MPLS-Enabled Applications: Emerging Developments and New Technologies

6.6. MPLS FAST REROUTE

A key attraction of P2MP LSPs signaled using RSVP is that MPLS fast reroute can be used for traffic protection, giving low failover times. In contrast, in normal IP multicast, the failover mechanisms are relatively slow (on the order of seconds), which is unacceptable for applications such as real-time video. In the Protection and Restoration chapter (Chapter 3), the following variants of fast reroute were described in the context of point-to-point LSPs:

• Link protection

• Node protection

In principle, either of these variants could be used in the point-to-multipoint case. The most straightforward case, for implementation and operations, is the link protection case, because the overall topology of the P2MP LSP in terms of the location of branch nodes remains unchanged. In this case, the task of protecting sub-LSPs related to P2MP LSPs is the same as that involved in protecting normal point-to-point LSPs. In the node protection case, the protection paths end downstream of the next-hop node that is being protected, which would result in the location of branch points changing if the node being protected is a branch node. In the facility protection schemes, where a single bypass tunnel protects multiple LSPs, the same bypass tunnel can be used to protect point-to-point LSPs and sub-LSPs of P2MP LSPs. This is illustrated in Figure 6.8. In the figure, there is a P2MP whose ingress is PE1 and whose egress points are PE3, PE4 and PE5. There is also a point-to-point ...