Patent Publication Number: US-7583698-B2

Title: Multicast communication method

Description:
This is a continuation application of U.S. Ser. No. 09/822,294, filed Apr. 2, 2001 now U.S. Pat. No. 7,012,931. 
    
    
     CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application relates to U.S. patent application Ser. No. 09/257,003 filed on Feb. 25, 1999 based on Japanese Patent Application Number 10-046739 filed on Feb. 27, 1998 and U.S. patent application Ser. No. 09/614,715 filed on Jul. 6, 2000 based on Japanese Patent Application Number 8-291480 and 9-212889, both of which are assigned to the present assignee. The contents of those applications are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a multicast communication method. The invention also relates to a multicast communication method which is applied to, for example, a method of making an IPv4 network-compatible multicast application operative on an IPv6 network, a packet generation method, an IP-network-dedicated translator, an NAT (Network Address Translator), a memory medium having a packet generation program recorded thereon, and the like. 
     In the field of information communication, generally, there is a method called multicast distribution as a method of simultaneously distributing same data from one host to a plurality of hosts. In the multicast distribution, one group is formed by a plurality of hosts and the same data is distributed from one of the hosts in the group to all of the other hosts by using one multicast packet. 
     The standard protocol in the Internet is a TCP/IP (Transmission Control Protocol/Internet Protocol) and the IP of version 4 (hereinafter, referred to as an IPv4) is widespread at the present time. Although the IP is at present being rapidly widespread for various communication services in cooperation with the spread of the Internet or the like, there is a serious problem such as a lack of IP addresses. As means for solving such a problem, the IP of version 6 (hereinafter, referred to as an IPv6) has been proposed at present. Also in the TCP/IPv4 and TCP/IPv6, there is a technique called an IP multicast using multicast distribution. 
     In the IP multicast, a specific IP address called an IP multicast address is specified every group and data is distributed to each host by using an IP multicast packet in which the IP multicast address is used as a destination IP address. As one of the protocols for the IPv4 multicast, for example, there is the IGMP (Internet Group Management Protocol) disclosed in RFC (Request For Comment) 1112 and RFC2236 as documents issued from the IETF (Internet Engineering Task Force). The IGMP is a protocol for allowing an IPv4 host to request an adjacent router to perform multicast distribution. Thus, the IPv4 host can receive the IPv4 multicast packet. 
     As one of protocols for the IPv6 multicast, there is the MLD (Multicast Listener Discovery) disclosed in RFC2710. The MLD is a protocol for allowing an IPv6 host to request an adjacent router to perform multicast distribution in a manner similar to the IGMP. Thus, the host can receive an IPv6 multicast packet. 
     At present, a large scale LAN is being formed in a form such that an LAN according to the IPv6 and an LAN according to the IPv4 mixedly exist. There is an RFC1933 as a document of standardization regarding the mutual adjacency of the LAN according to the IPv6 and the LAN according to the IPv4. According to the RFC1933 (Transition Mechanism for IPv6 Hosts and Routers: R. Gilligam, 1996. 4, IETF), in a communication control apparatus having IPv6 software, mutual adjacency of an IPv6 network is enabled by mapping an IPv4 address to an IPv6 address. A technique in which an IPv4-to-IPv6 protocol translation control module in the communication control apparatus enables an IPv4 application and an IPv6 host to communicate in unicast communication has been disclosed in JP-A-11-252172 (Japanese Patent Application No. 10-46739). 
     SUMMARY OF THE INVENTION 
     As mentioned above, a mixed existence environment of the IPv4 network and the IPv6 network is being formed at present. However, the number of IPv6 multicast-compatible applications (APs) is much smaller than the number of IPv4 multicast-compatible APs. Hitherto, there is not means for enabling the IPv4 multicast-compatible application on a personal computer/workstation (PC/WS) and the IPv6 multicast-compatible application on the PC/WS to communicate directly without intervention of a network apparatus such as an address translation router having an NAT function or the like. 
     In case of performing the IPv4 multicast communication, the IGMP for controlling the distribution of the IPv4 multicast data is indispensable. In case of performing the IPv6 multicast communication, the MLD for controlling the distribution of the IPv6 multicast data is indispensable. Therefore, although the IPv4-to-IPv6 translation communication control apparatus provided between the IPv4 host and the IPv6 host needs the function for translating the IGMP and the MLD, such means does not exist hitherto. The protocol translation control between the IGMP and the MLD is also indispensable in order to make the PC/WS on which the IPv4 multicast-compatible application operates operative on the IPv6 network. 
     In consideration of the above points, the invention mainly has the following objects. 
     (1) To enable the IPv4 multicast-compatible application on the PC/WS to communicate directly with the IPv6-compatible application on the PC/WS without intervention of the network apparatus such as an address translation router having the NAT function or the like. 
     (2) To enable the IP multicast packet which is outputted from the IPv4 host to be received by the IPv6 host and to enable the IP multicast packet which is outputted from the IPv6 host to be received by the IPv4 host. 
     The LAN control apparatus such as PC/WS or the like generally has an IPv4-compatible AP (application), an IPv4-compatible protocol control module, and a plurality of LAN control modules. Further, according to the invention, to accomplish the above objects, an IGMP-to-MLD translation control module is provided in the protocol translation control module between the protocol translation control module and the LAN control modules in the LAN control apparatus. Besides the IGMP-to-MLD translation control module, an Ipv4-to-IPv6 transmission switch control module, an IPv4-to-IPv6 reception switch control module, an IP header conversion control module, and an IPv6 transmission/reception control module are provided in the protocol translation control module. 
