Showing papers by "Ioannis Tomkos published in 2011"

Elastic Bandwidth Allocation in Flexible OFDM-Based Optical Networks

Abstract: Orthogonal Frequency Division Multiplexing (OFDM) has recently been proposed as a modulation technique for optical networks, because of its good spectral efficiency, flexibility, and tolerance to impairments. We consider the planning problem of an OFDM optical network, where we are given a traffic matrix that includes the requested transmission rates of the connections to be served. Connections are provisioned for their requested rate by elastically allocating spectrum using a variable number of OFDM subcarriers and choosing an appropriate modulation level, taking into account the transmission distance. We introduce the Routing, Modulation Level and Spectrum Allocation (RMLSA) problem, as opposed to the typical Routing and Wavelength Assignment (RWA) problem of traditional WDM networks, prove that is also NP-complete and present various algorithms to solve it. We start by presenting an optimal ILP RMLSA algorithm that minimizes the spectrum used to serve the traffic matrix, and also present a decomposition method that breaks RMLSA into its two substituent subproblems, namely 1) routing and modulation level and 2) spectrum allocation (RML+SA), and solves them sequentially. We also propose a heuristic algorithm that serves connections one-by-one and use it to solve the planning problem by sequentially serving all the connections in the traffic matrix. In the sequential algorithm, we investigate two policies for defining the order in which connections are considered. We also use a simulated annealing meta-heuristic to obtain even better orderings. We examine the performance of the proposed algorithms through simulation experiments and evaluate the spectrum utilization benefits that can be obtained by utilizing OFDM elastic bandwidth allocation, when compared to a traditional WDM network.

Dynamic bandwidth allocation in flexible OFDM-based networks

Abstract: We propose a general policy to allocate subcarriers to time-varying traffic in a flexible OFDM optical network. We compare the OFDM network performance to that of a fixed-grid WDM network using simulations.

Experimental Demonstration of an Impairment Aware Network Planning and Operation Tool for Transparent/Translucent Optical Networks

Abstract: Core optical networks using reconfigurable optical switches and tunable lasers appear to be on the road towards widespread deployment and could evolve to all-optical mesh networks in the coming future. Considering the impact of physical layer impairments in the planning and operation of all-optical (and translucent) networks is the main focus of the Dynamic Impairment Constraint Optical Networking (DICONET) project. The impairment aware network planning and operation tool (NPOT) is the main outcome of DICONET project, which is explained in detail in this paper. The key building blocks of the NPOT, consisting of network description repositories, the physical layer performance evaluator, the impairment aware routing and wavelength assignment engines, the component placement modules, failure handling, and the integration of NPOT in the control plane are the main contributions of this study. Besides, the experimental result of DICONET proposal for centralized and distributed control plane integration schemes and the performance of the failure handling in terms of restoration time is presented in this study.

Power consumption evaluation of hybrid WDM PON networks for data centers

Abstract: As the requirements for processing power of the datacenters continues to increase rapidly, higher performance networks are required to sustain the increased communication bandwidth demand within the data center. Current data center networks cannot affordably satisfy the required bandwidth of emerging application without consuming excessive power. Optical interconnects provide a viable solution offering high throughput, reduced latency and reduced energy consumption compared to current networks based on commodity switches. This paper presents a novel hybrid approach that use commodity Ethernet switches for intra-rack communication and WDM PON for inter-rack communication. The proposed scheme is based on readily available, passive optical components devices, thus eliminating the power dissipated in Top-of-the-Rack switches for the inter-rack communication. The performance evaluation based on simulation shows up to 10% power reduction with negligible increase on the packet latency.

Optical performance monitoring for translucent/transparent optical networks

Abstract: A comprehensive analysis and survey of the optical performance monitoring (OPM) is provided towards the deployment of translucent/transparent optical networks. OPM applications and technologies are reviewed for the different stages of the optical network life cycle: planning and provisioning, impairment mitigations, maintenance and failure location. Recommendations for the most relevant OPMs required to be integrated in translucent/transparent optical networks are provided.

