JP2005217989A - Communication system, router, communication terminal, receiving terminal and communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize multicast communication by setting an appropriate multicast tree without increasing communication system load even if a router unsupported by multicast protocol exists in a communication system. <P>SOLUTION: Only when UR 20a to 20c have been judged to act as branch routers, the UR 20a to 20c become duplicate points while preserving forwarding addresses of a plurality of routers. Further, when the UR 20a to 20c have became the branch routers, addresses of the UR 20a to 20c are added to a forwarding address to a terminal. Then, a Redirect message for requesting elimination of forwarding addresses of the branch routers from the forwarding address to the terminal is transmitted to the address of the transmitted terminal. Upstream URs and the transmitted terminal 10 eliminates the forwarding addresses of the branch routers from the forwarding addresses of the routers and the forwarding address to the terminal while preserving the branch router addresses as the forwarding addresses of the routers and the forwarding address to the terminal. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a communication system, a router, a transmission terminal, a reception terminal, and a communication method.

  Conventionally, multicast for transmitting packets to a plurality of receiving terminals has been performed (see, for example, Non-Patent Document 1). In communication systems, SSM (Source-Specific Multicast) (for example, see Non-Patent Document 2 and Non-Patent Document 3) standardized in IETF (Internet Engineering Task Force), IGMPv3 (Internet Management Protocol Version 3) (for example, Multi-casting is performed using protocols such as HBH (Hop by Hop Multicast Routing Protocol) (see Non-Patent Document 5, for example).

Also, MIP-BT (Mobile IP Bi-Directional Tunneling) has been proposed in order to continue communication even when a transmitting terminal that transmits a multicast packet moves and its address changes. In MIP-BT, communication is continued by transferring a multicast packet transmitted from a transmitting terminal moved to a foreign network via a home agent.
By Thomas A. Maufer, translated by Hiroyuki Enomoto, “Introduction to IP Multicast” Internet Draft, "draft-ietf-ssm-overviw-xx.txt" “The Institute of Electrical, Information and Communication Engineers Japanese Journal B”, Vol. J85-B, No.8, pp.1207-1214 RFC3376, "Internet Management Protocol Version 3" L.HMK Costa, S.Fidia and O CMB Duarte, `` HOP by HOP Multicast Routing Protocol '', ACM SIGCOM 2001, Aug. 2001

  However, in the conventional communication system, multicast packets cannot be transferred unless all the routers are compatible with the multicast protocol. For example, when using HBH, it is not necessary for all routers to store information for setting a multicast tree in a table (MCT: Multicast Control Table), but routers other than routers that perform multicast packet replication also use MCT. Needed to hold. For this reason, the load on the entire communication system has increased. In addition, in MIP-BT, although communication can be continued even if the transmission terminal moves, there is a problem that the transfer path becomes redundant because the multicast packet passes through the home agent.

  Therefore, an object of the present invention is to implement multicast by setting an appropriate multicast tree without increasing the load on the communication system even when a router that does not support the multicast protocol exists in the communication system. .

  The communication system according to the present invention includes a transmission terminal that transfers a multicast packet to a terminal transfer destination address, and a router that transfers the multicast packet to a router transfer destination address. The terminal transfer destination address is an address to which the transmission terminal transfers the multicast packet, and the router transfer destination address is an address to which the router transfers the multicast packet.

  When a router has a router holding means for holding a router transfer destination address and an address of a transmission terminal (hereinafter referred to as “transmission terminal address”) upstream of the multicast tree, the router sends a multicast packet to a plurality of router transfer destination addresses. Determining means for determining whether to become a branch router for forwarding to the router, router registration means for registering a plurality of router transfer destination addresses in association with the transmission terminal address in the router holding means, if determined to be a branch router, and a branch router If the router address is determined to be, the router address is added to the terminal transfer destination address, and the router transmission that sends a join / leave request message to the address of the sending terminal requesting that the router transfer destination address be deleted from the terminal transfer destination address Means. The transmission terminal deletes the router transfer destination address from the transmission terminal holding means based on the participation / leaving request message, and registers the branch router address in the transmission terminal holding means based on the transmission / reception request message. Transmitting terminal registration means.

  According to such a communication system, the router holds a plurality of router transfer destination addresses only when it is determined that the router becomes a branch router that transfers a multicast packet transferred by the transmission terminal to a plurality of router transfer destination addresses. It becomes a replication point. Furthermore, when the router becomes a branch router, the router adds the address of the router to the terminal transfer destination address and sends a join / leave request message requesting to delete the router transfer destination address from the terminal transfer destination address. Can be requested to add to the terminal transfer destination address of the branch router address and to delete the router transfer destination address from the terminal transfer destination address. Then, the transmitting terminal can hold the branch router address as the terminal transfer destination address and delete the router transfer destination address from the terminal transfer destination address.

  Thereby, the router corresponding to the multicast protocol of this invention can turn into a branch router suitably. Then, an appropriate multicast tree is set in which multicast packets are transferred from the transmission terminal to the reception terminal via the branch router. In addition, among the routers, only the branch router holds the router transfer destination address, and encapsulates and transfers the multicast packet to a plurality of transfer destinations. Therefore, the router existing between the transmitting terminal and the branch router need only forward the multicast packet by unicast. Therefore, the load on routers other than the branch router is reduced, and multicast can be realized as the entire communication system even if the router other than the branch router does not support the multicast protocol. Therefore, the communication system does not increase the load on the communication system, and even if there is a router that does not support the multicast protocol between the transmitting terminal and the branch router, an appropriate multicast tree is set to perform multicasting. realizable.

  In this way, in the present invention, some routers can transfer multicast packets by unicast. Therefore, hereinafter, in order to distinguish the multicast according to the present invention from the normal multicast protocol, it is particularly called “Unicast Extension Multicast Protocol (hereinafter referred to as“ UMP ”)”. Furthermore, a router that supports UMP is called a “UMP router”, and a router that does not support UMP is called a “non-UMP router”.

  The router registration means deletes the router transfer destination address of the downstream branch router from the router holding means based on the join / leave request message from the branch router downstream from itself, and the address of the downstream branch router is the router holding means. It is preferable to register with. As a result, an appropriate multicast tree in which multicast packets are transferred from the transmitting terminal to the receiving terminal via a plurality of branch routers is set.

  In addition, when the router registration means is a terminal router connected to the multicast packet receiving terminal, it is preferable that the router transfer destination address is registered in the router holding means in association with the transmission terminal address. As a result, an appropriate multicast tree in which multicast packets are transferred from the transmitting terminal to the receiving terminal via the branch router and the terminal router is set.

  When the transmission terminal address is changed, the transmission terminal is provided with transmission terminal transmission means for transmitting a location update message for notifying the transmission terminal address after the change to the multicast packet reception terminal. It is preferable to provide a receiving terminal transmitting means for transmitting a participation request message for requesting transmission of a multicast packet to the changed transmitting terminal address based on the message. According to this, for example, when the transmission terminal address is changed due to movement of the transmission terminal or the like, the transmission terminal can notify the reception terminal of the change of the transmission terminal address by the position update message. Then, the receiving terminal can grasp the change of the transmission terminal address by the location update message and can transmit the participation request message to the changed transmission terminal address. Therefore, an appropriate multicast tree is newly set at the changed transmission terminal address, triggered by the participation request message addressed to the changed transmission terminal address. Therefore, the communication system can realize multicast using an appropriate multicast tree even if the transmission terminal address changes.

  Furthermore, when the receiving terminal connects to a router that does not support the multicast protocol, the receiving terminal transmitting means preferably transmits a participation request message to which data instructing not to discard the participation request message is added. According to this, even when the receiving terminal connects to a router that does not support the multicast protocol, the participation request message is not discarded, and the router or transmitting terminal that supports the multicast protocol receives the participation request message. it can.

  The router registration unit deletes the router transfer destination address from the router holding unit when the router transfer destination address holding time expires, and maintains a multicast tree with the router transfer destination address as the source address. If the router receives the message within the holding time, the holding time is extended, and the sending terminal registration means deletes the terminal forwarding address from the sending terminal holding means when the holding time of the terminal forwarding address expires, When the transmission terminal receives the maintenance request message with the terminal transfer destination address as the transmission source address within the retention time, it is preferable to extend the retention time. The holding time is a time during which the router holding unit and the transmission terminal holding unit hold the router transfer destination address and the terminal transfer destination address. According to this, the communication system can always use an appropriate multicast tree even when the network topology changes by maintaining the multicast tree for the holding time. In addition, the communication system can maintain the multicast tree for as long as necessary by the maintenance request message.

  Also, the router registration means deletes the router transfer destination address associated with the transmission terminal address from the router holding means based on the leave request message for requesting leave from the multicast tree in which the transmission terminal address is specified, and transmits The terminal registration means preferably deletes the terminal transfer destination address associated with the transmission terminal address from the transmission terminal holding means based on the leave request message.

  According to this, the communication system can delete the multicast tree formed using the transmission terminal address specified by the leave request message. Therefore, the receiving terminal can explicitly leave the multicast tree without waiting for the hold time to expire. Therefore, for example, it is possible to suppress duplicate forwarding of multicast packets due to the coexistence of the multicast tree using the transmission terminal address before the change and the multicast tree using the transmission terminal address after the change.

  The router according to the present invention includes a router holding unit that holds a router transfer destination address of a multicast packet, and a branch router that transfers the multicast packet to a plurality of router transfer destination addresses when the transmission terminal address is upstream of the multicast tree. If it is determined that it becomes a branching router, if it is determined that it becomes a branching router, if it is determined that it becomes a branching router, a router registration unit that registers a plurality of router forwarding destination addresses in association with the transmission terminal address in the router holding unit, Router transmitting means for adding a router address to the terminal transfer destination address and transmitting a join / leave request message for requesting deletion of the router transfer destination address from the terminal transfer destination address to the transmission terminal address And

  The transmitting terminal according to the present invention includes transmitting terminal holding means for holding the terminal transfer destination address, adding the branch router address to the terminal transfer destination address, and deleting the router transfer destination address of the branch router from the terminal transfer destination address. And a transmission terminal registration unit that deletes the router transfer destination address from the transmission terminal holding unit and registers the branch router address in the transmission terminal holding unit. Furthermore, it is preferable that the transmitting terminal includes a transmitting terminal transmitting unit that transmits a location update message for notifying the receiving terminal of the changed address of the transmitting terminal when the transmitting terminal address is changed.

  The receiving terminal according to the present invention sends a participation request message for requesting transmission of a multicast packet based on a location update message notifying the changed transmitting terminal address when the transmitting terminal address for transferring the multicast packet is changed. Receiving terminal transmitting means for transmitting to the address of the changed transmitting terminal is provided.

  The communication method according to the present invention determines whether a router becomes a branch router when a transmission terminal address is upstream of a multicast tree, and determines whether the router becomes a branch router that forwards multicast packets to a plurality of router transfer destination addresses. In this case, a plurality of router transfer destination addresses are registered in the router holding means for holding the router transfer destination address in association with the transmission terminal address, the router address is added to the terminal transfer destination address, and the router transfer destination address is set to the terminal. A joining / leaving request message requesting deletion from the forwarding address is transmitted to the sending terminal address, and the sending terminal holds the router forwarding address and the terminal forwarding address based on the joining / leaving request message. Delete from the sending terminal holding means and register the branch router address in the sending terminal holding means And wherein the Rukoto.

  Furthermore, when the address of the transmitting terminal is changed, the communication method transmits a location update message for notifying the address of the changed transmitting terminal to the receiving terminal of the multicast packet. Based on the location update message, a participation request message for requesting transmission of a multicast packet is transmitted to the address of the transmission terminal after the change.

  As described above, according to the present invention, even if there is a router that does not support the multicast protocol in the communication system, an appropriate multicast tree is set without increasing the load on the communication system, and realizable.