     To solve the above problem, the IGMP-to-MLD translation control module mainly translates an IGMP packet which is outputted from the protocol control module into an MLD packet and outputs it to the network through the LAN control module. The IGMP-to-MLD translation control module translates an MLD packet inputted from the network into an IGMP packet and outputs it to the protocol translation control module. Thus, the IPv4 multicast application in the communication control apparatus can be communicated on the IPv6 network. 
     To solve the above problem, according to the invention, an IPv4-to-IPv6 transmission/reception switch control module in the LAN control apparatus discriminates the IGMP packet in the IPv4 packet which is inputted from the IPv4 network and sends it to the IGMP-to-MLD translation control module. The IGMP-to-MLD translation control module translates the IGMP packet into the MLD packet and outputs it to the IPv6 network through the LAN control module. After that, if the IPv4 multicast packet is inputted, an IP header conversion control module converts it into the IPv6 multicast packet and outputs it to the IPv6 network. 
     The IPv4-to-IPv6 transmission/reception switch control module in the LAN control apparatus discriminates the MLD packet in the IPv6 packet which is inputted from the IPv6 network and sends it to the IGMP-to-MLD translation control module. The IGMP-to-MLD translation control module translates the MLD packet into the IGMP packet and outputs it to the IPv4 network through the LAN control module. After that, if the IPv6 multicast packet is inputted, an IP header conversion control module converts it into the IPv4 multicast packet and outputs it to the IPv4 network. 
     As mentioned above, according to the invention, the IP multicast packet which is outputted from the IPv4 host can be received by the IPv6 host and the IP multicast packet which is outputted from the IPv6 host can be received by the IPv4 host. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a construction of an LAN control apparatus according to an embodiment of the invention; 
         FIG. 2  is a diagram showing a construction of an information processing apparatus; 
         FIG. 3  is a diagram for explaining an IPv4 header format; 
         FIG. 4  is a diagram for explaining an IPv6 header format; 
         FIG. 5  is a diagram showing a construction of entries in an IPv6 multicast subscription table; 
         FIG. 6  is a diagram for explaining an IGMP header format; 
         FIG. 7  is a diagram for explaining an MLD header format; 
         FIG. 8  is a diagram showing a processing flow for translating an MLD packet into an IGMP packet; 
         FIG. 9  is a diagram showing a processing flow for translating the IGMP packet into the MLD packet; 
         FIG. 10  is a diagram showing a construction of a communication network system; 
         FIG. 11  is a diagram showing a construction of an address translation table of a host A shown in  FIG. 10 ; 
         FIG. 12  is a diagram showing a construction of an address translation table of a host B shown in  FIG. 10 ; 
         FIG. 13  is a sequence diagram of packet data in the communication network system shown in  FIG. 10 ; 
         FIG. 14  is a diagram showing another construction of an LAN control apparatus; 
         FIG. 15  is a diagram showing another construction of a communication network system; 
         FIG. 16  is a sequence diagram of packet data in the communication network system shown in  FIG. 15 ; and 
         FIG. 17  is a sequence diagram of packet data in the communication network system shown in  FIG. 15 . 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     An embodiment of the invention will now be described. 
     First, a construction of an LAN control apparatus using the embodiment will be described.  FIG. 1  is a diagram showing a construction of an LAN control apparatus  1001 .  FIG. 2  is a diagram showing a construction of an information processing apparatus. The information processing apparatus shown in  FIG. 2  is, for example, a personal computer (PC), a workstation (WS), an inter-network connecting apparatus, or the like. As one component of the information processing apparatus shown in  FIG. 2 , the LAN control apparatus shown in  FIG. 1  is included in the information processing apparatus. Each component element of the LAN control apparatus shown in  FIG. 1  is included in, for example, a memory  2002  or a CPU  2001  in the information processing apparatus shown in  FIG. 2  and executed in the memory  2002  or CPU  2001 . 
     In  FIG. 1 , the LAN control apparatus  1001  has a user space  1002  where an application (AP) operates and a kernel space  1016  where a kernel operates. The user space  1002  has a TCP/IPv4-compatible multicast AP  1006 . The kernel space  1016  has a protocol control module  1003 , a protocol translation control module  1004 , and an LAN control module  1005 . The protocol control module  1003  has a TCP transmission/reception control module  1007  and an IPv4 transmission/reception control module  1008 . The protocol translation control module  1004  has an IPv4-to-IPv6 transmission switch control module  1009 , an IP header conversion control module  1010 , an IGMP-to-MLD translation control module  1011 , an IPv6 transmission/reception control module  1012 , and an IPv4-to-IPv6 reception switch control module  1013 . The IPv4-to-IPv6 reception switch control module  1013  can also include the IPv6 transmission/reception control module  1012 . 
     In the embodiment, each of the protocol control module  1003 , protocol translation control module  1004 , and LAN control module  1005  is constructed as a program (software) and executed in the kernel space. The protocol control module  1003 , protocol translation control module  1004 , and LAN control module  1005  can be also constructed as independent programs or two or more of them can be also combined and constructed as one program. Each program constructing the protocol control module  1003 , protocol translation control module  1004 , and LAN control module  1005  is installed into the information processing apparatus shown in  FIG. 2  and stored into an arbitrary area in the memory  2002  in the information processing apparatus. The user space  1002  and kernel space  1016  are also stored in arbitrary areas in the memory  2002 . The CPU  2001  in the information processing apparatus executes each program by using the kernel space  1016 , so that each of the protocol control module  1003 , protocol translation control module  1004 , and LAN control module  1005  operates. 
