A Taboo-based search algorithm to enhance Multicast Routing Under Multiple Additive Constraints Abdelfettah Belghith * , Adel Ben Mnaouer † , Naouel Ben Ali * * HANA Research Group, ENSI, University of Manouba, Tunis, Tunisia † ICT Dept., University of Trinidad and Tobago, Trinidad and Tobago Email: {abdelfattah.belghith,naouel.benali}@ensi.rnu.tn adel.mnaouer@utt.edu.tt Abstract— The fulfilment of guaranteed multiple criteria based quality of service (QoS) for Multimedia applications servicing multiple subscribers is known to be a NP complete problem. Moreover, finding the multicast graph respecting the defined QoS requirements and minimizing network resources is also a NP- complete optimization task. The well-known greedy algorithm Mamcra, proposed in the literature, computes the set of shortest paths from a source to all destination, and then reduces this set to an efficient set of multicast routes, without compromising the requested level of QoS. A closer look at Mamcra shows that it does not exploit further simple but possible reductions of the multicast sub-graph. In this paper, we propose a taboo search algorithm, named TabooQMR, that is augmented by some meta-heuristics to improve the multicast sub-graph computed by the greedy algorithm Mamcra, and leading to a considerable improvement, as demonstrated by the simulation results. I. I NTRODUCTION Recent, emerging multicast applications such as audio/video conferencing, video on demand, IP-telephony, etc. . . usually have Quality of Service (QoS) requirements, which may include bandwidth, bounded delay, jitter and loss rate. Several IP multicast techniques have been proposed to support point- to-multipoint communications by sharing link resources, a technique that usually leads to a reduction in network resource consumption. Almost all of these techniques are based on IP multicast routing protocols, which use shortest path tree algorithms based on a single metric, typically delay or hop count. However, today’s multicast applications require the optimization of more than one metric. In response to this requirement efficient multi-constrained QoS routing is a dire necessity. QoS routing is a scheme under which flow paths are attributed by taking into account flow requirements and using some knowledge of network resource availability. Considering a single metric, one way of achieving multicast source routing is by forwarding packets over the shortest path tree. When the overall cost of the tree must be minimized, the problem must be tackled differently. Determining the minimal cost multicast tree for a multicast group corresponds to the Minimum Steiner Tree problem which is shown to be NP-complete [11]. Constructing trees or sub-graphs satisfying multiple QoS requirements, is equivalent to adding another dimension to the multicast routing problem. Even in the unicast case, multi- constrained QoS Routing is known to be NP-complete. It has been extensively studied by the research community. In [17] an overview of the main proposed QoS routing algorithms which try to found a path between a source and a destination node that satisfies a set of constraints, is given. For the multicast case, a number of QoS routing algorithms based on single, dual and multiple metrics have been proposed. Single metric QoS multicast routing algorithms have been pro- posed, considering cost only, in [22], [2], [23], and considering delay only, in [6], [12]. Dual metric based routing algorithms have been proposed for the following combinations: cost-delay in [15], [21], [10] and delay-jitter in [20], [23]. With regards to the multi-constraint multicast routing prob- lem involving multiple QoS metrics, few algorithms have been proposed due to the complexity of this problem. Multicast Adaptive Multiple Constraints Routing Algorithm (Mamcra) [14] attempts to find multiple QoS constraint paths to a multicast group in an efficient way that does not guarantee optimality. Mamcra proposes a greedy heuristic approach to solve this optimality problem. However, the quality of the given approximation isn’t proved and the shortcoming of the proposed greedy algorithm can be improved. Multi-constrained multicast routing problem in essence be- longs to the set of multi-objective optimization problems which is the subject of our study in this paper. In this regards, we focus, essentially, on optimizing the set of available shortest paths to solve the multiple constraint QoS multicast routing problem. The set of paths can be obtained by the Samcra [18] or by any other multiple constraint QoS unicast routing algorithm. Considering the drawbacks of Mam- cra’s greedy algorithm, we propose the Taboo QoS Multicast Routing (Taboo-QMR) method, that is a global optimization scheme based on a meta-heuristic approach (namely taboo search algorithm) to provide a solution which can approach the optimal one. This paper is organized as follows. Section II specifies