Ioannis Tomkos

Humankind has entered a new era wherein a main characteristic is the convergence of various technologies providing services and exerting a major impact upon all aspects of human activity, be it social interactions with the natural environment. Fixed networks are about to play a major role in this convergence, since they form, along with mobile networks, the backbone that provides access to a broad gamut of services, accessible from any point of the globe. It is for this reason that we introduce… Εμφάνιση περισσότερων

Humankind has entered a new era wherein a main characteristic is the convergence of various technologies providing services and exerting a major impact upon all aspects of human activity, be it social interactions with the natural environment. Fixed networks are about to play a major role in this convergence, since they form, along with mobile networks, the backbone that provides access to a broad gamut of services, accessible from any point of the globe. It is for this reason that we introduce a forward-looking approach for fixed networks, particularly focused on Fixed 6th Generation (F6G) networks. First, we adopt a novel classification scheme for the main F6G services, comprising six categories. This classification is based on the key service requirements, namely latency, capacity, and connectivity. F6G networks differ from those of previous generations (F1G–F5G) in that they concurrently support multiple key requirements. We then propose concrete steps towards transforming the main elements of fixed networks, such as optical transceivers, optical switches, etc., such that they satisfy the new F6G service requirements. Our study categorizes the main networking paradigm of optical switching into two categories, namely ultra-fast and ultra-high capacity switching, tailored to different service categories. With regard to the transceiver physical layer, we propose (a) the use of all-optical processing to mitigate performance barriers of analog-to-digital and digital-to-analog converters (ADC/DAC) and (b) the exploitation of optical multi-band transmission, space division-multiplexing, and the adoption of more efficient modulation formats. Λιγότερα

Next upgrade to QAM256 poses formidable barriers in terms of attainable performance and energy-efficiency of DAC driver MZM based Transmitters (Tx). A promising alternative, potentially changing the ‘rules of the game’ is optical DACs (oDAC). In previous work, we proposed a PAM4-driven optical Tx generating up to 256QAM. Here we introduce a novel oDAC parallelizing a pair of optimized 2-segment MZMs, remarkably fed by 4 uncoupled NRZ signals. Based on a pair of IQ-nested new oDACs, the… Εμφάνιση περισσότερων

Next upgrade to QAM256 poses formidable barriers in terms of attainable performance and energy-efficiency of DAC driver MZM based Transmitters (Tx). A promising alternative, potentially changing the ‘rules of the game’ is optical DACs (oDAC). In previous work, we proposed a PAM4-driven optical Tx generating up to 256QAM. Here we introduce a novel oDAC parallelizing a pair of optimized 2-segment MZMs, remarkably fed by 4 uncoupled NRZ signals. Based on a pair of IQ-nested new oDACs, the resulting DAC-less QAM Tx is fed by 8 uncoupled NRZ drivers. The energy efficiency, photonic efficiency and resolution of the flexible oDAC and QAM Tx are at their utmost. Λιγότερα

We propose, model and optimize an optical Digital to Analog Converter (oDAC) significantly improving the tradeoffs between spectral-, energy- and footprint- efficiencies, based on modifying our recently introduced multi-parallel oDAC, by adopting Multi-Level-Driven modulation for the individual Mach-Zehnder Modulators (MZM) in the parallelized paths. The most compact instance of this improved oDAC structure coherently combines two parallel optical paths, each comprising an MZM electrically… Εμφάνιση περισσότερων

We propose, model and optimize an optical Digital to Analog Converter (oDAC) significantly improving the tradeoffs between spectral-, energy- and footprint- efficiencies, based on modifying our recently introduced multi-parallel oDAC, by adopting Multi-Level-Driven modulation for the individual Mach-Zehnder Modulators (MZM) in the parallelized paths. The most compact instance of this improved oDAC structure coherently combines two parallel optical paths, each comprising an MZM electrically driven by either PAM2 or PAM4. Λιγότερα

Forthcoming capacity scaling requirements of optical networks and advances in optical fiber communications beyond the omnipresent single-mode fiber operating over the conventional band introduces new opportunities and challenges for exploiting the expanded spectral and spatial resources available for fiber-optic network designs. The spectral and spatial degrees of freedom introduce utilization tradeoffs that can be leveraged under different applications. After briefly reviewing the supporting… Εμφάνιση περισσότερων