     An interface between the TCP/IPv4-compatible multicast AP  1006  and the protocol control module  1003  is executed by inputting and outputting a data packet which is generated by the TCP/IPv4-compatible multicast AP  1006 . An interface between the protocol control module  1003  and the protocol translation control module  1004  is executed by inputting and outputting the IPv4 packet. 
       FIG. 3  is a diagram for explaining an IPv4 header format.  FIG. 4  is a diagram for explaining an IPv6 header format. The IPv4 packet is a packet comprising: a data packet field in which the data packet is inserted; an IPv4 header field in which the IPv4 header shown in  FIG. 3  is inserted; and an MAC (Media Access Control) header field in which an MAC header (not shown) is inserted. An interface between the protocol translation control module  1004  and the LAN control module  1005  is executed by inputting and outputting the IPv4 packet or IPv6 packet. The IPv6 packet is a packet comprising: a data packet field; an IPv6 header field in which the IPv6 header shown in  FIG. 4  is inserted; and an MAC header field. 
     An input/output interface between the control modules in the protocol translation control module will now be described. A control is made between all of the control modules in the protocol translation control module by inputting and outputting the IPv4 packet or IPv6 packet. 
     Functions of each control module will now be described. 
     The IPv4-to-IPv6 transmission switch control module  1009  has a packet switching function for the IPv4 packet sent from the protocol control module  1003  and a local IPv4 address deciding function. Processing contents of them will be described in detail hereinlater. 
     The IPv6 transmission/reception control module  1012  executes an IPv6 protocol process. 
     An address translation table  1014  provided in the IP header conversion control module  1010  is a compatible table of an IPv4 address and an IPv6-address. The IP header conversion control module  1010  executes a conversion between the IPv4 header and the IPv6 header by using information registered in the address translation table  1014 . 
     The IGMP-to-MLD translation control module  1011  executes a translation between the IGMP packet and the MLD packet by using information registered in an IPv6 multicast subscription table  1015 . The IGMP packet is a packet such that the IGMP header and the data packet have been inserted in a data packet field in the IPv4 packet. The MLD packet is a packet such that the MLD header and the data packet have been inserted in a data packet field in the IPv6 packet. 
       FIG. 5  is a diagram showing a construction of entries in the IPv6 multicast subscription table  1015 . The IPv6 multicast subscription table  1015  in the IGMP-to-MLD translation control module  1011  is a table including a plurality of entries as shown in the diagram. In  FIG. 5 , an IGMP version indicates a version of the IGMP which is supported by the IGMP function of the protocol control module  1003 . The IPv4 multicast address and IPv6 multicast address show a correspondence relation of an IPv4/IPv6 multicast group for which the LAN control apparatus subscribes at present. A life time of the entry indicates the maximum time when the entry is valid. 
     The IPv4-to-IPv6 reception switch control module  1013  has a packet switching function for the reception packet (IPv4 packet or IPv6 packet) from the LAN control module  1005 . 
       FIG. 6  is a diagram for explaining an IGMP header format. A Type field shows a type of message of the IGMP. As types, there are Membership Query (multicast group query), Membership Report (multicast group report), and Leave Group (leaving from the multicast group). Max Resp Time indicates a maximum delay time which is necessary for transmitting the IGMP packet in which the type of IGMP header indicates Membership Report to the IGMP packet in which the type of IGMP header indicates Membership Query. Group Address indicates an IPv4 multicast address. 
       FIG. 7  is a diagram for explaining an MLD header format. A type field shows a type of MLD message. As types, there are Multicast Listener Query (multicast group query), Multicast Listener Report (Multicast group report), Multicast Listener Done (leaving from the multicast group), and the like. Maximum Response Delay shows a maximum delay time which is necessary for transmitting the MLD packet in which the type of MLD header indicates Multicast Listener Report to the MLD packet in which the type of MLD header indicates Multicast Listener Query. An IPv6 multicast address enters Multicast Address. 
     A flow of data upon transmission of the multicast data will now be described. 
     First, the TCP/IPv4-compatible multicast AP  1006  forms multicast data and sends it to the protocol control module  1003 . The protocol control module  1003  adds a TCP (Transmission Control Protocol) header, a UDP (User Datagram Protocol) header, or an IPv4 header to the multicast data and generates the IPv4 multicast packet. The protocol control module  1003  sends the IPv4 multicast packet to the protocol translation control module  1004 . At this time, a Destination Address field of the IPv4 header shows the IPv4 multicast address. When the IPv4 multicast packet is received, the IPv4-to-IPv6 transmission switch control module  1009  in the protocol translation control module  1004  discriminates that it is the ordinary data packet by checking the IPv4 header. 
     The IPv4-to-IPv6 transmission switch control module  1009  sends the IPv4 multicast packet to the IP header conversion control module  1010 . The IP header conversion control module  1010  refers to the address translation table  1014  and translates each of two IPv4 addresses inserted in the Destination Address field and the Source Address field in the IPv4 header into an IPv6 address. When the IPv4 address inserted in the Source Address field of the IPv4 header is not registered in the address translation table  1014 , for example, the IP header conversion control module  1010  adds a fixed pattern of 96 bits into the IPv4 address and forms the IPv6 address of 128 bits, thereby translating the IPv4 address into the formed IPv6-address. The whole IPv4 header is converted into the IPv6 header. By converting the header as mentioned above, the IPv4 multicast packet is translated into the IPv6 multicast packet. The IPv6 multicast packet is outputted from the LAN control module  1005  to the IPv6 network through the IPv6 transmission/reception control module  1012  and IPv4-to-IPv6 reception switch control module  1013 . 
