3com WX3000 User Manual

 

1-3 

Figure 1-2 Information transmission in the broadcast mode 

Server

Host A

Host B

Host C

Host D

Host E

Packets for all the network

 

 

Assume that Hosts B, D, and E need the information. The source server broadcasts this information 

through routers, and Hosts A and C on the network also receive this information.  

As we can see from the information transmission process, the security and legal use of paid service 

cannot be guaranteed. In addition, when only a small number of users on 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 specific users; moreover, broadcast 

occupies large bandwidth.  

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 

multicast distribution trees established for multicast data packets through multicast routing protocols, 

the packets are duplicated and distributed at the nearest nodes, as shown in 

: