3com S7906E 安装指导

 

1-5 

manage multicast group memberships on stub subnets with attached group members. A multicast 

router itself can be a multicast group member. 

For a better understanding of the multicast concept, you can assimilate multicast transmission to the 

transmission of TV programs, as shown in 

.  

Table 1-1 An analogy between TV transmission and multicast transmission 

A TV station transmits a TV program through 
a channel.  

A multicast source sends multicast data to a 
multicast group.  

A user tunes the TV set to the channel. 

A receiver joins the multicast group. 

The user starts to watch the TV program 
transmitted by the TV station via the channel. 

The receiver starts to receive the multicast data that 
the source is sending to the multicast group.  

The user turns off the TV set or tunes to 
another channel.  

The receiver leaves the multicast group or joins 
another group.  

 

Two notations are commonly used in multicast: 

z 

(*, G): Indicates a rendezvous point tree (RPT), or a multicast packet that any multicast source 

sends to multicast group G. Here “*” represents any multicast source, while “G” represents a 

specific multicast group. 

z 

(S, G): Indicates a shortest path tree (SPT), or a multicast packet that multicast source S sends to 

multicast group G. Here “S” represents a specific multicast source, while “G” represents a specific 

multicast group.  

 

For details about the concepts RPT and SPT, see PIM Configuration or IPv6 PIM Configuration in the IP 

Multicast Volume. 

 

Advantages of the multicast technique include: 

z 

Enhanced efficiency: reduces the CPU load of information source servers and network devices. 

z 

Optimal performance: reduces redundant traffic. 

z 

Distributive application: enables point-to-multipoint applications at the price of minimum network 

resources. 

Applications of the multicast technique include: