3com 5500-ei pwr Instrução De Instalação

 

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All receivers interested in the same information form a multicast group. Multicast groups are not 

subject to geographic restrictions. 

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A router that supports Layer 3 multicast is called multicast router or Layer 3 multicast device. In 

addition to providing multicast routing, a multicast router can also manage multicast group 

members.  

For a better understanding of the multicast concept, you can use the analogy of a transmission of TV 

programs, as shown in 

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

1 

A TV station transmits a TV program 
through a television channel.  

A multicast source sends multicast data to a 
multicast group.  

2 

A user tunes the TV set to the channel. 

A receiver joins the multicast group. 

3 

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 sends to the multicast 
group.  

4 

The user turns off the TV set.  

The receiver leaves the multicast group.  

 

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A multicast source does not necessarily belong to a multicast group. Namely, a multicast source is 

not necessarily a multicast data receiver. 

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A multicast source can send data to multiple multicast groups at the same time, and multiple 

multicast sources can send data to the same multicast group at the same time.  

 

Two notations are commonly used in multicast: 

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(*, 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. 

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(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 “

”.