XGS-5240-Series User Manual

Configuration Guide of XGS-5240-Series
42-4
Chapter 42 IPv4 Multicast Protocol
42.1 IPv4 Multicast Protocol Overview
This chapter will give an introduction to the configuration of IPv4 Multicast Protocol.
42.1.1 Introduction to Multicast
Various transmission modes can be adopted when the destination of packet (includi
ng data, sound and video) transmission is the minority users in the network. One way i
s 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, a
nd 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 tr
aditional solution is to send this packet for 200 times separately via Unicast to guarant
ee the users who need the data can get all data wanted, or send the data in the entir
e domain via Broadcast. Transferring the data in the whole range of network .The user
s who need these data can get directly from the network. Both modes waste a great d
eal 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 Multica
st source only sends out the message once, Multicast Routing Protocol sets up tree-ro
uting for Multicast data packet, and then the transferred packet just starts to be duplica
ted 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 t
he group itself. There can be more than one source sending packets to a Multicast gro
up simultaneously. There may exist routers in the network which do not support Multica
st, 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 th
e Unicast IP header and continue the Multicast transmission process, thus a big alterati
on of network structure is avoided. The primary advantages of Multicast are: