Helio Waldman

Distributed approaches for impairment-aware routing and wavelength assignment algorithms in GMPLS networks

This work proposes two different distributed strategies for provisioning lightpaths in the presence of optical physical-layer impairments in GMPLS networks. The first approach is a more classical one, which introduces new extensions to the OSPF-TE routing protocol. The other approach makes use of an Ant Colony Optimization (ACO) algorithm to adaptively calculate routes in the network by actively monitoring the aggregate optical power of each link. By using an analytical model to incorporate the constraints of the Amplified Spontaneous Emission (ASE) noise of the optical amplifiers into the routing, we demonstrate the effectiveness of our approaches by means of an illustrative numerical example.

Routing and wavelength assignment with crankback re-routing extensions by means of ant colony optimization

Crankback re-routing extensions can offer significant improvements in the successful setup of Label Switched Paths (LSPs) by allowing new retries on alternate paths that circumvent blocked links or nodes. These extensions can be incorporated into a fully-distributed algorithm based on Ant Colony Optimization metaheuristics, taking advantage of its self-adapting, emergent behavior. By comparing with traditional fixed-alternate re-routing mechanisms, simulations have demonstrated that the proposed algorithm can efficiently mitigate lightpath blocking, both during normal operation and in case of network failure, by locally repairing failed LSP setups due to blocked/failed resources.

Feedforward carrier recovery for polarization demultiplexed signals with unequal signal to noise ratios.

We investigate feedforward carrier recovery (FFCR) in coherent polarization diversity receivers where the signal to noise ratio (SNR) of polarization demultiplexed signals can be unequal, such as in polarization-dependent loss impaired systems. A joint-polarization FFCR mechanism for estimating the carrier phase noise based on samples from both polarizations is proposed and compared with three other plausible alternatives. We evaluated each architecture using Monte Carlo simulations and observed that the joint-polarization FFCR yields a 1.1 dB SNR penalty for a given laser linewidth x baud rate product, while the other three architectures offer 1.8 dB, 2.0 dB and 3.9 dB, for QPSK at BER = 10(-3) and 3 dB SNR imbalance.

Interval availability estimation for protected connections in optical networks

Routing and wavelength assignment under availability constraints has been extensively researched recently. Availability (or more precisely, steady-state availability) can be defined as the average probability of a connection operating over a time window that tends to infinity. However, service level agreements (SLAs) commit a minimum connection uptime fraction over a finite contract duration. This random variable is known in reliability engineering as interval availability. If the minimum agreed interval availability is not honored, the service provider is penalized. In order to balance the risk of non-compliance fines against asset protection costs, network planners must know the interval availability distribution. However, its estimation with existing numerical techniques is computationally expensive, motivating the search for approximate analytical methods. Under the hypotheses of Poissonian node and link failures and repairs, and assuming no more than two link failures or one node failure in the network, we propose, for connections protected by shared or dedicated methods:*an approximate Markov model that allows the derivation of a closed-form expression for the connection steady-state availability; *under the approximate Markov model, analytical bounds on the interval availability distribution. The proposed methods are validated by discrete-event simulations of an Italian network.

Restoration in wavelength-routed optical networks by means of ant colony optimization

Because of the distributed control of the network, the dynamic nature of the traffic and the unpredictability of a failure event, the flexibility and robustness of ant colony optimization (ACO) make it a suitable candidate for provisioning lightpaths in an optical network. In this work, we propose a fault-tolerant dynamic routing and wavelength assignment (RWA) algorithm based on the ACO framework, presenting its integration into the Generalized multi-protocol label switching (GMPLS) control plane. By simulating two different scenarios, we demonstrate the effectiveness of this algorithm when a single link or node failure occurs.

Addressing self-similarity in optical switching networks by means of ant colony optimization

In this work, we propose the use of an Ant Colony Optimization (ACO) algorithm to mitigate packet loss in an optical packet switching network that carries self-similar traffic, which is known to have a great impact in the buffer performance in terms of loss probability as exemplified in this work. By adaptively routing the packets and balancing the network load, we demonstrate by some simulations the effectiveness of this approach when compared with a shortest-path routing scheme, achieving a performance that is comparable to the Poisson traffic scenario in some cases. The proposed algorithm can be used as a viable alternative to traffic shaping techniques.

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.

Fast spectrum exhaustion under incremental traffic in the elastic single link

The paper discusses the mean time to exhaust the spectrum of a single link under an incremental traffic of requests for connections with a variable number of slots. It is shown that optimal assignment policies exist under awareness of the traffic profile. For instance, if the traffic rates decrease with the number of requested slots, greedy policies that accept all requests that may be accommodated will speed up the spectrum exhaustion. On the other hand, if the traffic rates increase with the number of requested slots, spectrum exhaustion is favored by wholesale policies that accept only requests for the entire available spectrum. An optimal algorithm is derived for any given traffic profile.

Spectrum-sliced elastic optical networking

Current communication environments present a wide range of traffic granularities, making it hard to use the optical spectrum efficiently under the WDM framework. In elastic networking, the WDM rigid frequency grid is replaced by a more flexible structure, in which the spectrum is organized in frequency slots, and each traffic flow is assigned to an appropriate set of contiguous slots. The classical RWA problem is then replaced by a Routing and Spectrum assignment (RSA) problem, which presents different characteristics when compared to the former. In this paper, we discuss a novel approach to tackle the spectrum assignment problem in elastic networks.