CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is based upon and claims the benefit of priority under 35 U.S.C. § 119 from prior Japanese Patent Application P2004-282775 filed on Sep. 28, 2004, the entire contents of which are incorporated by reference herein. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a radio communication apparatus, a radio communications system, and a radio-communications method based on IEEE 802.11, especially supporting virtual LAN. 
   2. Description of the Background 
   IEEE 802.3 is a well known standard for communicating on a wired LAN, and IEEE 802.11 is a well known standard for communicating on wireless LAN. They are established by the IEEE (Institute of Electrical and Electronics Engineers, Inc.). 
   IEEE 802.3 is a standard generally known as “Ethernet”™. According to this standard, “Ether frame” packets are transferred between wired terminals in 60-1514 bytes per second. 
   On the other hand, IEEE 802.11, which is a standard for the wireless LAN, has several versions (e.g. IEEE 802.11a, IEEE 802.11b, and IEEE 802.11g). There are differences in communication frequency and transfer rate between them. 
   IEEE also recommends IEEE 802.1Q relating to a VLAN (Virtual LAN). IEEE 802.1Q can be used together with IEEE 802.3 and IEEE 802.11. A VLAN includes two or more virtual local area networks built in a network. 
   Moreover, IEEE 802.11i for communication security is also recommended. IEEE 802.1Q defines a security mechanism with encrypting transferred data based on IEEE 802.11. 
   However, the security mechanism of IEEE 802.11i cannot work in the VLAN of IEEE 802.IQ because security parameters of IEEE 802.11i are selected based on a destination MAC (Media Access Control) address of the Ether frame. 
   For example, a terminal that can receive a multicasted or broadcasted Ether frame destined for a MAC address of another terminal that belongs to a VLAN may also be able to receive Ether frames destined for other VLANs. 
   If an encryption key of first a VLAN is different from encryption keys for other VLANs, a terminal that belongs to one of the other VLANs cannot interpret an Ether frame that is destined for the first VLAN. However, that terminal of the other VLAN also cannot recognize Ether frames sent as part of a third party attack or by mistake. Thus, a terminal that supports IEEE 802.11i cannot fulfill the requirements of IEEE 802.1Q VLAN. 
   As an attempt to solve this problem, JP-A-2004-200812 describes a method to provide new session information on multicast communication to provide security between multicast groups. 
   SUMMARY OF THE INVENTION 
   According to an exemplary embodiment, the present invention provides a communication device configured to receive a first packet from a first network including a virtual network, and to transmit a second packet to a second network, the communication device including: a receiver section configured to receive the first packet from the first network; a converter section configured to convert a second destination address of the first packet to the first destination address of the second packet using identifying information of the virtual network; a selector configured to select a security parameter based at least in part on the first destination address of the second packet; an encryption section configured to encrypt the second packet based on the security parameter; and a transmitter section configured to multicast the encrypted second packet to the second network. 
   Another non-limiting aspect of the present invention provides a communication system, including: a first network configured to support a virtual network; a first communication device configured to transmit a first packet, which includes identifying information of the virtual network, through the first network; a second network configured to transfer a second packet, the second packet being encrypted based on a security parameter selected according to a first destination address of the second packet; a second communication device configured to connect the second network; and a third communication device configured to receive the first packet from the first network, to convert a second destination address of the first packet to the first destination address of the second packet using the identifying information of the virtual network, to encrypt the second packet based on the security parameter selected according to the first destination address of the second packet, and to multicast the encrypted second packet to the second network. 
   Yet another non-limiting aspect of the present invention includes a communication method for receiving a first packet from a first network including a virtual network, and for transmitting a second packet to a second network, the method including: receiving the first packet from the first network; converting a second destination address of the first packet to a first destination address of the second packet using identifying information of the virtual network; encrypting the second packet based on a security parameter selected according to the second destination address; and multicasting the encrypted second packet to the second network. 