Performance of optical Fast-OFDM in MMF-based links

Abstract: 19.375Gb/s optical Fast-OFDM signals can be transmitted over 500m worst-case MMF DML-based links having 3-dB effective bandwidths of 150MHz.km. This performance is similar to that corresponding to a conventional OFDM having twice the bandwidth.

A Novel Impairment Aware RWA Algorithm With Consideration of QoT Estimation Inaccuracy

Abstract: In all-optical networks the physical layer impairments accumulate along a light-path and also vary dynamically, and a number of impairment aware routing and wavelength assignment (IA-RWA) techniques have been proposed in order to mitigate the physical layer impairments and find lightpaths that meet a required quality of transmission (QoT) constraint predefined by the network operator. However, in order to compute lightpaths, IA-RWAs typically rely on analytical models, which cannot be guaranteed to be fully accurate, and hence acceptance of lightpaths with poor QoT or rejection of lightpaths with acceptable QoT may ensue. We present a novel IA-RWA algorithm that not only considers the impact of physical impairments on RWA decisions, but also, for the first time, accounts for inaccuracy of the QoT estimators. The performance of our algorithm is compared with algorithms selected from the recent literature. All algorithms are evaluated through simulations in a realistic scenario. Our proposed novel algorithm outperforms the selected algorithms in terms of blocking rate and also the amount of required resources for achieving a very low (i.e., 5 x 10-6 ) blocking rate under similar assumptions. In addition we show that accounting for QoT estimation inaccuracy changes the performance of the proposed IA-RWA substantially, and hence that the QoT estimator inaccuracy is an important design parameter in transparent optical networking.

Value analysis methodology for flexible optical networks

Abstract: A methodology for the estimation of the value of flexible networking in comparison with standard WDM solutions is presented, and specifications for the cost of the required flexible transponders and WSSs are extracted.

Energy-efficiency study of optical OFDM in data centers

Abstract: This paper presents a study on the energy efficiency of adaptive optical OFDM in data center's networks. The DSP architecture of the proposed scheme is targeted to an FPGA and achieves more than 70% lower energy consumption compared to conventional OFDM modulation.

An overview of MAC issues in OFDMA-PON networks

Abstract: The OFDMA-PON paradigm has recently emerged as a serious contender for next generation optical access networks. Its main characteristics are enhanced capacity, flexibility and scalability as opposed to current and upcoming TDMA-PONs as well as to the proposed WDM-PON concepts. In particular, OFDMA-PONs provide the opportunity for dynamically allocating the available optical bandwidth in multiple levels of granularity, both among different providers/services and users (groups of individual OFDM subcarriers can be arbitrarily assigned to different ONUs each time). Moreover, OFDM allows for adjustable modulation/bitrate on a subcarrier basis. It is evident that new challenges are imposed to the MAC layer and the associated Dynamic Bandwidth Assignment (DBA). This paper discusses all relevant issues and provides general guidelines for the design of an OFDMA-PON MAC layer protocol.

An All-Optical Grooming Switch for Interconnecting Access and Metro Ring Networks [Invited]

Abstract: A regenerative all-optical grooming switch for interconnecting 130 Gbit/s on-off keying (OOK) metro/core ring and 43 Gbit/s-OOK metro/access ring networks with switching functionality in time, space, and wavelength domains is demonstrated. Key functionalities of the switch are traffic aggregation with time-slot interchanging functionality, optical time division multiplexing (OTDM) to wavelength division multiplexing (WDM) demultiplexing, and multi-wavelength 2R regeneration. Laboratory and field demonstrations show the excellent performance of the new concept with error-free signal transmission and Q-factors above 20 dB.

Demonstration and field trial of a scalable resilient hybrid ngPON

Abstract: The built multi-layer SARDANA prototype proves the feasibility of extended hybrid DWDM/TDM-XGPON FTTH networks with resilient optically-integrated ring-trees architecture, supporting broadband multimedia services.