     A multicast control upon reception of the multicast data and a flow of the multicast data will now be described. 
     When the TCP/IPv4-compatible multicast AP  1006  wants to receive the multicast packet having a certain multicast address as a destination address, the TCP/IPv4-compatible multicast AP  1006  needs to subscribe for a multicast group to which the multicast packet is distributed. For this purpose, the TCP/IPv4-compatible multicast AP  1006  issues a control command to the protocol control module  1003 ; that is, the control command to output a control packet for requesting the subscription for the multicast group (for requesting the distribution of the multicast packet) to the network. In response to such a control command, the IPv4 transmission/reception control module  1008  of the protocol control module  1003  generates the IGMP packet and sends it to the protocol translation control module  1004 . When the IGMP packet is received, the IPv4-to-IPv6 transmission switch control module  1009  in the protocol translation control module  1004  refers to the IGMP header and sends the IGMP packet to the IGMP-to-MLD translation control module  1011 . The IGMP-to-MLD translation control module  1011  converts the IGMP header into the MLD header and translates the IGMP packet into the MLD packet. At this time, the IGMP-to-MLD translation control module  1011  registers correspondence information between the IPv4 multicast address inserted in the Destination Address field of the IGMP header and the IPv6 multicast address inserted in the Destination Address field of the MLD header into the IPv6 multicast subscription table  1015  and address translation table  1014 , respectively. The MLD packet is transmitted from the IGMP-to-MLD translation control module  1011  to the IPv4-to-IPv6 reception switch control module  1013  and outputted from the LAN control module  1005  to the IPv6 network via the IPv4-to-IPv6 reception switch control module  1013 . 
     When the IPv6 multicast packet is received from the IPv6 network, the LAN control module  1005  sends the IPv6 multicast packet to the IPv4-to-IPv6 reception switch control module  1013 . The IPv4-to-IPv6 reception switch control module  1013  discriminates whether the two IPv6 addresses inserted in the Destination Address field and the Source Address field of the IPv6 header in the IPv6 multicast packet received from the LAN control module  1005  have been registered in the address translation table  1014  or not, respectively. If they have been registered, the IPv6 multicast packet is sent to the IP header conversion control module  1010 . The IP header conversion control module  1010  translates the two IPv6 addresses included in the IPv6 header into the IPv4 addresses in accordance with the information registered in the address translation table  1014  and converts the whole IPv6 header into the IPv4 header. If the IPv6 address inserted in the Source Address field of the IPv6 header is not registered in the address translation table  1014 , for example, the IP header conversion control module selects an arbitrary one of the one or more IPv4 addresses which have previously been obtained and pooled and translates the IPv6 address into the selected IPv4 address. Correspondence information between those IPv6 address and IPv4 address is registered into the address translation table  1014 . By converting the header as mentioned above, the IP header conversion control module  1010  translates the IPv6 multicast packet into the IPv4 multicast packet and sends the IPv4 multicast packet to the protocol control module  1003  through the IPv4-to-IPv6 transmission switch control module  1009 . The protocol control module  1003  protocol processes the IPv4 multicast packet, extracts the multicast data, and sends it to the TCP/IPv4-compatible multicast AP  1006 . 
     Subsequently, a processing flow of the IGMP-to-MLD translation control module  1011  will be described.  FIG. 8  is a diagram showing a processing flow for translating the MLD packet into the IGMP packet.  FIG. 9  is a diagram showing a processing flow for translating the IGMP packet into the MLD packet. 
     The processing flow for translating the MLD packet into the IGMP packet will be first described with reference to  FIG. 8 . When the MLD packet is received from the IPv4-to-IPv6 reception switch control module  1004 , the IGMP-to-MLD translation control module  1011  starts a process for translating the MLD packet into the IGMP packet ( 11001 ). The IGMP-to-MLD translation control module  1011  refers to the TYPE field of the MLD header. When the TYPE field indicates “Multicast Listener General Query” ( 11002 ), the IGMP-to-MLD translation control module  1011  translates the IPv6 multicast address inserted in the Multicast Address field of the MLD header into the IPv4 multicast address in accordance with the information registered in the IPv6 multicast subscription table  1015  and converts the whole MLD header into the IGMP header. The IGMP-to-MLD translation control module  1011  refers to the address translation table  1014  in the IP header conversion control module  1010 , translates the IPv6 address included in the IPv6 header into the IPv4 address by using the information registered in the address translation table  1014  or by the foregoing method, and converts the whole IPv6 header into the IPv4 header ( 11003 ). The IGMP-to-MLD translation control module  1011 , consequently, translates the MLD packet into the IGMP packet. If the TYPE field of the MLD header indicates “Multicast Listener Specific Query” or “Multicast Listener Report” ( 11004 ,  11008 ), the IGMP-to-MLD translation control module  1011  searches whether the IPv6 multicast address inserted in the Multicast Address field of the MLD header has been registered in the IPv6 multicast subscription table  1015  or not ( 11005 ,  11009 ). If there is not the entry in which the IPv6 multicast address has been registered, the received MLD packet is aborted ( 11006 ,  11010 ). If there is the entry in which the IPv6 multicast address has been registered, the IPv6 multicast address is translated into the IPv4 multicast address in accordance with the information registered in such an entry and the whole MLD header is converted into the IGMP header ( 11007 ,  11011 ). The IGMP-to-MLD translation control module  1011 , consequently, translates the MLD packet into the IGMP packet. If the TYPE field of the MLD header indicates “Multicast Listener Done” ( 11012 ), the received MLD packet is aborted ( 11013 ). 
