CS43815Multicast.pptVIP

Broadcast and Multicast Overview Last time: routing protocols for the Internet Hierarchical routing RIP, OSPF, BGP This time: broadcast and multicast Definitions Unicast Single source, single receiver Broadcast Send same packet to all receivers “all” usually limited in some way LAN, subnet, organization Multicast Send same packet to many receivers In-network Duplication Source duplication inefficient Source does not know all destinations Flooding Loops Broadcast storms Controlled Flooding Ignore duplicate messages Cache to remember what’s been sent before Special case: sequence numbers Used with broadcast updates Source assigns increasing seq no to broadcast Record latest seq no from each source Discard messages with old seq no’s Ensures always use the latest update Reverse Path Forwarding Idea: use unicast routing information Forward only messages coming from the shortest path to source Note: problem with asymmetric paths Reverse Path Forwarding Reverse Path Forwarding Reverse Path Forwarding Spanning Tree Subset of graph edges that forms a tree Flood messages along all edges on spanning tree, ignore all others Minimal Spanning Tree Minimal cost spanning tree Minimal by sum of all edge costs Provably optimal broadcast cost, for any source in the tree NP-complete problem (not true) Approximation: Shortest unicast paths to some root Minimum Spanning Tree Shortest Path Tree Multicast Motivation? Multicast Issues Naming Membership Management Routing IP Multicast Naming Class D address represents multicast group E.g. 226.17.30.197 Datagram with destination address set to group delivered to all hosts in the group Indirection 226.17.30.197 = 65.30.1.2, 66.8.3.53, 128.32.75.60, … Sender may or may not be in the group No address hierarchy or subnets How is routing done? Membership Management Some other questions: Who is part of the group? How does one join? How does one leave? Who decides if it’s OK? Membership management answers these IGMP Internet Group Managemen