3Com Switch 8800 Advanced Software V5 Configuration Guide

PIM Overview 573
Figure 181 Relationship between BSR admin-scope regions and the global scope zone in
group address ranges
In Figure 181, the group address ranges of admin-scope-scope regions BSR1 and
BSR2 have no intersection, whereas the group address range of BSR3 is a subset of
the address range of BSR1. The group address range of the global scope zone
covers all the group addresses other than those of all the BSR admin-scope
regions. That is, the group address range of the global scope zone is G-G1-G2. In
other words, there is a supplementary relationship between the global scope zone
and all the BSR admin-scope regions in terms of group address ranges.
Relationships between BSR admin-scope regions and the global scope zone are as
follows:
■ The global scope zone and each BSR admin-scope region have their own C-RPs
and BSR. These devices are effective only in their respective admin-scope
regions. Namely, the BSR election and RP election are implemented
independently within each admin-scope region.
■ Each BSR admin-scope region has its own boundary. The multicast information
(such as C-RP-Adv messages and BSR bootstrap messages) can be transmitted
only within the domain.
■ Likewise, the multicast information in the global scope zone cannot enter any
BSR admin-cope region.
■ In terms of multicast information propagation, BSR admin-scope regions are
independent of one another and each BSR admin-scope region is independent
of the global scope zone, and no overlapping is allowed between any two BSR
admin-scope regions.
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
BSR 3
G3 address
BSR 2
G2 address
BSR 1
G1 address
Global
G-G1-G2 address