     Subsequently, the processing flow for translating the IGMP packet into the MLD packet will be described with reference to  FIG. 9 . 
     When the IGMP packet is received from the IPv4-to-IPv6 transmission switch control module  1009 , the IGMP-to-MLD translation control module  1011  starts a process for translating the IGMP packet into the MLD packet ( 12001 ). The IGMP-to-MLD translation control module  1011  refers to the TYPE field of the IGMP header. If the TYPE field indicates “Membership Query”, the IGMP-to-MLD translation control module  1011  finishes the process. If the TYPE field of the IGMP header indicates “Membership Report” ( 12003 ), the IGMP-to-MLD translation control module  1011  translates the IPv4 multicast address inserted in the Group Address field of the IGMP header into the IPv6 multicast address in accordance with a predetermined translation method. As a translation method, for example, there is a method of forming the IPv6 multicast address of 128 bits by adding a predetermined pattern of 96 bits to the IPv4 multicast address. The IGMP-to-MLD translation control module  1011  executes a process for converting the IGMP header into the MLD header ( 12004 ) and translates the IGMP packet into the MLD packet. The IGMP-to-MLD translation control module  1011  registers correspondence information between the IPv4 multicast address inserted in the Group Address-field of the IGMP header and the IPv6 multicast address obtained by translating it into the IPv6 multicast subscription table  1015  and the address translation table  1014  in the IP header conversion control module  1010 , and updates each table, respectively ( 12005 ,  12006 ). Also in the case where the TYPE field of the IGMP header indicates “Leave Group” ( 12007 ), processes similar to those in the case where the TYPE field indicates “Membership Report” are executed. 
     A data sequence in a multicast communication network system will be described.  FIG. 10  is a diagram showing a construction of a communication network system using an information processing apparatus (server and client) including the LAN control apparatus shown in  FIG. 1 .  FIG. 11  is a diagram showing a construction of an address translation table of the host A.  FIG. 12  is a diagram showing a construction of an address translation table of the host B.  FIG. 13  is a sequence diagram of a data packet in the communication network system shown in  FIG. 10 . 
     In  FIG. 10 , a host A  7001  is connected to an LAN 1 . In the host A  7001 , a TCP/IPv4-compatible multicast AP for the server operates. A host B  7007  is connected to an LAN 2 . In the host B  7007 , a TCP/IPv4-compatible multicast AP for the client operates. 
     In the system of  FIG. 10 , a data sequence by which the host B  7007  receives the multicast data packet which is transmitted by the host A  7001  will now be described with reference to  FIG. 13 . 
     A TCP/IPv4-compatible multicast AP  7002  of the host A  7001  forms multicast data and sends it to a protocol control module  7003 . The protocol control module  7003  generates an IPv4 multicast data packet from the received multicast data and sends it to a protocol translation control module  7004 . The protocol translation control module  7004  translates the IPv4 address included in the IPv4 header into an IPv6 address in accordance with information registered in an address translation control table  8001  shown in  FIG. 11  and converts the IPv4 header into the IPv6 header. Thus, the IPv4 multicast data packet is translated into the IPv6 multicast data. The protocol translation control module  7004  sends the IPv6 multicast data packet to an LAN control module  7005 . The LAN control module  7005  transmits the received the IPv6 multicast data packet to the LAN 1 . An IPv6 multicast router  7006  receives the IPv6 multicast data packet from the LAN 1 . However, at this time point, since the IPv6 multicast router  7006  does not recognize the host B  7007  connected to the LAN 2  or the host B  7007  is not registered as a member of a group of the multicast communication, the received IPv6 multicast data packet is not routed to the LAN 2 . 
     On the other hand, a TCP/IPv4-compatible multicast AP (client software) of the host B  7007  instructs a protocol control module  7010  to output the IGMP packet in which the Type field of the IGMP header indicates “Membership Report” in order to receive the multicast data packet which is outputted from the host A  7001 . The IGMP packet is a packet for requesting the IPv6 multicast router  7006  to distribute the multicast data packet. The protocol control module  7010  generates the IGMP packet in accordance with the instruction and sends it to a protocol translation control module  7009 . The protocol translation control module  7009  translates the IPv4 multicast address inserted in the Group Address field of the IGMP header into the IPv6 multicast address in accordance with the translation method as mentioned above and converts the IGMP header into the MLD header. Consequently, the IGMP packet is translated into the MLD packet. In the MLD packet, the Type field of the MLD header indicates “Multicast Listener Report”. The protocol translation control module  7009  sends the MLD packet to an LAN control module  7008 . The LAN control module  7008  outputs the MLD packet to the LAN 2 . 
     When the MLD packet is received from the LAN 2 , the IPv6 multicast router  7006  recognizes the fact that the host B  7007  as a client has been connected to the LAN 2  side. The IPv6 multicast router  7006  routes the IPv6 multicast data packet sent from the host A  7001  to the LAN 1  to the LAN 2 . 