Forthcoming capacity scaling requirements of optical networks and advances in optical fiber communications beyond the omnipresent single-mode fiber operating over the conventional band introduces new opportunities and challenges for exploiting the expanded spectral and spatial resources available for fiber-optic network designs. The spectral and spatial degrees of freedom introduce utilization tradeoffs that can be leveraged under different applications. After briefly reviewing the supporting network building elements (emerging fiber types, multiplexers, optical switches, and amplifiers), we consider networking scenarios such as intra/inter datacenter, terrestrial, undersea, and wireless 5G/6G hauling networks and identify the best utilization plan and key attributes that can be harnessed by the offered spectral and spatial degrees of freedom for each scenario and how optical switching can be employed therein for traffic management. Networks supporting these scenarios are experiencing tremendous traffic growth pushing their existing implementations to their physical capacity-distance limits. New network builds must offer significant capacity multipliers in an efficient and cost-effective manner, requiring new switching solutions for supporting the unabated traffic growths foreseen in the years to come. We discuss how space-division multiplexed networks can help address this challenge in key communication scenarios. Λιγότερα

We develop a ‘perfect’ design for PAM4 Segmented Mach-Zehnder Modulators (SEMZM), featuring a fully linear (uniform) optical DAC (oDAC) staircase (i.e., having equi-spaced PAM4 levels) and no intrinsic modulation loss (the qualifier ‘perfect’ pertains to ideal conditions, barring optical excess losses and other impairments). This is achieved by leveraging our recently introduced maximin optimization strategy, enabling to locate the hitherto unknown optimal operating point in the serial oDAC… Εμφάνιση περισσότερων

We develop a ‘perfect’ design for PAM4 Segmented Mach-Zehnder Modulators (SEMZM), featuring a fully linear (uniform) optical DAC (oDAC) staircase (i.e., having equi-spaced PAM4 levels) and no intrinsic modulation loss (the qualifier ‘perfect’ pertains to ideal conditions, barring optical excess losses and other impairments). This is achieved by leveraging our recently introduced maximin optimization strategy, enabling to locate the hitherto unknown optimal operating point in the serial oDAC parameters space, gaining ~7 dB relative to conventional PAM4 designs (typically based on a pair of segment electrodes in 2:1 lengths ratio and using 3 dB modulation backoff in order to compensate for degradation in oDAC linearity). The same photonic design may be reused to generate DAC-free coherent PAM4 (bipolar symmetric field-domain equi-spaced max-full-scale constellations), for efficient I/Q tributaries of 16QAM. Λιγότερα

In optical transmitters generating multi-level constellations, optical modulators are preceded by Electronic Digital-to-Analog-Converters (eDAC). It is advantageous to use eDAC-free Optical Analog to Digital Converters (oDAC) to directly convert digital bitstreams into multilevel PAM/QAM optical signals. State-of-the-art oDACs are based on Segmented Mach-Zehnder-Modulators (SEMZM) using multiple modulation segments strung along the MZM waveguides to serially accumulate binary-modulated optical… Εμφάνιση περισσότερων

In optical transmitters generating multi-level constellations, optical modulators are preceded by Electronic Digital-to-Analog-Converters (eDAC). It is advantageous to use eDAC-free Optical Analog to Digital Converters (oDAC) to directly convert digital bitstreams into multilevel PAM/QAM optical signals. State-of-the-art oDACs are based on Segmented Mach-Zehnder-Modulators (SEMZM) using multiple modulation segments strung along the MZM waveguides to serially accumulate binary-modulated optical phases. Here we aim to assess performance limits of the Serial oDACs (SEMZM) and introduce an alternative improved Multi-Parallel oDAC (MPoDAC) architecture, in particular based on arraying multiple binary-driven MZMs in parallel: Multi-parallel MZM (MPMZM) oDAC. We develop generic methodologies of oDAC specification and optimization encompassing both SEMZM and MPMZM options in Direct-Detection (DD) and Coherent-Detection (COH) implementations. We quantify and compare intrinsic performance limits of the various serial/parallel DD/COH subclasses for general constellation orders, comparing with the scant prior-work on the multi-parallel option. A key finding: COH-MPMZM is the only class synthesizing ‘perfect’ (equi-spaced max-full-scale) constellations while maximizing energy-efficiency-SEMZM/MPMZM for DD are less accurate when maximal energy-efficiency is required. In particular, we introduce multiple variants of PAM4|8 DD and QAM16|64 COH MPMZMs, working out their accuracy vs. energy-efficiency-and-complexity tradeoffs, establishing their format-reconfigurability (format-flexible switching of constellation order and/or DD/COH). Λιγότερα

