SNR S2989G-48TX [251/553] Multicast address

S2989G-24TX Operation Manual

Chapter 5 Multicast Protocol Related Configuration

4-26

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

1. Optimize performance: reduce redundant traffic

1. Distributed application: Enable Multipoint Application

5.1.2

Multicast Address

The destination address of Multicast message uses class D IP address with range

from 224.0.0.0 to 239.255.255.255. D class address can not appear in the source IP

address field of an IP message. In the process of Unicast data transmission, the

transmission path of a data packet is from source address routing to destination address,

and the transmission is performed with hop-by-hop principle. However, in IP Multicast

environment, the destination addresses is a group instead of a single one, they form a

group address. All message receivers will join in a group, and once they do, the data

flowing to the group address will be sent to the receivers immediately and all members in

the group will receive the data packets. The members in a Multicast group are dynamic,

the hosts can join and leave the Multicast group at any time.

Multicast group can be permanent or temporary. Some of the Multicast group

addresses are assigned officially; they are called Permanent Multicast Group. Permanent

Multicast Group keeps its IP address fixed but its member structure can vary within. The

member amount of Permanent Multicast Group can be arbitrary, even zero. The IP

Multicast addresses which are not kept for use by Permanent Multicast Group can be

utilized by temporary Multicast groups.

224.0.0.0 ～ 224.0.0.255 are reserved Multicast addresses (Permanent Group

Address), address 224.0.0.0 is reserved but not assigned, and other addresses are used