     When the IPv6 multicast data packet is received from the LAN 2 , the LAN control module  7008  of the host B  7007  sends it to the protocol translation control module  7009 . The protocol translation control module  7009  translates the IPv6 address included in the IPv6 header into the IPv4 address in accordance with information registered in an address translation table  9001  shown in  FIG. 12 . If it is not registered in the address translation table  9001 , the IPv6 address is translated into the IPv4 address by the method as mentioned above. The protocol translation control module  7009  converts the IPv6 header into the IPv4 header and translates the IPv6 multicast data packet into the IPv4 multicast data packet. The protocol translation control module  7009  sends the IPv4 multicast data packet to the protocol control module  7010 . The protocol control module  7010  extracts the multicast data from the received IPv4 multicast data packet and sends it to a TCP/IPv4-compatible multicast AP  7011 . Thus, the TCP/IPv4-compatible multicast AP  7011  can receive the multicast data. 
     Subsequently, another example of a construction of the LAN control apparatus will be described.  FIG. 14  is a diagram showing another construction of the LAN control apparatus. 
     In  FIG. 14 , an LAN control apparatus  13001  comprises: an IGMP-to-MLD translation control module  13002 ; an IP header translation control module  13004 ; an IPv4-to-IPv6 transmission/reception switch control module  13006 ; an LAN 1  control module  13008 ; an LAN 2  control module  13007 ; and an IPv6 transmission/reception control module  13009 . The IGMP-to-MLD translation control module  13002  performs a translation between the IGMP packet and the MLD packet by using information registered in an IPv6 multicast subscription table  13003 . The IP header conversion control module  13004  performs a conversion between the IPv4 header and the IPv6 header by using information registered in an address translation table  13005 . The LAN control apparatus  13001  has at least two interfaces. One of the interfaces is connected to the IPv4 network and the other is connected to the IPv6 network. The LAN 1  control module  13008  controls the transmission and reception of the data packet to/from the IPv4 network. The LAN 2  control module  13007  controls the transmission and reception of the data packet to/from the IPv6 network. 
     In a manner similar to the LAN control apparatus  1001  shown in  FIG. 1 , each component element of the LAN control apparatus  13001  is constructed as a program (software). For example, the other component elements excluding the LAN 1  control module  13008  and LAN 2  control module  13007  are constructed as one program. Each of the LAN 1  control module  13008  and LAN 2  control module  13007  is constructed as an independent program. Each of those programs is installed into, for example, the information processing apparatus shown in  FIG. 2  and stored into an arbitrary area in the memory  2002  in the information processing apparatus. The CPU  2001  in the information processing apparatus executes those programs, so that the LAN control apparatus  13001  operates. 
     An input/output interface between the control modules of the LAN control apparatus  13001  will now be described. 
     A case where the LAN control apparatus  13001  transmits the data packet received from the IPv4 network to the IPv6 network will be first explained. When the data packet is received from the IPv4 network, the LAN 1  control module  13008  sends it to the IPv4-to-IPv6 transmission/reception switch control module  13006 . The IPv4-to-IPv6 transmission/reception switch control module  13006  checks a header in the data packet and discriminates whether the data packet is the IGMP packet or the other IPv4 packet. If the data packet is the IPv4 packet other than the IGMP packet, the IPv4-to-IPv6 transmission/reception switch control module  13006  sends the IPv4 packet to the IP header conversion control module  13004 . When the data packet is the IGMP packet, the control module  13006  sends the IGMP packet to the IGMP-to-MLD translation control module  13002 . 
     When the IPv4 packet is received, the IP header conversion control module  13004  translates the two IPv4 addresses inserted in the Destination Address field and the Source Address field of the IPv4 header into the IPv6 addresses by using information registered in the address translation table  13005 , respectively. If the IPv4 address inserted in the Source Address field of the IPv4 header is not registered in the address translation table  1014 , for example, the IP header conversion control module  1010  forms the IPv6 address of 128 bits by adding a fixed pattern of 96 bits to the IPv4 address. The control module  1010  converts the IPv4 header into the IPv6 header and translates the received IPv4 packet into the IPv6 packet. The IP header conversion control module  13004  sends the translated IPv6 packet to the IPv4-to-IPv6 transmission/reception switch control module  13006 . The IPv4-to-IPv6 transmission/reception switch control module  13006  sends the received IPv6 packet to the LAN 2  control module. The LAN 2  control module sends the IPv6 packet to the IPv6 network. 
     When the IGMP packet is received, the IGMP-to-MLD translation control module  13002  translates the IPv4 multicast address inserted in the Group Address field of the IGMP header into the IPv6 multicast address by using the IPv6 multicast subscription table  13003  and converts the IGMP header into the MLD header. The IGMP-to-MLD translation control module  13002  translates the two IPv4 addresses inserted in the Destination Address field and the Source Address field of the IPv4 header of the IGMP packet into the IPv6 addresses by using information registered in the multicast subscription table  13003  or address translation table  13005 , respectively. If the IPv4 address inserted in the Source Address field of the IPv4 header is not registered in the address translation table  1014 , the IPv4 address is translated into the IPv6 address by, for example, a method similar to that for the IP header conversion control module  1010  and the IPv4 header is converted into the IPv6 header. Thus, the received IGMP packet is translated into the MLD packet. The IGMP-to-MLD translation control module  13002  sends the MLD packet to the IPv4-to-IPv6 transmission/reception switch control module  13006 . The IPv4-to-IPv6 transmission/reception switch control module  13006  sends the received MLD packet to the LAN 2  control module. The LAN 2  control module sends the MLD packet to the IPv6 network. 