Adaptive Modulation-Induced Reduction in Filter Concatenation Impairment for Optical OFDM Metro/Regional Systems

Abstract: The impact of optical OFDM (orthogonal frequency division multiplexing) with adaptive modulation on reducing the filter concatenation effect is investigated, for the first time, in intensity modulation and direct-detection transparent metropolitan/regional network systems incorporating cascaded reconfigurable optical add/drop multiplexers (ROADMs). The ROADMs considered are based on different optical filters including fiber Bragg grating, Chebyshev, thin film and wavelength-blocker/wavelength-selective switch devices. It is shown that, in comparison with conventional identical modulation, adaptive modulation can improve the system performance by a factor of up to 60%. The utilization of adaptive modulation can also significantly enhance the network tolerance to filter loss ripple, group delay ripple and frequency dip.

A novel monitor placement algorithm for accurate performance monitoring in optical networks

Abstract: We propose a novel monitor placement algorithm that reduces significantly the number of monitors required to accurately assess the QoT of all lightpaths established in an optical network, compared to other monitor placement methods.

Experimental evaluation of centralized failure restoration in a dynamic impairment-aware all-optical network

Abstract: A centralized impairment-aware lightpath restoration scheme is experimentally demonstrated. Through the implementation of the QoT estimator module on FPGA technology, restoration times of 1.36s are achieved for the high priority traffic class.

Advantages of using cognition when solving impairment-aware virtual topology design problems

Abstract: In this paper, the advantages of using cognition when solving the impairment-aware virtual topology design problem are demonstrated. To this end, an algorithm to design the virtual topology, GAPDELT, previously proposed by the University of Valladolid, has been extended to ensure that all the lightpaths of the virtual topology comply with quality of transmission constraints. The new version, called IA-GAPDELT, is a multiobjective genetic algorithm which uses Pareto optimality to reduce both the network congestion and the number of transmitters in operation, and so the energy consumption. By means of simulation, we show that when the algorithm is enhanced with a simple cognitive technique, it obtains a higher number of feasible solutions (virtual topologies) and, moreover, they are generally better in terms of the optimization parameters, than those obtained without cognition.

SARDANA: an all-optical access-metro WDM/TDM-PON

Abstract: A new optical access network, named “Scalable Advanced Ring-based passive Dense Access Network Architecture” (SARDANA), is presented It transparently integrates WDM metro and TDM PON access technologies, implementing ring protection, 100 km reach and up to 1024 users served at 10 Gb/s, with passive highly-shared infrastructure The introduced innovations are hybrid ring/tree WDM/TDM Passive Optical Network (PON) architecture; a resilient remote node (RN), which is distantly pumped from the Optical Line Terminal (OLT); and a reflective ONU (Optical Network Unit); as well as an enhanced Medium Access Control (MAC) protocol

Techno-economic study of high-splitting ratio PONs and comparison with conventional FTTH-PONs/FTTH-P2P/FTTB and FTTC deployments

Abstract: We present a techno-economic study on the outside plant costs comparison between the standard FTTH-PON deployments with future high-splitting ratio PONs. The high-splitting ratio PONs are also compared with other FTTx deployments.

Experimental demonstration of an enhanced impairment-aware path computation element

Abstract: An enhanced impairment-aware path computation element (EPCE) for dynamic transparent optical networks is proposed and experimentally evaluated. The obtained results show that by using the EPCE, light-path setup times of few seconds are achieved.

Agile photonic integrated systems-on-chip enabling WDM terabit networks

Abstract: The ICT-APACHE research project is focusing on the development of cost-effective, compact, scalable and agile integrated components capable of generating, regenerating and receiving multi-level encoded data signals for high capacity (>100 Gb/s) WDM optical networks. APACHE technology relies on InP active, monolithic chips, hybridly integrated on silica-on-silicon planar lightwave platforms in order to achieve cost-efficiency, high yield, low power consumption and device scaling beyond the level commercially available today. The APACHE integration approach is implemented in a two-dimensional plan, horizontally and vertically, in order to enable multi-functionality and increased capacity, respectively. The final goal of the APACHE project is the fabrication of integrated arrays of transmitters, receivers and regenerators that will operate with 100 Gb/s OOK, DPSK and DQPSK modulated signals, allowing for 1 Terabit/s on-chip capacity. In this paper, we will review the latest results from the system-level characterization of the developed components and will outline the roadmap for future endeavours.