Abstract:

Large scale Data Centers (DC) and High Performance Computing (HPC) systems require more and more computing power at higher energy efficiency. Conventional CMOS-based electronic interconnects are not expected to keep up with the envisioned future board-to-board and chip-to-chip (within multi-chip-modules) interconnect requirements because of bandwidth-density and power-consumption limitations. However, low-power and high-speed optics-based interconnects are emerging as… Εμφάνιση περισσότερων

Abstract:

Large scale Data Centers (DC) and High Performance Computing (HPC) systems require more and more computing power at higher energy efficiency. Conventional CMOS-based electronic interconnects are not expected to keep up with the envisioned future board-to-board and chip-to-chip (within multi-chip-modules) interconnect requirements because of bandwidth-density and power-consumption limitations. However, low-power and high-speed optics-based interconnects are emerging as alternatives for DC and HPC communications; they offer unique opportunities for continued energy-efficiency and bandwidth-density improvements, although cost is a challenge. In this paper, we survey the relevant technologies and discuss the relevant technology issues for commercial deployment. Λιγότερα

As traffic volumes carried by optical networks continue to grow by tens of percent year over year, we are rapidly approaching the capacity limit of the conventional communication band within a single-mode fiber. New measures such as elastic optical networking, spectral extension to multi-bands, and spatial expansion to additional fiber overlays or new fiber types are all being considered as potential solutions, whether near term or far. In this tutorial paper, we survey the photonic switching… Εμφάνιση περισσότερων

As traffic volumes carried by optical networks continue to grow by tens of percent year over year, we are rapidly approaching the capacity limit of the conventional communication band within a single-mode fiber. New measures such as elastic optical networking, spectral extension to multi-bands, and spatial expansion to additional fiber overlays or new fiber types are all being considered as potential solutions, whether near term or far. In this tutorial paper, we survey the photonic switching hardware solutions in support of evolving optical networking solutions enabling capacity expansion based on the proposed approaches. We also suggest how reconfigurable add/drop multiplexing nodes will evolve under these scenarios and gauge their properties and relative cost scalings. We identify that the switching technologies continue to evolve and offer network operators the required flexibility in routing information channels in both the spectral and spatial domains. New wavelength-selective switch designs can now support greater resolution, increased functionality and packing density, as well as operation with multiple input and output ports. Various switching constraints can be applied, such as routing of complete spatial superchannels, in an effort to reduce the network cost and simplify the routing protocols and managed pathway count. However, such constraints also reduce the transport efficiency when the network is only partially loaded, and may incur fragmentation. System tradeoffs between switching granularity and implementation complexity and cost will have to be carefully considered for future high-capacity SDM–WDM optical networks. In this work, we present the first cost comparisons, to our knowledge, of the different approaches in an effort to quantify such tradeoffs. Λιγότερα

Lightwave communications is a necessity for the information age. Optical links provide enormous bandwidth, and the optical fiber is the only medium that can meet the modern society's needs for transporting massive amounts of data over long distances. Applications range from global high-capacity networks, which constitute the backbone of the internet, to the massively parallel interconnects that provide data connectivity inside datacenters and supercomputers. Optical communications is a diverse… Εμφάνιση περισσότερων

Lightwave communications is a necessity for the information age. Optical links provide enormous bandwidth, and the optical fiber is the only medium that can meet the modern society's needs for transporting massive amounts of data over long distances. Applications range from global high-capacity networks, which constitute the backbone of the internet, to the massively parallel interconnects that provide data connectivity inside datacenters and supercomputers. Optical communications is a diverse and rapidly changing field, where experts in photonics, communications, electronics, and signal processing work side by side to meet the ever-increasing demands for higher capacity, lower cost, and lower energy consumption, while adapting the system design to novel services and technologies. Due to the interdisciplinary nature of this rich research field, Journal of Optics has invited 16 researchers, each a world-leading expert in their respective subfields, to contribute a section to this invited review article, summarizing their views on state-of-the-art and future developments in optical communications. Λιγότερα