     A case where the LAN control apparatus  13001  transmits the data packet received from the IPv6 network to the IPv4 network will now be described. When the data packet is received from the IPv6 network, the LAN 2  control module  13007  sends it to the IPv4-to-IPv6 transmission/reception switch control module  13006 . The IPv4-to-IPv6 transmission/reception switch control module  13006  checks the header in the data packet and discriminates whether the data packet is the MLD packet or the other IPv6 packet. If the data packet is the IPv6 packet other than the MLD packet, the IPv4-to-IPv6 transmission/reception switch control module  13006  sends the IPv6 packet to the IP header conversion control module  13004 . When the data packet is the MLD packet, the MLD packet is sent to the IGMP-to-MLD translation control module  13002 . 
     When the IPv6 packet is received, the IP header conversion control module  13004  translates the two IPv6 addresses inserted in the Destination Address field and the Source Address field of the IPv6 header into the IPv4 addresses by using the information registered in the address translation table  13005 , respectively. For example, if the IPv6 address inserted in the Source Address field of the IPv6 header is not registered in the address translation table  1014 , the IP header conversion control module  1010  selects an arbitrary one of the one or more IPv4 addresses which have previously been obtained and pooled and translates the IPv6 address into the selected IPv4 address. The correspondence information between the IPv6 address and the IPv4 address is registered into the address translation table  1014 . As mentioned above, the IPv6 header is converted into the IPv4 header and the received IPv6 packet is translated into the IPv4 packet. The IP header conversion control module  13004  sends the translated IPv4 packet to the IPv4-to-IPv6 transmission/reception switch control module  13006 . The IPv4-to-IPv6 transmission/reception switch control module  13006  sends the received IPv4 packet to the LAN 1  control module. The LAN 1  control module sends the IPv4 packet to the IPv4 network. 
     When the MLD packet is received, the IGMP-to-MLD translation control module  13002  translates the IPv6 multicast address inserted in the Multicast Address field of the MLD header into the IPv4 multicast address by using the IPv6 multicast subscription table  13003  and converts the MLD header into the IGMP header. The IGMP-to-MLD translation control module  13002  translates the two IPv6 addresses inserted in the Destination Address field and the Source Address field of the IPv6 header of the MLD packet into the IPv4 addresses by using the information registered in the multicast subscription table  13003  or address translation table  13005 , respectively. For example, if the IPv4 address inserted in the Source Address field of the IPv6 header is not registered in the address translation table  1014 , the IPv6 address is translated into the IPv4 address by a method similar to that for the IP header conversion control module  1010 . The IPv4 header is converted into the IPv6 header. Thus, the received MLD packet is translated into the IGMP packet. The IGMP-to-MLD translation control module  13002  sends the IGMP packet to the IPv4-to-IPv6 transmission/reception switch control module  13006 . The IPv4-to-IPv6 transmission/reception switch control module  13006  sends the received IGMP packet to the LAN 1  control module. The LAN 1  control module sends the IGMP packet to the IPv4 network. 
     Subsequently, a flow of data in the communication network system will now be described.  FIG. 15  is a diagram showing another construction of the communication network system.  FIGS. 16 and 17  are sequence diagrams of the data packet in the communication network system shown in  FIG. 15 . 
     In  FIG. 15 , an IPv6 client  14001  is connected to the LAN 1 . An IPv6 server  14003  is connected to the LAN 2 . The LAN 1  and LAN 2  are connected by an IPv6 router  14002 . A TCP/IPv6-compatible multicast AP operates in the IPv6 client  14001  and IPv6 server  14003 . An IPv4 client  14004  is connected to an LAN 3 . An IPv4 server  14006  is connected to an LAN 4 . The LAN 3  and LAN 4  are connected by an IPv4 router  14005 . A TCP/IPv4-compatible multicast AP operates in the IPv4 client  14004  and IPv4 server  14006 . The LAN control apparatus  13001  connects an IPv6 multicast network which is formed by the LAN 1  and LAN 2  and an IPv4 multicast network which is formed by the LAN 3  and LAN 4 . 
     First, a data sequence until the IPv6 client  14001  receives the multicast data packet which is transmitted from the IPv4 server  14006  will be described with reference to  FIG. 16 . 
     The IPv4 server  14006  continuously transmits the IPv4 multicast data packet to the LAN 4 . However, since the IPv4 router  14005  does not recognize the client connected to the LAN 3  or does not register it as a member of the group of the multicast communication, the IPv4 multicast data packet is not routed to the LAN 3 . 
     To receive the multicast data packet which is transmitted from the IPv4 server  14006 , the IPv6 client  14001  sends the MLD packet in which the TYPE field of the MLD header indicates “Multicast Listener Report” to the LAN 1 . 
     When the MLD packet is received from the 
     LAN 1 , the LAN 2  control module  13007  of the LAN control apparatus  13001  sends the MLD packet to the IPv4-to-IPv6 transmission/reception switch control module  13006 . The IPv4-to-IPv6 transmission/reception switch control module  13006  sends the MLD packet to the IGMP-to-MLD translation control module  13002 . The IGMP-to-MLD translation control module  13002  translates the MLD packet into the IGMP packet as mentioned above. In the IGMP packet, the TYPE field of the IGMP header indicates “Membership Report”. The IGMP-to-MLD translation control module  13002  sends the IGMP packet to the IPv4-to-IPv6 transmission/reception switch control module  13006 . The IPv4-to-IPv6 transmission/reception switch control module  13006  sends the IGMP packet to the LAN 1  control module  13008 . The LAN 1  control module  13008  sends the IGMP packet to the LAN 3 . 
