following, it is assumed that the radio terminal  101  has an address “X1” on the 2.4 GHz band radio LAN and an address “X2” on the 5 GHz band radio LAN, the radio terminal  102  has an address “Y1” on the 2.4 GHz band radio LAN and an address “Y2” on the 5 GHz band radio LAN, and the radio terminal  103  has an address “Z” on the 5 GHz band radio LAN.  
      According to the IEEE 802.11 protocol, when one radio terminal carries out a communication with a desired correspondent radio terminal, a radio terminal authentication processing should be carried out between these radio terminal prior to the communication. Also, when one radio terminal makes a connection to a desired radio LAN, a radio LAN admission processing should be carried out between the radio terminal and the P.C. (the radio terminal  101  in the case of  FIG. 1 ) as a processing for making the connection. In the configuration of  FIG. 1 , the radio terminal  102  has only a reception function with respect to the 5 GHz band radio LAN, so that this radio terminal  102  cannot directly carry out the authentication/admission processing using the 5 GHz band radio frequencies at a time of carrying out a communication with another radio terminal (the radio terminal  101  or the radio terminal  103 , for example).  
      In this embodiment, the radio terminal  102  having only a reception function with respect to the 5 GHz band radio LAN carries out the authentication/admission processing with respect to the 5 GHz band radio LAN, via the 2.4 GHz band radio LAN.  
      In order to carry out the authentication processing according to the IEEE 802.11, it is necessary for both terminals to notify each other an authentication algorithm that is executable on the own terminal as well as the MAC address of the own terminal. For this reason, in order for the radio terminal  102  that has only a reception function with respect to the 5 GHz band radio LAN to carry out the authentication processing with another radio terminal in the 5 GHz band radio LAN, there is a need to notify the information necessary for the authentication processing (the executable authentication algorithm and the MAC address) using a different route. In  FIG. 1 , the 2.4 GHz band radio LAN is utilized for this purpose. Similarly, in the case where the radio terminal  102  makes a connection to the radio terminal  101  which is the P.C. of the 5 GHz band radio LAN, there is a need for the radio terminal  102  to notify the MAC address of the own terminal to the radio terminal  101 , and in  FIG. 1 , the 2.4 GHz band radio LAN is also utilized for this purpose.  
       FIG. 2  shows a protocol stack indicating how the authentication/admission processing is carried out between the radio terminal  101  and the radio terminal  103  in this case. In  FIG. 2 , the authentication/admission processing with respect to the 5 GHz band radio LAN is abbreviated as “5G control”, and the authentication/admission processing with respect to the 2.4 GHz band radio LAN is abbreviated as “2.4G control”. As can be seen from  FIG. 2 , in this embodiment, the authentication/admission processing of the radio terminal  102  with respect to the 5 GHz band radio LAN is carried out at the radio terminal  101  which is the P.C. of the 5 GHz band radio LAN, via the 2.4 GHz band radio LAN. On the other hand, between the radio terminal  101  and the radio terminal  103  which has both transmission and reception functions with respect to the 5 GHz band radio LAN, the authentication/admission processing with respect to the 5 GHz band radio LAN is carried out via the 5 GHz band radio LAN.  
       FIG. 3  shows a protocol stack indicating how the actual data transfer is carried out between the radio terminal  101  and the radio terminal  102 , as well as between the radio terminal  101  and the radio terminal  103 . As can be seen from  FIG. 3 , the actual data are transferred via the 5 GHz band radio LAN, but only data transmitted from the radio terminal  101  towards the radio terminal  102  will be transferred to the radio terminal  102 .  
      In the case of carrying out the authentication/admission processing on the 5 GHz band radio LAN via the 2.4 GHz band radio LAN and transferring the actual data via the 5 GHz band radio LAN, a packet identification method on the 2.4 GHz band radio LAN must be devised. Namely, it is necessary to specify which layer should be used by the radio terminal  101  in order to identify a packet on which the control information for the 5 GHz band radio LAN is loaded among the packets received at an interface with respect to the 2.4 GHz band radio LAN.  
      Two examples for this packet identification processing and the actual data transfer processing will now be described with references to  FIG. 4  and  FIG. 5 .  
       FIG. 4  and  FIG. 5  show various drivers operating on each MAC layer, in addition to the physical and MAC layers of the 2.4 GHz band radio LAN and the 5 GHz band radio LAN (denoted in the figures as 2.4G-PHY, 2.4G-MAC, 5G-PHY, and 5G-MAC respectively). Here, control drivers for handling the authentication/admission, the data transfer request, etc., and data drivers for handling the actual data transfer are distinguished.  
       FIG. 4  and  FIG. 5  also show various applications to be executed using these drivers, including an ordinary application to be executed on the 2.4 GHz band radio LAN (abbreviated as 2.4G application in the figures), an ordinary application to be executed on the 5 GHz band radio LAN (abbreviated as 5G application in the figures), and an AWL (Asymmetric Wireless Link) application in which the control information is exchanged via the 2.4 GHz band radio LAN and the actual data are transferred on the 5 GHz band radio LAN.  
      In  FIG. 4  and  FIG. 5 , a dotted line indicates a packet transfer route in the case of executing the ordinary application on the 2.4 GHz band radio LAN, a dashed line indicates a packet transfer route in the case of executing the ordinary application on the 5 GHz band radio LAN, and a solid line indicates a packet transfer route in the case of executing the AWL application. In both  FIG. 4  and  FIG. 5 , the radio terminal  103  is an ordinary terminal on the 5 GHz band radio LAN so that the processing according to the ordinary (IEEE 802.11) protocol of the 5 GHz band radio LAN is carried out between the radio terminal  101  and the radio terminal  103 .  
      Now a concrete processing for the control packet transfer and the data packet transfer in the case of executing the AWL application between the radio terminal  101  and the radio terminal  102  will be described.  
      First, the case of using the exemplary configuration of  FIG. 4  will be described.  
      After receiving a packet at a physical layer processing unit (2.4G-PHY in  FIG. 4 ) for the 2.4 GHz band radio LAN, the radio terminal  101  carries out the “packet distributing” processing for identifying whether the received packet is a packet corresponding to the application on the 2.4 GHz band radio LAN or a packet corresponding to the AWL application at a MAC layer processing unit (2.4G-MAC in  FIG. 4 ) which is an upper layer processing unit of the physical layer processing unit. A “packet distributing” processing unit is provided in the MAC layer processing unit for this purpose.  
