H3C Technologies H3C S7500E Series Switches - Manual (Page 147)

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receivers for that multicast group. If not, the router continues to forward the prune message to
its upstream router.
Multicast source registration
The purpose of multicast source registration is to inform the RP about the existence of the
multicast source.
Figure 6-6 Multicast source registration
Source
Server
Host A
Host B
Host C
Receiver
Receiver
Multicast packets
SPT
Join message
Register message
RP DR
As shown in Figure 6-6 , the multicast source registers with the RP as follows:
1) When the multicast source S sends the first multicast packet to multicast group G, the DR
directly connected with the multicast source, upon receiving the multicast packet,
encapsulates the packet in a PIM register message, and sends the message to the
corresponding RP by unicast.
2) When the RP receives the register message, it extracts the multicast packet from the
register message and forwards the multicast packet down the RPT, and sends an (S, G)
join message hop by hop toward the multicast source. Thus, the routers along the path
from the RP to the multicast source constitute an SPT branch. Each router on this branch
generates an (S, G) entry in its forwarding table. The DR at the multicast source side is the
root, while the RP is the leaf, of the SPT.
3) The subsequent multicast data from the multicast source travels along the established SPT
to the RP, and then the RP forwards the data along the RPT to the receivers. When the
multicast traffic arrives at the RP along the SPT, the RP sends a register-stop message to
the source-side DR by unicast to stop the source registration process.