PIM Overview

PIM SSM builds shortest-path trees (SPTs) rooted at the source immediately because in SSM, the router closest to the interested receiver host is informed of the unicast IP address of the source for the multicast traffic. That is, PIM SSM bypasses the RP connection stage through shared distribution trees, as in PIM sparse mode, and goes directly to the source-based distribution tree.

Internet Protocol Television (IPTV) is a service where digital TV signal data is delivered by using Internet protocol (IP). IPTV service networks typically use PIM-SSM as the multicast routing protocol which has the following characteristics:

  • Source specific host membership report for a particular multicast group. IGMPv3 allows a host to describe specific sources from which it would like to receive data.

  • PIM shortest path forwarding. Source-specific host report for a particular multicast group and initiating PIM (S,G) joins directly and immediately as result.

  • No shared tree forwarding. In order to achieve global effectiveness of SSM, all networks must agree to restrict data forwarding to source trees for some recognized group range. The address range has been allocated by IANA for use by source specific multicast (SSM).

Supported Platforms

Not all features are necessarily supported on each hardware platform. Refer to the Platform Guide for the features and the sub-features that are or are not supported by each platform.