Mitigation techniques for Peak-to-Average Power Ratio and Optical Beat Interference in OFDMA-PONs

Abstract: The Peak-to-Average Power Ratio (PAPR) and Optical Beat Interference (OBI) is examined thoroughly in Orthogonal Frequency Division Multiplexing Access (OFDMA)-Passive Optical Networks (PONs). Four techniques for mitigating the PAPR/OBI problem are evaluated, namely the bit-loading algorithm and clipping for the PAPR, and the power-loading and thermal detuning for the OBI.

Comb generator for 100 Gbit/s OFDM and low-loss comb-line combiner using the optical inverse fourier transform (IFFT)

Abstract: The generation of comb spectra is essential for optical OFDM transmitters. We describe a simple solution to this problem, feeding a dual drive Mach-Zehnder modulator with a 12.5 GHz sinusoidal at one arm and with a 25 GHz sinusoidal at the other arm separately. Up to eight optical subcarriers with 12.5 GHz spacing and a spectral flatness of < 1 dB can be produced. Much lower drive voltage swings are required than with other techniques reported so far. The modulated optical subcarrier fields are multiplexed to a compound field employing a lossless optical inverse Fourier transform circuit. Further, this circuit strongly suppresses inter-subcarrier cross-talk.

Corrections to "Elastic Bandwidth Allocation in Flexible OFDM-Based Optical Networks" [May 11 1354-1366]

Abstract: Table II and Table III were omitted in the above mentioned paper (ibid., vol. 29, no. 9, pp. 1354-1366, May 2011). They are presented here.

Demonstration of a remotely pumped long-reach WDM/TDM 10 Gb/s PON with reflective user terminals

Abstract: A ring+tree PON is demonstrated from a 78 km reach rural to an urban 1:128 split configuration with field-deployed fibers at >31 dB budget and RSOA or SOA/REAM at the ONU

Performance optimization of adaptive loading algorithms for SMF-based optical OFDM transceivers

Abstract: Detailed investigations of the effectiveness of three widely adopted optical orthogonal frequency division multiplexing (OOFDM) adaptive loading algorithms, including power loading (PL), bit loading (BL), and bit-and-power loading (BPL), are undertaken, over < 100km single-mode fibre (SMF) system without incorporating inline optical amplification and chromatic dispersion (CD) compensation. It is shown that the BPL (PL) algorithm always offers the best (worst) transmission performance. The absolute transmission capacity differences between these algorithms are independent of transmission distance and launched optical power. Moreover, it is shown that in comparison with the most sophisticated BPL algorithm, the simplest PL algorithm is effective in escalating the OOFDM SMF links performance to its maximum potential. On the other hand, when employing a large number of subcarriers and a high digital-to-analogue (DAC)/analogue-to-digital (ADC) sampling rate, the sophisticated BPL algorithm has to be adopted.

Dynamic Elastic and Scalable Photonic Infrastructures and Network Architectures

Abstract: In this article we discuss a new optical networking paradigm based on the co-called “Dynamic Elastic and Scalable Photonic Infrastructures and Network Architectures - DESPINA” approach. The concept, main elements and associated research directions are highlighted.

Techno-economic comparison of next generation optical access network architectures

Abstract: We discuss an overview of the most advanced next generation optical access network architectures and technologies, followed by the presentation of results from a techno-economic study on the outside plant costs comparison among various FTTx architectures. Our study provides answers to questions posed by governments and network operators on the actual costs to pass households with a next generation access fiber-optic based network.

Techno-economics of resilient extended FTTH PONs

Abstract: This work analyses different architectures of protected FTTH passive optical networks in terms of device and infrastructure requirements and costs, considering different home density scenarios and volume projections. The results show that the Sardana hybrid resilient network presents a wider scalability range in terms of cost efficiency.