      In order to identify a packet on the MAC layer in this way, there is a need to define a flag indicating that the information corresponding to the AWL application is loaded in that packet, within a MPDU (MAC Protocol Data Unit) that is defined as a packet for the MAC layer processing in the IEEE 802.11. By checking presence/absence of such a flag, the MAC layer processing unit for that 2.4 GHz band radio LAN judges whether the received packet should be transferred to the control driver of the AWL application or to the control driver of the ordinary 2.4 GHz application.  
      Also, data to be transmitted from the AWL application on the radio terminal  101  towards the radio terminal  102  are transferred to the “packet distributing” processing unit within the MAC layer processing unit (5G-MAC in  FIG. 4 ) for the 5 GHz band radio LAN via its data driver. Here, the fact that this data packet is transmitted from the AWL application is indicated by a flag on the MPDU, and then the packet transmission processing is carried out according to a packet transmission algorithm using a unidirectional downlink from the radio terminal  101  to the radio terminal  102 . If it is possible to carry out the unidirectional packet transfer processing from the radio terminal  101  to the radio terminal  102  without changing the ordinary MAC algorithm on the 5 GHz band radio LAN, the “packet distributing” processing unit within the MAC layer processing unit for the 5 GHz band radio LAN will be unnecessary.  
      Next, the processing in the case of executing the AWL application at the radio terminal  102  will be described.  
      In the case where the radio terminal  102  executes the AWL application on the own terminal, the control processing necessary for it is carried out on the 2.4 GHz band radio LAN. For this reason, a packet carrying the control information that is transmitted from the AWL application is transferred to the “packet distributing” processing unit within the MAC layer processing unit (2.4G-MAC in  FIG. 4 ) for the 2.4 GHz band radio LAN via the control driver of the AWL application. Here, the fact that this packet is a control packet for executing the AWL application is indicated by a flag on the MPDU, and then this packet is transferred to the radio terminal  101  via the MAC/physical layer processing units for the 2.4 GHz band radio LAN.  
      Also, the radio terminal  102  has only a reception function (5G-PHY(R), 5G-MAC(R) in  FIG. 4 ) with respect to the 5 GHz band radio LAN, and is capable of executing only the AWL application using this function. The radio terminal  102  receives only data packets of the AWL application from the 5 GHz band radio LAN. Thus packets received at an interface with respect to the 5 GHz band radio LAN of the radio terminal  102  are all to be transferred to the AWL application, so that all the packets from the MAC layer processing unit for the 5 GHz band radio LAN will be transferred to the data driver of the AWL application, and the “packet distributing” processing as used in the radio terminal  101  is unnecessary in the radio terminal  102 .  
      As described here, the radio terminal  102  executes only the packet reception processing with respect to the 5 GHz band radio LAN so that the execution of the AWL application between the radio terminal  101  and the radio terminal  102  is possible even when the same MAC address is used as the MAC address on the 2.4 GHz band radio LAN and the MAC address on the 5 GHz band radio LAN of the radio terminal  102 . In such a case, it is necessary for the “packet distributing” processing unit of the radio terminal  101  to recognize in advance that the MAC address on the 2.4 GHz band radio LAN and the MAC address on the 5 GHz band radio LAN of the radio terminal  102  are the same.  
      Next, the case of using the exemplary configuration of  FIG. 5  will be described.  
      First, the processing in the case of executing the AWL application at the radio terminal  101  will be described.  
      In  FIG. 5 , unlike  FIG. 4 , no new function is added to the MAC layer processing for each radio LAN in the radio terminal  101  and the radio terminal  102 , and whether the received packet is a packet for the application on the  2 . 4  GHz band or 5 GHz band radio LAN or a packet for the AWL application is identified at an upper level driver of the MAC layer.  
      First, the radio terminal  101  transfers a packet received by the physical layer processing unit (2.4G-PHY in  FIG. 5 ) and the MAC layer processing unit (2.4G-MAC in  FIG. 5 ) for the 2.4 GHz band radio LAN, to the corresponding control driver. Then, the MPDU header is removed from the packet received from the MAC layer processing unit, and the information on internal data is checked. Here, a field for identifying that the information corresponding to the AWL application is loaded on this packet is defined as one of the information on internal data, and whether the received packet is a packet corresponding to the AWL application or not is judged according to this field. This packet identification processing is carried out by the AWL driver defined as an upper level driver of the control and data drivers in  FIG. 5 .  
      Also, data transmitted from the AWL application on the radio terminal  101  towards the radio terminal  102  are transferred as follows. Namely, a packet on which this data is loaded is transferred to the AWL driver at which the information indicating that this is a packet corresponding to the AWL application is attached to this packet, and this packet is transferred to the lower level data driver. Then, this packet with the above information attached is transferred to the radio terminal  102  via the MAC/physical layer processing units for the 5 GHz band radio LAN through the unidirectional downlink. Here, in  FIG. 5 , it is assumed that the unidirectional packet transfer processing from the radio terminal  101  to the radio terminal  102  can be executed without modifying the ordinary MAC algorithm on the 5 GHz band radio LAN, but if some processing for the purpose of carrying out the unidirectional packet transfer processing is required, a function for executing that processing will be provided in the MAC layer processing unit for the 5 GHz band radio LAN.  
      Next, the processing in the case of executing the AWL application at the radio terminal  102  will be described.  
      In the case of executing the AWL application on the own terminal, the radio terminal  102  executes the control processing necessary for that purpose on the 2.4 GHz band radio LAN. For this reason, the control packet transmitted from the AWL application is attached with an indication that this packet is a packet corresponding to the AWL application at the AWL driver, and then transferred to the radio terminal  101  via its control driver and the MAC/physical layer processing units for the 2.4 GHz band radio LAN.  
      Also, the radio terminal  102  has only a reception function (5G-PHY(R), 5G-MAC(R) in  FIG. 5 ) with respect to the 5 GHz band radio LAN, and is capable of executing only the AWL application using this function. The radio terminal  102  receives only data packets of the AWL application from the 5 GHz band radio LAN. Thus packets received at an interface with respect to the 5 GHz band radio LAN of the radio terminal  102  are all to be transferred to the AWL application, so that all the packets from the MAC layer processing unit for the 5 GHz band radio LAN will be transferred to the data driver of the AWL application.  
      The execution of the AWL application between the radio terminal  101  and the radio terminal  102  can be realized using this scheme.  