[First Embodiment]
〔Communications system〕
As illustrated in FIG. 1, the communication system 1 includes a transmission terminal 10, a plurality of UMP routers (UMP Router, hereinafter referred to as “UR”) 20 a to 20 c, and a plurality of non-UMP routers (Non-UMP Router, hereinafter “ NR ”) 30a-30c and a plurality of receiving terminals 40a-40c. The transmission terminal address “S” is given to the transmission terminal 10. Addresses “R1”, “R2”, and “R3” are assigned to the receiving terminals 40a, 40b, and 40c, respectively. The addresses “UR2”, “UR3”, and “UR4” are assigned to the URs 20a, 20b, and 20c, respectively. Addresses “NR1”, “NR5”, and “NR6” are assigned to NR30a, 30b, and 30c, respectively. In the communication system 1, IPv6 is used, but IPv4 may be used.

  The transmission terminal 10 transfers the multicast packet to the terminal transfer destination address. The receiving terminals 40a to 40c receive the multicast packet. The URs 20a to 20c and the NRs 30a to 30c transfer the multicast packet to the router transfer destination address according to the multicast packet transfer path (hereinafter referred to as “multicast tree”) set between the transmitting terminal 10 and the receiving terminals 40a to 40c. To do. The receiving terminals 40a to 40c and the UR 20c, NR30b, and NR30c perform wireless communication. The transmission terminal 10, the URs 20a to 20c, and the reception terminals 40a to 40c set a multicast tree. The URs 20a to 20c can be branch routers that transfer multicast packets to a plurality of router transfer destination addresses.

(Configuration of UR)
First, the configuration of the UR will be described using the UR 20a as an example. As shown in FIG. 2A, the UR 20a includes an entry holding unit 21a, a receiving unit 22, a transfer unit 23, a data processing unit 24, a message processing unit 25, and a message generation unit 26. The URs 20b and 20c have the same configuration as the UR 20a.

  The receiving unit 22 receives multicast packets and control messages from the transmission terminal 10, other URs and NRs, and the reception terminals 40a to 40c. The multicast packet includes data from the transmission terminal 10. The multicast packet is encapsulated and transferred between the transmitting terminal and the branch router and between the branch routers. The control message is a message related to control of the multicast tree, such as setting, maintaining, and changing the multicast tree. The control message includes a Join message, a Membership Report, a Join message in which the Stable option is set (hereinafter referred to as “Stable Join message”), a Membership Report in which the Stable option is set (hereinafter referred to as “Stable Member Report”, hereinafter). There are a Leave Group message, a Redirect message, a Binding Update message (hereinafter referred to as “BU message”), a Location Update message (hereinafter referred to as “LU message”), and the like. A special option indicating a control message is set in the headers of the Join message, the stable join message, the prune message, and the redirect message.

  The Join message and Membership Report are participation request messages for requesting transmission of multicast packets. A multicast tree has an initial state and a stable state. If a multicast tree has already been set for the multicast packet, the Join message and Membership Report are maintenance request messages for maintaining the multicast tree transmitted in the initial state of the multicast tree. The Stable Join message and the Stable Membership Report are maintenance request messages for maintaining the multicast tree transmitted after the multicast tree has transitioned to a stable state. The Prune message and Leave Group message are leave request messages for requesting leave from the multicast tree. The Join message and the Prune message are transmitted by the URs 20a to 20c and the receiving terminals 40a to 40c. The receiving terminals 40a to 40c transmit the Membership Report and the Leave Group message.

  The Redirect message is a join / leave request message including a Join message and a Prune message. Specifically, the Rdirect message includes an address requesting addition to the router transfer destination address and the terminal transfer destination address, and an address requesting deletion from the router transfer destination address and the terminal transfer destination address.

  The BU message is a transfer destination update message that notifies the terminal transfer destination address of the change of the transmission terminal address when the transmission terminal address is changed. The LU message is a location update message that notifies the receiving terminal of the changed transmission terminal address when the transmission terminal address is changed. For example, when the transmission terminal address is changed due to movement of the transmission terminal 10 or the like, the LU message notifies the transmission terminal address before the change and the transmission terminal address after the change in association and moves to the reception terminal. To be notified. The transmitting terminal may transmit the LU message as an LU message alone, or may forward the LU message by adding it to a multicast packet.

  The receiving unit 22 determines whether the packet is a multicast packet or a control message based on the header option. Further, the receiving unit 22 determines whether or not the destination address of the encapsulated multicast packet matches the address of the UR 20a itself. When they match, the receiving unit 22 inputs the multicast packet to the data processing unit 24 because the UR 20a is a branch router. The receiving unit 22 inputs the data to the transfer unit 23 when these conditions are not met. When receiving the control message, the receiving unit 22 inputs the control message to the message processing unit 25.

  The transfer unit 23 transmits a control message to the transmission terminal 10, other URs and NRs, and the reception terminals 40a to 40c. The transfer unit 23 transfers multicast packets to other URs, NRs, and receiving terminals 40a to 40c. The transfer unit 23 acquires a multicast packet from the reception unit 22 or the data processing unit 24. The transfer unit 23 acquires a control message from the message processing unit 25 and the message generation unit 26.

  The entry holding unit 21a is a router holding unit that holds a router transfer destination address. As shown in FIG. 2B, the entry holding unit 21a associates a router transfer destination address, KAT (Keep Alive Timer) with a table type, a transmission terminal address, a multicast group address, a tunnel source address, and a previous tunnel source address. ), JT (Join Timer) is held.

  Table types include a multicast control table (hereinafter referred to as “MCT”) and a multicast transmission table (hereinafter referred to as “MFT”). The MCT holds information used for setting a multicast tree. The MFT holds information used for multicast tree setting and multicast packet transfer.

  The transmission terminal address may be changed due to movement of the transmission terminal 10 or the like. Therefore, the entry holding unit 21a can hold the MCT entry and MFT entry of the current transmission terminal address at the current position of the transmission terminal 10 and the MCT entry and MFT entry of the transmission terminal address before the change.

  The multicast group address is an address indicating a multicast group. A multicast tree or a multicast packet can specify which multicast group from which transmission terminal 10 is associated with a combination of a transmission terminal address and a multicast group address. A multicast group address “G” is assigned to the multicast group to which the transmission terminal 10 forwards the multicast packet.

  The router transfer destination address is an address indicating the transfer destination of the UR multicast packet. The tunnel source address is a source address used for encapsulation of a multicast packet received by the UR. Therefore, for example, in FIG. 1, when the UR 20a is a branch router, the tunnel source address registered in the entry holding unit 21a of the UR 20a is the transmission terminal address “S”. The previous tunnel source address is the tunnel source address before the change when the tunnel source address is changed.

  KAT is a timer value for measuring the holding time of the router transfer destination address and the terminal transfer destination address. The KAT is held in association with the router transfer destination address. In FIG. 2B, KAT (UR3) indicates the KAT of the router transfer destination address “UR3”, and KAT (R3) indicates the KAT of the router transfer destination address “R3”. The router forwarding address whose KAT has expired is deleted from the entry holding unit 21a. JT is a timer value that measures the time until transmission of a Join message starts. A Join message is sent when JT expires. JT is stored in association with the transmission terminal address and the multicast group address. When the table type is MCT, it is not necessary to hold the tunnel source address, the previous tunnel source address, and JT.

  The data processing unit 24 processes multicast packets. Specifically, the data processing unit 24 acquires the encapsulated multicast packet from the receiving unit 22, decapsulates it, and extracts the multicast packet. The data processing unit 24 acquires the router transfer destination address associated with the transmission terminal address and the multicast group address included in the multicast packet from the entry holding unit 21a.

  The data processing unit 24 refers to the entry holding unit 21a, and duplicates the multicast packet so that the multicast packet becomes the number of router transfer destination addresses. The data processing unit 24 sets the acquired router transfer destination address as the destination address, sets the address of the UR 20a itself as the source address, and encapsulates the multicast packet. The data processing unit 24 inputs the encapsulated multicast packet to the transfer unit 23. The data processing unit 24 can perform encapsulation using, for example, an encapsulation technique shown in “IP in IP Tunneling” (RFC1853) or “Generic Packet Tunneling in Ipv6 Specification” (RFC2473).

  The message processing unit 25 processes the control message. The message processing unit 25 acquires the control message received by the UR 20a from the receiving unit 22. The message processing unit 25 registers information in the entry holding unit 21a and holds the entry holding unit 21a based on the type of the control message, the destination address and transmission source address of the control message, and the information held in the entry holding unit 21a. Update or delete information. The message processing unit 25 creates an MFT entry or an MCT entry when registering a new router transfer destination address. Specifically, the message processing unit 25 sets MFT or MCT as the table type of the entry holding unit 21a, and creates an MFT entry or MCT entry for each transmission terminal address and multicast group address. For example, the message processing unit 25 creates an MFT entry or an MCT entry for each transmission terminal address and multicast group address specified by the Join message newly received by the UR 20a. The MFT entry and MCT entry created in this way function as MFT and MCT.

  The message processing unit 25 registers the created MFT entry in association with the transmission terminal address, multicast group address, tunnel source address, previous tunnel source address, router transfer destination address, KAT, and JT. The message processing unit 25 registers the created MCT entry in association with the transmission terminal address, multicast group address, router transfer destination address, and KAT.

  The message processing unit 25 functions as a determination unit that determines whether the router becomes a branch router when the transmission terminal address is upstream of the multicast tree. The message processing unit 25 makes a determination based on the control message and the router transfer destination address held by the entry holding unit 21a. Further, when it is determined that the message processing unit 25 is a branch router, the message processing unit 25 also functions as a router registration unit that registers a plurality of router transfer destination addresses in association with the transmission terminal address in the router holding unit. Specifically, when the message processing unit 25 determines that the UR 20a becomes a branch router, the message processing unit 25 creates an MFT entry in the entry holding unit 21a and registers the router transfer destination address.

  Further, the message processing unit 25 deletes the router forwarding destination address of the downstream branch router from the entry holding unit 21a based on the Redirect message that is a join / leave message from the branch router downstream from the router 20a, and The branch router address is registered in the entry holding unit 21a. Note that the message processing unit 25 creates an MFT entry and sets a router transfer destination address when the UR 20a becomes a terminal router connected to the receiving terminals 40a to 40c in addition to the case where the UR 20a is determined to be a branch router. register. The message processing unit 25 creates an MCT entry and registers the router transfer destination address except when the UR 20a is a branch router or a terminal router.

  Further, the message processing unit 25 determines whether to transmit the received control message as it is based on whether or not the UR 20a becomes a branch router, or to generate and transmit a new control message based on the received control message. to decide. If the message processing unit 25 does not become a branch router, the message processing unit 25 determines to transmit the message as it is, and inputs the received control message to the transfer unit 23. When the message processing unit 25 becomes a branch router, the message processing unit 25 determines that it is newly generated, and inputs the received control message to the message generation unit 26.

  The message generator 26 generates a control message. The message generating unit 26 generates a control message based on the control message received by the UR 20a acquired from the message processing unit 25 and the information held by the entry holding unit 21a. The message generation unit 26 inputs the generated control message to the transfer unit 23.

(Configuration of sending terminal)
Next, the configuration of the transmission terminal 10 will be described. As illustrated in FIG. 3A, the transmission terminal 10 includes an entry holding unit 11, a reception unit 12, a transmission unit 13, a message processing unit 14, and a packet generation unit 15.

  The receiving unit 12 receives control messages from the URs 20a to 20c, the NRs 30a to 30c, and the receiving terminals 40a to 40c. The receiving unit 12 inputs the received control message to the message processing unit 14.

  The entry holding unit 11 is a transmission terminal holding unit that holds a terminal transfer destination address. As shown in FIG. 3B, the entry holding unit 11 holds the terminal transfer destination address and the KAT in association with the table type, the transmission terminal address, and the multicast group address. Since the transmitting terminal 10 uses only MFT, “MFT” is set as the table type. The terminal transfer destination address is a transfer destination address to which the transmission terminal 10 transfers a multicast packet. The terminal transfer destination address held by the transmission terminal 10 is any one of a branch router, a terminal router, and a reception terminal. Similarly to FIG. 2B, KAT (UR2) indicates the KAT of the terminal transfer destination address “UR2”. The transmission terminal address may be changed due to movement of the transmission terminal 10 or the like. Therefore, the entry holding unit 11 can hold the MFT entry of the current transmission terminal address at the current position of the transmission terminal 10 and the MFT entry of the transmission terminal address before the change.

