Avoidance of multicast incapable branching nodes for multicast routing in WDM networks

In this articlewestudy themulticast routing problem in all-opticalWDMnetworks under the spare light splitting constraint. To implement a multicast session, several light-trees may have to be used due to the limited fanouts of network nodes. Although many multicast routing algorithms have been proposed in order to reduce the total number of wavelength channels used (total cost) for a multicast session, the maximum number of wavelengths required in one fiber link (link stress) and the end-to-end delay are two parameters which are not always taken into consideration. It is known that the shortest path tree (SPT) results in the optimal end-to-end delay, but it can not be employed directly for multicast routing in sparse light splitting WDM networks. Hence, we propose a novel wavelength routing algorithm which tries to avoid the multicast incapable branching nodes (MIBs, branching nodes without splitting capability) in the shortest-path-based multicast tree to diminish the link stress. Good parts of the shortest-path-tree are retained by the algorithm to reduce the end-to-end delay. The algorithm consists of tree steps: (1) aDijkstraPro algorithmwith priority assignment and node adoption is introduced to produce a SPT with up to 38% fewer MIB nodes in the NSF topology and 46% fewerMIB nodes in the USA Longhaul topology, (2) critical articulation and deepest branch heuristics are used to process the MIB nodes, (3) a distance-based light-tree reconnection algorithm is proposed to create the multicast light-trees. Extensive simulations demonstrate the algorithm's efficiency in terms of link stress and end-to-end delay

Algorithms for Provisioning Survivable Multicast Sessions Against Link Failures in Mesh Networks

In this paper, we investigate new algorithms for efficiently establishing a multicast session in a mesh network while protecting the session from a link failure, e.g., a fiber cut in an optical network. First, we study these algorithms for protecting a multicast tree in a mesh network and then extend them for dynamic provisioning of survivable multicast connections where connections come and go. Although we study these algorithms in an optical WDM context, the approaches are applicable to other contexts as well, such as SONET or Gigabit Ethernet (GBE). One of the new algorithms, IMPROVED SEGMENT, protects each segment in the primary tree. The other new algorithm, IMPROVED PATH, discovers backup resources for protecting each path, from source to destination, in the tree. We find that IMPROVED SEGMENT performs significantly better (around 14 % in terms of resource utilization in a typical wide-area mesh network) than a simple-minded segment-protection algorithm, called SEGMENT, for provisioning a survivable multicast tree. We also find that our Algorithm IMPROVED PATH performs marginally better than a simple-minded path-protection algorithm, called PATH. We also study the application of these algorithms to dynamic traffic comprising of unicast, multicast, and broadcast connections. For dynamic connection provisioning, IMPROVED PATH is found to perform significantly better than PATH, and IMPROVED SEGMENT is found to perform significantly better than SEGMENT. And, among all these algorithms, IMPROVED PATH is found to perform the best

Cost Bounds of Multicast Light-trees in WDM Networks

International audienceThe construction of light-trees is one principal subproblem for multicast routing in sparse splitting Wavelength Division Multiplexing (WDM) networks. Due to the light splitting constraint and the absence of wavelength converters, several light-trees may be required to establish a multicast session. However, the computation of optimal multicast light-trees is NP-hard. In this paper, we study the wavelength channel cost (i.e., total cost) of the light-trees built for a multicast session. An equal cost of 1 unit hop-count cost is assumed over all the fiber links in the network. We prove that the total cost of a multicast session is tightly lower limited to K and upper bounded to (1) K(N −K) when K < N/2 ; (2) (N^2 −1)/4 or (N^2)/4 respectively when K ≥ N/2 and N is odd or even, where K is the number of destinations in the multicast session and N is the number of nodes in the network. Classical sparse splitting multi- cast routing algorithms such as Reroute-to-Source and Member-Only [3] also follow these bounds. And particularly in WDM rings, the optimal multicast light-tree has a cost inferior to N − ⌈ N/( K+1) ⌉