       FIG. 6  shows an exemplary processing sequence at a time of actually transferring data from the radio terminal  101  to the radio terminal  102  in the radio network operated in this scheme. Here, it is assumed that the data transfer processing is carried out by the Contention Mode of the IEEE 802.11 as the transfer protocol on the radio LANs, and the carrier sense processing is carried out prior to a series of data transfer processing from each radio terminal. This processing sequence proceeds as follows.  
      (0) The radio terminal  102  carries out the authentication processing with the radio terminal  101 , and becomes a state in which communications using the 2.4 GHz band radio LAN are possible.  
      (1) The radio terminal  103  carries out the authentication processing with the radio terminal  101 , and then makes a connection to the 5 GHz band radio LAN for which the radio terminal  101  is the P.C., via the 5 GHz band radio LAN.  
      (2) The radio terminal  102  carries out the authentication processing for the 5 GHz band radio LAN with the radio terminal  101 , via the 2.4 GHz band radio LAN, and then makes a connection to the 5 GHz band radio LAN for which the radio terminal  101  is the P.C.  
      Here, the radio terminal  102  notifies its own MAC address (=Y2) on the 5 GHz band radio LAN to the radio terminal  101  via the 2.4 GHz band radio LAN. As a result, the radio terminal  101  memorizes that the MAC address (=Y1) on the 2.4 GHz band radio LAN corresponds to the MAC address (=Y2) on the 5 GHz band radio LAN.  
      (3) The radio terminal  102  transmits a request indicating the data transfer from the radio terminal  101  to the radio terminal  102  via the 5 GHz band radio LAN, to the radio terminal  101  via the 2.4 GHz band radio LAN.  
      Here, the radio terminal  102  may issue an RTS request for the 5 GHz band radio LAN by using an RTS (Request to Send) packet on the 2.4 GHz band radio LAN, or define a packet for transferring control information for the 5 GHz band radio LAN on the 2.4 GHz band radio LAN and issue the RTS request by using this packet.  
      (4) The radio terminal  101  transmits the RTS packet on the 5 GHz band radio LAN on behalf of the radio terminal  102  according to the request of (3), so as to reserve media.  
      Here, the radio terminal  101  may reserve media by transmitting a CTS (Clear to Send) packet corresponding to this RTS packet, on the 5 GHz band radio LAN.  
      (5) The radio terminal  101  transmits a packet towards the radio terminal  102 .  
      (6) The radio terminal  101  transmits an Ack packet corresponding to the packet transmitted by the processing of (5), on the 5 GHz band radio LAN on behalf of the radio terminal  102 .  
      Here, a packet transmission interval in the series of packet transmissions from (4) to (6) is the SIFS interval which is the minimum packet transmission interval specified in the IEEE 802.11.  
      (7) The radio terminal  103  transmits the RTS packet on the 5 GHz band radio LAN, so as to reserve media for the data transfer from the radio terminal  103  to the radio terminal  101  (the carrier sense processing is carried out prior to this RTS packet transmission).  
      (8) The radio terminal  101  transmits the CTS packet corresponding to the RTS packet of (7) on the 5 GHz band radio LAN, so as to reserve media.  
      (9) The radio terminal  103  transmits a packet towards the radio terminal  101 .  
      (10) The radio terminal  101  transmits an Ack packet corresponding to the packet transmitted by the processing of (9), to the radio terminal  103 .  
      Here, a packet transmission interval in the series of packet transmissions from (7) to (10) is also the SIFS interval which is the minimum packet transmission interval specified in the IEEE 802.11.  
      (11) While the processing from (7) to (10) is carried out, the radio terminal  102  transmits another request indicating the data transfer from the radio terminal  101  to the radio terminal  102  via the 5 GHz band radio LAN, to the radio terminal  101  via the 2.4 GHz band radio LAN (the processing as (3)).  
      (12) The radio terminal  101  transmits the RTS packet on the 5 GHz band radio LAN on behalf of the radio terminal  102  according to the request of (11), so as to reserve media.  
      Here, the radio terminal  101  may reserve media by transmitting a CTS (Clear to Send) packet corresponding to this RTS packet, on the 5 GHz band radio LAN.  
      (13) The radio terminal  101  transmits a packet towards the radio terminal  102 .  
      (14) The radio terminal  101  transmits an Ack packet corresponding to the packet transmitted by the processing of (13), on the 5 GHz band radio LAN on behalf of the radio terminal  102 .  
      Here, a packet transmission interval in the series of packet transmissions from (12) to (14) is also the SIFS interval which is the minimum packet transmission interval specified in the IEEE 802.11.  
      By this series of processing, even the radio terminal  102  which has only a reception function with respect to the 5 GHz band radio LAN can receive data from the 5 GHz band radio LAN without affecting the radio terminal  103  that is operated by the ordinary radio LAN protocol, so that it becomes possible to provide a unidirectional data downloading service on the radio LAN operated by the protocol such as the IEEE 802.11.  
      Note that, the above example is directed to the case where the radio terminal  102  uses different addresses for the MAC address on the 2.4 GHz band radio LAN and the MAC address on the 5 GHz band radio LAN, but as already mentioned above, these MAC addresses are not necessarily different and it is also possible to use the same MAC address for the MAC address on the 2.4 GHz band radio LAN and the MAC address on the 5 GHz band radio LAN.  
      Note also that, in the above processing (2), the radio terminal  101  can store the MAC address correspondence in a correspondence table shown in  FIG. 7 . In the correspondence table of  FIG. 7 , the MAC address of each interface of the radio terminal with which the radio terminal  101  can communicate is registered. Using such a correspondence table, it is possible to carry out communications using the 2.4 GHz band radio LAN and the unidirectional downlink on the 5 GHz band radio LAN as described above.  
      Referring now to  FIG. 8  to  FIG. 10 , the second embodiment of a radio communication system and a radio terminal device according to the present invention will be described in detail.  
      In the first embodiment, the data transfer from the radio terminal  101  which is the P.C. to the radio terminal  102  has been described. In this second embodiment, the data transfer from the radio terminal  103  to the radio terminal  102  (in a configuration basically similar to that of the first embodiment) will be described. Also, in this second embodiment, the case of the data transfer from the radio terminal  103  to the radio terminal  102  using the ordinary MAC processing (by the radio terminal  103 ) and the case of the data transfer from the radio terminal  103  to the radio terminal  102  relayed by the radio terminal  101  which is the P.C. will be described.  
