INTERNETWORKING: Part IV

•IP multicasting

•Hardware Origins of Multicast

•Multicasting allows each system to choose whether it wants to participate in a given multicast

•Hardware technology reserves a large set of addresses for use with multicast

•When a group of machines wants to communicate, they choose one particular multicast address to use for communication

•After a configuring the network interface hardware to recognize the selected multicast address, all machines in the group will receive a copy of any packet sent to that multicast address

•IP Multicast

•It is internet abstraction of hardware multicasting

•It follows the paradigm of allowing to a subset of host computers but allow the subset to spread across arbitrary physical networks throughout an internet

•In IP terminology, the subset is known as multicast group

•IP multicasting has general characteristics

•Group address: Each multicast group is a unique class D address. A few IP multicast addresses are permanently assigned by the Internet authorities and other addresses are temporary(private use)

•Number of Groups: IP provides addresses up to  238  multicast address. Number of groups are limited by practical constraints on routing table size rather than addressing

•Dynamic group membership: A host can join or leave an IP multicast group at any time. A host may be member of many multicast groups

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•Use of hardware: If the underlying network hardware supports multicast, IP uses hardware multicast to send IP multicast. If h/w dose not support multicast, IP uses  broadcast or multicast to deliver IP multicast

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•Inter-network Forwarding: members of multicast group are attached to multiple physical networks, special multicast routers are  required to forward IP multicast; the capability is also added to conventional routers

•Delivery Semantics: IP multicasting uses same best-effort delivery semantics I,e) the multicast datagrams can be lost, delayed, duplicated or delivered out of order

•Membership and Transmission: Any host can send datagrams to any multicast group; the group membership is only used to determine whether the host  recieves datagram s sent to the group

•Use of conceptual pieces
required for multicasting

•A multicast address scheme

•An effective notification and delivery mechanisms- notification to inform routers about multicast groups  and routers need a delivery mechanism transfer multicast packets or hosts

•An efficient internetwork forwarding delivery- along shortest paths, should not send a copy of  datagram along the path if the path does not lead to a member.