QTECH QSW-3400 Инструкция по настройке - Manual (Page 277)

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Chapter 36 IPv4 Multicast Protocol
36.1 IPv4 Multicast Protocol Overview
This chapter will give an introduction to the configuration of IPv4 Multicast Protocol.
36.1.1 Introduction to Multicast
Various transmission modes can be adopted when the destination of packet (including data,
sound and video) transmission is the minority users in the network. One way is to use Unicast
mode, i.e. to set up a separate data transmission path for each user; or, to use Broadcast
mode, which is to send messages to all users in the network, and they will receive the
Broadcast messages no matter they need or not. For example, if there are 200 users in a
network who want to receive the same packet, then the traditional solution is to send this
packet for 200 times separately via Unicast to guarantee the users who need the data can get
all data wanted, or send the data in the entire domain via Broadcast. Transferring the data in
the whole range of network .The users who need these data can get directly from the network.
Both modes waste a great deal of valuable bandwidth resource, and furthermore, Broadcast
mode goes against the security and secrecy.
The emergence of IP Multicast technology solved this problem in time. The Multicast source
only sends out the message once, Multicast Routing Protocol sets up tree-routing for Multicast
data packet, and then the transferred packet just starts to be duplicated and distributed in the
bifurcate crossing as far as possible. Thus the packet can be sent to every user who needs it
accurately and effectively.
It should be noticed that it is not necessary for Multicast source to join in Multicast group. It
sends data to some Multicast groups, but it is not necessarily a receiver of the group itself.
There can be more than one source sending packets to a Multicast group simultaneously.
There may exist routers in the network which do not support Multicast, but a Multicast router
can encapsulate the Multicast packets into Unicast IP packets with tunnel mode to send them
to the Multicast router next to it, which will take off the Unicast IP header and continue the
Multicast transmission process, thus a big alteration of network structure is avoided. The
primary advantages of Multicast are:
1. Enhance efficiency: reduce network traffic, lighten the load of server and CPU
2. Optimize performance: reduce redundant traffic
3. Distributed application: Enable Multipoint Application
36.1.2 Multicast Address
The destination address of Multicast message uses class D IP address with range from