     When the IGMP packet is received from the LAN 3 , the IPv4 router  14005  recognizes the fact that the client exists on the LAN 3  side. The IPv4 router routes the IPv4 multicast data packet sent from the IPv4 server  14006  to the LAN 3 . 
     When the IPv4 multicast data packet is received from the LAN 3 , the LAN 1  control module  13008  of the LAN control apparatus  13001  sends it to the IPv4-to-IPv6 transmission/reception switch control module  13006 . The IPv4-to-IPv6 transmission/reception switch control module  13006  sends the IPv4 multicast data packet to the IP header conversion control module  13004 . The IP header conversion control module  13004  translates the IPv4 multicast data packet into the IPv6 multicast data packet as mentioned above and sends it to the IPv4-to-IPv6 transmission/reception switch control module  13006 . The IPv4-to-IPv6 transmission/reception switch control module  13006  sends the IPv6 multicast data packet to the LAN 2  control module  13007 . The LAN 2  control module  13007  sends the IPv6 multicast data packet to the LAN 1 . 
     The IPv6 client  14001  receives the IPv6 multicast data packet from the LAN 1 . Thus, the multicast communication from the IPv4 server  14006  to the IPv6 client  14001  is established. 
     Subsequently, a data sequence until the IPv4 client  14004  receives the multicast data packet which is sent from the IPv6 server  14003  will be described with reference to  FIG. 17 . 
     The IPv6 server  14003  continuously transmits the IPv6 multicast data packet to the LAN 2 . However, at this time point, since the IPv6 router  14002  does not recognize the client connected to the LAN 1  or it is not registered as a member of the group of the multicast communication, the IPv6 multicast data packet is not routed to the LAN 1 . 
     The IPv4 client  14004  sends the IGMP packet in which the Type field of the IGMP header indicates “Membership Report” to the LAN 3  in order to receive the multicast data packet which is transmitted from the IPv6 server  14003 . 
     When the IGMP packet is received from the LAN 3 , the LAN 1  control module  13008  of the LAN control apparatus  13001  sends it to the IPv4-to-IPv6 transmission/reception switch control module  13006 . The IPv4-to-IPv6 transmission/reception switch control module  13006  sends the IGMP packet to the IGMP-to-MLD translation control module  13002 . The IGMP-to-MLD translation control module  13002  translates the IGMP packet into the MLD packet as mentioned above. In the MLD packet, the TYPE field of the MLD header indicates “Multicast Listener Report”. The IGMP-to-MLD translation control module  13002  sends the MLD packet to the IPv4-to-IPv6 transmission/reception switch control module  13006 . The IPv4-to-IPv6 transmission/reception switch control module  13006  sends the MLD packet to the LAN 2  control module  13007 . The LAN 2  control module  13007  sends the MLD packet to the LAN 1 . 
     When the MLD packet is received from the LAN 1 , the IPv6 router  14002  recognizes the fact that the client exists on the LAN 1  side. The IPv6 router  14002  routes the IPv6 multicast data packet sent from the IPv6 server  14003  to the LAN 1 . 
     When the IPv6 multicast data packet is received from the LAN 1 , the LAN 2  control module  13007  of the LAN control apparatus  13001  sends it to the IPv4-to-IPv6 transmission/reception switch control module  13006 . The IPv4-to-IPv6 transmission/reception switch control module  13006  sends the IPv6 multicast data packet to the IP header conversion control module  13004 . The IP header conversion control module  13004  translates the IPv6 multicast data packet into the IPv4 multicast data packet as mentioned above and sends it to the IPv4-to-IPv6 transmission/reception switch control module  13006 . The IPv4-to-IPv6 transmission/reception switch control module  13006  sends the IPv4 multicast data packet to the LAN 1  control module  13008 . The LAN 1  control module  13008  sends the IPv4 multicast data packet to the LAN 3 . 
     The IPv4 client  14004  receives the IPv4 multicast data packet from the LAN 3 . Thus, the multicast communication from the IPv6 server  14003  to the IPv4 client  14004  is established. 
     The foregoing LAN control apparatus and the translation method, processing method, and communication method of the data packet in the protocol translation control module can be provided as an LAN control apparatus, a recording medium on which a program constructing the protocol translation control module has been recorded, or a program product including such a medium can be provided. 
     As mentioned above, the protocol translation control module is provided between the protocol control module and LAN control module constructing the LAN control apparatus and the IGMP-to-MLD translation control module is further provided in the protocol translation control module. Thus, the conversion of the headers (MLD header and IGMP header) of the control packets (MLD packet and IGMP packet) which are transmitted and received between the protocol control module and the LAN control module can be performed. Therefore, the TCP/IPv4-compatible multicast AP on the PC/WS can directly request the IPv6 network to distribute the multicast data packet and can directly transmit and receive the multicast data packet. 
     The IP header conversion control module and the IGMP-to-MLD translation control module are provided for the LAN control apparatus in the inter-network connecting apparatus (router, switch, etc.). Thus, the IPv6 host can receive the multicast data packet which is outputted from the IPv4 host and the IPv4 host can receive the IP multicast packet which is outputted from the IPv6 host.