   Another aspect of the present invention includes a communication device, including: a receiver configured to receive a first packet from a virtual network; a converter configured to convert the first packet to a second packet addressed to a second network; a selector configured to select a security parameter based at least in part on at least one characteristic of the second packet; an encryption device configured to encrypt the second packet based on the security parameter; and a transmitter configured to transmit the encrypted second packet to the second network. 
   The present invention further provides communication system, including: a virtual network; a first communication device configured to transmit a first packet; and a second communication device configured to receive the first packet from the virtual network and to convert a second destination address of the first packet to a first destination address of a second packet based on identification information of the virtual network. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is best understood from the following description of the non-limiting embodiments when read in connection with the accompanying drawings, wherein: 
       FIG. 1  is a diagram illustrating a virtual LAN communication system according to a non-limiting aspect of the invention; 
       FIG. 2  is a diagram illustrating a structure of a MAC address based on IEEE 802.3 according to a non-limiting aspect of the invention; 
       FIG. 3  is a diagram illustrating a destination MAC address of multicasted Ether frame according to a non-limiting aspect of the invention; 
       FIG. 4  is a diagram illustrating an Ether frame according to a non-limiting aspect of the invention; 
       FIG. 5  is a diagram illustrating an access point according to a non-limiting aspect of the invention; 
       FIG. 6  is a diagram illustrating an encryption key table according to a non-limiting aspect of the invention; 
       FIG. 7  is a diagram illustrating a modified Key Descriptor message according to a non-limiting aspect of the invention; 
       FIG. 8  is a diagram illustrating an access point according to a non-limiting aspect of the second modification of the invention; 
       FIG. 9  is a diagram illustrating an encryption key table according to a non-limiting aspect of the second modification of the invention; and 
       FIG. 10  is a diagram illustrating a modified Key Descriptor message according to a non-limiting aspect of the second modification of the invention. 
   


   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawings, in which like reference numerals designate identical or corresponding parts throughout the several views,  FIG. 1  illustrates an example of a first non-limiting embodiment of a virtual LAN communication system according to the invention. 
   The virtual LAN communication system includes a network  101 , a host  102 , a host  103 , a PC  104 , a PC  105 , a PC  106 , and an access point  107 . The network  101  is a wired LAN network based on IEEE 802.3. 
   The host  102  is a server having a network connection interface based on IEEE 802.1Q and IEEE 802.3. The host  102  can communicate with the access point  107 , the PC  104 , and the PC  105  via the network  101 . The host  102  belongs to a virtual LAN (VLAN1) based on IEEE 802.1Q. 
   The host  103  is a server having a network connection interface based on IEEE 802.1Q and IEEE 802.3. The host  103  can communicate with the access point  107 , the PC  104 , and the PC  105  via the network  101 . The host  103  belongs to another virtual LAN (VLAN2) based on IEEE 802.1Q. 
   The PC  104  and the PC  105  may be portable type PCs (e.g., laptop computers). The PC  104  and the PC  105 , respectively, have a wireless LAN connection interfaces based on IEEE 802.11i. The PC  104  and the PC  105  belong to the VLAN1, and can communicate securely with the host  102  connected to the network  101  through the access point  107 . 
   The PC  106  may be a portable type PC (e.g., a laptop computer). The PC  106  has a wireless LAN connection interface based on IEEE 802.11i. The PC  106  belongs to the VLAN2, and can communicate securely with the host  103  connected to the network  101  through the access point  107 . 
   The access point  107  includes both the wired LAN network connection interface based on IEEE 802.3 and the wireless LAN connection interface based on IEEE 802.11. Terminals that belong to the wireless LAN or connect to the wired LAN network communicate with each other via the access point  107 . 
   The access point  107  provides VLAN1 environment and VLAN2 environment based on IEEE 802.1Q for the wired LAN. The access point  107  can separately treat the communications of VLAN1 and the communications of VLAN2. The access point  107  provides security based on IEEE 802.11i for the wireless LAN. 