       FIG. 8  shows a configuration similar to that of the first embodiment, in which the data transfer from the radio terminal  103  to the radio terminal  102  is realized. In this example, it is assumed that the radio terminal  102  can ascertain the MAC address of a terminal existing on the 5 GHz band radio LAN from the framework of the IEEE 802.11, and requests a packet transfer from the radio terminal  103  by ascertaining its MAC address accordingly.  
      Here, the radio terminal is operated according to the IEEE 802.11 protocol used in the 5 GHz band radio LAN, but the radio terminal  102  is a terminal in which only a reception function with respect to the 5 GHz band radio LAN is provided. Consequently, in this embodiment, there are two cases including the case where the data transfer from the radio terminal  103  to the radio terminal  102  can be realized directly through the 5 GHz band radio LAN and the case where data are transferred from the radio terminal  103  via the radio terminal  101  which has a function for transferring data to the radio terminal  102 .  
      Normally, in the MAC protocol of the IEEE 802.11, if the Ack packet is not returned from a terminal to which a packet is transmitted, a terminal that transmitted the packet will judge that a packet transfer has failed and re-transmit the packet. Therefore, in the case of transferring a packet to a terminal like the radio terminal  102  which only has a packet reception function, the same packet would be transmitted many times repeatedly unless some measure to prevent this from happening is provided. As a measure to prevent this from happening, it is possible to provide a processing for ignoring presence/absence of the Ack packet reception at a terminal that transmitted a packet depending on the destination of the packet, or a processing to transmit the Ack packet from a terminal other than the destination terminal of the packet (a source terminal, for example) on behalf of the destination terminal. In the following, it is assumed that a terminal that transmits a packet is a terminal in accordance with the IEEE 802.11 such as the radio terminal  103 , so that the former method to ignore the Ack packet cannot be adopted. Consequently, this example is directed to the case of realizing a direct packet transfer from the radio terminal  103  to the radio terminal  102  in which the Ack packet corresponding to a packet transmission from the radio terminal  103  to the radio terminal  102  is transmitted from the radio terminal  101  on behalf of the radio terminal  102 .  
       FIG. 9  shows an exemplary processing sequence in the case of realizing the direct packet transfer from the radio terminal  103  to the radio terminal  102  using this scheme for transmitting the Ack packet from the radio terminal  101 . Here, it is assumed that the data transfer processing is carried out by the Contention Mode of the IEEE 802.11 as the transfer protocol on the 5 GHz band radio LAN. It is also assumed that the radio terminal  102  makes a connection to the 5 GHz band radio LAN using a procedure as described in the first embodiment. This processing sequence proceeds as follows.  
      (0) The radio terminal  102  carries out the authentication processing with the radio terminal  101 , and becomes a state in which communications using the 2.4 GHz band radio LAN are possible.  
      (1) The radio terminal  103  carries out the authentication processing with the radio terminal  101 , and then makes a connection to the 5 GHz band radio LAN for which the radio terminal  101  is the P.C., via the 5 GHz band radio LAN.  
      (2) The radio terminal  102  carries out the authentication processing for the 5 GHz band radio LAN with the radio terminal  101 , via the 2.4 GHz band radio LAN, and then makes a connection to the 5 GHz band radio LAN for which the radio terminal  101  is the P.C.  
      (3) The radio terminal  101  notifies information on the MAC addresses of the radio terminals existing in the 5 GHz band radio LAN according to the IEEE 802.11 protocol.  
      (4) The radio terminal  102  transmits a request indicating the data transfer from the radio terminal  103  to the radio terminal  102  via the 5 GHz band radio LAN, to the radio terminal  101  via the 2.4 GHz band radio LAN.  
      (5) The radio terminal  101  transmits the RTS packet on the 5 GHz band radio LAN on behalf of the radio terminal  102  according to the request of (4), so as to reserve media. At this point, the source terminal of the requested packet is set as the radio terminal  103  and the destination terminal of the requested packet is set as the radio terminal  102 .  
      (6) The radio terminal  103  transmits the CTS packet corresponding to the RTS packet of (5) on the 5 GHz band radio LAN, so as to reserve media.  
      (7) The radio terminal  103  transmits a packet towards the radio terminal  102 .  
      (8) The radio terminal  101  transmits an Ack packet corresponding to the packet transmitted by the processing of (7), on the 5 GHz band radio LAN on behalf of the radio terminal  102 .  
      Here, a packet transmission interval in the series of packet transmissions from (5) to (8) is the SIFS interval which is the minimum packet transmission interval specified in the IEEE 802.11.  
      Next, the processing in the case where the direct packet transfer from the radio terminal  103  to the radio terminal  102  is impossible will be described. Here, it is assumed that, in the configuration of  FIG. 8 , the radio terminal  103  is capable of communicating only with the radio terminal  101 , and the radio terminal  102  is capable of receiving packets only from the radio terminal  101 . Therefore, in the case of transferring a packet from the radio terminal  103  to the radio terminal  102 , it is necessary to relay the packet at the radio terminal  101 . This example is directed to the case where the radio terminal  101  that received “a request for packet transfer from the radio terminal  103  to the radio terminal 102” from the radio terminal  102  via the 2.4 GHz band radio LAN will activate two packet transfers including a packet transfer from the radio terminal  103  to the own terminal (radio terminal  101 ) and a packet transfer from the own terminal (radio terminal  101 ) to the radio terminal  102 .  
       FIG. 10  shows an exemplary processing sequence in the case of realizing the packet transfer from the radio terminal  103  to the radio terminal  102  using this scheme. Here, it is also assumed that the data transfer processing is carried out by the Contention Mode of the IEEE 802.11 as the transfer protocol on the 5 GHz band radio LAN. It is also assumed that the radio terminal  102  makes a connection to the 5 GHz band radio LAN using a procedure as described in the first embodiment. This processing sequence proceeds as follows.  
      (0) The radio terminal  102  carries out the authentication processing with the radio terminal  101 , and becomes a state in which communications using the 2.4 GHz band radio LAN are possible.  
      (1) The radio terminal  103  carries out the authentication processing with the radio terminal  101 , and then makes a connection to the 5 GHz band radio LAN for which the radio terminal  101  is the P.C., via the 5 GHz band radio LAN.  
      (2) The radio terminal  102  carries out the authentication processing for the 5 GHz band radio LAN with the radio terminal  101 , via the 2.4 GHz band radio LAN, and then makes a connection to the 5 GHz band radio LAN for which the radio terminal  101  is the P.C.  
      (3) The radio terminal  101  notifies information on the MAC addresses of the radio terminals existing in the 5 GHz band radio LAN according to the IEEE 802.11 protocol.  
