QTECH QSW-8300 Инструкция по настройке - Manual (Page 206)

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Data repository, finance application (stock) etc
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.
28.2 PIM-DM
28.2.1 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 Multicast transmission table entry (S, G) corresponds. Thus a
SPT(Shortest Path Tree, SPT) tree with source S as root is created. The Prune process is
initiated by leaf router first.
The process above is called Flooding & Prune process. Each pruned node also provides time-
out mechanics at the same time. When Prune is timed-out, the router will restart Flooding &
Prune process. The PIM-DM Flooding & Prune is periodically processed.
3. RPF Check
With RPF Check, PIM-DM makes use of existing Unicast routing table to establish a Multicast
transmission tree initiating from data source. When a Multicast packet arrives, the router will
determine whether the coming path is correct first. If the arrival interface is the interface