   The access point  107  changes the destination MAC address of a multicasted packet or a broadcasted packet according to the VLAN to which the sender terminal and the destination terminal belong. The access point  107  encrypts the packet according to the encryption parameter for the destination MAC address, and transmits the encrypted packet to the wireless LAN. 
   A packet multicasted or broadcasted in a VLAN on the wired LAN can reach the same terminal in the VLAN on the wireless LAN because a particular destination MAC address treated in the wired LAN is associated with the particular VLAN on the wireless LAN. 
     FIG. 2  illustrates a structure of a MAC address based on IEEE 802.3.  FIG. 2(   a ) illustrates each field of a 48 bit MAC address.  FIG. 2(   b ) illustrates an example of the 48 bit MAC address of a multicasted packet in little endian format. 
   An I/G  201  is a bit for identifying that the MAC address is for Individual (unicast) or for Group (multicast). The I/G  201  is set to 0 when the MAC address is for an Individual (individual destination). The I/G  201  is set to 1 when the MAC address is for a Group (multicast for terminals in a particular group). 
   A U/L  202  is a bit for identifying that the MAC address is for Universal (Global address) use or for Local (Private address) use. The U/L  202  is set to 0 when the MAC address is universally unique. The U/L  202  is set to 1 when the MAC address is only locally available. 
   An OUI (Organizationally Unique Identifier)  203  is a field that indicates the value managed for every manufacturer. Each manufacturer has unique value of OUI  203  and IEEE distributes the values of OUI  203 . The value of OUI  203  prevents the existence of identical MAC addresses because the value of OUI  203  is different for each manufacturer. 
   A DEVICE ID  204  is a value that is distributed by the manufacturer. The manufacturer distributes different values for the DEVICE ID  204  for each network interface device. 
   In  FIG. 2(   b ), when the value of the I/G  201  is 1, it represents that the destination MAC address indicates a group for multicasting. When the value of U/L  202  is 0, it represents that the MAC address is unique in the whole world. 
   According to RFC (Request for Comment)  1112  that specifies a MAC address on multicasting, the value of the OUI  203  should be “0x00005e”, irrespective of the manufacturer. 
   RFC1112 also specifies that the length of the MAC address on multicasting should be 23 bits when using IPv4. So the value of the leftmost bit of the DEVICE ID  204  is given as 0. 
   A multicast address is stored from the neighbor bit of the leftmost bit of the DEVICE ID  204 . The MAC address may be interpreted as a broadcast address if the value of the DEVICE ID  204  is “ff:ff:ff”. 
   As described above, the structure of the MAC address in the case of multicasting is specified. Communication devices can interpret what kind of MAC address it is by reading each field of the MAC address. 
   The example of  FIG. 2(   b ) is in little endian format. Other configurations than described above may be employed if a format other than little endian is employed for the MAC address. 
     FIG. 3  illustrates an example of conversion of a destination MAC address of multicasted Ether frame stipulated in IEEE 802.3. Ether frame  301  pursuant to IEEE 802.3, a field of the destination MAC address in wired LAN  302 , and a field of the destination MAC address in wireless LAN  303  are illustrated in  FIG. 3 . The MAC address in  FIG. 3  is in big endian format, so each bit position is different from the MAC address in  FIG. 2  in little endian format. 
   The Ether frame  301  includes information such as a destination MAC address, a source MAC address, a first protocol type (it is “VLAN” in this example), a VLAN ID, and a second protocol type (it is “IPv4” in this example). The destination MAC address indicates the destination of the Ether frame  301 . The source MAC address indicates a MAC address of the communication device that transmits the Ether frame. The first protocol type indicates that a communication device belonging to a VLAN multicasts the Ether frame. The VLAN ID indicates the VLAN to which the communication device that multicasts the Ether frame belongs. 
