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Chapter 14. Multicasting And Multicast Routing Protocols. INTRODUCTION MULTICAST ROUTING MULTICAST TREES MULTICAST ROUTING PROTOCOLS DVMRP MOSPF CBT PIM MBONE. Figure 14-1. 14.1 Introduction: Unicasting. In unicast routing, the router forwards
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Chapter 14 Multicasting And MulticastRouting Protocols • INTRODUCTION • MULTICAST ROUTING • MULTICAST TREES • MULTICAST ROUTING PROTOCOLS • DVMRP • MOSPF • CBT • PIM • MBONE
Figure 14-1 14.1 Introduction: Unicasting In unicast routing, the router forwards the received packet through only one of its interfaces.
Figure 14-2 Multicasting In multicast routing, the router may forward the received packet through several of its interfaces.
Figure 14-3 Multicasting versus multiple unicasting Emulation of multicasting through multiple unicasting is not efficient and may create long delays, particularly with a large group.
Application of Multicasting • Access to Distributed Databases • Information Dissemination: e.g. multicast software updates to customers • News Delivery • Teleconferencing, Web Seminars • Distant Learning
14.3 Multicast Routing Objectives • Every member receives EXACTLY ONE copy of the packet • Non-members receive nothing • No loops in route • Optimal path from source to each destination. Terminology • Spanning Tree: Source is the root, group members are the leaves. • Shortest Path Spanning Tree: Each path from root to a leaf is the shortest according to some metric
14.3 Multicast Trees • Source-Based Tree: • For each combination of (source , group), there is a shortest path spanning tree. • Approach 1: DVMRP; an extension of unicast distance vector routing (e.g. RIP) • Approach 2: MOSPF; an extension of unicast link state routing (e.g. OSPF) • Group-Share Tree • One tree for the entire group • Rendezvous-Point Tree: one router is the center of the group and therefore the root of the tree. • CBT and PIM-SP protocols.
Figure 14-4 14.4 Multicast routing protocols
14.5 Distance Vector Multicast Routing Protocol - DVMRP • No pre-defined route from source to destination. Tree is gradually created by successive routers along the path. • Uses shortest path (fewest hops) • Prevent loops: apply Reverse Path Forwarding (RFP) • Prevent Duplication: apply Reverse Path Broadcasting (RPB) • Multicast with dynamic membership: apply Reverse Path Multicasting (RPM) with pruning, grafting, and lifetime.
Figure 14-5 Reverse Path Forwarding In reverse path forwarding (RPF), the router forwards only the packets that have traveled the shortest path from the source to the router; all other copies are discarded. No Loops
Figure 14-6 Reverse Path Broadcasting Prevent Duplication in RPF
Figure 14-7 RPF versus RPB • The router with the shortest path to the source becomes the designated parent of a network • A Router forwards packets only to its designated child networks
RPB creates a shortest path broadcast tree from the source to each destination. It guarantees that each destination receives one and only one copy of the packet.
Figure 14-8 RPF, RPB, and RPM RPM adds pruning and grafting to RPB to create a multicast shortest path tree that supports dynamic membership changes.
14.6 MOSPF
Figure 14-9 Unicast tree and multicast tree
14.7 Core-Based Tree CBT
Figure 14-10 Shared-group tree with rendezvous router
Figure 14-11 Sending a multicast packet to the rendezvous router
In CBT, the source sends the multicast packet (encapsulated in a unicast packet) to the core router. The core router decapsulates the packet and forwards it to all interested hosts.