  The message processing unit 14 processes the control message. The message processing unit 14 acquires the control message received by the transmitting terminal 10 from the receiving unit 12. The message processing unit 14 registers information in the entry holding unit 11 and updates information held in the entry holding unit 11 based on the type of control message, the transmission source address of the control message, and information held in the entry holding unit 11. Or delete. In particular, the message processing unit 14 deletes the router transfer destination address of the branch router from the transmission terminal holding unit based on the Redirect message that is a join / leave message, and transmits the branch router address to the transmission terminal holding unit. Functions as a registration means.

  The message processing unit 14 sets MFT as the table type of the entry holding unit 11 and creates an MFT entry for each transmission terminal address and multicast group address. For example, the message processing unit 14 creates an MFT entry for each transmission terminal address and multicast group address specified by the Join message or Redirect message newly received by the transmission terminal 10. The message processing unit 14 registers the created MFT entry in association with the transmission terminal address, multicast group address, terminal transfer destination address, and KAT.

  The packet generator 15 generates a multicast packet including data. The packet generation unit 15 generates a multicast packet to which a control message such as a BU message or an LU message or an LU message is added as necessary. The packet generation unit 15 acquires the terminal transfer destination address from the entry holding unit 11. The packet generation unit 15 acquires data by input from the application unit or external input.

  First, the packet generation unit 15 generates a multicast packet in which a transmission terminal address is added to the data and a multicast group address is added as a destination address. The packet generation unit 15 refers to the entry holding unit 11 and duplicates the generated multicast packet so that the multicast packet has the number of terminal transfer destination addresses. The packet generation unit 15 encapsulates the multicast packet, sets the transmission terminal address as the transmission source address, and sets the terminal transfer destination address as the destination address. The packet generator 15 inputs the encapsulated multicast packet to the transmitter 13.

  The transmission unit 13 transmits multicast packets and control messages to the URs 20a to 20c, the NRs 30a to 30c, and the reception terminals 40a to 40c. The transmission unit 13 acquires the encapsulated multicast packet from the packet generation unit 15 and acquires a control message from the message processing unit 14.

  Next, the setting of the multicast tree in the communication system 1 will be described in detail with reference to FIGS. As described above, the multicast tree has an initial state and a stable state. Therefore, the process in the initial state and the process in the stable state will be described separately. In the description of FIGS. 4 to 7, the entry holding units 21 a to 21 c included in the URs 20 a to 20 c and the entry holding unit 11 included in the transmission terminal 10 are written together. For simplicity of explanation, only the table type, transmission terminal address, multicast group address, terminal transfer destination address, or router transfer destination address among the information held by the entry holding units 11, 21a to 21c is shown. Specifically, the transmission terminal address, multicast group address, terminal transfer destination address or router transfer destination address is expressed as (transmission terminal address, multicast group address): [terminal transfer destination address or router transfer destination address]. . By (transmission terminal address, multicast group address), it is possible to specify which multicast group from which transmission terminal the multicast tree or multicast packet relates to. Further, the transmission terminal 10 will be described as the most upstream.

(initial state)
In the initial state, the entry holding units 11, 21a to 21c do not hold the terminal transfer destination address and the router transfer destination address. As shown in FIG. 4, when the receiving terminal 40a wants to start receiving a multicast packet transmitted from the transmitting terminal 10, it requests transmission of the multicast packet. When the router to which the receiving terminal 40a is connected via the radio link is UR, the receiving terminal 40a performs transmission according to MLDv2 (see Multicast Listener Discovery Version 2, “draft-vida-mld-v2-xx.txt”). Can request. Specifically, the receiving terminal 40a transmits Membership Report 2 to the UR 20c. Note that the receiving terminal 40a follows MLDv2 when using IPv6, but transmits Membership Report2 according to IGMPv3 when using IPv4.

  Using the Membership Report 2, the receiving terminal 40a requests transmission of a multicast packet specified by the transmitting terminal address “S” and the multicast group address “G”, that is, (S, G). In the Membership Report 2, the multicast group address “G” is set as the destination address, the address “R1” of the receiving terminal 40a is set as the transmission source address, and includes designation of the multicast group address “G”.

  The UR 20c existing on the most downstream side of the path from the receiving terminal 40a to the transmitting terminal 10 receives the Membership Report2. The message processing unit 25 of the UR 20c creates an MFT entry in the entry holding unit 21c because the UR 20c is a terminal router connected to the receiving terminal 40a. The message processing unit 25 registers (S, G): [G] in the MFT entry. The message processing unit 25 activates the JT relating to the KAT and (S, G) of the router transfer destination address “G”. When the router transfer destination address is the multicast group address “G”, it indicates that the receiving terminal 40a desiring to receive the multicast packet specified by (S, G) is connected to the UR 20c. Therefore, when the destination address is the multicast group address “G”, the transfer unit 23 of the UR 20c may transmit the multicast packet decapsulated by the data processing unit 24 to the receiving terminal 40a connected to the UR 20c itself. .

  The message processing unit 25 of the UR 20 c inputs the received Membership Report 2 to the message generation unit 26. The message generation unit 26 of the UR 20c generates a Join message 3 for requesting the transmission terminal 10 to transmit a multicast packet requested by the reception terminal 40a using the Membership Report 2. Specifically, the message generator 26 sets the sending terminal address “S” as the destination address, the address “UR4” of the UR 20 c as the source address, and the Join message 3 specifying the multicast group address “G”. Is generated.

  At this time, the message generation unit 26 of the UR 20 c sets a special option in the header of the Join message 3. As a special option, for example, when IPv6 is used, a Hop-by-Hop option specified by RFC2460 can be set, and when IPv4 is used, a Router Alert option specified by RFC2113 can be set. Thereby, the UR 20c can notify the other URs 20a and 20b and the transmission terminal 10 that the Join message 3 is a special control message. Furthermore, as a special option, the message generation unit 26 sets the top of the option type to “00” in the case of data instructing not to discard the message even when the option cannot be interpreted, for example, in the case of a Hop-by-Hop option. Add an option starting with As a result, a router that cannot interpret an option on the route from the UR 20c to the transmission terminal 10, for example, NR, is not discarded even if NR exists, and the UR 20a, 20b and the transmission terminal 10 can receive the Join message 3.

  Then, the message generation unit 26 of the UR 20 c inputs the generated Join message 3 to the transfer unit 23, and the transfer unit 23 of the UR 20 c transmits the Join message 3 to the transmission terminal 10. Thereby, the UR 20c can transfer the Join message 3 to the upstream URs 20b and 20a.

  The UR 20b existing on the route from the UR 20c to the transmitting terminal 10 receives the Join message 3. The message processing unit 25 of the UR 20b refers to the entry holding unit 21b. The message processing unit 25 determines that the router transfer destination address to which the UR 20b transfers the multicast packet is one determined by the received Join message 3 because the entry holding unit 21b does not hold the router transfer destination address. . Therefore, the message processing unit 25 determines that the UR 20b does not become a branch router.

  Therefore, the message processing unit 25 of the UR 20b creates an MCT entry in the entry holding unit 21b. The message processing unit 25 determines that “UR4” set as the transmission source address of the Join message 3 is the router transfer destination address, and registers (S, G): [UR4] in the MCT entry. The message processing unit 25 activates the KAT of the router transfer destination address “UR4”. Thus, in the initial state, the UR that is not the branch router also holds the MCT. Further, the message processing unit 25 inputs the received Join message 3 to the transfer unit 23 as it is. The transfer unit 23 of the UR 20b transmits the Join message 3 to the transmission terminal 10, and transfers the Join message to the upstream UR 20a.

  Then, the UR 20a existing upstream of the path from the UR 20c to the transmission terminal 10 receives the Join message 3. Similarly to the UR 20b, the message processing unit 25 of the UR 20a creates an MCT entry in the entry holding unit 21a, registers (S, G): [UR4] in the MCT entry, and stores the router transfer destination address “UR4”. Start KAT. Since the NR 30a cannot interpret a special option, the NR 30a transfers the Join message 3 to the transmitting terminal 10 as a normal unicast packet.

  Finally, the transmission terminal 10 receives the Join message 3. The message processing unit 14 creates an MFT entry in the entry holding unit 11. The message processing unit 14 determines that “UR4” set as the transmission source address of the Join message 3 is the terminal transfer destination address, and registers (S, G): [UR4] in the MFT entry. The message processing unit 25 activates the KAT of the terminal transfer destination address “UR4”.

  Through the above processing, a multicast tree is set in which multicast packets are transferred from the most upstream transmitting terminal 10 to the receiving terminal 40a via the UR 20c as a terminal router. In the state shown in FIG. 4 in which the receiving terminal 40a participates in the multicast tree specified by (S, G), when the receiving terminal 40b wants to start receiving a multicast packet transmitted by the transmitting terminal 10, FIG. Join the multicast tree as shown in For the entry holding units 11, 21a, and 21b, in order to distinguish the state in FIG. 4 in which only the receiving terminal 40a is participating from the state in FIG. 5 in which the receiving terminal 40b has participated, the entry holding unit in FIG. The states of 11, 21a, and 21b are illustrated as pre-change entry holding units 111, 211a, and 211b in FIG.

  First, since the receiving terminal 40b is connected to the NR 30b, it is detected that the router to which the receiving terminal 40b is connected via the wireless link is NR. The receiving terminal 40b can detect the presence / absence of reception of the Membership Query. For example, if the receiving terminal 40b cannot receive the Membership Query for a predetermined time or longer, the receiving terminal 40b can determine that there is no UR that transmits the Membership Query, and can detect that it is connected to the NR. Alternatively, the receiving terminal 40b can determine that there is no UR capable of processing the Membership Report even if the multicast packet cannot be received after the lapse of the specified time after transmitting the Membership Report, and confirms that it is connected to the NR. It can be detected.

  When the receiving terminal 40b is connected to the NR, the receiving terminal 40b transmits a Join message 3 in which a special option is set to request participation in the multicast tree specified by (S, G). Since the receiving terminal 40b transmits the Join message 3 in which the special option is set, the NR 30b does not discard the Join message 3, so the UR 20b existing in the path from the receiving terminal 40b to the transmitting terminal 10 receives the Join message 3. it can. The reception terminal 40b sets the transmission terminal address “S” as the destination address, sets the address “R2” of the reception terminal 40b as the transmission source address, and transmits the Join message 3 specifying the multicast group address “G”.

  Among the URs, the UR 20b existing on the most downstream side of the path from the receiving terminal 40b to the transmitting terminal 10 receives the Join message 3. The message processing unit 25 of the UR 20b refers to the pre-change entry holding unit 211b of the UR 20b. The message processing unit 25 receives “UR4” that the pre-change entry holding unit 211b that holds the MCT entry already holds as the router transfer destination address corresponding to (S, G) and the received (S, G). Since the source address “R2” of the Join message 3 is different, it is determined that there are a plurality of router transfer destination addresses “UR4” and “R2” to which the UR 20b transfers the multicast packet specified by (S, G). To do. Therefore, the message processing unit 25 determines that the UR 20b is a branch router. Thus, in the initial state, the MCT entry is used to determine whether to become a branch router.

  The message processing unit 25 of the UR 20b that has been determined to be a branch router deletes the MCT entry from the pre-change entry holding unit 211b and creates a new MFT entry. The message processing unit 25 sets (S, G): [UR4, R2] to the MFT entry of the entry holding unit 21b based on the information held by the entry holding unit 211b before the change and the received Join message 3. Register and copy the KAT of the router transfer destination address “UR4” used in the MCT entry. In addition, the message processing unit 25 activates the JT relating to the KAT and (S, G) of the router transfer destination address “R2”. Further, the message processing unit 25 inputs the received Join message 3 to the message generation unit 26 of the UR 20b.

  The message generation unit 26 of the UR 20b generates the Redirect message 4 based on the router transfer destination address held by the entry holding unit 21b and the received Join message 3. After generating the redirect message 4, the message generator 26 discards the received join message 3. The message generation unit 26 of the UR 20b adds a Join message requesting to add the address “UR3” of the UR 20b serving as a branch router to the terminal transfer destination address, and the router transfer destination address “UR 20b serving as the branch router from the terminal transfer destination address. A Redirect message 4 including a Prune message requesting to delete “UR4” and “R2” is generated.