      (4) The radio terminal  102  transmits a request indicating the data transfer from the radio terminal  103  to the radio terminal  102  via the 5 GHz band radio LAN, to the radio terminal  101  via the 2.4 GHz band radio LAN.  
      (5) The radio terminal  101  transmits the RTS packet on the 5 GHz band radio LAN on behalf of the radio terminal  102  according to the request of (4), so as to reserve media. At this point, the source terminal of the requested packet is set as the radio terminal  103  and the destination terminal of the requested packet is set as the radio terminal  101 .  
      (6) The radio terminal  103  transmits the CTS packet corresponding to the RTS packet of (5) on the 5 GHz band radio LAN, so as to reserve media.  
      (7) The radio terminal  103  transmits a packet towards the radio terminal  101 .  
      (8) The radio terminal  101  transmits an Ack packet corresponding to the packet transmitted by the processing of (7), on the 5 GHz band radio LAN.  
      Here, a packet transmission interval in the series of packet transmissions from (5) to (8) is the SIFS interval which is the minimum packet transmission interval specified in the IEEE 802.11.  
      (9) After a certain period of time (the DIFS interval, for example) has elapsed, the radio terminal  101  transmits the RTS packet on the 5 GHz band radio LAN on behalf of the radio terminal  102  according to the request of (4) again, so as to reserve media. At this point, the source terminal of the requested packet is set as the radio terminal  101  and the destination terminal of the requested packet is set as the radio terminal  102 .  
      Here, the radio terminal  101  may reserve media by transmitting a CTS packet corresponding to this RTS packet, on the 5 GHz band radio LAN.  
      (10) The radio terminal  101  transmits the packet received by the processing of (7), towards the radio terminal  101 .  
      (11) The radio terminal  101  transmits an Ack packet L corresponding to the packet transmitted by the processing of (10), on the 5 GHz band radio LAN.  
      Here, a packet transmission interval in the series of packet transmissions from (9) to (11) is the SIFS interval which is the minimum packet transmission interval specified in the IEEE 802.11.  
      Using this scheme, it becomes possible to realize the packet transfer between the radio terminal in accordance with the specification of the 5 GHz band radio LAN (radio terminal  103 ) and the radio terminal which has only a reception function with respect to the 5 GHz band radio LAN (radio terminal  102 ).  
      Referring now to  FIG. 11  to  FIG. 15 , the third embodiment of a radio communication system and a radio terminal device according to the present invention will be described in detail.  
      This third embodiment is directed to the case of operating the radio network (using the 2.4 GHz band radio LAN and the 5 GHz band radio LAN) together with the IEEE 1394 bus.  
      In this embodiment, a radio terminal having a P.C. function which is capable of carrying out communications by both the 2.4 GHz band radio LAN and the 5 GHz band radio LAN is provided on the IEEE 1394 bus, and this radio terminal relays the data transfer to the radio terminal which has (or which is capable of utilizing) only a reception function with respect to the 5 GHz band radio LAN from a device on the IEEE 1394 bus such as a DVD.  
      The example described here is directed to the case where the radio terminal on the radio network downloads image information from a DVD existing on the IEEE 1394 bus, and in particular the AV control protocol is executed between this radio terminal and the DVD via the 2.4 GHz band radio LAN, and the actual image data are received via the 5 GHz band radio LAN.  
       FIG. 11  shows an exemplary configuration of a network system in this case. It is assumed that the radio LANs are operated according to the IEEE 802.11 protocol similarly as in the first and second embodiments. The network system of  FIG. 11  includes a radio terminal  601  which provides a P.C. function in the 5 GHz band radio LAN  621 , a radio terminal  603  which has transmission and reception functions with respect to the 5 GHz band radio LAN, and a radio terminal  602  which has only a reception function with respect to the 5 GHz band radio LAN. In addition, the radio terminal  601  and the radio terminal  602  have transmission and reception functions with respect to the 2.4 GHz band radio LAN by which they can communicate with each other. Moreover, the radio terminal  601  has an interface with respect to the IEEE 1394 bus  623 , and is connected to a TV  604  and a DVD  605  via the IEEE 1394 bus.  
      This embodiment is directed to the case where the AV control protocol (AV/C protocol) to be executed between the radio terminal  602  and the DVD  605  is executed via the 2.4 GHz band radio LAN and the IEEE 1394 bus, and as a result the MPEG2 data transmitted from the DVD  605  are transferred to the radio terminal  602  via the IEEE 1394 bus and the 5 GHz band radio LAN.  
      Here, in the AV/C protocol, 1394 nodes having 1394 interfaces are recognized in units called Unit, and constituent elements (such as a cassette table section or a CD section in an audio component system, for example) within the 1394 terminal are recognized in units called SubUnit. In this embodiment, it is assumed that the AV/C protocol is to be executed between the DVD  605  on the IEEE 1394 bus and the radio terminal  602  by recognizing each other at a level of their constituent elements (SubUnits of the AV/C protocol), rather than directly recognizing each other. More specifically, in the case of  FIG. 11 , the constituent element (SubUnit) in the DVD  605  is recognized from a viewpoint of the radio terminal  602  as if it is existing in the radio terminal  601 , while the constituent element (SubUnit) in the radio terminal  602  is recognized from a viewpoint of the DVD  605  on the IEEE 1394 bus as if it is existing in the radio terminal  601 .  
      In the following, the case of transferring the MPEG2 data in the DVD  605  to the radio terminal  602  will be described, assuming that the AV/C protocol is executed between the radio terminal  602  and the DVD  605  based on such a recognition.  
       FIG. 12  shows a protocol stack indicating how the AV/C protocol is executed in this embodiment, and  FIG. 13  shows a protocol stack indicating how the actual MPEG2 data transfer is carried out in this embodiment. As can be seen from  FIG. 12  and  FIG. 13 , the radio terminal  601  provides a function for terminating the IEEE 1394 bus protocol and connecting the IEEE 1394 bus with the 2.4 GHz band radio LAN or the 5 GHz band radio LAN at a level of an upper layer protocol (such as FCP layer in the AV/C protocol or CIP layer in the MPEG2 data transfer, for example).  
      In the radio network operated in this way, the processing for actually transferring the MPEG2 data on the DVD  605  to the radio terminal  602  according to a request from the radio terminal  602  is carried out as follows. This example is directed to the case where a VTR SubUnit exists in the DVD  605  on the IEEE 1394 bus, a Display SubUnit exists in the radio terminal  602 , and the MPEG2 data transfer is carried out between these SubUnits.  
