Failure protection is desirable for multicast traffic, whether
signaled via PIM or mLDP. Different mechanisms are suitable for
different use-cases and deployment scenarios. This document
describes the architecture for global protection (aka multicast live-
live) and for local protection (aka fast-reroute).
The general methods for global protection and local protection using
alternate-trees are dependent upon the use of Maximally Redundant
Trees. Local protection can also tunnel traffic in unicast tunnels
to take advantage of the routing and fast-reroute mechanisms
available for IP/LDP unicast destinations.
The failures protected against are single link or node failures.
While the basic architecture might support protection against shared
risk group failures, algorithms to dynamically compute MRTs
supporting this are for future study.