Due to the rapid increase of network traffic in the last few years, many telecommunication operators have started transitions to 100 Gb/s optical networks and beyond. However, high speed optical networks need more efficient Forward Error Correction (FEC) codes to deal with the optical-impairments, such as uncompensated chromatic dispersion (CD), polarization mode dispersion (PMD) and non-linear effects, and keep the biterror- rate (BER) at long distances sufficiently low. To address these… Εμφάνιση περισσότερων

Due to the rapid increase of network traffic in the last few years, many telecommunication operators have started transitions to 100 Gb/s optical networks and beyond. However, high speed optical networks need more efficient Forward Error Correction (FEC) codes to deal with the optical-impairments, such as uncompensated chromatic dispersion (CD), polarization mode dispersion (PMD) and non-linear effects, and keep the biterror- rate (BER) at long distances sufficiently low. To address these issues, new FEC codes, called 3rd generation codes, have been proposed. The majority of these codes are based on soft-decision decoders and can provide higher coding gain as compared to their predecessors. This paper presents a thorough survey of 3rd generation FEC codes, suitable for 100G and beyond optical networks. Furthermore, the paper discusses the main advantages and drawbacks of each scheme and provides a qualitative categorization and comparison of the proposed schemes based on their main features, such as net coding gain (NCG) and BER. Information about the complexity of each scheme is given, as well. Λιγότερα

Rigid fixed-grid wavelength division multiplexing (WDM) optical networks can no longer keep up with the emerging bandwidth-hungry and highly dynamic services in an efficient manner. As the available spectrum in optical fibers becomes occupied and is approaching fundamental limits, the research community has focused on seeking more advanced optical transmission and networking solutions that utilize the available bandwidth more effectively. To this end, the flexible/elastic optical networking… Εμφάνιση περισσότερων

Rigid fixed-grid wavelength division multiplexing (WDM) optical networks can no longer keep up with the emerging bandwidth-hungry and highly dynamic services in an efficient manner. As the available spectrum in optical fibers becomes occupied and is approaching fundamental limits, the research community has focused on seeking more advanced optical transmission and networking solutions that utilize the available bandwidth more effectively. To this end, the flexible/elastic optical networking paradigm has emerged as a way to offer efficient use of the available optical resources. In this work, we provide a comprehensive view of the different pieces composing the “flexible networking puzzle” with special attention given to capturing the occurring interactions between different research fields. Only when these interrelations are clearly defined, an optimal network-wide solution can be offered. Physical layer technological aspects, network optimization for flexible networks, and control plane aspects are examined. Furthermore, future research directions and open issues are discussed. Λιγότερα

Flexible optical networks appear as the most prevalent candidates for next-generation core transport networks. The transition from a fixed to a flexible frequency grid calls for novel spectrum allocation techniques. This work focuses on the notion of dynamic cooperative spectrum sharing and addresses the issue of dynamic cooperative spectrum allocation for flexible optical networks. In orderto cope with the dynamicity of the traffic demands, spectrum expansion/contraction (SEC) policies attempt… Εμφάνιση περισσότερων

Flexible optical networks appear as the most prevalent candidates for next-generation core transport networks. The transition from a fixed to a flexible frequency grid calls for novel spectrum allocation techniques. This work focuses on the notion of dynamic cooperative spectrum sharing and addresses the issue of dynamic cooperative spectrum allocation for flexible optical networks. In orderto cope with the dynamicity of the traffic demands, spectrum expansion/contraction (SEC) policies attempt to accommodate incoming requests by means of expanding/contracting the allocations of connections. When spectrum expansion is limited by neighboring connections, appropriate spectrum defragmentation (SD) policies undertake the task of reallocating connections in order to free up the spectrum. In this work, a novel cooperative SEC policy is examined, which takes into consideration the spectrum allocation of neighboring connections. Additionally, a class of cooperative SD policies is proposed, based on the capabilities of current technology. Simulation results from two reference core networks quantify the benefits that can be reaped in terms of blocking rate. Trade-offs with respect to the achieved reduction in blocking rate and the number of reallocated connections during the SD procedure are examined. Λιγότερα