   In the field of the destination MAC address in wired LAN  302 , as same as in  FIG. 2(   b ), if the value of the I/G is 1, it represents that the MAC address indicates a group for multicasting. When the value of U/L is 0, it represents that the MAC address is unique in the whole world. When the value of OUI is “0x00005e”, it indicates that the Ether frame is multicasted. The value of the leftmost bit of the DEVICE ID  204  is given as 0, and other bits of the DEVICE ID  204  may be arbitrary values. 
   In the field of the destination MAC address in wireless LAN  303 , the value of the bit of the U/L  202  is 1 that indicates the MAC address is Local. As a result, the field of OUI  203  can be used to contain the VLAN ID. 
   As described above, the destination MAC address in wired LAN indicates the destination VLAN to be multicasted. Different security parameters can be set for each VLAN if IEEE 802.11i is employed, since IEEE 802.11i enables different security parameters for each destination MAC address. 
     FIG. 4  illustrates an example of conversion of a multicasted Ether frame stipulated in IEEE 802.3.  FIG. 4(   a ) illustrates an Ether frame in wired LAN (Ether frame (a)).  FIG. 4(   b ) illustrates an Ether frame in wireless LAN converted from the Ether frame (a) by the access point  107  (Ether frame (b)). 
   The Ether frame (a) has the same structure as the Ether frame  301  shown in  FIG. 3 . That is, the Ether frame (a) includes information such as a destination MAC address, a source MAC address, a first protocol type (it is “0x8100” in this example), and a VLAN (it is “0x0001” in this example). 
   When the Ether frame (a) is transmitted to the wireless LAN, the access point  107  converts the Ether frame (a). The Ether frame (b) has information of a new destination MAC address. The new destination MAC address is found by using the VLAN ID quoted from the Ether frame (a). The Ether frame (b) also has information of the MAC address “03:00:01:00:00:01” as the destination MAC address. 
   The Ether frame (b) may not have fields of the first protocol type and the VLAN ID. The Ether frame (b) may be shorter than the Ether frame (a) as long as fields of the first protocol type and the VLAN ID are included in the Ether frame (b). 
   The access point  107  transmits the Ether frame (b), instead of the Ether frame (a) to the communication device that connects to the wireless LAN. 
     FIG. 5  illustrates an example of the block diagram of the access point  107 . The access point  107  comprises a wired LAN communication section  501 , a transfer section  502 , a wireless LAN communication section  503 , an antenna  504 , a storage section  505 , and an address conversion section  506 . 
   The wired LAN communication section  501  communicates with the host  102  and the host  103  through the network  101  based on IEEE 802.3. The wired LAN communication section  501  has a VLAN function specified in IEEE 802.1Q. 
   The transfer section  502  transfers a converted multicasted/broadcasted Ether frame, which has converted destination MAC address, between the wired LAN and the wireless LAN with a support of the address conversion section  506 . The transfer section  502  may converts the structure of the Ether frame as shown in  FIG. 4 . 
   The wireless LAN communication section  503  communicates with the communication devices through the wireless LAN based on IEEE 802.11 according to transfer directions from the transfer section  502 . The storage section  505  stores an encryption key table for encrypting the Ether frame based on IEEE 802.11i. The encryption key table has information of a relationship between an encryption system and an encryption key. The encryption key table is inputted in advance of the communication. 
   The antenna  504  transmits and receives radio waves used for communication in the wireless LAN. 
   The address conversion section  506  converts the destination MAC address of the Ether frame transferred transfer section  502 . The address conversion section  506  converts the destination MAC address of the Ether frame muticasted/Broadcasted on the network  101  from a terminal that belongs to some VLAN. 
     FIG. 6  illustrates an example of the encryption key table  601  stored in the storage section  505 . The encryption key table  601  has information related to a MAC address, an encryption system, and an encryption key associated with each other. The MAC address is associated with a VLAN on the wireless LAN, rather than with a particular device. 
