Resource-partitioned spectrum assignment to realize efficient multicasting for flexible grid optical networks

Abstract With the increasing demand of some novel point-to-multi-point services, such as live video delivering and interactive distance learning, efficient multicasting is highly desirable in flexible grid optical networks (FGONs). Thus, many sophisticated multicast-enabled routing and resource allocation algorithms have been proposed to realize efficient multicasting in FGONs. These algorithms, known as multicast routing and spectrum assignment (MRSA) algorithms, optimized the light-trees and the allocated spectrum resources for multicast services in FGONs. But, most of them ignored some small-sized, isolated, and un-occupied spectrum bands, which are remained after multicast services being accommodated. Due to the continuity and the contiguity constraints in service accommodation, these remained spectrum bands can hardly be allocated to subsequent multicast services and are thus known as spectrum fragments. Their existence and accumulation may exhaust available spectral resources and affect the networking performance (e.g. service blocking performance) for the multicast traffic in FGONs. In this way, the efficiency of FGONs in supporting multicast traffic may be greatly deteriorated. Therefore, the spectrum fragments generated in accommodating multicast services has become an important issue in FGONs. In this paper, we propose a resource-partitioned interval-maximized (RPIM) MRSA algorithm to restrain the generation of spectrum fragments for the multicast traffic in FGONs. The proposed RPIM MRSA algorithm does not utilize the metric, “cut”, to reduce spectrum fragments via avoiding splitting the whole spectrum band into too many band pieces as in fragmentation-aware MRSA algorithms. Instead, the proposed RPIM MRSA algorithm partitions the spectrum resources on each sought light-tree into several elastic groups according to the types of multicast services, and maximizes the group interval between two adjacent groups on the sought light-trees. Since the spectrum resources in each group can always be utilized by the multicast services of the same type, the proposed algorithm restricts the generation of spectrum fragments in group intervals. In this way, the proposed RPIM MRSA algorithm can remarkably reduce spectrum fragments generated in accommodating multicast services. Note that, different from previous group-based algorithms, the proposed RPIM algorithm allows one elastic group for the multicast services of a certain type to contain different amount of spectrum resources on different light-trees. This helps guarantee the flexibility in constructing elastic groups on diverse light-trees. Additionally, the proposed RPIM MRSA algorithm maximizes the group intervals on the sought light-trees, which helps reserve more vacant spectrum resources between two adjacent groups on the light-trees. Since these vacant spectrum resources can be merged into their adjacent groups if needed, the proposed algorithm can reduce not only the spectrum fragments generated in group intervals but also the blocked multicast services in groups by maximizing group intervals on the light-trees. Simulation results verify that the proposed RPIM algorithm can realize efficient multicasting with significantly reduced spectrum fragments and low service blocking probability in FGONs.