3Com 4210 PWR Configuration Manual page 196

194 C 15: M
HAPTER ULTICAST
O
VERVIEW
Figure 60 Positions of Layer 3 multicast protocol
Receiver
IGMP
PIM
Multicast management protocols
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Typically, the Internet Group Management Protocol (IGMP) is used between
hosts and Layer 3 multicast devices directly connected with the hosts. These
protocols define the mechanism of establishing and maintaining group
memberships between hosts and Layer 3 multicast devices.
Multicast routing protocols
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A multicast routing protocol runs on Layer 3 multicast devices to establish and
maintain multicast routes and forward multicast packets correctly and
efficiently. Multicast routes constitute a loop-free data transmission path from a
data source to multiple receivers, namely a multicast distribution tree.
In the ASM model, multicast routes come in intra-domain routes and
inter-domain routes.
An intra-domain multicast routing protocol is used to discover multicast
■
sources and build multicast distribution trees within an autonomous system
(AS) so as to deliver multicast data to receivers. Among a variety of mature
intra-domain multicast routing protocols, protocol independent multicast
(PIM) is a popular one. Based on the forwarding mechanism, PIM comes in
two modes - dense mode (often referred to as PIM-DM) and sparse mode
(often referred to as PIM-SM).
An inter-domain multicast routing protocol is used for delivery of multicast
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information between two ASs. So far, mature solutions include multicast
source discovery protocol (MSDP).
For the SSM model, multicast routes are not divided into inter-domain routes
and intra-domain routes. Since receivers know the position of the multicast
source, channels established through PIM-SM are sufficient for multicast
information transport.
AS 1
MSDP
Source
AS 2
Receiver
IGMP
PIM
IGMP
Receiver