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Modified over 2 years ago
Multicasting© Dr. Ayman Abdel-Hamid, CS4254 Spring 20061 CS4254 Computer Network Architecture and Programming Dr. Ayman A. Abdel-Hamid Computer Science Department Virginia Tech Multicasting
© Dr. Ayman Abdel-Hamid, CS4254 Spring 20062 Outline Multicasting (Chapter 21) Multipoint Communications IP Multicast IPv4 Multicast addresses Sending and Receiving Messages Multicasting on a LAN Multicasting on a WAN Multicast Issues
Multicasting© Dr. Ayman Abdel-Hamid, CS4254 Spring 20063 Multipoint Communications Multipoint communications support communications between more than two hosts One-to-many Many-to-many Unlike broadcast, allows a proper subset of hosts to participate Example standards IP Multicast (RFC 1112, standard)RFC 1112
Multicasting© Dr. Ayman Abdel-Hamid, CS4254 Spring 20064 Logical Multipoint Communications Two basic logical organizations Rooted: hierarchy (perhaps just two levels) that structures communications Non-rooted: peer-to-peer (no distinguished nodes) Different structure could apply to control and data “planes” Control plane determines how multipoint session is created Data plane determines how data is transferred between hosts in the multipoint session
Multicasting© Dr. Ayman Abdel-Hamid, CS4254 Spring 20065 Logical Multipoint Communications Control Plane The control plane manages creation of a multipoint session Rooted control plane One member of the session is the root, c_root Other members are the leafs, c_leafs Normally c_root establishes a session Root connects to one or more c_leafs c_leafs join c_root after session established Non-rooted control plane All members are the same (c_leafs) Each leaf adds itself to the session
Multicasting© Dr. Ayman Abdel-Hamid, CS4254 Spring 20066 Logical Multipoint Communications Data Plane The data plane is concerned with data transfer Rooted data plane Special root member, d_root Other members are leafs, d_leafs Data transferred between d_leafs and d_roots d_leaf to d_root d_root to d_leaf There is no direct communication between d_leafs Non-rooted data plane No special members, all are d_leafs Every d_leafs communicate with all d_leafs
Multicasting© Dr. Ayman Abdel-Hamid, CS4254 Spring 20067 Forms of Multipoint Communications Server-based -- rooted multipoint communications with server as d_root Passive or inactive Relay Reflector Active Bridge or multipoint control unit (MCU) Strictly peer-to-peer multipoint – Non-rooted Multicast
Multicasting© Dr. Ayman Abdel-Hamid, CS4254 Spring 20068 Multipoint Servers Passive Multipoint Server a relay or reflector service Provides no processing of the data Minimum requirement is for transport-level semantics, so can operate at the transport or application level Active Multipoint Server Does application-level processing transcoding uses application-level semantics
Multicasting© Dr. Ayman Abdel-Hamid, CS4254 Spring 20069 Multicast Communication Multicast abstraction is peer-to-peer Application-level multicast Network-level multicast Requires router support (multicast-enabled routers) Multicast provided at network protocol level IP multicast
Multicasting© Dr. Ayman Abdel-Hamid, CS4254 Spring 200610 Multicast Communication Transport mechanism and network layer must support multicast Internet multicast limited to UDP (not TCP) Unreliable: No acknowledgements or other error recovery schemes (perhaps at application level) Connectionless: No connection setup (although there is routing information provided to multicast-enabled routers) Datagram: Message-based multicast
Multicasting© Dr. Ayman Abdel-Hamid, CS4254 Spring 200611 IP Multicast IP supports multicasting Uses only UDP, not TCP Special IP addresses (Class D) identify multicast groups Internet Group Management Protocol (IGMP) to provide group routing information Multicast-enabled routers selectively forward multicast datagrams IP TTL field limits extent of multicast Requires underlying network and adapter to support broadcast or, preferably, multicast Ethernet (IEEE 802.3) supports multicast
Multicasting© Dr. Ayman Abdel-Hamid, CS4254 Spring 200612 IP Multicast: Group Address How to identify the receivers of a multicast datagram? How to address a datagram sent to these receivers? Each multicast datagram to carry the IP addresses of all recipients? Not scalable for large number of recipients Use address indirection A single identifier used for a group of receivers
Multicasting© Dr. Ayman Abdel-Hamid, CS4254 Spring 200613 IP Multicast: IGMP Protocol RFC 3376 (IGMP v3): operates between a host and its directly attached routerRFC 3376 host informs its attached router that an application running on the host wants to join or leave a specific multicast group another protocol is required to coordinate multicast routers throughout the Internet network layer multicast routing algorithms Network layer multicast IGMP and multicast routing protocols IGMP enables routers to populate multicast routing tables Carried within an IP datagram
Multicasting© Dr. Ayman Abdel-Hamid, 