The possibility of flexibly assigning spectrum resources with channels of different sizes greatly improves the spectral efficiency of optical networks, but can also lead to unwanted spectrum fragmentation. We study this problem in a scenario where traffic demands are categorized in two types (low or high bit-rate) by assessing the performance of three allocation policies. Our first contribution consists of exact Markov chain models for these allocation policies, which allow us to numerically compute the relevant performance measures. However, these exact models do not scale to large systems, in the sense that the computations required to determine the blocking probabilities—which measure the performance of the allocation policies—become intractable. In order to address this, we first extend an approximate reduced-state Markov chain model that is available in the literature to the three considered allocation policies. These reduced-state Markov chain models allow us to tractably compute approximations of the blocking probabilities, but the accuracy of these approximations cannot be easily verified. Our main contribution then is the introduction of reduced-state imprecise Markov chain models that allow us to derive guaranteed lower and upper bounds on blocking probabilities, for the three allocation policies separately or for all possible allocation policies simultaneously.
Routing and Spectrum Allocation (RSA) algorithms are used to compute both routing and spectrum allocation of connection demands in Elastic Optical Networks (EONs). A number of RSA algorithms have been proposed. Their performance is usually measured in terms of overall blocking probability. In this paper the authors pursue an additional performance indicator that is introduced to quantify the level of fairness (or unfairness) experienced by two types of demands, each type requiring a distinct spectrum bandwidth size. A new RSA algorithm is also proposed to jointly control blocking and fairness by partitioning the spectrum into dedicated and shared bands. Simulation results are used to estimate the trade-off between the blocking probability experienced by all demands and the level of fairness as it is achieved by a total of six RSA algorithms. Elastic Optical Networks (EONs) have the potential to improve the fiber spectrum utilization by allocating spectrum resources to multiple traffic requests proportionally to the amount of carried traffic. However, achieving high spectrum utilization in this elastic scenario is hindered by the resulting spectrum fragmentation. A number of studies have addressed and made attempts to mitigate spectrum fragmentation. Most of these studies are based on simulation techniques and target the overall blocking probability experienced by the offered traffic requests due to the lack of available spectrum resources. Some studies have also shown that blocking probability in EON can be uneven, i.e., high-rate circuit requests are more likely to be blocked when compared to low-rate requests due to the shortage of contiguously available spectrum resources. The contribution of this paper is to extend an existing Markov Chain (MC) model previously proposed by the authors to quantify blocking probability in a two-service elastic fiber link. The model extension accounts for a self-limited and partial sharing of the fiber spectrum to accommodate the two types of service. The MC model is used to quantify both the blocking probability and its fairness across the two types of service, documenting how the EON uneven blocking behavior can be significantly mitigated by performing partial (as opposed to full) sharing of the fiber spectrum. Routing and Spectrum Assignment (RSA) algorithms play a key role in achieving good spectrum utilization in Elastic Optical Networks (EONs). A metric that is often used to evaluate RSA algorithms is the overall blocking probability experienced by circuit requests. In a previous study, the authors introduced an additional performance indicator that can be used to quantify the level of fairness (or lack thereof) experienced by two types of service requests, each type requiring a distinct amount of reserved spectrum. Their study is extended in this paper to account for circuit requests with uneven arrival rates.