Graph theoretic approaches for routing and wavelength assignment of scheduled lightpath demands in WDM optical networks

In WDM optical networks, depending on the offered services the service provider will have precise information for some traffic demands such as the number of required lightpaths and the instants at which these lightpaths must be set-up and torn-down. These types of traffic demands are called as scheduled lightpath demands (SLDs). It may so happen that in a given set of SLDs, some of the demands are not simultaneous in time, and hence the same network resource could be used to satisfy several demands at different times. In this paper we develop two complementary algorithms-independent sets algorithm (ISA) and time window algorithm (TWA), based on circular arc graph theory, which respectively capture time-disjointness or time-overlap that could exist among SLDs. These two algorithms are complementary in the sense that, ISA divides the set of SLDs into subsets of time-disjoint demands, whereas, TWA divides the set of SLDs into subsets of time-overlapping demands; before routing them. We conduct extensive simulation experiments on ARPANET, USANET, mesh 8 times 8, mesh 10 times 10, and mesh 12 times 12 networks. In simulation experiments, we consider two different cases: 1) non-blocking case: where the number of wavelengths on each link is set to infinity and 2) blocking case: where the number of wavelengths on each link is set to a certain number. We compare and evaluate the algorithms based on the number of wavelengths required, number of reused wavelengths, average call acceptance ratio, and the reuse factor: the ratio of reused wavelengths to the sum of number of wavelengths used and the reused wavelengths. The numerical results obtained from simulation experiments indicate that TWA reuses significant number of wavelengths (reuse factor up to 53%) followed by ISA (reuse factor up to 14%). By reusing the wavelengths these algorithms reduce the total number of wavelengths required, and hence increase the average call acceptance ratio. Algorithm TWA performs better than - - ISA w.r.t. all parameters except the number of wavelengths required. Further, we observe that as the size of the network increases the number of reused wavelengths for TWA increases