Constructing primary and backup explicit path Point-to-Multipoint
Label Switched Paths is important from the point of view of providing
protection switching in case the primary fails.
It is absolutely essential that the backup P2MP LSPs constructed do
not share risk with any of the links and nodes of the primary path.
In the case of inter-AS P2MP TE-LSPs or in the case of inter-sub-AS
(in the case of BGP-Confederations being deployed) P2MP TE-LSPs where
BGP confederations are deployed within an AS, such protection
switching can be provided by calculating primary and backup multicast
distribution trees (read P2MP TE-LSPs) that dont intersect with each
In this paper we propose a method by which inter-sub-AS P2MP TE-LSPs
(hence even inter-AS P2MP TE-LSPs) can be constructed by first
finding the AS level topology of the network (be it inter-AS or
inter-sub-AS within a single AS) in question and secondly to compute
the paths in such a way that they dont intersect or if necessary in
the worst case partially intersect each other. The proposed scheme is
explained with an example and subsequent discussion is done to
elucidate its benefits to multicast in particular.