   In other words, when the transfer section  502  transfers an Ether frame to the MAC address associated with a VLAN on the wireless LAN, the wireless LAN communication section  503  finds the MAC address written in the Ether frame as destination MAC address from the encryption key table  601 , and encrypts the Ether frame according to the encryption system and the encryption key associated with the MAC address on the encryption key table  601 . 
   The MAC address written on the encryption key table  601  represents the new MAC address found by using the VLAN ID. Thus, different MAC addresses for multicasting/broadcasting in the wireless LAN are associated with each VLAN. It enables the multicasting/broadcasting in a VLAN from the wired LAN side to the wireless LAN side. This invention also enables different wireless LAN security parameters to be established for each VLAN. 
   Therefore, multicasting/broadcasting communication for every VLAN based on IEEE 802.1Q can be done seamlessly between the wired LAN based on IEEE 802.3 and the wireless LAN based on IEEE 802.11i. 
   First Non-Limiting Modification: 
   In this modification, the encryption key on the encryption key table  601  is provided by a key exchange protocol. IEEE 802.1×, IEEE 802.11i, and WPA (Wi-Fi Protected Access) are known key exchange protocols. 
     FIG. 7  illustrates an example of a modified Key Descriptor message. The modified Key Descriptor message has not only information stipulated in IEEE 802.1×, but also key exchange information. 
   In this example, a field of a MAC address for multicasting and a field of key information are added to the Key Descriptor message stipulated in IEEE 802.1×. In other key exchange protocols, these fields can be added similarly. 
   The exchange of the encryption key for multicasting may be, for example, (1) a part of a key exchanging procedure of a general authentication procedure when receiving a connection request from other communication device, or (2) a part of an IGMP (Internet Group Management Protocol) procedure when a communication device wants to receive a multicasted Ether frame. In the case of (1), the key information for multicasting may be exchanged in authentication and key exchange procedure. In the case of (2), the key information for multicasting may be exchanged in authentication procedure on higher protocol. 
   By this modification, multicasting/broadcasting communication for every VLAN based on IEEE 802.1Q with the security system based on IEEE 802.11i can be done seamlessly between the wired LAN based on IEEE 802.3 and the wireless LAN based on IEEE 802.11i. 
   Second Non-Limiting Modification: 
   In this modification, a first encryption key is associated with a MAC address, and a second encryption key is associated with a VLAN ID on the encryption key table  601 . 
     FIG. 8  illustrates a diagram of an example of the access point  107  in this modification. The difference from  FIG. 5  is the line connecting the address conversion section  506  and the wireless LAN communication section  503 . 
     FIG. 9  illustrates an example of the encryption key table  901  in this modification. The encryption key table  901  contains the MAC address before the conversion and VLAN ID are associated with each other. 
   In this case, the transfer section  502  directs the combination of the destination MAC address and the VLAN ID, and the wireless LAN communication section  503  finds out the combination from the encryption key table  901 . 
   The address conversion section  506  provides the new destination MAC address converted from the found MAC address and the found VLAN. The wireless LAN communication section  503  encrypts the Ether frame, and transmits it to the new destination MAC address. 
   As in  FIG. 7 ,  FIG. 10  illustrates an example of a modified Key Descriptor message. Information of the VLAN ID is added to the modified Key Descriptor message shown in  FIG. 7 . The timing and the procedure of key exchange are same as in the first modification. Thus, multicasting/broadcasting communication for every VLAN based on IEEE 802.1Q can be done seamlessly and automatically between the wired LAN based on IEEE 802.3 and the wireless LAN based on IEEE 802.11i. 
   While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.
A communication device configured to receive a first packet from a first network including a virtual network, and to transmit a second packet to a second network, the communication device including: a receiver section configured to receive the first packet from the first network; a converter section configured to convert a second destination address of the first packet to the first destination address of the second packet using identifying information of the virtual network; a selector configured to select a security parameter based at least in part on the first destination address of the second packet; an encryption section configured to encrypt the second packet based on the security parameter; and a transmitter section configured to multicast the encrypted second packet to the second network.