Assert, Ssm model implementation in pim – H3C Technologies H3C SecPath F1000-E User Manual
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abstracts the multicast data and sends the multicast data down the RPT to the DRs at the receiver side. The
RP acts as a transfer station for all multicast packets. The whole process involves three issues:
•
The DR at the source side and the RP need to implement complicated encapsulation and
de-encapsulation of multicast packets.
•
Multicast packets are delivered along a path that may not be the shortest one.
•
When the multicast traffic increases, a great burden is added to the RP, increasing the risk of failure.
To solve the issues, PIM-SM allows an RP or the DR at the receiver side to initiate an SPT switchover
process:
1.
The RP initiates an SPT switchover process
Upon receiving the first multicast packet, the RP sends an (S, G) join message hop by hop toward the
multicast source to establish an SPT between the DR at the source side and the RP. The subsequent
multicast data from the multicast source travels along the established SPT to the RP.
NOTE:
For more information about the SPT switchover initiated by the RP, see
.
2.
The receiver-side DR initiates an SPT switchover process
Upon receiving the first multicast packet, the receiver-side DR initiates an SPT switchover process, as
follows:
•
The receiver-side DR sends an (S, G) join message hop by hop toward the multicast source. When
the join message reaches the source-side DR, all the routers on the path have installed the (S, G)
entry in their forwarding table, and thus an SPT branch is established.
•
When the multicast packets travel to the router where the RPT and the SPT deviate, the router drops
the multicast packets received from the RPT and sends an RP-bit prune message hop by hop to the
RP. Upon receiving this prune message, the RP sends a prune message toward the multicast source
(suppose only one receiver exists). Thus, SPT switchover is completed.
•
Finally, multicast data is directly sent from the source to the receivers along the SPT.
PIM-SM builds SPTs through SPT switchover more economically than PIM-DM does through the “flood
and prune” mechanism.
Assert
PIM-SM uses a similar assert mechanism as PIM-DM does. For more information, see
SSM Model Implementation in PIM
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.