Flexible optical networking has been introduced recently as a way to offer efficient utilization of the available optical resources. Flexible transceivers capable of generating and receiving tributaries with variable bandwidth characteristics are key subsystem elements for the realisation of a flexible optical networking system. This paper presents the main concept and developments envisioned by the EU funded project ASTRON, which targets the design, development and evaluation of a… Εμφάνιση περισσότερων

Flexible optical networking has been introduced recently as a way to offer efficient utilization of the available optical resources. Flexible transceivers capable of generating and receiving tributaries with variable bandwidth characteristics are key subsystem elements for the realisation of a flexible optical networking system. This paper presents the main concept and developments envisioned by the EU funded project ASTRON, which targets the design, development and evaluation of a high-capacity, energy-efficient and bit-rate flexible optical transceiver capable of supporting rates from 10 Gb/s to beyond 1 Tb/s. The ASTRON technology relies on the combination of InP monolithic chips and Silica planar lightwave circuits to develop compact photonic integrated modules that exploit hybrid integration technologies. Λιγότερα

The emerging field of plasmonics promises the generation, processing, transmission, sensing and detection of signals at optical frequencies along metallic surfaces much smaller than the wavelengths they carry. Plasmonic technology has applications in a wide range of fields, including biophotonics, sensing, chemistry and medicine. But perhaps the area where it will have the most profound impact is in optical communications, since plasmonic waves oscillate at optical requencies and thus can carry… Εμφάνιση περισσότερων

The emerging field of plasmonics promises the generation, processing, transmission, sensing and detection of signals at optical frequencies along metallic surfaces much smaller than the wavelengths they carry. Plasmonic technology has applications in a wide range of fields, including biophotonics, sensing, chemistry and medicine. But perhaps the area where it will have the most profound impact is in optical communications, since plasmonic waves oscillate at optical requencies and thus can carry information at optical bandwidths. Λιγότερα

We demonstrate a remotely seeded flexible passive optical network (PON) with multiple low-speed subscribers but only a single optical line terminal transceiver operating at a data rate of 31.25  Gbits/s. The scheme is based on a colorless frequency division multiplexing (FDM)-PON with centralized wavelength control. Multiplexing and demultiplexing in the optical network unit (ONU) is performed in the electronic domain and relies either on FDM with Nyquist sinc-pulse shaping or on orthogonal… Εμφάνιση περισσότερων

We demonstrate a remotely seeded flexible passive optical network (PON) with multiple low-speed subscribers but only a single optical line terminal transceiver operating at a data rate of 31.25  Gbits/s. The scheme is based on a colorless frequency division multiplexing (FDM)-PON with centralized wavelength control. Multiplexing and demultiplexing in the optical network unit (ONU) is performed in the electronic domain and relies either on FDM with Nyquist sinc-pulse shaping or on orthogonal frequency division multiplexing (OFDM). This way the ONU can perform processing at low speed in the baseband. Further, the ONU is colorless by means of a remote seed for upstream transmission and a remote local oscillator for heterodyne reception, all of which helps in keeping maintenance and costs for an ONU potentially low and will simplify wavelength allocation in a future software defined network architecture. To extend the reach, semiconductor optical amplifiers are used for optical amplification in the downstream and upstream. Λιγότερα

Optical Interconnects for Future Data Center Networks covers optical networks and how they can provide high bandwidth, energy efficient interconnects with increased communication bandwidth. This volume, with contributions from leading researchers in the field, presents an integrated view of the expected future requirements of data centers and serves as a reference for some of the most advanced and promising solutions proposed by researchers from leading universities, research labs, and… Εμφάνιση περισσότερων

Optical Interconnects for Future Data Center Networks covers optical networks and how they can provide high bandwidth, energy efficient interconnects with increased communication bandwidth. This volume, with contributions from leading researchers in the field, presents an integrated view of the expected future requirements of data centers and serves as a reference for some of the most advanced and promising solutions proposed by researchers from leading universities, research labs, and companies. The work also includes several novel architectures, each demonstrating different technologies such as optical circuits, optical switching, MIMO optical OFDM, and others. Additionally, Optical Interconnects for Future Data Center Networks provides invaluable insights into the benefits and advantages of optical interconnects and how they can be a promising alternative for future data center networks. Λιγότερα