  The message generator 26 sets the transmission terminal address “S” as the destination address, the address “UR3” of the UR 20 b as the transmission source address, and sets the redirect message 4 as the multicast group address “G”. Further, the message generator 26 sets a special option in the header of the Redirect message 4. Then, the message generation unit 26 of the UR 20 b inputs the generated redirect message 4 to the transfer unit 23, and the transfer unit 23 of the UR 20 b transmits the redirect message 4 to the transmission terminal 10. As a result, the UR 20b can transfer the redirect message 4 to the upstream UR 20a. In this way, the transfer unit 23 adds the address of the branch router to the terminal transfer destination address and sends a join / leave message requesting to delete the router transfer destination address of the branch router from the terminal transfer destination address to the transmission address. It functions as a router transmission means for transmitting to.

  Then, the UR 20a existing on the route from the UR 20b to the transmission terminal 10 receives the Redirect message 4. The message processing unit 25 of the UR 20a updates the entry holding unit 21a according to the Redirect message 4. Specifically, the message processing unit 25 retains “UR4” held as the router transfer destination address among “UR4” and “R2” that have received the deletion instruction from the MCT entry of the pre-change entry holding unit 211a. "And its KAT are deleted, and" UR3 "for which an additional instruction has been received is registered in the MCT entry as a router transfer destination address. The message processing unit 25 activates the KAT of the router transfer destination address “UR3”. As a result, the MCT entry in the entry holding unit 21a is updated to (S, G): [UR3]. In this way, the UR located upstream from the branch router also adds the branch router address included in the Redirect message 4 to the router transfer destination address and deletes the router transfer destination address of the branch router from the router transfer destination address.

  Further, the message processing unit 25 inputs the received Redirect message 4 to the transfer unit 23 as it is. Then, the transfer unit 23 of the UR 20a transmits the Redirect message 4 to the transmission terminal 10, and the NR 30a transfers the Redirect message 4 to the transmission terminal 10 as a unicast packet.

  Finally, the transmission terminal 10 receives the redirect message 4. The message processing unit 14 updates the entry holding unit 11 according to the Redirect message 4. Specifically, the message processing unit 14 stores “UR4” held as the terminal transfer destination address among “UR4” and “R2” that have received an instruction to delete from the MFT entry of the pre-change entry holding unit 111. ”And its KAT are deleted, and the address“ UR3 ”of the branch router receiving the addition instruction is registered in the MFT entry as the terminal transfer destination address. The message processing unit 14 activates the KAT of the terminal transfer destination address “UR3”. Thereby, the MFT entry of the entry holding unit 11 is updated to (S, G): [UR3]. In this manner, the message processing unit 14 deletes the router transfer destination address of the branch router from the transmission terminal holding unit based on the join / leave message, and registers the transmission terminal for registering the branch router address in the transmission terminal holding unit. Acts as a means.

  By the above processing, the multicast packet is transferred from the most upstream transmitting terminal 10 to the receiving terminal 40a via the UR 20b that is the branch router and the UR 20c that is the terminal router, and is transmitted to the receiving terminal 40b via the UR 20b. A multicast tree to which is transferred is set. Thus, in the initial state of the multicast tree, new receiving terminals participate in the multicast tree one after another. Each time there is a new participation, the multicast tree is changed and set.

  The receiving terminal 40b, the UR 20c serving as a terminal router, and the UR 20b serving as a branch router periodically transmit a Join message to the UR 20b serving as a branch router and the transmitting terminal 10, respectively. In addition, the receiving terminal 40a periodically transmits Membership Report 2 to the UR 20c which is a terminal router. The transmission terminal 10 and the UR 20b receive the Join message, and the UR 20c receives the Membership Report, thereby maintaining the terminal transfer destination addresses and the router transfer destination addresses of the entry holding units 11, 21a to 21c.

  Specifically, the message generation unit 26 of the UR 20b that has become the branch router refers to the entry holding unit 21b, and when the JT expires, the destination address is “S” and the transmission source address is “UR3”. The Join message is generated. Then, the transfer unit 23 of the UR 20b transmits the generated Join message. The message processing unit 14 of the transmission terminal 10 refers to the entry holding unit 11, and when the KAT of the terminal transfer destination address “UR3” expires, the terminal transfer destination address “S, G” corresponding to (S, G) is transmitted from the entry holding unit 11. UR3 "is deleted. On the other hand, the message processing unit 14 receives the Join message with the source address “UR3” from the branch router UR20b within the holding time when the KAT of the terminal transfer destination address “UR3” expires. In this case, the KAT of the terminal transfer destination address “UR3” is restarted to extend the holding time.

  Similarly to UR 20b, UR 20c that became the end router also has a destination address of “S” as the destination address when there is at least one router transfer destination address for which KAT has not expired when JT expires. A Join message whose original address is “UR4” is transmitted. The receiving terminal 40b also transmits a Join message whose destination address is the transmission terminal address “S” and whose transmission source address is “R2”.

  The message processing unit 25 of the UR 20b that has become the branch router refers to the entry holding unit 21b, and when the KAT of the router transfer destination address “UR4” has expired, deletes the MFT entry in the entry holding unit 21b and deletes the MCT entry. And the router transfer destination address “R2” is registered. The message processing unit 25 determines that the UR 20b has changed from a branch router to a router that is not a branch router (hereinafter referred to as “non-branch router”) because the router transfer destination address has become one “R2”. Then, the message processing unit 25 instructs the message generation unit 26 to generate a redirect message. Then, the message generator 26 adds the router transfer destination address “R2” of the UR 20b that has become the non-branching router to the terminal transfer destination address, and the address “UR3” of the UR 20b that has become the non-branching router from the terminal transfer destination address. A Redirect message requesting deletion is generated. Then, the transfer unit 23 transmits the Redirect message to the transmission terminal address “S”.

  In this way, the message processing unit 25 determines whether the UR changes from a branch router to a non-branch router. Then, when the message processor 25 determines that the message processing unit 25 becomes a non-branching router, the transfer unit 23 adds the router transfer destination address of the non-branching router to the terminal transfer destination address, and adds the address of the non-branching router from the terminal transfer destination address. A join / leave request message requesting deletion is transmitted to the transmission terminal address. Thereby, in the communication system 1, even when the UR that has once become a branch router is changed to a non-branch router, it can be changed to an appropriate multicast tree. Next, when the KAT of the router transfer destination address “R2” expires, the message processing unit 25 of the UR 20b deletes the MCT entry in which the router transfer destination address “R2” is registered from the entry holding unit 21b.

  On the other hand, before the KAT of the router transfer destination addresses “UR4” and “R2” expires, the message processing unit 25 of the UR 20b receives the source address from the UR 20c, which is the terminal router, and the receiving terminal 40b. Receives the “UR4” and “R2” Join messages, the router forwarding destination addresses “UR4” and “R2” KAT are restarted to extend the holding time. Note that the message processing unit 25 of the UR 20c, which is the terminal router, also refers to the entry holding unit 21c in the same manner as the UR 20b, and when the KAT of the router transfer destination address “G” expires, from the MFT entry of the entry holding unit 21c, ( The router forwarding address “G” corresponding to S, G) is deleted. In addition, when the receiving unit 22 of the UR 20c receives the Membership Report from the receiving terminal 40a, the message processing unit 25 of the UR 20c restarts the KAT of the router transfer destination address “G”. In this way, the multicast tree is maintained in the initial state. Also, the Join message and Membership Report can function as a maintenance request message for maintaining the multicast tree.

(Stable state)
The multicast tree moves from the initial state to the stable state. For example, the multicast tree shifts to a stable state due to a decrease in newly participating receiving terminals. For example, after the start of live broadcasting, the number of receiving terminals that newly participate decreases. The transmitting terminal 10 can determine that it has shifted to the stable state when it can be determined that the number of newly receiving receiving terminals has decreased.

  The process after the transition to the stable state will be described with reference to FIG. 6 by taking as an example the case of shifting to the stable state in the state of the multicast tree shown in FIG. For the entry holding unit 21a, the state of the entry holding unit 21a in FIG. 5 is illustrated as the pre-change entry holding unit 211a in FIG. 6 in order to distinguish the state in FIG. To do.

  When the multicast tree shifts to the stable state, the packet generation unit 15 of the transmission terminal 10 generates a multicast packet in which the Stable option indicating the shift to the stable state is set, and the transmission unit 13 transmits the multicast packet. Thereby, the transmitting terminal 10 notifies the participating receiving terminals 40a and 40b that the multicast tree has shifted to a stable state. After receiving the multicast packet in which the Stable option is set, the receiving terminals 40a and 40b transmit the Stable Membership Report in the case of the receiving terminal 40a and the Stable Join message 3a in the case of the receiving terminal 40b. For example, after receiving the multicast packet in which the Stable option is set, the receiving terminal 40b transmits the Stable Join message 3a whose destination address is “S” and whose transmission source address is “R2”.

  Then, after receiving the Stable Join message 3a from the receiving terminals 40a and 40b or the downstream UR, the URs 20b and 20c transmit the Stable Join message 3a. For example, the message generation unit 26 of the UR 20c, which is a terminal router, determines that the destination address is the transmission terminal address “S” and the transmission source address when there is even one router transfer destination address for which the KAT has not expired when the JT has expired. A stable join message 3a in which the address is “UR4” and “G” is specified as the multicast group address is generated. The transfer unit 23 of the UR 20c transmits the generated stable join message 3a.

  And UR20b which exists in the path | route from UR20c to the transmission terminal 10 receives the Stable Join message 3a from UR20c. The message processing unit 25 of the UR 20b refers to the entry holding unit 21b, and determines whether the entry holding the source address of the received stable join message 3a as the router transfer destination address is an MFT entry or an MCT entry. . When the MFT entry holds the source address of the stable join message 3a as the router transfer destination address, the message processing unit 25 extends the holding time of the router transfer destination address. The message processing unit 25 does not extend the holding time when the MCT entry holds the source address of the stable join message 3a as the router transfer destination address. When the MFT entry holds the source address of the stable join message 3a as the router transfer destination address, naturally, before the KAT of the router transfer destination address expires, that is, within the holding time, the UR 20b The table join message 3a is received.

  Since the MFT entry in the entry holding unit 21b holds the source address “UR4” of the received stable join message 3a as the router transfer destination address, the message processing unit 25 of the UR 20b stores the router transfer destination address “UR4”. Restart KAT and extend retention time. Similarly, the UR 20b existing on the path from the receiving terminal 40b to the transmitting terminal 10 receives the Stable Join message 3a from the receiving terminal 40b. Then, since the message processing unit 25 of the UR 20b holds the source address “R2” of the received stable join message 3a as the router transfer destination address in the MFT entry of the entry holding unit 21b, the router transfer destination address “R2” Reboot the KAT to extend the holding time.

  Further, the message processing unit 25 of the UR 20b instructs the message generation unit 26 to set the Stable option for a Join message to be generated in the future. Then, the message generator 26 of the UR 20b determines that the destination address is “S” and the source address is “UR3” if there is at least one router transfer destination address for which the KAT has not expired when the JT expires. ”, A Stable Join3a message specifying“ G ”as the multicast group address is generated. Then, the transfer unit 23 of the UR 20b transmits the generated stable join message 3a. In this way, the branch router itself transmits the stable join message 3a after receiving the stable join message 3a.

  And UR20a which exists in the path | route from UR20b to the transmission terminal 10 receives the Stable Join message 3a. The message processing unit 25 of the UR 20a refers to the pre-change entry holding unit 211a. In the message processing unit 25, the pre-change entry holding unit 211a holds only the MCT entry, and the router transfer destination address registered in the MCT entry is the transmission source address “UR3” of the received stable join message 3a. Therefore, the KAT of the router transfer destination address “UR3” is not restarted and the holding time is not extended. Thus, the Stable Join message 3a is not used for restarting the KAT of the router transfer destination address held by the MCT entry. Further, the message processing unit 25 of the UR 20a inputs the Stable Join message 3a to the transfer unit 23 as it is. The transfer unit 23 of the UR 20a transmits a stable join message 3a to the transmission terminal 10, and the NR 30a transfers the stable join message 3a to the transmission terminal 10 as a unicast packet.

