Raul C. Almeida

Performance analysis of an optical packet switch with shared parametric wavelength converters

Wavelength conversion capability has been shown to significantly improve the blocking performance of all-optical networks. In order to transport payloads that may be of different bit-rates and modulation formats, a transparent wavelength conversion method is desirable. Recently, parametric wavelength converters, that are capable of multi-channel wavelength conversion for heterogeneous optical services, have been experimentally demonstrated for optical circuits. In this letter, we analyse the performance of an asynchronous optical packet-switch (OPS) architecture that exploits such devices. A sensitivity analysis of the number of converters, as a function of the main switch design parameters, demonstrate a significant reduction in the number of converters when compared with architectures employing single- channel wavelength conversion.

A New Analytical Approach for the Estimation of Blocking Probabilities in Wavelength Routing Networks

The paper introduces a new analytical approach for estimating blocking probabilities in all-optical networks. The assumptions of the classical Lee approximation are discussed and their effects are evaluated. The paper proposes a better substitute for the independent link assumption. The new assumption takes all active paths, as well as all free links, as independent objects on the network topology. The new model is shown to generate estimates that fit exactly the blocking probabilities obtained through simulations on linear topologies using Poissonian, spatially homogeneous traffic. An extension to regular meshes is presented that is asymptotically good for very small and very large nodal degrees. Finally, the independent wavelength assumption is also evaluated for two different wavelength assignment algorithms.

An evolutionary spectrum assignment algorithm for Elastic Optical Networks

A fundamental issue in Elastic Optical Networks (EONs) relies on choosing a proper route and necessary number of contiguous frequency slots from end-to-end to accommodate the traffic demands. Spectrum assignment based on the traditional First-Fit assignment has been extensively employed in EON investigations due to its inherent simplicity and favorable capacity of leaving end-to-end free slots in the network. This paper proposes a possible structure of an evolutionary algorithm that can be used to search for an appropriate spectrum ordering of the First-Fit spectrum assignment to mitigate request blocking probability. We here analyse the path request blocking probability when just lack of resource is emphasized. However, the proposal is general enough to be used in other situations.

Efficient resource allocation of heterogeneous services in transparent optical networks

Feature Issue on Transmission in Optically Transparent Core NetworksTransparent optical networking provides a common optical transport platform for services with different bit rates, transmission formats, and technologies that is adaptive to varying traffic demands from either edge aggregation networks or high-bandwidth end users. This paper describes a method of efficiently allocating resources to heterogeneous services that have diverse optical performance requirements at 10 and 40Gbit/s in terms of tolerance to chromatic dispersion (CD) and optical signal-to-noise ratio degradations. We particularly focus on exploiting the wavelength-dependent nature of CD and demonstrate that by including such information in the routing subproblem and introducing a new just-enough wavelength assignment method, significant improvements in resource utilization can be obtained.

Delay-line buffer modeling for asynchronous optical networks

In this paper we develop an analytical model for the FIFO delay-line buffer in asynchronous optical networks with any packet length distribution, under the assumption that arrivals are Poissonian. We consider that the incoming traffic is distributed among an infinite number of inputs (Aloha traffic) and show that this consideration represents very suitably a real system. The model enables the exact calculation of packet loss probability and average delay, which makes it a very powerful tool for performance evaluation and planning/dimensioning of networks that use this kind of contention resolution technique. The buffer performance as predicted by the model is compared with simulations and discussed for some packet length distributions.

Limited-range wavelength conversion modeling for asynchronous optical packet-switched networks

Packet contention is a very important issue in optical packet-switched networks. This paper analyzes asynchronous optical packet switches when wavelength conversion is used as contention resolution mechanism. A wavelength converter can convert one wavelength to another and consequently improve the network performance. In practical systems, a wavelength converter normally presents limited range conversion capability. In this paper we propose a Markov model that enables the calculation of packet blocking probability for asynchronous optical packet switches equipped with single per channel limited-range wavelength converters. The analytical model is based on an infinitely fine input granularity assumption and it is shown to present a good approximation with simulation results.

Heuristic algorithms for regenerator assignment in dynamic translucent elastic optical networks

In this paper, we propose two heuristics to perform regenerator assignment in translucent elastic optical networks. The first one tries to use the modulation format with the highest spectral efficiency, whereas the other one aims to transmit the optical signal as far as possible before it undergoes into a regeneration process. The former deploys several regenerators but saves bandwidth. On the other hand, the latter uses a lower number of regenerators, but it uses more bandwidth than the previous one. Different transmission bit rates and format modulations are considered in our simulations. The transmitter SSE noise and optical amplifiers ASE noises are considered in the physical impairments evaluation. We perform simulations to analyse the CapEx-performance trade-off of both strategies in terms of number of regenerators, available slots and blocking probability.

The NrPSR-Elastic routing algorithm for flexible grid optical networks

The Routing and Spectrum Assignment (RSA) algorithm has a direct influence on the performance of flexible grid optical networks. We propose in this paper a novel routing algorithm, named NrPSR-Elastic, which aims to find Nr routes with minor cost for a given source-destination pair according to a cost function expanded in a Power Series (PSR). In this proposal, the coefficients are determined by a global optimizer, called Particle Swarm Optimizer (PSO). We also propose a new input variable to be used in the PSR cost function, called contiguous frequency slot availability. The selected route to be assigned to the call request is chosen among the Nr found routes, depending on a Minimum Hop based policy, which takes into account the number of links in each route. We compared the performance of our proposal through simulation with the Shortest Path (SP) routing algorithm for two different link-capacity scenarios in well-known network topology. For both cases, the NrPSR-Elastic algorithm far outperformed the SP routing algorithm.

Deadlock avoidance under incremental traffic in the elastic single link

The paper investigates the conditions that lead to deadlocked resources in a single link that services an incremental traffic of requests for a variable number of contiguous slots. The paper shows that such deadlocks result from a mismatch between the traffic profile and the number of available slots for assignment in a spectral void. For each traffic profile with no demand for single slots, a set of forbidden void sizes that inevitably lead to deadlock is identified, so deadlock-avoiding spectrum assignment algorithms must avoid them whenever starting from a non-forbidden void size.

Flexgrid optical networks design under multiple modulation formats

This paper proposes an MILP (Mixed Integer Linear Programming) formulation for the design of flexgrid optical networks under multiple modulation formats and noise constraints. The proposed MILP benefits from the flexibility of using multiple modulation formats, each of which with its spectrum efficiency and individual noise constraints, to properly perform routing and spectrum assignment of the demanded traffic. The model is capable of maximizing the amount of traffic that is established in the network for a limited number of slots per link. Cases studies are carried out in order to analyze the benefits of the proposal as well as the basic properties of the formulation.