Multi-step Migration of Optical Connections in Flex-grid Networks to Minimize Disruption Time

Abstract

Reconfiguration of optical connections in flex-grid networks become increasingly necessary as the arrivals and departures of optical connection requests are more dynamic. For example, optical spectrum fragmentation can be alleviated by migrating existing connections so as to eliminate, align, and merge fragmented spectrum vacancies in order to improve request acceptance. To mitigate disruptions of existing lightpaths during migration, former research applies the concept of resource dependency digraph (RDD) to allow for sequential migration of optical connections. In this paper, we argue that with this RDD approach, each connection has a quota of one migration step only, and that this one-step-quota constraint can be safely lifted in order to accomplish an even lower disruption time due to the greater degree of migration freedom. We consider the whole reconfiguration process to be composed of multiple lightpath assignment states, where the transition between two consecutive states represents a migration step. The multiple lightpath assignment states constitute a progressive advancement from the current configuration towards the desired target configuration. The approach is named Multi-step Optical Connection Migration (MOCM) and is modeled as an integer-linear program (ILP). In addition, while former works restrict parallel migrations and adopt sequential migrations to mitigate connection disruptions, we show that more parallel migrations with the one-step-quota constraint lifted in MOCM can actually further minimize disruptions.