  The KAT of the router transfer destination address “UR3” held by the entry holding unit 211a before change expires because it is not restarted. The message processing unit 25 of the UR 20a deletes the router transfer destination address “UR3” whose KAT has expired from the pre-change entry holding unit 211a. As a result, the entry holding unit 21a is updated to a state in which the MCT entry is discarded and the router transfer destination address is not held.

  Finally, the transmission terminal 10 receives the Stable Join message 3a. The message processing unit 14 restarts the KAT of the terminal transfer destination address “UR3” because the entry holding unit 11 holds the transmission source address “UR3” of the received stable join message 3a as the terminal transfer destination address. , Extend the holding time. Note that the KAT of the router transfer destination address “G” held by the entry holding unit 21c of the UR 20c that is the terminal router is the UR 20c when the UR 20c receives the Membership Report, as in the case of maintaining the multicast tree in the initial state. Message processing unit 25 is restarted.

  As described above, the communication system 1 uses the stable join message 3a used only for extending the holding time of the router transfer destination address held by the MFT entries of the entry holding units 21a to 21c after the transition to the stable state. Only the router transfer destination address held by the MFT entries of the holding units 21a to 21c is held, and the router transfer destination address held by the MCT entry is deleted. As a result, the URs 20a to 20c can continue to hold the router transfer destination address only when the MFT entry of the entry holding units 21a to 21c is a branch router or a terminal router that holds the router transfer destination address. A multicast tree can be maintained.

  The MCT is used for setting a multicast tree, and more specifically, for determining whether or not the UR becomes a branch router. Therefore, it is useful in the initial state of a multicast tree where reception terminals frequently participate. However, since the number of receiving terminals that newly join the multicast tree decreases after the multicast tree transitions to a stable state, the opportunity to determine whether or not the UR becomes a branch router is reduced, and the MCT entry is used. Opportunities are also reduced. Therefore, the router transfer destination address held by the MCT entry is held only in the initial state, and is deleted after the multicast tree has shifted to the stable state, thereby further reducing the load on URs other than the branch router and the end router.

  If the receiving terminal 40c wants to start receiving a multicast packet transmitted by the transmitting terminal 10 in the state shown in FIG. Join the stable multicast tree as shown in For the entry holding units 11 and 21a, the state in FIG. 6 in which the receiving terminals 40a and 40b participate, the state in FIG. 7 in which the receiving terminal 40c participates, and the transition from the state in FIG. 6 to the state in FIG. In FIG. 7, the state of the entry holding units 11 and 21a in FIG. 6 is illustrated as the pre-change entry holding units 112 and 212a, and the state of the entry holding units 11 and 21a in the transition state is illustrated in FIG. This is illustrated as the entry holding units 111 and 211a during migration.

  First, since the receiving terminal 40c is connected to the NR 30c, in the same manner as the receiving terminal 40b, the router connected to the receiving terminal 40c via the wireless link is detected to be NR, and the Join message 3 is transmitted. To do. At this time, since the receiving terminal 40c does not participate in the multicast tree, the receiving terminal 40c has not received the multicast packet in which the Stable option is set. Therefore, the receiving terminal 40c transmits a normal Join message 3 in which the Stable option is not set. The reception terminal 40c sets the transmission terminal address “S” as the destination address, sets the address “R3” of the reception terminal 40c as the transmission source address, and transmits the Join message 3 specifying the multicast group address “G”.

  Among the URs, the UR 20a existing on the most downstream side of the path from the receiving terminal 40c to the transmitting terminal 10 receives the Join message 3. The message processing unit 25 of the UR 20a refers to the pre-update entry holding unit 212a of the UR 20a. The message processing unit 25 has received the normal Join message 3 that is not the stable join tree 3a used for maintaining the stable multicast tree, and the pre-update entry holding unit 212a does not hold the router forwarding address. Therefore, “R3” set as the transmission source address of the received Join message 3 is determined as the router transfer destination address to which the UR 20a transfers the multicast packet. Moreover, since there is only one router transfer destination address, the message processing unit 25 determines that the UR 20a does not become a branch router.

  Therefore, the message processing unit 25 of the UR 20a creates an MCT entry in the pre-update entry holding unit 212a, registers (S, G): [R3], and sets the in-migration entry holding unit 211a. Furthermore, the message processing unit 25 inputs the received Join message 3 as it is to the transfer unit 23 of the UR 20 a, and the transfer unit 23 transmits the Join message 3 to the transmission terminal 10.

  The transmission terminal 10 receives the Join message 3. The message processing unit 14 determines that “R3” is a new router transfer destination address because the pre-update entry holding unit 112 does not hold “R3” set as the transmission source address of the received Join message 3. To do. The message processing unit 14 creates an MFT entry, adds the router transfer destination address “R3”, and sets the pre-update entry holding unit 112 to the in-migration entry holding unit 111 state (S, G): [UR3, R3]. Update to Thereby, a multicast tree in which multicast packets are directly transferred from the transmission terminal 10 to the reception terminal 40c is once constructed.

  Thereafter, the UR 20b transmits a stable join message 3a in which the destination address is “S”, the source address is “UR3”, and “G” is specified as the multicast group address when JT expires. And UR20a which exists in the path | route from UR20b to the transmission terminal 10 receives the Stable Join message 3a.

  The message processing unit 25 of the UR 20a refers to the migration entry holding unit 211a. The message processing unit 25 transmits “R3” already held as the router transfer destination address corresponding to (S, G) by the migration entry holding unit 211a, and transmission of the received Stable Join message 3a regarding (S, G). Since the original address “UR3” is different, it is determined that the stable join message 3a is not used for maintaining the multicast tree in the stable state. Further, the message processing unit 25 determines that the UR 20a becomes a branch router because there are a plurality of router transfer destination addresses “UR3” and “R3” to which the UR 20a transfers the multicast packet specified by (S, G). Therefore, the message processing unit 25 of the UR 20a deletes the MCT entry from the migration entry holding unit 211a, and newly creates an MFT entry. The message processing unit 25 registers (S, G): [UR3, R3] in the MFT entry of the entry holding unit 21a.

  Further, the message generation unit 26 of the UR 20a adds a Join message requesting to add the address “UR2” of the UR 20a to be the new branch router to the terminal transfer destination address, and the router of the UR 20a that is the branch router from the terminal transfer destination address. A Redirect message 4 including a forwarding message “UR3” and a Prune message requesting to delete “R3” is generated. In addition, the message generator 26 sets the transmission terminal address “S” as the destination address, the address “UR3” of the UR 20a as the transmission source address, and sets the redirect message 4 as the multicast group address “G”. And then. The transfer unit 23 of the UR 20 a transmits the Redirect message 4 to the transmission terminal 10.

  The transmission terminal 10 receives the redirect message 4. The message processing unit 14 updates the entry holding unit 11 according to the Redirect message 4. Specifically, the message processing unit 14 deletes “UR3” and “R3” that have been instructed to be deleted from the MFT entry of the in-migration entry holding unit 111, and the branch router that has received the instruction for addition. The address “UR2” is registered in the MFT entry as the terminal transfer destination address. As a result, the MFT entry in the entry holding unit 11 is updated to (S, G): [UR2].

  Through the above processing, from the most upstream transmitting terminal 10, the UR 20a that has newly become the upstream branch router, the UR 20b that has become the downstream branch router because the upstream UR 20a has become the branch router, and the UR 20c that is the terminal router A multicast tree is set in which multicast packets are transferred to the receiving terminal 40a via the UR, multicast packets are transferred to the receiving terminal 40b via the UR 20a and UR 20b, and multicast packets are transferred to the receiving terminal 40c via the UR 20a. Is done. In this way, a stable multicast tree is set.

〔Communication method〕
A communication method using the communication system 1 shown in FIG. 1 will be described. First, a processing procedure when a Join message is received will be described. As illustrated in FIG. 8, the receiving units 22 of the URs 20a to 20c receive the Join message (S101). The message processing unit 25 of the URs 20a to 20c determines whether the entry holding units 21a to 21c hold the source address of the Join message as a router transfer destination address (S102).

  In step (S102), if the c message processing unit 25 of the URs 20a to 20 determines that the source address is not held, whether or not the received Join message is a Stable Join message in which the Stable option is set. Is determined (S103). If the message processing unit 25 of the URs 20a to 20c determines that the message is a stable join message, the transfer unit 23 of the URs 20a to 20c transfers the stable join message upstream (S106).

  On the other hand, when the message processing unit 25 of the URs 20a to 20c determines that it is not a stable join message but a normal join message in step (S103), it creates an MCT entry in the entry holding units 21a to 21c (S105). . Further, the message processing unit 25 of the URs 20a to 20c registers the source address of the received Join message in the created MCT entry as a router transfer destination address, and activates the KAT (S107). Then, the transfer unit 23 of the URs 20a to 20c transfers the Join message upstream (S108).

  In step (S102), if the message processing unit 25 of the URs 20a to 20c determines that the source address is held, which of the MCT entry or the MFT entry of the entry holding unit 21a to 21c is held? Is determined (S104). If it is determined that the MFT entry is held, the message processing unit 25 of the URs 20a to 20c uses the transmission terminal address and the multicast group address indicated by the Join message, that is, the MFT entry corresponding to (S, G) as the router transfer destination address. , It is determined whether or not the source address of the Join message is held (S109). When the message processing unit 25 of the URs 20a to 20c determines that the MFT entry corresponding to (S, G) is not held, the entry holding unit 21a to It is registered in the MFT entry corresponding to (S, G) of 21c (S114). Then, the message processing unit 25 of the URs 20a to 20c discards the received Join message (S115). Further, the message processing unit 25 of the URs 20a to 20c activates the KAT of the router transfer destination address held by the MFT entry corresponding to the registered (S, G) (S118).

  On the other hand, when the message processing unit 25 of the URs 20a to 20c determines in step (S109) that the MFT entry corresponding to (S, G) is held, the process proceeds to step (S115) and the received Join is received. Discard the message. Further, the message processing unit 25 of the URs 20a to 20c proceeds to step (S118), and restarts the KAT of the router transfer destination address held by the MFT entry corresponding to (S, G).

  If it is determined in step (S104) that the MCT entry is held, the message processing unit 25 of the URs 20a to 20c has the transmission terminal address and multicast group address indicated by the Join message, that is, the MCT entry corresponding to (S, G). Then, it is determined whether or not the sender address of the Join message is held as the router transfer destination address (S110). When it is determined that the MCT entry corresponding to (S, G) is not held, the message processing unit 25 of the URs 20a to 20c creates an MFT entry corresponding to (S, G) (S111).

  Further, the message generation unit 26 of the URs 20a to 20c generates a redirect message corresponding to (S, G), and the transfer unit 23 of the URs 20a to 20c transmits “to the transmission terminal address (S113). 20c proceeds to steps (S114) and (S115), registers the transmission source address as the router transfer destination address in the MFT entry corresponding to the created (S, G), and discards the Join message. Proceeds to step (S118), and activates the KAT of the router transfer destination address held by the MFT entry corresponding to the registered (S, G) In this case, the URs 20a to 20c also activate JT.

  On the other hand, if the message processing unit 25 of the URs 20a to 20c determines in step (S110) that the MCT entry corresponding to (S, G) is held, the received Join message is set with the Stable option. It is then determined whether the message is a stable join message (S112). When the message processing unit 25 of the URs 20a to 20c determines that the message is a stable join message, the transfer unit 23 of the URs 20a to 20c transfers the stable join message upstream (S116). On the other hand, when the message processing unit 25 of the URs 20a to 20c determines that it is not a stable join message but a normal join message in step (S112), the transfer unit 23 of the URs 20a to 20c transfers the join message upstream. After that (S117), the process proceeds to step (S118), and the KAT of the router transfer destination address held by the MCT entry corresponding to (S, G) is restarted. In this way, the communication system 1 sets a multicast tree.

