Information Transmission In The Multicast Mode - Huawei Quidway S3900 Series Operation Manual

Operation Manual – Multicast Protocol
Quidway S3900 Series Ethernet Switches-Release 1510
the same network need the information, the utilization ratio of the network resources is
very low and the bandwidth resources are greatly wasted.
Therefore, broadcast is disadvantageous in transmitting data to specified users;
moreover, broadcast occupies large bandwidth.

1.1.3 Information Transmission in the Multicast Mode

As described in the previous sections, unicast is suitable for networks with sparsely
distributed users, whereas broadcast is suitable for networks with densely distributed
users. When the number of users requiring information is not certain, unicast and
broadcast deliver a low efficiency.
Multicast solves this problem. When some users on a network require specified
information, the multicast information sender (namely, the multicast source) sends the
information only once. With tree-type routes established for multicast data packets
through a multicast routing protocol, the packets are duplicated and distributed at the
nearest nodes as shown in Figure 1-3:
Server
Figure 1-3 Information transmission in the multicast mode
Assume that users B, D and E need the information. To transmit the information to the
right users, it is necessary to group users B, D and E into a receiver set. The routers on
the network duplicate and distribute the information based on the distribution of the
receivers in this set. Finally, the information is correctly delivered to users B, D, and E.
The advantages of multicast over unicast are as follows:
No matter how many receivers exist, there is only one copy of the same multicast
data flow on each link.
With the multicast mode used to transmit information, an increase of the number of
users does not add to the network burden remarkably.
The advantages of multicast over broadcast are as follows:
A multicast data flow can be sent only to the receiver that requires the data.
Multicast brings no waste of network resources and makes proper use of
bandwidth.
Multicast
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1-3
Chapter 1 Multicast Overview
User A
User B
User D
User E