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Chapter 16 Multicast Protocol
Configuration
16.1 Multicast Protocol Overview
16.1.1 Introduction to Multicast
When sending information (including data, voice and video) to a small number of users in
the network, there are several ways of transmission, for instance, the unicast method that
establish a separate data transmission channel for each user or the broadcast method
sending information to all users in the network regardless of whether they need the
information or not. Suppose 200 users in a network need to receive the same information,
traditionally, the unicast method is employed to sends the same information 200 times to
ensure users requiring the data can get what they need; or the information is broadcasted
throughout the network so that users requiring the data can obtain what they need directly
from the network. Both two methods waste a large amount of precious bandwidth
resource, and the broadcast method is unfavorable to the security of the information or
keep it secret.
The advent of IP multicast technology solved this problem. Multicast source sends the
information only once, and the multicast routing protocol create a tree route for the
multicast packet; the information being transferred will start duplicating and distribution in
the fork as far as possible. This way, the information can be sent to each user requiring it
accurately and efficiently.
It should be noted that the multicast source is not necessarily a member of the multicast
group. When sending data to some multicast group, the sender itself is not necessarily a
receiver of that group. Multiple sources are allowed to send packets to the same multicast
group at the same time. There may be routers not support multicast in the network.
Multicast routers can transfer the multicast packets encapsulated in unicast IP packets in
tunnel mode to the neighbor multicast routes, the neighbor multicast routers will strip the
unicast IP head can continue multicast transmission. This way, large modification to the
network structure can be avoided. The major benefits of multicast are:
1) Improved efficiency and reduced network traffic and server/CPU load.
2) Improved performance and reduced unnecessary traffic.
3)
Distributed application: enabling multiple points application.