  Next, a processing procedure when a Prune message is received will be described. As shown in FIG. 9, first, the receiving units 22 of the URs 20a to 20c receive a Prune message (S201). The message processing unit 25 of the URs 20a to 20c determines whether the entry holding units 21a to 21c hold the source address of the Prune message as a router transfer destination address (S202). If the message processing unit 25 of the URs 20a to 20c determines that it does not hold the source address of the Prune message, it forwards the received Prune message upstream (S208).

  On the other hand, when the message processing unit 25 of the URs 20a to 20c determines in step (S202) that it holds the source address of the Prune message, either the MCT entry or the MFT entry of the entry holding unit 21a to 21c is held. It is determined whether or not (S203). If it is determined that the MCT entry is held, the message processing unit 25 of the URs 20a to 20c deletes the MCT entry from the entry holding units 21a to 21c (S205). Then, the URs 20a to 20c proceed to Step (S208).

  On the other hand, when the message processing unit 25 of the URs 20a to 20c determines in step (S203) that the MFT entry is held, it deletes the source address of the Prune message from the MFT entry of the entry holding units 21a to 21c ( S204). In step (S204), the message processing unit 25 of the URs 20a to 20c determines whether the MFT entry is changed to the MCT entry by deleting the source address of the Prune message from the MFT entry (S206).

  In step (S206), when it is determined that the message processing unit 25 of the URs 20a to 20c is changed to the MCT entry, the message generation unit 26 is instructed to generate a redirect message. The message generation unit 26 of the URs 20a to 20c generates a Redirect message in which a special option is set, and the transfer unit 23 transmits the Redirect message to the transmission terminal 10 (S207). Then, the message processing unit 25 of the URs 20a to 20c discards the Prune message (S209). On the other hand, in step (S206), the message processing unit 25 of the URs 20a to 20c has the MFT entry holding a plurality of router forwarding addresses, and even if the source address is deleted from the MFT entry, the message processing unit 25 does not change to the MCT entry. If it is determined, the process proceeds to step (S209).

  Next, a multicast packet transfer method using the set multicast tree will be described. FIG. 10 shows a transfer method using the multicast tree in the initial state shown in FIG.

  First, the transmission terminal 10 sets a transmission terminal address “S” as a transmission source address and a multicast group address “G” as a destination address in the data, and generates a multicast packet. Then, the transmission terminal 10 sets the transmission terminal address “S” as the transmission source address and the terminal transfer destination address “UR3” held by the entry holding unit 11 as the destination address in the generated multicast packet, and encapsulates the multicast packet To do. Then, the transmitting terminal 10 transfers the encapsulated multicast packet 5a to the UR 20b, which is a branch router, by unicast (S301). As a result, the NR 30a and UR 20a existing on the route between the transmitting terminal 10 and the UR 20b which is the branch router can be transferred by a normal unicast process without being aware that the multicast packet 5a is a multicast packet.

  The UR 20b sets the transmission source address “S” of the encapsulated multicast packet 5a to the tunnel source address of the entry holding unit 21b, and decapsulates the encapsulated multicast packet 5a. The UR 20b duplicates the multicast packet using the data processing unit 24 in order to transmit to the router transfer destination addresses “UR4” and “R2” held by the entry holding unit 21b. Then, the UR 20b sets the UR 20b address “UR3” as the source address and encapsulates the router transfer destination address “UR4” as the destination address. The encapsulated multicast packet 5b is sent to the terminal router UR 20c. Transfer (S302). The UR 20c decapsulates the encapsulated multicast packet 5b, extracts the multicast packet 5c, and transfers it to the receiving terminal 40a (S303).

  The UR 20b encapsulates the UR 20b by setting the address “UR3” of the UR 20b itself and another router transfer destination address “R2” as the destination address. The encapsulated multicast packet 5d is received by the receiving terminal 40b. (S304). In this way, data can be multicast distributed to a plurality of transmission destinations, the receiving terminal 40a and the receiving terminal 40b.

〔effect〕
According to the communication system 1, the URs 20a to 20c, and the communication method, only when the URs 20a to 20c are determined to be branch routers that transfer multicast packets transmitted by the transmission terminal 10 to a plurality of router transfer destination addresses. Holds multiple router forwarding addresses and becomes a replication point. Further, when the URs 20a to 20c become branch routers, a redirect request is made to add the addresses of the URs 20a to 20c to the terminal transfer destination address and to delete the router transfer destination address of the branch router from the terminal transfer destination address. By adding a join / leave request message such as a message to the sending terminal address, add the branch router address to the router transfer destination address or terminal transfer destination address to the UR or sending terminal 10 upstream from itself. Then, it is possible to request deletion of the router transfer destination address of the branch router from the router transfer destination address or the terminal transfer destination address. The upstream UR and the transmission terminal 10 hold the downstream branch router address as the router transfer destination address and the terminal transfer destination address, and the downstream branch router router transfer destination address and the router transfer destination address. Can be deleted from the address.

  Thereby, UR20a-20c can become a branch router suitably. That is, in the communication system 1, the branch router is dynamically determined. Then, an appropriate multicast tree in which multicast packets are transferred from the transmission terminal 10 to the reception terminals 40a to 40c via the branch router is set. Moreover, among the URs 20a to 20c and NRs 30a to 30c, only the branch router holds the router transfer destination address and transfers the multicast packet to a plurality of transfer destinations. Therefore, the UR and NR existing between the transmitting terminal 10 and the branch router need only transfer the encapsulated multicast packet by unicast. For this reason, the load on the UR other than the branch router is reduced, and even if the router other than the branch router is NR, the entire communication system 1 can realize multicast. Therefore, the communication system 1 does not increase the load of the communication system 1, and even if there is an NR between the transmission terminal and the branch router or between the branch routers, an appropriate multicast tree is set to Cast can be realized.

  Further, the message processing units 14 and 25 send the terminal transfer destination address and the router transfer destination address KAT, that is, the terminal transfer destination address and the router transfer destination address from the entry holding units 11 and 21a to 21c when the holding time has expired. Is deleted and the holding time is extended if the sending terminal 10 or the stable join message 3a having the router forwarding destination address or the terminal forwarding destination address as the source address is received by the sending terminal 10 or the URs 20a to 20c within the holding time. To do. Therefore, the communication system 1 can always use an appropriate multicast tree even when the network topology changes by maintaining the multicast tree for the holding time. Moreover, the communication system 1 can maintain the multicast tree as long as necessary by the Join message 3 or the stable join message 3a.

[Second Embodiment]
〔Communications system〕
Next, a case where the transmission terminal address is changed due to movement of the transmission terminal 10 or the like will be described using the communication system 201 shown in FIG. The communication system 201 includes a transmission terminal 10, a plurality of URs 20a to 20f, a plurality of NRs 30a and 30b, and a plurality of reception terminals 40a to 40c. Compared with the communication system 1 shown in FIG. 1, the communication system 201 has increased URs 20d to 20f, and the connection relationship between the transmission terminal 10, the URs 20a to 20f, the NRs 30a and 30b, and the reception terminals 40a to 40c has changed. The others are substantially the same. UR20d-20f is also equipped with the structure similar to UR20a shown to Fig.2 (a).

  Consider a case where the transmission terminal 10 moves through the network and the transmission terminal address changes from “S” to “S ′”. Hereinafter, the changed transmission terminal address, that is, the address of the current position of the transmission terminal 10 is referred to as “ISA (Instantaneous Source Address)”. The transmission terminal address before the change is referred to as “oISA (old ISA)”. Further, the addresses “UR6”, “UR7”, and “UR8” are assigned to the URs 20d, 20e, and 20f, respectively.

(Configuration of receiving terminal)
Next, the configuration of the receiving terminals 40a to 40c will be described. As illustrated in FIG. 12A, the receiving terminal 40a includes an entry holding unit 41, a receiving unit 42, a transmitting unit 43, a packet processing unit 44, and a message generating unit 45. The receiving terminals 40b and 40c also have the same configuration as the receiving terminal 40a.

  The receiving unit 42 receives control messages and multicast packets from the URs 20a to 20c, the NRs 30a to 30c, and the transmission terminal 10. The receiving unit 42 inputs the received control message and multicast packet to the packet processing unit 44.

  The entry holding unit 41 is an address holding unit that holds an ISA, that is, a transmission terminal address and a multicast group address. As shown in FIG. 12B, the entry holding unit 41 holds an ISA, a multicast group address, an oISA, an MPT (Message Pending Timer), and an ST (Stale Timer). The entry holding unit 41 holds ISA and oISA in association with each other. MPT is a timer value that measures a message suppression time for suppressing transmission of a Prune message or a Leave Group message. While the MPT expires and is off, a Prune message or a Leave Group message is sent. While MPT is on, no Prune message or Leave Group message is sent. ST is a timer value for measuring the retention time of oISA. The ST is held in association with the oISA. When the ST expires, the corresponding oISA is deleted from the entry holding unit 41.

  The packet processing unit 44 processes the control message and the multicast packet. The packet processing unit 44 acquires the control message and multicast packet received by the receiving terminal 40a from the receiving unit 42. When receiving the LU message or the multicast packet to which the LU message is added, the packet processing unit 44 sets the ISA “S” currently held by the entry holding unit 41 to the oISA of the entry holding unit 41, The ST is activated. Further, the packet processing unit 44 sets the ISA “S ′” included in the LU message to the ISA of the entry holding unit 41.

  Further, the packet processing unit 44 refers to the entry holding unit 41 and determines whether or not the transmission source address of the multicast packet is oISA. When the transmission source address is oISA, the packet processing unit 44 refers to the entry holding unit 41 and determines whether MPT is on or off. When the MPT is off, the packet processing unit 44 instructs the message generation unit 45 to generate a Prune message or a Leave Group message specifying oISA. Further, the packet processing unit 44 activates the MPT of the entry holding unit 41. Further, the packet processing unit 44 deletes the oISA whose ST has expired from the entry holding unit 41.

  The message generation unit 45 generates a control message. The message generation unit 45 acquires the ISA and multicast group address from the entry holding unit 41. The message generation unit 45 generates a Join message, a Membership Report, a Stable Join message, and the like using the acquired ISA and multicast group address. The message generation unit 45 generates a Prune message or a Leave Group message in accordance with an instruction for generating a Prune message or a Leave Group message specifying the oISA from the packet processing unit 44. The message generation unit 45 inputs the generated control message to the transmission unit 43.

  The transmission unit 43 transmits a control message to the URs 20a to 20c, the NRs 30a to 30c, and the transmission terminal 10. The transmission unit 43 acquires a control message from the message generation unit 45 and transmits it. In particular, the transmission unit 43 uses the ISA held by the entry holding unit 41 that is updated based on the LU message that is the location update message, and changes the sending terminal address after changing the join request message such as the Join message or Membership Report. It functions as a receiving terminal transmitting means for transmitting to ISA. Furthermore, when the receiving terminal 40a connects to the NR, the transmission unit 43 transmits a participation request message to which data instructing not to discard the participation request message is added. Specifically, the transmission unit 43 transmits a Join message in which a special option is set. Accordingly, since the NR does not discard the Join message, the UR existing on the path from the receiving terminal 40a to the transmitting terminal 10 can receive the Join message.

  Next, processing in the communication system 201 when the transmission terminal address is changed will be described with reference to FIGS. In the description of FIGS. 11, 13, and 14, the entry holding units 11 and 21 a to 21 f included in the transmission terminal 10 and the URs 20 a to 20 f are also shown. For the sake of simplicity, only the table type, transmission terminal address, multicast group address, terminal transfer destination address, or router transfer destination address among the information held by the entry holding units 11, 21a to 21f is shown.

  FIG. 11 shows a state immediately after the transmitting terminal 10 has moved from oISA “S” to ISA “S ′”. Therefore, in FIG. 11, the entry holding units 21 a to 21 f hold the router forwarding destination address in the multicast tree specified by (S, G) using oISA “S”. When the transmitting terminal 10 exists in the oISA “S”, the multicast tree is set so as to be optimal when the oISA “S” is set upstream of the multicast tree. All of the receiving terminals 40a to 40c participate in the multicast tree. Therefore, the entry holding unit 11 of the transmission terminal 10 holds (S, G): [UR2], the entry holding unit 21a of the UR 20a holds (S, G): [UR4, UR8] as an MFT entry, and the UR 20c The entry holding unit 21c holds (S, G): [UR6, UR7] as an MFT entry and serves as a branch router. Further, the entry holding units 21d to 21f of the URs 20d to 20f hold (S, G): [G] as MFT entries and serve as terminal routers.

