CAM02-5: On the Number of MPLS LSPs using Multicast Tree Aggregation

Multicast tree aggregation is an efficient proposition that can solve the multicast forwarding state scalability problem. Existing works on tree aggregation have focused on developing and simulating protocols that build trees dynamically. However, the underlying problem of the impact of the tree construction algorithm on the performance of the protocols remains untouched. In this paper, we propose a study on the number of trees that need to be configured in a domain depending on the tree construction algorithm. We ran extensive simulations on several real domains and with different tree construction algorithms. Our results show that for a given set of multicast groups, even when this set includes all the possible groups, the number of trees that need to be configured is small. This allows a network administrator to configure off-line all these trees in order to maintain a stable set of trees and to have knowledge of the routes used by the multicast packets. Knowing the set of all the possible trees is also useful to determine the best subset to configure and to give an upper bound of the number of different trees.