Darli A. A. Mello

A matrix-based analytical approach to connection unavailability estimation in shared backup path protection

This letter introduces a matrix-based approach to connection unavailability estimation in shared backup path protection (SBPP). The proposed approach yields accurate results for networks of national size using simple matrix operations, being therefore suitable for online routing algorithms. The accuracy of the unavailability estimates is verified through simulations.

Optical Networking With Variable-Code-Rate Transceivers

We evaluate the impact of variable-code-rate transceivers on cost, capacity and survivability of wavelength-routed optical networks. The transmission rate and reach trade-off is quantified for two hypothetical coded modulation schemes (aggressive and conservative) in a wavelength routing network with 50-GHz-spaced channels. The aggressive scenario assumes the 64-QAM modulation format, a small gap to capacity, and a small excess bandwidth. The conservative scenario considers the 16-QAM modulation format, and a larger capacity gap and excess bandwidth. The performance of the conservative and aggressive technologies is evaluated in three representative networks. Transparent reaches are calculated by means of an existing analytical method which assumes the AWGN hypothesis for the nonlinear noise. It is shown that variable-code-rate transceivers enable the concept of soft protection, in which the protection lightpath operates at a data rate which is lower than the corresponding working lightpath, in a way to avoid regeneration. This is specially attractive in the transport of IP traffic, where capacity reduction (in average up to 25%) may be tolerable during a repair time. It is also shown that variable-code-rate transceivers have the potential to offer significant savings in terms of transceiver usage and wavelength occupation, when compared to current fixed-rate transceivers operating at 100, 200 or 400 Gb/s. Finally, practical variable-code-rate transceivers may achieve a discrete set of N code rates, yielding a quantized capacity-versus-reach curve. The system impact of N is evaluated for several network scenarios.

Availability maps for connections in WDM optical networks

The provisioning of services in optical networks demands reliable transmission paths. This paper investigates the availability of optical connections with respect to the failure probability of the involved network components. Outages of the fiber links as well as potential hardware failures for different opaque and transparent node architectures are analyzed. The results are presented in terms of map diagrams which allow to determine the availability of a wavelength connection subject to the transmission distance and the number of traversed hops.

Dynamic provisioning of shared-backup path protected connections with guaranteed availability requirements

In optical networks, shared-backup path protection (SBPP) can optimize network resources utilization in scenarios where connection resilience requirements are not achieved without protection, but are exceeded with dedicated-path protection (DPP). However, savings in capacity allowed by backup capacity sharing are achieved at the cost of connection availability degradation. This paper presents a strategy for provisioning connections with guaranteed availability in a dynamic traffic scenario that attempts to minimize the allocation of spare capacity. Connections can be unprotected or protected by SBPP - which in some cases degenerate to DPP - depending on the connection availability requirements. This provisioning strategy employs the previously published matrix-based approach for connection unavailability estimation in SBPP protected networks which offers accurate results for networks of national size. We investigate the performance, in terms of blocking and resource sharing, of three availability classes (availability of 0.999, 0.9999 and 0.99999) that coexist in two representative network topologies without wavelength conversion. The results indicate that SBPP is a viable option for networks of national dimensions, but the backup sharing of high availability connections is strongly limited in networks of continental dimensions

Specification of SLA survivability requirements for optical path protected connections

This paper proposes guidelines for the specification of survivability requirements and economic planning of SLAs for optical path protected connections. The interval availability and outage duration metrics are investigated.

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.

Error arrival statistics for FEC design in four-wave mixing limited systems

We confirmed experimentally by direct bit sequence analysis that systems limited by four-wave mixing exhibit a noise-like and memoryless error distribution. However a slight increase in sequential two bit error bursts was also observed.

Experimental Analysis of the Power Auto-Correlation-Based Chromatic Dispersion Estimation Method

We experimentally investigate the performance of the signal power autocorrelation-based method for chromatic dispersion (CD) estimation in a polarization-multiplexing quadrature phase-shift keying (PM-QPSK) 100G coherent optical system conveying optical channel transport unit level-4 (OTU4) frames. It is shown that the typical laboratory setup, where the signal components are generated from delayed versions of the same pseudorandom binary sequence (PRBS), is inadequate for experimental validation because of artifacts in the signal auto-correlation function. This problem is circumvented by the use of a commercial line card transporting independent data sequences. The algorithm is used to estimate accumulated CD values from 0 to 50 000 ps/nm under up to 80-ps differential group delay (DGD). We further evaluate its convergence properties in terms of the length of the sample vector required for correct CD estimation and address the hardware resource requirements. The CD-shifted version of the algorithm yielded a maximum estimation error of 186 ps/nm in all tested conditions.

Analysis of signal processing techniques for optical 112 Gb/s DP-QPSK receivers with experimental data

This paper evaluates several signal processing techniques for optical dual-polarization quadrature phase-shift keying (DP-QPSK) coherent receivers, using offline post-processing of experimental data. In addition to electronically separating the two polarization multiplexed signals, the investigated signal processing algorithms also compensate for chromatic dispersion (CD) and polarization mode dispersion (PMD). In particular, we investigate two distinct architectures: 1) Constant modulus algorithm (CMA) equalization followed by feedforward phase recovery. 2) Decision-directed least mean square (DD-LMS) equalization combined with decision-directed phase recovery. The interplay of both architectures with bulk dispersion compensators and carrier recovery algorithms is also analyzed.