<title>Benefits of multicasting in all-optical networks</title>

Abstract

All-optical WDM networks are fast becoming the natural choice for future backbone. In this paper, we establish the efficiency of multicasting over unicasting in all-optical WIDM networks, assess the usefulness of wavelength conversion for multicasting, and explore the issues related to the splitting (or copying) capability of the nodes. The comparison between multicasting and unicasting is based on the number of wavelengths as well as the amount of bandwidth required for a given set of multicasting sessions. For each multicasting session, a source-specific multicasting forest (or trees) is constructed first, taking into account the sparse splitting capability of the nodes in the network. Then, each multicasting tree is partitioned into segmenis according to the sparse wavelength conversion capability of the nodes on the tree such that each segment needs to be assigned the same wavelength. Simulation results obtained for a practical network such as NSFNET and randomly generated networks show that multicasting can reduce both the bandwidth consumed and the number of wavelengths required by as much as 50% or more when the size (i.e. the number of destinations) of each multicasting session is reasonably large. Such a reduction due to multicasting is not affected much by the wavelength conversion capability, the number of multicasting sessions and the size of the networks whose topology is more or less random. The results have also shown that sparse splitting can be nearly as effective as full splitting for multicasting.

Reliable multicast routing for software-defined networks

“…Compared with unicast, multicast can effectively reduce the bandwidth consumption in backbone networks by around 50% [4], because it exploits a tree, instead of disjoint paths, to connect the source and destinations; thus, it avoids unnecessary traffic duplication in intermediate nodes. For multimedia traffic, previous studies [5] further pointed out that multicast is able to release the load in the network links and I/O at the video servers, while VCR-like interactivity required by videoon-demand services can also be supported in multicast [5], [6].…”

Light-hierarchy: the optimal structure for multicast routing in WDM mesh networks

“…To support multicast in WDM networks, the network nodes should be equipped with optical power splitters, which is capable of splitting the incoming light signal into all the outgoing ports. Thus they are called multicast capable nodes (MC) [4]. However, if a light signal is split into m copies, the signal power of one copy will be reduced to or less than 1/m of the original signal power [5].…”

“…As proved in [8], it is a Steiner problem and NPhard to find the light-tree with the optimal wavelength channel cost. In spare splitting WDM networks [4], only a small ratio of nodes are MC nodes while the rest are MI nodes. In this case, the light-tree [7] structure was still thought to be optimal for all-optical multicast routing based on the false assumption that the MI nodes could not be traversed twice on the same wavelength.…”

“…Hence, the drawbacks of light splitters yield to the employment of TaC (Tap and Continue) [6] functionality on all the network nodes, which is able to tap into the light signal for local consumption and forward it to only one output port. The nodes only equipped with TaC capacity are called multicast incapable nodes (MI) [4].…”

Light-hierarchies: Optimal multicast routes under optical constraints

“…To comput e multicast routes, most of the multicast algorithms propose to use ''light-trees'' or a set of trees called ''lightforest'' [3,4,7,11,12]. More recently, "light-trails" were also proposed [14] to decrease the network resource consumption using non elementary light-paths.…”