       FIG. 14  shows how the DVD  605  and the radio terminal  602  are recognizing each other and what communication resources are reserved in executing the MPEG2 data transfer. In  FIG. 14 , from a viewpoint of the DVD  605 , the Display SubUnit in the radio terminal  602  appears as if it is existing in the radio terminal  601 , and this Display SubUnit and the VTR SubUnit is connected through an internal connection B inside the DVD  605 , an isochronous channel X on the IEEE 1394 bus, and an internal connection A inside the radio terminal  601 . On the other hand, from a viewpoint of the radio terminal  602 , the VTR SubUnit in the DVD  605  appears as if it is existing in the radio terminal  601 , and this VTR SubUnit and the Display SubUnit is connected through an internal connection D inside the radio terminal  602 , a channel Y on the 5 GHz band radio LAN, and an internal connection C inside the radio terminal  601 .  
      Here, O_Plug and I_Plug provided in the DVD  605  and the radio terminals  601  and  602  are interfaces for carrying out data transmission and reception with respect to the isochronous channel on the IEEE 1394 bus, which are defined by the ISO-IEC 61883 protocol. Also, the internal connections A, B, C and D provided in the DVD  605  and the radio terminals  601  and  602  are connections for connecting between SubUnits or between SubUnit and Plug in the 1394 nodes or the radio terminals, which are set up or released by the AV/C protocol. Thus, in order to transfer the MPEG2 data from the DVD  605  to the radio terminal  602 , the transfer of the MPEG2 data will be commanded after setting up such a communication route using the ISO-IEC 61883 protocol and the AV/C protocol in the configuration of  FIG. 11 . The transfer command will be executed by the AV/C protocol.  
       FIG. 15  shows an exemplary processing sequence for transferring the MPEG2 data from the DVD  605  to the radio terminal  602  after reserving communication resources as shown in  FIG. 14 . Here, it is assumed that the ISO-IEC 61883 protocol is executable even on the 5 GHz band radio LAN, so that the MPEG2 data communication on the 5 GHz band radio LAN is transferred through some communication channel (channel Y in  FIG. 14 ) on the 5 GHz band radio LAN. It is also assumed that the data transfer processing is carried out by the Contention Mode of the IEEE 802.11 as the transfer protocol on the 2.4 GHz band radio LAN and the 5 GHz band radio LAN. It is also assumed that the radio terminal  602  makes a connection to the 5 GHz band radio LAN using a procedure as described in the first embodiment. This processing sequence proceeds as follows.  
      (0) The radio terminal  602  carries out the authentication processing with the radio terminal  601 , and becomes a state in which communications using the 2.4 GHz band radio LAN are possible.  
      (1) The radio terminal  602  notifies information on SubUnits in the own terminal to the radio terminal  601 , and the DVD  605  notifies information on SubUnits in the own node to the radio terminal  601 .  
      (2) The radio terminal  602  requests the radio terminal  601  to disclose information on the SubUnits in the radio terminal  601 .  
      (3) The radio terminal  601  discloses the VTR SubUnit actually existing in the DVD  605  as information on the SubUnits in the own terminal.  
      (4) The radio terminal  602  carries out the authentication processing for the 5 GHz band radio LAN with the radio terminal  601 , via the 2.4 GHz band radio LAN, and then makes a connection to the 5 GHz band radio LAN for which the radio terminal  601  is the P.C. Here, the MAC address (=Y) used in the 2.4 GHz band radio LAN is also used as the MAC address in the 5 GHz band radio LAN.  
      (5) The radio terminal  602  executes a request for channel acquisition on the 5 GHz band radio LAN, via the 2.4 GHz band radio LAN (and the radio terminal  601  acquires the channel Y).  
      (6) The radio terminal  602  sets up a data transmission to the radio channel Y from the O_Plug in the radio terminal  601  and a data reception from the radio channel Y using the I_Plug in the own terminal, according to the ISO-IEC 61883 protocol.  
      (7) The radio terminal  602  transmits an AV/C command (Connect command) for connecting between the VTR SubUnit and the O_Plug that are recognized as existing in the radio terminal  601  by the internal connection C. At the same time, the Display SubUnit and the I_Plug in the own terminal are connected by the internal connection D.  
      (8) The radio terminal  601  acquires the isochronous channel X on the IEEE 1394 bus in response to the Connect command from the radio terminal  602 .  
      (9) The radio terminal  601  sets up a data transmission to the isochronous channel X from the O_Plug in the DVD  605  and a data reception from the isochronous channel X using the I_Plug in the own terminal, according to the ISO-IEC 61883 protocol.  
      (10) The radio terminal  601  transmits an AV/C command (Connect command) for connecting between the VTR SubUnit and the O_Plug existing in the DVD  605  by the internal connection B. At the same time, the Display SubUnit and the I_Plug in the own terminal are connected by the internal connection A.  
      (11) Upon receiving the AV/C response for the Connect command, the radio terminal  602  transmits an AV/C command (Play command) to the VTR SubUnit according to the AV/C protocol.  
      (12) The radio terminal  601  transfers the AV/C command (Play command) transmitted with respect to the VTR SubUnit, to the DVD  605 .  
      (13) The desired MPEG2 data are transferred from the DVD  605  to the Display SubUnit in the radio terminal  601 .  
      (14) The radio terminal  601  transfers the transferred MPEG2 data towards the Display SubUnit of the radio terminal  602  which is the actual data transfer destination, via the 5 GHz band radio LAN.  
      By this series of processing, it becomes possible for the radio terminal  602  which has only a reception function with respect to the 5 GHz band radio LAN to receive the video data on the IEEE 1394 bus connected to the 5 GHz band radio LAN. In particular, it is possible to execute the communication resource processing for the purpose of transferring wideband data such as MPEG2 data and the AV control protocol necessary for the MPEG2 data transfer.  
      Referring now to  FIG. 16  to  FIG. 18 , the fourth embodiment of a radio communication system and a radio terminal device according to the present invention will be described in detail.  
      This fourth embodiment is directed to the case of the radio network in which the 2.4 GHz band radio LAN and the 5 GHz band radio LAN are operated independently, where both the radio terminal providing the P.C. function on the 2.4 GHz band radio LAN and the radio terminal providing the P.C. function on the 5 GHz band radio LAN are existing on the same IEEE 1394 bus. The example described here is also directed to the case where the radio terminal on the radio network downloads image information from a DVD existing on the IEEE 1394 bus, and in particular the AV control protocol is executed between this radio terminal and the DVD via the 2.4 GHz band radio LAN, and the actual image data are received via the 5 GHz band radio LAN.  
