194 CHAPTER 15: MULTICAST OVERVIEWFigure 60 Positions of Layer 3 multicast protocolâ– Multicast management protocolsTypically, the Internet Group Management Protocol (IGMP) is used betweenhosts and Layer 3 multicast devices directly connected with the hosts. Theseprotocols define the mechanism of establishing and maintaining groupmemberships between hosts and Layer 3 multicast devices.â– Multicast routing protocolsA multicast routing protocol runs on Layer 3 multicast devices to establish andmaintain multicast routes and forward multicast packets correctly andefficiently. Multicast routes constitute a loop-free data transmission path from adata source to multiple receivers, namely a multicast distribution tree.In the ASM model, multicast routes come in intra-domain routes andinter-domain routes.â– An intra-domain multicast routing protocol is used to discover multicastsources and build multicast distribution trees within an autonomous system(AS) so as to deliver multicast data to receivers. Among a variety of matureintra-domain multicast routing protocols, protocol independent multicast(PIM) is a popular one. Based on the forwarding mechanism, PIM comes intwo modes - dense mode (often referred to as PIM-DM) and sparse mode(often referred to as PIM-SM).â– An inter-domain multicast routing protocol is used for delivery of multicastinformation between two ASs. So far, mature solutions include multicastsource discovery protocol (MSDP).For the SSM model, multicast routes are not divided into inter-domain routesand intra-domain routes. Since receivers know the position of the multicastsource, channels established through PIM-SM are sufficient for multicastinformation transport.AS 1 AS 2SourceReceiver ReceiverReceiverPIM PIMMSDPIGMP IGMPIGMP
