1 International Journal of Communication Networks and Information Security (IJCNIS) Vol. 6, No. 1, April 2014 QoS-VNS-CS: QoS constraints Core Selection Algorithm based on Variable Neighborhood Search Algorithm Youssef Baddi and Mohamed DafirEch-Cherif El Kettani Information Security Research Team – ISeRT, ENSIAS Mohammed V-Souissi University,Rabat, Morocco Youssef.baddi@um5s.net.ma, dafir@um5s.net.ma Abstract:Within the development of network multimedia technology, more and more real-time multimedia applications arrive with the need to transmit information using multicast communication. Multicast IP routing is an important topic, covering both theoretical and practical interest in different networks layers. In network layer, there are several multicast routing protocols using multicast routing trees different in the literature. However PIM-SM and CBT protocols remain the most used multicast routing protocols; they propose to use a shared Core-based Tree CBT. This kind of tree provides efficient management of multicast path in changing group memberships, scalability and performance. The main problem concerning the construction of a shared tree is to determine the best position of the core. QoS-CS’s problem (QoS constraints core Selection) consists in choosing an optimal multicast router in the network as core of the Shared multicast Tree (CBT), within specified associated QoS constraints. The choice of this specific router, called RP in PIM-SM protocol and core in CBT protocol, affects the structure of multicast routing tree, and therefore influences performances of both multicast session and routing scheme. QoS-CS is an NP complete problem which needs to be solved through a heuristic algorithm: in this paper, we propose a new core Selection algorithm based on Variable Neighborhood Search algorithm and a new CMP fitness function. Simulation results show that good performance is achieved in multicast cost, end-to-end delay, tree construction delay and others metrics. Keywords: Core, QoS-VNS-CS, QoS, PIM-SM, CBT, Multicast routing, QoS-CS. 1. Introduction Many distributed real-time applications, such as audio- and video-conferencing, collaborative environments and distributed interactive simulation require simultaneous communication between groups of computers with quality of service (QoS) guarantee; these applications involve a source in sending messages to a selected group of receptors. Classic unicast and broadcast network communication is not optimal; therefore, Deering[1] proposed a technique called IP multicast routing for one-to-multiple and multiples-to- multiple communication, which entrusts the task of data duplication to the network: applications can send one copy of each packet and address it to the group of involved computers; the network takes care of message duplication to the receivers of the group. Multicast technology has become a research hotspot. Group communications on Internet are increasingly pervasive parallel to the wider acceptance of group communication applications over the Internet. Multicast IP is a bandwidth conserving technology that reduces traffic in the network, and by the many, the bandwidth consumption. Multicast communication is based on a multicast tree for data routing; multicast routing protocols are built using two kinds of multicast trees: Source Based Tree SBT and shared Core-Based Tree CBT. With Source Based Tree, a separate tree is built for each source. With a shared Core-Based Tree, one tree is built for the entire group and shared among all senders; core based trees have a significant advantage in terms of routing resources more than source-based trees in that only one routing table entry is needed for the group [2]. PIM-SM [3] and CBT [4] protocols are multicast routing protocols based in shared Core-Based multicast Tree to forward multicast packets. Construction of this kind of tree requires the selection of a center router called "Rendezvous point" RP in PIM-SM [3] protocol and Core in CBT [4] protocol; With the proliferation of existing multimedia group applications, the construction of Shared multicast tree satisfying the quality of service (QoS) requirements is becoming a problem of prime importance. Find out an optimal router as a core with Qos guarantee is known by QoS Constraints Core selection Problem. This problem is known to be an NP complete problem [1], [5], [6], which needs to be solved with a heuristic algorithm. Current implementations of the PIM-SM [3] and CBT [4] protocols decide on the Core router administratively [7], based only in priority and IP address of each candidate. This leads to high cost, high delay, and high congestion, by the many, directly impact tree structure and performance of the routing scheme of multicast. In this paper, we introduce newQoS constraints Core Selection Algorithm QoS-VNS-CS that can improve the delay and delay variation constraint in a multi-source shared Core-Based Tree. In this work we adopted a heuristic search algorithm [7] named Variable Neighborhood Search VNS [8]. This paper is organized as follows. In the next section, we describe the core selection problem. Section 3 is devoted to the description of a mathematical modeling of core selection problem. Section 4 presents the state of research of the core selection problem in the literature. Section 5 describes the proposed QoS-VNS-CS algorithm for the core selection problem. Simulation results are reported in Section 6. Finally, Section 7 provides concluding remarks. 2. Background The main role of a multicast routing protocol consists in managing multicast groups and routing multicast messages through constructed optimal multicast tree in order to reach