      The difference between this fourth embodiment and the third embodiment is that a terminal for carrying out communications on the 2.4 GHz band radio LAN and a terminal for carrying out communications on the 5 GHz band radio LAN are different in this fourth embodiment, and that a protocol for notifying control information on the 5 GHz band radio LAN that is transmitted via the 2.4 GHz band radio LAN is executed between these terminals.  
      In other words, the processing (4) of  FIG. 15  for making a connection to the 5 GHz band radio LAN and the processing (6) of  FIG. 15  for reflecting the request for plug control processing on the 5 GHz band radio LAN according to the ISO-IEC 61883 protocol into the 5 GHz band radio LAN side that were carried out by the radio terminal  601  of  FIG. 11  via the 2.4 GHz band radio LAN in the third embodiment will be executed as a communication protocol between different radio terminals. It is assumed that the control message transfer protocol for this purpose is defined in advance.  
       FIG. 16  shows an exemplary configuration of a network system in this case. It is assumed that the radio LANs are operated according to the IEEE 802.11 protocol similarly as in the third embodiment. The network system of  FIG. 16  includes a radio terminal  1101  which provides a P.C. function in the 5 GHz band radio LAN  1201 , a radio terminal  1103  which has transmission and reception functions with respect to the 5 GHz band radio LAN, and a radio terminal  1102  which has only a reception function with respect to the 5 GHz band radio LAN. In addition, the radio terminal  1102  has transmission and reception functions with respect to the 2.4 GHz band radio LAN by which it can communicate with a radio terminal  1106 . Moreover, the radio terminal  1101  and the radio terminal  1106  have interfaces with respect to the same IEEE 1394 bus  1203  and are connected to a TV  1104  and a DVD  1105  via the IEEE 1394 bus.  
      This embodiment is also directed to the case where the AV/C protocol to be executed between the radio terminal and the node on the IEEE 1394 bus is executed via the 2.4 GHz band radio LAN, and the MPEG2 data are actually transferred via the IEEE 1394 bus and the 5 GHz band radio LAN.  
      In the following, the case of transferring the MPEG2 data in the DVD  1105  to the radio terminal  1102  will be described, assuming that the AV/C protocol is executed between the radio terminal  1102  and the DVD  1105  based on the recognition of the network as shown in  FIG. 14 , similarly as in the third embodiment.  
       FIG. 17  and  FIG. 18  show an exemplary processing sequence for transferring the MPEG2 data from the DVD  1105  to the radio terminal  1102  in this case. Here, it is also assumed that the ISO-IEC 61883 protocol is executable even on the 5 GHz band radio LAN. It is also assumed that the radio terminal  1102  makes a connection to the 5 GHz band radio LAN using a procedure as described in the first embodiment. This processing sequence proceeds as follows.  
      (0) The radio terminal  1102  carries out the authentication processing with the radio terminal  1106 , and becomes a state in which communications using the 2.4 GHz band radio LAN are possible.  
      (1) The radio terminal  1101  notifies the  1394  interface address (=A) of the own terminal to the radio terminal  1102 . Here, it is also possible for the radio terminal  1101  to broadcast the 1394 interface address of the own terminal on the 5 GHz band radio LAN.  
      (2) The radio terminal  1102  notifies the 1394 address (=A) of the radio terminal  1101  notified by the processing (1), to the radio terminal  1106 .  
      (3) The radio terminal  1106  confirms that the received 1394 address (=A) exists on the IEEE 1394 bus, and makes an initial setting indicating that the control messages regarding the 5 GHz band radio LAN that will be transmitted to the own device (radio terminal  1106 ) thereafter are to be transferred to the radio terminal  1101 .  
      (4) The radio terminal  1102  notifies information on SubUnits in the own terminal to the radio terminal  1106 , and the DVD  1105  notifies information on SubUnits in the own node to the radio terminal  1106 .  
      (5) The radio terminal  1102  requests the radio terminal  1106  to disclose information on the SubUnits in the radio terminal  1106 .  
      (6) The radio terminal  1106  discloses the VTR SubUnit actually existing in the DVD  1105  as information on the SubUnits in the own terminal.  
      (7) When the radio terminal  1102  transmits a request for the authentication processing for the 5 GHz band radio LAN or a request for a connection (admission) to the 5 GHz band radio LAN for which the radio terminal  1101  is the P.C., to the radio terminal  1106  via the 2.4 GHz band radio LAN, the radio terminal  1106  transfers this authentication request or connection request to the radio terminal  1101 , and the authentication request or the connection request of the radio terminal  1102  is processed at the radio terminal  1101 . Here, the MAC address (=Y1) used in the 2.4 GHz band radio LAN can be also used as the MAC address in the 5 GHz band radio LAN.  
      (8) When the radio terminal  1102  transmits a request for channel acquisition on the 5 GHz band radio LAN, via the 2.4 GHz band radio LAN, the radio terminal  1106  transfers this channel acquisition request to the radio terminal  1101 , and the processing for channel acquisition on the 5 GHz band radio LAN is carried out at the radio terminal  1101  (and the radio terminal  1101  acquires the channel Y).  
      (9) When the radio terminal  1102  transmits a request for setting up a data transmission to the radio channel Y from the O_Plug in the radio terminal  1101  according to the ISO-IEC 61883 protocol, via the 2.4 GHz band radio LAN, the radio terminal  1106  transfers this data transmission set up request to the radio terminal  1101 , and the data transmission set up processing is carried out at the radio terminal  1101 .  
      (10) The radio terminal  1102  transmits an AV/C command (Connect command) for connecting between the VTR SubUnit and the O_Plug that are recognized as existing in the radio terminal  1106  by the internal connection C, via the 2.4 GHz band radio LAN. At the same time, the Display SubUnit and the I_Plug in the own terminal are connected by the internal connection D.  
      (11) The radio terminal  1106  acquires the isochronous channel X on the IEEE 1394 bus in response to the Connect command from the radio terminal  1102 .  
      (12) The radio terminal  1106  sets up a data transmission to the isochronous channel X from the  0 _Plug in the DVD  1105  and a data reception from the isochronous channel X using the I_Plug in the radio terminal  1101 , according to the ISO-IEC 61883 protocol.  