A homodyne coherent receiver for ultra-dense WDM-PON with off the shelf components is presented. It consists of a conventional DFB, phase switched clock signal, an optical coupler instead of a 90º hybrid, balanced photodetectors and digital signal processing. The phase swing for a DBPSK signal was optimized and the performance was experimentally evaluated in terms of the sensitivity for several laser linewidths. The acceptable frequency offset and clock time delay was also assessed. The results… Εμφάνιση περισσότερων

A homodyne coherent receiver for ultra-dense WDM-PON with off the shelf components is presented. It consists of a conventional DFB, phase switched clock signal, an optical coupler instead of a 90º hybrid, balanced photodetectors and digital signal processing. The phase swing for a DBPSK signal was optimized and the performance was experimentally evaluated in terms of the sensitivity for several laser linewidths. The acceptable frequency offset and clock time delay was also assessed. The results exhibit a sensitivity of -48 dBm at a BER of 10-3 and indicate a high
tolerance to phase noise. Λιγότερα

This article presents ACCORDANCE, a novel optical access network architecture based on OFDMA technology and applied on a PON topology. In compliance with next generation optical access requirements, this architecture aims to outperform existing PON solutions in terms of total capacity, bandwidth allocation flexibility, number of users, and network reach. Moreover, it provides the opportunity for convergence with wireless technologies and a smooth migration path from legacy access solutions like… Εμφάνιση περισσότερων

This article presents ACCORDANCE, a novel optical access network architecture based on OFDMA technology and applied on a PON topology. In compliance with next generation optical access requirements, this architecture aims to outperform existing PON solutions in terms of total capacity, bandwidth allocation flexibility, number of users, and network reach. Moreover, it provides the opportunity for convergence with wireless technologies and a smooth migration path from legacy access solutions like TDMA-PONs and DSL. Λιγότερα

Optical networking is the cornerstone of the Future Internet as it
provides the physical infrastructure of the core backbone networks. Recent developments have enabled much better quality of service/experience for the end users, enabled through the much higher capacities that can be supported.
Furthermore, optical networking developments facilitate the reduction of
complexity of operations at the IP layer and therefore reduce the latency of the connections and the expenditures to… Εμφάνιση περισσότερων

Optical networking is the cornerstone of the Future Internet as it
provides the physical infrastructure of the core backbone networks. Recent developments have enabled much better quality of service/experience for the end users, enabled through the much higher capacities that can be supported.
Furthermore, optical networking developments facilitate the reduction of
complexity of operations at the IP layer and therefore reduce the latency of the connections and the expenditures to deploy and operate the networks. New research directions in optical networking promise to further advance the capabilities of the Future Internet. In this book chapter, we highlight the latest activities of the optical networking community and in particular what has been the focus of EU funded research. The concepts of flexible and cognitive optical networks are introduced and their key expected benefits are highlighted. The
overall framework envisioned for the future cognitive flexible optical networks are introduced and recent developments are presented. Λιγότερα

While all-optical networking has reached a vibrant state, further advances are still needed to continue to cope with the explosive growth of future optical networks according to the current special issue of the Proceedings of the IEEE, the most highly-cited general-interest journal in electrical engineering and computer science. Many new technologies have the ability to provide enormous bandwidth for data transport, cost-effective upgrades of networks and greater savings in power… Εμφάνιση περισσότερων

While all-optical networking has reached a vibrant state, further advances are still needed to continue to cope with the explosive growth of future optical networks according to the current special issue of the Proceedings of the IEEE, the most highly-cited general-interest journal in electrical engineering and computer science. Many new technologies have the ability to provide enormous bandwidth for data transport, cost-effective upgrades of networks and greater savings in power consumption.
Titled "The Evolution of Optical Networking," this special 14-paper issue celebrates both the impact and enhanced quality of life that optical networking has brought to our society and the centennial anniversary of the Proceedings of the IEEE. Guest editors for this issue are Ioannis Tomkos, Biswanath Mukherjee, Steven K. Korotky, Rodney S.Tucker and Leda Lunardi. Topics, selected by these guest editors, cover the evolution of the optical networking solutions that have shown the greatest impact over the past years and the largest potential for the future. Specific subjects range from optical network technologies to optical network architecture, algorithms and protocols, from core to access network segments and from the past to the future of optical networking. Λιγότερα