  When the transmission terminal 10 moves from oISA “S” to ISA “S ′”, the packet generator 13 generates a BU message 6 in which oISA “S” and ISA “S ′” are associated with each other. Then, the transmission unit 13 transmits the BU message 6 to the address “UR2” of the UR 20a according to the entry holding unit 11. The message processing unit 25 of the UR 20 a holds the ISA “S ′” and the oISA “S” in association with each other based on the BU message 6 received by the receiving unit 22. Then, the message processing unit 25 of the UR 20a causes the transfer unit 23 to transfer the control message addressed to the oISA “S” received by the receiving unit 22 to the ISA “S ′”. In this way, the UR 20a establishes a tunnel (Bi-Directional Tunneling) 9 with the transmitting terminal 10 and functions as a home agent.

  Furthermore, the transmission unit 13 of the transmission terminal 10 transmits the multicast packet 5 to the UR 20a based on the entry holding unit 11, and transmits using the multicast tree specified by (S, G). The multicast tree specified by (S, G) is set to be optimal when oISA “S” is set upstream of the multicast tree, and thus includes a redundant path. Therefore, the communication system 201 needs to reset the multicast tree specified by (S ′, G) based on ISA “S ′”. Therefore, the packet generator 15 generates the multicast packet 5 without setting the Stable option.

  Further, the packet generator 15 adds an LU message for notifying the ISA in which the oISA “S” and the ISA “S ′” are associated with each other to the multicast packet 5. The transmission unit 13 transmits such a multicast packet 5 to notify the receiving terminals 40a to 40c that the transmitting terminal 10 has moved from the oISA “S” to the ISA “S ′”. Thus, when the transmission terminal address is changed, the transmission unit 13 first transmits a transfer destination update message (BU message) for notifying the change of the transmission terminal address to the terminal transfer destination address. Furthermore, the transmission unit 13 transmits a location update message (LU message) for notifying the changed transmission terminal address to the reception terminal that receives the multicast packet, and functions as a transmission terminal transmission unit.

  As illustrated in FIG. 13, the receiving terminals 40 a to 40 c transmit Membership Report 2 in which the destination address is set to ISA “S ′” based on the LU message added to the received multicast packet 5. Specifically, the packet processing unit 44 updates the entry holding unit 41 based on the LU message. Then, the message generation unit 45 generates Membership Report 2 using the ISA “S ′” held in the updated entry holding unit 41, and the transmission unit 43 transmits it. When a plurality of receiving terminals are connected to one terminal router, the receiving terminal transmits Membership Report 2 in accordance with the congestion avoidance control defined in the MLD. According to this, it is possible to avoid congestion caused by all the receiving terminals trying to participate in the multicast tree specified by the newly set (S ′, G).

  When the receiving unit 22 of the UR 20d to 20f, which is the terminal router, receives the Membership Report 2 with the ISA “S ′” set as the destination address, the message processing unit 25 of the UR 20d to 20f sends the received Membership Report 2 to the message generating unit 26. input. Upon obtaining the Membership Report 2, the message generation unit 26 of the URs 20d to 20f generates a Join message 3 in which special options are set and the destination address is set to ISA “S ′”. Then, the transfer unit 23 of the URs 20d to 20f transmits the Join message 3 addressed to the ISA “S ′”.

  In response to the Membership Report 2 and the Join message 3 addressed to the ISA “S ′”, the transmitting terminal 10 and the URs 20a to 20f perform processing when the initial state multicast tree in the communication system 1 illustrated in FIGS. Similarly, the router transfer destination address corresponding to (S ′, G) is registered in the entry holding units 11, 21 a to 21 f so as to be optimal when ISA “S ′” is set upstream of the multicast tree. To go.

  Specifically, the message processing unit 25 of the URs 20a to 20f determines whether the URs 20a to 20f become branch routers when the changed transmission terminal address ISA “S ′” is set upstream of the multicast tree. . The message processing units 25 of the URs 20a to 20f determined to be branch routers register a plurality of router forwarding destination addresses in the entry holding units 21a to 21f in association with (S ′, G) using the ISA “S ′”. To do. Then, the message generation unit 26 of the URs 20a to 20f determined to be a branch router generates a redirect message in which the destination address is set to ISA “S ′”, and the transfer unit 23 transmits it.

  As a result, as shown in FIG. 13, the entry holding unit 21b of the UR 20b that did not hold the router transfer destination address holds (S ′, G): [UR4, UR6] as an MFT entry, and (S ′ , G) becomes a branch router in the multicast tree specified by The entry holding unit 21c of the UR 20c holds (S ', G): [UR7, UR8] as an MFT entry in addition to (S, G): [UR6, UR7] held as an MFT entry. , (S ′, G) also becomes a branch router in the multicast tree specified. Further, the entry holding unit 21a of the UR 20a holds (S ', G): [UR8] as an MCT entry in addition to (S, G): [UR4, UR8] held as an MFT entry.

  The entry holding units 21d to 21f of the URs 20d to 20f hold (S ′, G): [G] as MCT entries in addition to (S, G): [G] held as MFT entries. , (S ′, G), it is also a terminal router in the multicast tree specified. Then, in addition to (S, G): UR2] held by the entry holding unit 11 of the transmission terminal 10, (S ', G): [UR3] is held.

  Immediately after setting the optimum multicast tree for the ISA “S ′” in this way, the communication system 201 performs (S, G) optimum for the oISA “S” as shown in FIG. The specified multicast tree and the multicast tree specified by (S ′, G) optimum for ISA “S ′” coexist. Therefore, in the communication system 201, the multicast packets are transferred redundantly by the two multicast trees, and the receiving terminals 40a to 40c receive the multicast packets redundantly.

  For this reason, the message processing units 14 and 24 of the transmission terminal 10 and the URs 20a to 20f perform the oISA “S” based on at least one of the Leave Group message and the Prune message, or the retention time of the terminal transfer destination address and the router transfer destination address. It is preferable to delete the terminal transfer destination address and the router transfer destination address associated with "" from the entry holding units 11, 21a to 21f.

  Receiving terminals 40a to 40c that have received the LU message stop transmitting the Stable Join message specifying (S, G). Specifically, the message generation unit 45 of the reception terminals 40 a to 40 c generates a stable join message using the ISA “S ′” of the entry holding unit 41. For this reason, after the ISA of the entry holding unit 41 is updated by the LU message, the message generation unit 45 does not generate a stable join message using “S” that has become oISA.

  As a result, the receiving terminals 40a to 40c transmit only the stable join message specifying (S ', G). As a result, the message processing units 14 and 25 restart only the KAT of the terminal transfer destination address and the router transfer destination address corresponding to (S ′, G), and extend the holding time. Therefore, only the MFT entry corresponding to (S ′, G) of the entry holding units 11, 21a to 21f is held, and the terminal transfer destination address and the router transfer destination address held by the MFT entry corresponding to (S, G) are Deleted. Therefore, the transmission terminal 10 and the URs 20a to 20f can delete the multicast tree corresponding to (S, G) and keep only the MFT entry corresponding to (S ′, G). Therefore, the transmission terminal 10 and the URs 20a to 20f can maintain only the multicast tree corresponding to (S ′, G).

  Also, as shown in FIG. 14, the receiving terminals 40a to 40c can explicitly leave the multicast tree using the oISA “S” by using the Leave Group message or the Prune message without waiting for the KAT to expire. . After receiving the multicast packet from the multicast tree specified by (S ′, G), the receiving terminals 40a to 40c send a Leave Group message 7 requesting the departure from the multicast tree specified by (S, G). , It is transmitted to the URs 20d to 20f which are end routers. Specifically, the message generation unit 45 of the reception terminals 40a to 40c generates a Leave Group message 7 designating oISA “S”, and the transmission unit 43 transmits the message.

  The message processing units 25 of the URs 20d to 20f are stored in (S, G) by the entry holding units 21d to 21f based on the Leave Group message 7 requesting the departure from the multicast tree specified by (S, G). Delete the corresponding MFT entry. Further, the message processing unit 25 inputs the received Leave Group message 7 to the message generation unit 26.

  Based on the Leave Group message 7, the message generation unit 26 of the URs 20d to 20f sets the oISA “S” to the destination address, and generates the Prune message 8 that requests deletion of the MFT entry corresponding to (S, G). . Then, the transfer unit 23 of the URs 20d to 20f transmits the Prune message 8. When receiving the Prune message 8, the UR 20a transfers the Prune message 8 to the ISA “S ′” through the tunnel 9 in accordance with the association between the ISA “S ′” and the oISA “S”. In this way, the Prune message 8 reaches the transmitting terminals 10 located in the URs 20a to 20c and the ISA “S ′”.

  The message processing unit 14 of the transmission terminal 10 and the message processing unit 25 of the URs 20a to 20c delete the MFT entry corresponding to (S, G) from the entry holding units 11, 21a to 21c based on the Prune message 8. As a result, as illustrated in FIG. 14, the entry holding units 11 and 21a to 21f of the transmission terminal 10 and the URs 20a to 20f can hold only the MFT entry corresponding to (S ′, G).

〔Communication method〕
A procedure of a communication method using the communication system 201 shown in FIG. 11 will be described. First, the operation of the URs 20a to 20f will be described. The receiving units 22 of the URs 20a to 20f receive the multicast packet (S401). The data processing unit 24 of the URs 20a to 20f acquires the tunnel source address from the multicast packet and temporarily stores it (S402). The URs 20a to 20f decapsulate the multicast packet (S403). The URs 20a to 20f determine whether the entry holding units 21a to 21f hold the corresponding MFT entry or MCT entry based on the transmission terminal address and multicast group address set in the multicast packet (S404). If the URs 20a to 20f determine that they are not held, the URs 20a to 20f discard the multicast packet (S406).

  On the other hand, if it is determined in step (S404) that the message processing unit 25 of the URs 20a to 20f holds, it determines whether the MCT entry or the MFT entry is held (S405). If it is determined that the MCT entry is held, the message generation unit 26 of the URs 20a to 20f adds the router transfer destination address of the URs 20a to 20f to the terminal transfer destination address, and transfers the address of the UR 20a to 20f itself to the terminal. A Redirect message addressed to the transmission terminal address in which the Hop-by-Hop option is set is generated to request deletion from the destination address. Then, the transfer unit 23 transmits a Redirect message (S412).

  On the other hand, if it is determined in step (S405) that the MFT entry is held, the data processing unit 24 of the URs 20a to 20f holds the tunnel source address of the received multicast packet in the entry holding units 21a to 21f. It is determined whether or not it matches the tunnel source address to be executed (S407).

  If the tunnel source address does not match in step (S407), the data processing unit 24 of the URs 20a to 20f determines that the tunnel source address of the received multicast packet is the same as the previous tunnel source address held by the entry holding units 21a to 21f. It is determined whether they match (S408). If it matches the previous tunnel source address, the message generation unit 26 of the URs 20a to 20f generates a Prune message in which the Hop-by-Hop option is not set, and the transfer unit 23 transmits to the previous tunnel source address (S409). ).

  On the other hand, if it does not match the previous tunnel source address in step (S408), the data processing unit 24 of the URs 20a to 20f uses the tunnel source address currently held by the entry holding units 21a to 21f as the entry holding unit 21a. It is set to the previous tunnel source address of ˜21f (S410). At this time, the data processing unit 24 may use the KAT of the entry holding units 21a to 21f as the ST, and may be set so that the previous tunnel source address is deleted when the ST expires. Thereafter, the data processing unit 24 of the URs 20a to 20f registers the tunnel source address stored in step (S402) in the entry holding units 21a to 21f (S411). The URs 20a to 20f proceed to step (S413) after steps (S409) and (S411).

