计算机网络_系统方法5eMK-PPT Chapter 4.ppt

The University of Adelaide, School of Computer Science * Chapter 2 — Instructions: Language of the Computer * Overview Basic IP multicast model is many-to-many based on multicast groups Each group has its own IP multicast address Hosts that are members of a group receive copies of any packets sent to that group’s multicast address A host can be in multiple groups A host can join and leave groups Overview Using IP multicast to send the identical packet to each member of the group A host sends a single copy of the packet addressed to the group’s multicast address The sending host does not need to know the individual unicast IP address of each member Sending host does not send multiple copies of the packet Overview IP’s original many-to-many multicast has been supplemented with support for a form of one-to-many multicast One-to-many multicast Source specific multicast (SSM) A receiving host specifies both a multicast group and a specific sending host Many-to-many model Any source multicast (ASM) Overview A host signals its desire to join or leave a multicast group by communicating with its local router using a special protocol In IPv4, the protocol is Internet Group Management Protocol (IGMP) In IPv6, the protocol is Multicast Listener Discovery (MLD) The router has the responsibility for making multicast behave correctly with regard to the host Multicast Routing A router’s unicast forwarding tables indicate for any IP address, which link to use to forward the unicast packet To support multicast, a router must additionally have multicast forwarding tables that indicate, based on multicast address, which links to use to forward the multicast packet Unicast forwarding tables collectively specify a set of paths Multicast forwarding tables collectively specify a set of trees Multicast distribution trees Multicast Routing To support source specific multicast, the multicast forwarding tables must indicate which links to use based on the combination of multicast address and