Инструкции По Установке для 3com S7906E

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The source-specific multicast (SSM) model and the any-source multicast (ASM) model are two opposite 

models. Presently, the ASM model includes the PIM-DM and PIM-SM modes. The SSM model can be 

implemented by leveraging part of the PIM-SM technique. 

The SSM model provides a solution for source-specific multicast. It maintains the relationships between 

hosts and routers through IGMPv3. 

In actual application, part of the PIM-SM technique is adopted to implement the SSM model. In the SSM 

model, receivers know exactly where a multicast source is located by means of advertisements, 

consultancy, and so on. Therefore, no RP is needed, no RPT is required, there is no source registration 

process, and there is no need of using the multicast source discovery protocol (MSDP) for discovering 

sources in other PIM domains. 

Compared with the ASM model, the SSM model only needs the support of IGMPv3 and some subsets 

of PIM-SM. The operation mechanism of PIM-SSM can be summarized as follows: 

z 

Neighbor discovery 

z 

DR election 

z 

SPT building 

PIM-SSM uses the same neighbor discovery mechanism as in PIM-DM and PIM-SM. Refer to 

. 

PIM-SSM uses the same DR election mechanism as in PIM-SM. Refer to 

. 

Whether to build an RPT for PIM-SM or an SPT for PIM-SSM depends on whether the multicast group 

the receiver is to join falls in the SSM group range (SSM group range reserved by IANA is 232.0.0.0/8).  

Figure 1-9 SPT establishment in PIM-SSM