H3C S3600 Series User Manual

Operation Manual – Multicast
H3C S3600 Series Ethernet Switches-Release 1510 Chapter 7 PIM Configuration
7-9
V. Multicast source registration
In order to inform RP about the existence of multicast source S, when multicast source
S sends a multicast packet to the multicast group G, the router directly connected to S
will encapsulate the received packet into a Register packet and send it to the
corresponding RP through unicast, as shown in
Figure 7-6:
RP
Server
Multicast
User A
User B
User C
User D
User E
Source
Receiver
Receiver
Receiver
packets
Join
SPT
Join
Join
Register
Register
Figure 7-6 Diagram for SPT building in PIM-SM
When RP receives the registration information from S, it decapsulates the Register
message and forwards the multicast information to the receiver along RPT, and on the
other hand, it sends (S, G) Join messages to S hop by hop. The passed routers form a
branch of SPT. The multicast source S is the root of SPT and RP is the destination of
RP.
The multicast information sent by the multicast source S reaches RP along the built
SPT, and then RP forwards the multicast information along the built RPT.
VI. Switching from RPT to SPT
When the multicast router nearest the receiver detects that the rate of the multicast
packet from RP to the multicast group G exceeds the threshold value, it sends (S, G)
Join messages to the upper-layer router of the multicast source S. The Join message
reaches the router nearest the multicast source (namely, the first hop router) hop by
hop and all the passed routers have the (S, G) entry. As a result, a branch of SPT is
built.
Then, the last hop router sends a Prune message with the RP bit to RP hop by hop.
When RP receives the message, it reversely forwards the Prune message to the
multicast source. Thus, the multicast information stream is switched from RPT to SPT.
After the switching from RPT to SPT, the multicast information is sent from the multicast
source S to the receiver directly. Through the switching from RPT to SPT, PIM-SM can
build SPT in a more economical way than PIM-DM.

H3C S3600 Series Specifications

General

Brand	H3C
Model	S3600 Series
Category	Switch
Language	English