H3C Technologies H3C S3100 Series Switches - Manual (Page 228)

Operation Manual – Multicast
H3C S3100-52P Ethernet Switch Chapter 1 Multicast Overview
1-1
Chapter 1 Multicast Overview
1.1 Multicast Overview
With development of networks on the Internet, more and more interaction services
such as data, voice, and video services are running on the networks. In addition,
services highly dependent on bandwidth and real-time data interaction, such as
e-commerce, web conference, online auction, video on demand (VoD), and
tele-education have come into being. These services have higher requirements for
information security, legal use of paid services, and network bandwidth.
In the network, packets are sent in three modes: unicast, broadcast and multicast. The
following sections describe and compare data interaction processes in unicast,
broadcast, and multicast.
1.1.1 Information Transmission in the Unicast Mode
In unicast, the system establishes a separate data transmission channel for each user
requiring this information, and sends separate copy information to the user, as shown in
Figure 1-1:
Server
Unicast
User A
User B
User C
User D
User E
Server
Unicast
Server
Unicast
User A
User B
User C
User D
User E
e
Figure 1-1
Information transmission in the unicast mod
Assume that users B, D and E need this information. The source server establishes
transmission channels for the devices of these users respectively. As the transmitted
traffic over the network is in direct proportion to the number of users that receive this
information, when a large number of users need this information, the server must send
many pieces of information with the same content to the users. Therefore, the limited
bandwidth becomes the bottleneck in information transmission. This shows that unicast
is not good for the transmission of a great deal of information.