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… Εμφάνιση περισσότερων

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. Λιγότερα

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… Εμφάνιση περισσότερων

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. Λιγότερα

Core networks of the future will have a translucent and eventually transparent optical structure. Ultra-high-speed end-to-end connectivity with high quality of service and high reliability will be realized through the exploitation of optimized protocols and lightpath routing algorithms. These algorithms will complement a flexible control and management plane integrated in the proposed solution. Physical layer impairments and optical performance are monitored and incorporated in impairment-aware… Εμφάνιση περισσότερων

Core networks of the future will have a translucent and eventually transparent optical structure. Ultra-high-speed end-to-end connectivity with high quality of service and high reliability will be realized through the exploitation of optimized protocols and lightpath routing algorithms. These algorithms will complement a flexible control and management plane integrated in the proposed solution. Physical layer impairments and optical performance are monitored and incorporated in impairment-aware lightpath routing algorithms. These algorithms will be integrated into a novel dynamic network planning tool that will consider dynamic traffic characteristics, a reconfigurable optical layer, and varying physical impairment and component characteristics. The network planning tool along with extended control planes will make it possible to realize the vision of optical transparency. This article presents a novel framework that addresses dynamic cross-layer network planning and optimization while considering the development of a future transport network infrastructure. Λιγότερα

Optical networks are moving from opaque and translucent architectures towards all-optical (transparent) architectures. In translucent architectures a small amount of regeneration (e.g. optical-electronic-optical conversion) is available in the network. The incorporation of the physical impairments in the routing and wavelength assignment (RWA) problem in transparent optical networks has recently received some attention from the research communities. This work compiles a comprehensive survey of… Εμφάνιση περισσότερων

Optical networks are moving from opaque and translucent architectures towards all-optical (transparent) architectures. In translucent architectures a small amount of regeneration (e.g. optical-electronic-optical conversion) is available in the network. The incorporation of the physical impairments in the routing and wavelength assignment (RWA) problem in transparent optical networks has recently received some attention from the research communities. This work compiles a comprehensive survey of the proposed algorithms that address this issue. The physical layer impairments and related classification in optical networks are initially presented followed by physical layer impairments (PLI) constrained and aware RWA algorithms. Algorithmic approach, current PLI-RWA proposals, impact of wavelength conversion on these algorithms, protection and resilience considerations, and proposed extensions to control planes are covered in this work. Further research topics are presented in this study. Λιγότερα

We presented in this paper the first results on 80 x 10.7-Gb/s based ULH transparent optical networks utilizing OADMs and OXCs based on LCoS based WSSs (that later on became the industry standard).

We describe an experimental realization of ultra-long-haul (ULH) networks with dynamically reconfigurable transparent optical add-drop multiplexers (OADMs) and optical cross-connects (OXCs). A simple new approach to dispersion management in ULH dense-wavelength-division-multiplexing (DWDM)… Εμφάνιση περισσότερων

We presented in this paper the first results on 80 x 10.7-Gb/s based ULH transparent optical networks utilizing OADMs and OXCs based on LCoS based WSSs (that later on became the industry standard).

We describe an experimental realization of ultra-long-haul (ULH) networks with dynamically reconfigurable transparent optical add-drop multiplexers (OADMs) and optical cross-connects (OXCs). A simple new approach to dispersion management in ULH dense-wavelength-division-multiplexing (DWDM) transparent optical networks is proposed and implemented, which enables excellent transmission performance while avoiding dispersion compensation on a connection-by-connection basis. We demonstrate "broadcast-and-select" node architectures that take full advantage of this method. Our implementation of signal leveling ensures minimum variations of path-averaged power among the wavelength-division-multiplexing (WDM) channels between the dynamic gain-equalizing nodes and results in uniform nonlinear and spontaneous-emission penalties across the WDM spectrum. We achieve 80×10.7-Gb/s DWDM networking over 4160 km (52 spans×80 km each) of all-Raman-amplified symmetric dispersion-managed fiber and 13 concatenated OADMs or 320×320 wavelength-port OXCs with 320-km node spacing. Λιγότερα