Accton Technology ES4626 - Manual (Page 614)

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point and receiving in multipoint. It has achieved the effective data transmission from a
point to multiple points, saved a great deal of network bandwidth and reduced network
load. Making use of the Multicast property of network, some new value-added operations
can be supplied conveniently. In Information Service areas such as online living
broadcast, network TV, remote education, remote medicine, real time video/audio
meeting, the following applications may be supplied:
1) Application of Multimedia and Streaming Media
2) Data repository, finance application (stock) etc;
3) Any data distribution application of “one point to multiple points”
In the situation of more and more multimedia operations in IP network, Multicast
has tremendous market potential and Multicast operation will be generalized and
popularized.
16.2 PIM-DM
16.2.1 Introduction to PIM-DM
PIM-DM（Protocol Independent Multicast, Dense Mode）is a Multicast Routing
Protocol in dense mode which applies to small network. The members of multicast group
are relatively dense under this kind of network environment.
The working process of PIM-DM can be summarized as: Neighbor Discovery,
Flooding&Prune, and Graft.
1. Neigh hour Discovery
After PIM-DM router is enabled, Hello message is required to discover neighbors.
The network nodes which run PIM-DM use Hello message to contact each other.
PIM-DM Hello message is sent periodically.
2. Flooding&Prune of process
PIM-DM assumes all hosts on the network are ready to receive Multicast data. When
some Multicast Source begins to send data to a Multicast Group G, after receiving the
Multicast packet, the router will make RPF check first according to the Unicast table. If
the check passes, the router will create a (S, G) table entry and transmit the Multicast
packet to all downstream PIM-DM nodes on the network (Flooding). If the RPF check
fails, i.e. the Multicast packet is input from the incorrect interface, and then the message
is discarded. After this procedure, in the PIM-DM Multicast domain, every node will
create a (S, G) table entry. If there is no Multicast group member in the downstream
nodes, then a Prune message is sent to upstream nodes to notify them not to transmit
data of this Multicast group any more. After receiving Prune message, the upstream
nodes will delete the corresponding interface from the output interface list to which their