      (13) The radio terminal  1106  transmits an AV/C command (Connect command) for connecting between the VTR SubUnit and the O_Plug existing in the DVD  1105  by the internal connection B. At the same time, the Display SubUnit and the I_Plug in the own terminal are connected by the internal connection A.  
      (14) The DVD  1105  carries out the processing corresponding to the AV/C command transmitted by (13), and then returns an AV/C response for notifying the processing result. This AV/C response is transferred from the radio terminal  1106  to the radio terminal  1102  via the 2.4 GHz band radio LAN.  
      (15) The radio terminal  1106  transmits an AV/C command (Connect command) for connecting between the O_Plug and the I_Plug in the radio terminal  1101 .  
      (16) The radio terminal  1101  carries out the processing corresponding to the Av/C command transmitted by (15), and then returns an AV/C response for notifying the processing result.  
      (17) Upon receiving the AV/C response for the Connect command transmitted by (10), via the 2.4 GHz band radio LAN, the radio terminal  1102  transmits an AV/C command (Play command) to the VTR SubUnit that is recognized as existing in the radio terminal  1106 .  
      (18) The radio terminal  1106  transfers the AV/C command (Play command) transmitted with respect to the VTR SubUnit, to the DVD  1105 .  
      (19) The DVD  1105  carries out the processing corresponding to the AV/C command transmitted by (18), and then returns an AV/C response for notifying the processing result. This AV/C response is transferred from the radio terminal  1106  to the radio terminal  1102  via the 2.4 GHz band radio LAN.  
      (20) The desired MPEG2 data are transmitted from the DVD  1105  onto the isochronous channel X.  
      (21) The radio terminal  1101  receives data on the isochronous channel X and transfers this data to the channel Y on the 5 GHz band radio LAN, such that the received MPEG2 data are transmitted towards the Display SubUnit in the radio terminal  1102  which is the actual data transfer destination, via the 5 GHz band radio LAN.  
      By this series of processing, it becomes possible for the radio terminal  1102  which has only a reception function with respect to the 5 GHz band radio LAN to receive the video data on the IEEE 1394 bus connected to the 5 GHz band radio LAN. In particular, even when the 2.4 GHz band radio communication function and the 5 GHz band radio communication function are existing independently on the IEEE 1394 bus, it is possible to carry out the control and the set up of the 5 GHz band radio LAN via the 2.4 GHz band radio LAN using the initial setting between the 2.4 GHz band radio communication function and the 5 GHz band radio communication function. Moreover, it is possible to execute the communication resource processing for the purpose of transferring wideband data such as MPEG2 data and the AV control protocol necessary for the MPEG2 data transfer.  
      As described above, according to the present invention, in a network in which at least a first network and a second network are used (a home network in which the 2.4 GHz band radio LAN and the 5 GHz band radio LAN are used, for example), a terminal device (a radio terminal, for example) which is capable of packet transmission and reception in the second network but which is capable only of packet reception in the first network can carry out a procedure necessary in receiving data through the first network by utilizing the second network, so that this terminal device can be effectively utilized as a packet receiving node in the first network without transmitting any packet to the first network from this terminal device (that is, without requiring a packet transmission function with respect to the first network in this terminal device).  
      Thus according to the present invention, it becomes possible to transfer information to a radio terminal having a transmission and reception interface for the 2.4 GHz band radio LAN and a reception interface for the 5 GHz band radio LAN from another radio terminal on the 5 GHz band radio LAN, for example.  
      In addition, it is also possible to transmit various data transferred on the other non-radio network such as the IEEE 1394 bus, for example, by relaying the data transfer at another radio terminal having a transmission and reception Interface for the 5 GHz band radio LAN, so that it becomes possible to realize the data communications as if it is connected to the IEEE 1394 bus through a radio interface.  
      Namely, even when the radio terminal has only a reception function with respect to the 5 GHz band radio LAN, the authentication/admission processing in the 5 GHz band radio LAN or the AV control protocol between the radio terminal and the node on the IEEE 1394 bus can be carried out via the 2.4 GHz band radio LAN, and the actual data transfer can be carried out via the 5 GHz band radio LAN, so that the video data on the IEEE 1394 bus can be received through the 5 GHz band radio interface.  
      Consequently, according to the present invention, it is possible to reduce the cost of the radio terminal using expensive components for the 5 GHz band radio communication, for example. In particular, by providing only a reception function among the radio communication function, and utilizing an inexpensive radio system for the bidirectional communications, it is possible to reduce the number of expensive radio components that are required in the terminal, and thereby reduce the cost of the terminal.  
      Note that the video information utilization in the home is mostly in a form of receiving/displaying video transmitted by a TV or satellite broadcast for the purpose of watching broadcast programs. This implies that the most users are likely to only receive the video information and hardly transmit any video information. In view of this fact, it is effective to provide only a reception function in the terminal in order to realize wider spread of the 5 GHz band radio function to many homes at low cost. Thus, by providing only a reception function as an expensive radio function such as the 5 GHz band radio function while also providing a transmission function using another inexpensive radio function such as the 2.4 GHz band radio function, it is possible to provide radio terminals that can receive wideband image data and that can be easily accepted in the home environment.  
      It is to be noted that the above embodiments have been described for an exemplary case of using the IEEE 1394 bus as a network other than the radio network, but the present invention is equally applicable to the case of using a network other than the IEEE 1394 bus in conjunction with the radio network.  
      It is also to be noted that the above embodiments have been described for an exemplary case of the home network, but the present invention is equally applicable to a network other than the home network.  
      It is also to be noted that the above described embodiments according to the present invention may be conveniently implemented using a conventional general purpose digital computer programmed according to the teachings of the present specification, as will be apparent to those skilled in the computer art. Appropriate software coding can readily be prepared by skilled programmers based on the teachings of the present disclosure, as will be apparent to those skilled in the software art.  
      In particular, each of the radio terminals of the above described embodiments can be conveniently implemented in a form of a software package.  
      Such a software package can be a computer program product which employs a storage medium including stored computer code which is used to program a computer to perform the disclosed function and process of the present invention. The storage medium may include, but is not limited to, any type of conventional floppy disks, optical disks, CD-ROMs, magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, magnetic or optical cards, or any other suitable media for storing electronic instructions.  
      It is also to be noted that, besides those already mentioned above, many modifications and variations of the above embodiments may be made without departing from the novel and advantageous features of the present invention. Accordingly, all such modifications and variations are intended to be included within the scope of the appended claims.