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This Concept Map, created with IHMC CmapTools, has information related to: ch12 coor mult, Multicast communication has IP multicast – an implementation of group communication built on top of IP (note IP packets are addressed to computers) allows the sender to transmit a single IP packet to a set of computers that form a multicast group (a class D internet address with first 4 bits 1110) Dynamic membership of groups. Can send to a group with or without joining it To multicast, send a UDP datagram with a multicast address To join, make a socket join a group (s.joinGroup(group) - Fig 4.17) enabling it to receive messages from the group, Multicast communication has The system consists of a collection of processes which can communicate reliably over 1-1 channels Processes fail only by crashing (no arbitrary failures) Processes are members of groups - which are the destinations of multicast messages In general process p can belong to more than one group, IP multicast – an implementation of group communication built on top of IP (note IP packets are addressed to computers) allows the sender to transmit a single IP packet to a set of computers that form a multicast group (a class D internet address with first 4 bits 1110) Dynamic membership of groups. Can send to a group with or without joining it To multicast, send a UDP datagram with a multicast address To join, make a socket join a group (s.joinGroup(group) - Fig 4.17) enabling it to receive messages from the group has Multicast routers Local messages use local multicast capability. Routers make it efficient by choosing other routers on the way. Failure model Omission failures some but not all members may receive a message. e.g. a recipient may drop message, or a multicast router may fail IP packets may not arrive in sender order, group members can receive messages in different orders, Multicast communication has validity: any message in the outgoing message buffer is eventually delivered to the incoming message buffer; (used by retires) integrity: the message received is identical to one sent, and no messages are delivered twice. (used by checksums), Multicast communication has Closed groups- only members can send to group, a member delivers to itself they are useful for coordination of groups of cooperating servers Open- they are useful for notification of events to groups of interested processes, The system consists of a collection of processes which can communicate reliably over 1-1 channels Processes fail only by crashing (no arbitrary failures) Processes are members of groups - which are the destinations of multicast messages In general process p can belong to more than one group has Operations multicast(g, m) sends message m to all members of process group g deliver (m) is called to get a multicast message delivered. It is different from receive as it may be delayed to allow for ordering or reliability. Multicast message m carries the id of the sending process sender(m) and the id of the destination group group(m) We assume there is no falsification of the origin and destination of messages, Multicast communication has A correct process will eventually deliver the message provided the multicaster does not crash note that IP multicast does not give this guarantee The primitives are called B-multicast and B-deliver A straightforward but ineffective method of implementation: use a reliable 1-1 send (i.e. with integrity and validity as above) Problem if the number of processes is large, the protocol will suffer from ack-implosion