  If the tunnel source addresses match in step (S407), or if steps (S409) and (S411) are completed, the data processing unit 24 of the URs 20a to 20f uses the tunnel source address stored in step (S402). Then, it is determined whether the MFT entry is held (S413). When it is determined that the MFT entry is held, the data processing unit 24 of the URs 20a to 20f encapsulates the multicast packet with respect to the router transfer destination address held by the MFT entry excluding the tunnel source address, and the transfer unit 23 transmits the packet. (S414). On the other hand, if it is determined in step (S413) that the MFT entry is not held, the data processing unit 24 of the URs 20a to 20f encapsulates the multicast packet with respect to the router transfer destination address held by the MFT entry, and the transfer unit 23 Transmit (S415). Note that steps (S407) to (S411) can be omitted.

  Next, the operation of the receiving terminals 40a to 40c will be described. The receiving unit 42 of the receiving terminals 40a to 40c receives the multicast packet (S501). The packet processing unit 44 of the receiving terminals 40a to 40c refers to the entry holding unit 41 and determines whether or not the source address of the received multicast packet is ISA (S502).

  When the source address of the multicast packet is ISA, the packet processing unit 44 of the receiving terminals 40a to 40c determines whether or not the entry holding unit 41 holds oISA (S503). When the entry holding unit 41 holds the oISA, the packet processing unit 44 determines whether the MPT is on or off (S504). When the MPT is in an off state, the message generator 45 of the receiving terminals 40a to 40c generates a Prune message addressed to the oISA in which the Hop-by-Hop option is set, and the transmitter 43 transmits the message. Alternatively, the message generation unit 45 generates a Leave Group message addressed to the oISA, and the transmission unit 43 transmits the message (S505). Further, the packet processing unit 44 activates the MPT of the entry holding unit 41 (S506).

  In step (S502), if the source address of the multicast packet is not ISA, if entry holding unit 41 does not hold oISA in step (S503), if MPT is on in step (S504), receive The terminals 40a to 40c do not perform special processing, and the packet processing unit 44 processes data included in the multicast packet.

〔effect〕
According to the communication system 201, the URs 20a to 20f, the reception terminals 40a to 40c, and the communication method, the transmission terminal 10 changes the transmission terminal address to the terminal transfer destination address when the transmission terminal address is changed. Is transmitted, and the transmission unit 13 is configured to transmit the LU message notifying the ISA “S ′” to the receiving terminals 40a to 40c. The receiving terminals 40a to 40c include a transmitting unit 43 that transmits a Join message or a Membership Report to the ISA based on the LU message.

  For this reason, when the transmission terminal address is changed due to movement of the transmission terminal 10 or the like, the transmission terminal 10 transmits a BU message to the terminal transfer destination address, so that a tunnel is established between the transmission terminal and the UR of the terminal transfer destination address. Can be built. Therefore, the control message addressed to the oISA is transferred to the transmission terminal 10.

  Further, the transmission terminal 10 can notify the reception terminals 40a to 40c of the change of the transmission terminal address by the LU message. Then, the receiving terminals 40a to 40c can grasp the change of the transmitting terminal address by the LU message, and can transmit the Join message or the Membership Report to the ISA “S ′”. Therefore, an appropriate multicast tree is newly set in ISA “S ′” triggered by a Join message addressed to ISA “S ′” or Membership Report. Therefore, the communication system 201 can realize multicast using an appropriate multicast tree even if the transmission terminal address changes.

  Moreover, the branch router holds a plurality of router transfer destination addresses in association with ISA “S ′”. Therefore, the URs 20a to 20f clearly distinguish between a multicast tree corresponding to oISA “S”, that is, (S, G), and a multicast tree corresponding to ISA “S ′”, that is, (S ′, G). it can.

  In addition, the transmission unit 43 of the reception terminals 40a to 40c transmits a Leave Group message or a Prune message that specifies the address of the transmission terminal before the change. Then, the message processing units 14 and 25 of the transmitting terminal 10 and the URs 20a to 20f perform the oISA “S”, that is, (S), based on the retention group message, the Prune message, the terminal transfer destination address and the router transfer destination address retention time. , G) is deleted from the entry holding units 11, 21a to 21f.

  Therefore, the communication system 201 can delete the multicast tree formed using the oISA “S” by using the Leave Group message, the Prune message, the terminal transfer destination address, and the router transfer destination address holding time. Therefore, it is possible to suppress the redundant transfer of multicast packets due to the coexistence of the multicast tree using oISA “S” and the multicast tree using ISA “S ′”. In particular, according to the Leave Group message and the Prune message, the receiving terminals 40a to 40c do not wait for the hold time to expire, and the multicast tree formed using the oISA “S” specified by the Leave Group message or the Prune message. You can leave explicitly. Therefore, the communication system 201 can further reduce duplicate transfers.

It is a figure which shows the structure of the communication system which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the structure of UR which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the structure of the transmission terminal which concerns on the 1st Embodiment of this invention. It is a figure which shows the process in the initial state of the multicast tree which concerns on the 1st Embodiment of this invention. It is a figure which shows the participation of the receiving terminal in the initial state of the multicast tree which concerns on the 1st Embodiment of this invention. It is a figure which shows the process in the stable state of the multicast tree which concerns on the 1st Embodiment of this invention. It is a figure which shows the participation of the receiving terminal in the stable state of the multicast tree which concerns on the 1st Embodiment of this invention. It is a flowchart which shows the process sequence at the time of Join message reception which concerns on the 1st Embodiment of this invention. It is a flowchart which shows the process sequence at the time of the Prune message reception which concerns on the 1st Embodiment of this invention. It is a sequence diagram which shows the transfer procedure of the multicast packet which concerns on the 1st Embodiment of this invention. It is a figure which shows the state immediately after the transmission terminal of the communication system which concerns on the 2nd Embodiment of this invention moves. It is a block diagram which shows the structure of the receiving terminal which concerns on the 2nd Embodiment of this invention. It is a figure which shows the state where the multicast tree before and behind the transmission terminal address change which concerns on the 2nd Embodiment of this invention coexists. It is a figure which shows the state by which only the multicast tree after the transmission terminal address change which concerns on the 2nd Embodiment of this invention was maintained. It is a flowchart which shows the operation | movement procedure of UR which concerns on the 2nd Embodiment of this invention. It is a flowchart which shows the operation | movement procedure of the receiving terminal which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

1,201 communication system 10 transmitting terminal 11 entry holding unit 12 receiving unit 13 transmitting unit 14 message processing unit 15 packet generating unit 20a, 20b, 20c, 20d, 20e, 20f UR
21a, 21b, 21c, 21d, 21e, 21f Entry holding unit 22 Receiving unit 23 Transfer unit 24 Data processing unit 25 Message processing unit 26 Message generation unit 30a, 30b, 30c NR
40a, 40b, 40c receiving terminal 41 entry holding unit 42 receiving unit 43 transmitting unit 44 packet processing unit 45 message generating unit

Claims (13)

A communication system comprising: a transmission terminal that transfers a multicast packet to a terminal transfer destination address; and a router that transfers the multicast packet to a router transfer destination address,
The router
Router holding means for holding the router forwarding address;
Judgment means for judging whether to become a branch router that forwards the multicast packet to a plurality of router forwarding destination addresses when the address of the transmitting terminal is set upstream of the multicast tree;
If it is determined to be the branch router, the router registration means for registering the plurality of router transfer destination addresses in association with the address of the transmission terminal in the router holding means,
If it is determined that the router becomes the branch router, a join / leave request message requesting to add the router address to the terminal forwarding address and to delete the router forwarding address from the terminal forwarding address is sent to the sending terminal. Router transmission means for transmitting to the address of
The transmitting terminal is
Transmitting terminal holding means for holding the terminal transfer destination address;
Transmission terminal registration means for deleting the router transfer destination address from the transmission terminal holding means based on the join / leave request message and registering the address of the branch router in the transmission terminal holding means. Communication system.   The router registration means deletes the router transfer destination address of the downstream branch router from the router holding means based on the join / leave request message from the downstream branch router, and sets the address of the downstream branch router. The communication system according to claim 1, wherein the communication system is registered in the router holding unit.   The router registration unit registers the router forwarding destination address in association with the address of the transmission terminal in the router holding unit when it becomes a terminal router connected to the reception terminal of the multicast packet. The communication system according to 1 or 2. The transmission terminal comprises a transmission terminal transmission means for transmitting a location update message notifying the address of the transmission terminal after the change to the reception terminal of the multicast packet when the address of the transmission terminal is changed,
The receiving terminal comprises receiving terminal transmitting means for transmitting a participation request message for requesting transmission of the multicast packet to the address of the changed transmitting terminal based on the location update message. The communication system according to any one of 1 to 3.   The receiving terminal transmitting means transmits the participation request message to which data instructing not to discard the participation request message is added when the receiving terminal is connected to a router that does not support the multicast protocol. The communication system according to claim 4, characterized in that: The router registration unit deletes the router transfer destination address from the router holding unit when the holding time of the router transfer destination address expires, and maintains the multicast tree with the router transfer destination address as a source address If the router receives a maintenance request message for holding within the holding time, the holding time is extended,
The transmission terminal registration means deletes the terminal transfer destination address from the transmission terminal holding means when the holding time of the terminal transfer destination address has expired, and the maintenance request with the terminal transfer destination address as the source address The communication system according to any one of claims 1 to 5, wherein when the transmitting terminal receives a message within the holding time, the holding time is extended. The router registering means, based on a leaving request message for requesting leaving from the multicast tree designating the address of the transmitting terminal, a router transfer destination address associated with the address of the transmitting terminal; Removed from
The transmission terminal registration unit deletes a terminal transfer destination address associated with the address of the transmission terminal from the transmission terminal holding unit based on the leaving request message. The communication system according to any one of the above. Router holding means for holding the router forwarding destination address of the multicast packet;
Judgment means for judging whether or not to become a branch router that forwards the multicast packet to a plurality of router forwarding destination addresses when an address of a transmission terminal that forwards the multicast packet is set upstream of a multicast tree;
If it is determined to be the branch router, the router registration means for registering the plurality of router transfer destination addresses in association with the address of the transmission terminal in the router holding means,
Participation requesting that the address of the router is added to the terminal forwarding destination address to which the sending terminal forwards the multicast packet and the router forwarding destination address is deleted from the terminal forwarding destination address when it is determined that the router becomes the branch router A router transmitting means for transmitting a leave request message to the address of the transmitting terminal. Transmitting terminal holding means for holding the terminal transfer destination address of the multicast packet;
A request for adding a branch router address for forwarding the multicast packet to a plurality of router transfer destination addresses to the terminal transfer destination address and deleting the router transfer destination address of the branch router from the terminal transfer destination address. A transmission terminal comprising: a transmission terminal registration unit that deletes the router transfer destination address from the transmission terminal holding unit based on a leave request message and registers the branch router address in the transmission terminal holding unit .   The transmission terminal transmitting means for transmitting a location update message notifying the address of the transmission terminal after the change to the reception terminal of the multicast packet when the address of the transmission terminal is changed. The transmitting terminal described in.   When the address of the transmitting terminal that forwards the multicast packet is changed, based on the location update message that notifies the address of the changed transmitting terminal, the participation request message that requests transmission of the multicast packet is transmitted after the change. A receiving terminal comprising receiving terminal transmitting means for transmitting to the address of the terminal. A router determines whether it becomes a branch router that forwards the multicast packet to a plurality of router transfer destination addresses when the address of the transmission terminal that forwards the multicast packet is upstream of the multicast tree;
If it is determined to be the branch router, the router holding means holding the router transfer destination address is registered with the plurality of router transfer destination addresses in association with the address of the transmitting terminal,
A joining / leaving request message for requesting that the address of the router be added to a terminal forwarding address to which the sending terminal forwards a multicast packet and to delete the router forwarding address from the terminal forwarding address is sent to the sending terminal. Send to address,
Based on the join / leave request message, the transmitting terminal deletes the router transfer destination address from the transmitting terminal holding means that holds the terminal transfer destination address, and sends the branch router address to the transmitting terminal holding means. A communication method characterized by registering. When the address of the transmitting terminal is changed, the transmitting terminal transmits a location update message notifying the address of the changed transmitting terminal to the receiving terminal of the multicast packet;
The communication method according to claim 12, wherein the receiving terminal transmits a participation request message for requesting transmission of the multicast packet to the address of the changed transmitting terminal based on the location update message. .

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