Polarization mode dispersion (PMD), a potentially limiting impairment in high-speed long-distance fiber-optic communication systems, refers to the distortion of propagating optical pulses due to random birefringences in an optical system. Because these perturbations (which can be introduced through manufacturing imperfections, cabling stresses, installation procedures, and environmental sensitivities of fiber and other in-line components) are unknowable and continually changing, PMD is unique among optical impairments. This makes PMD both a fascinating research subject and potentially one of the most challenging technical obstacles for future optoelectronic transmission. Mitigation and compensation techniques, proper emulation, and accurate prediction of PMD-induced outage probabilities critically depend on the understanding and modeling of the statistics of PMD in installed links. Using extensive data on buried fibers used in long-haul high-speed links, the authors discuss the proposition that most of the temporal PMD changes that are observed in installed routes arise primarily from a relatively small number of "hot spots" along the route that are exposed to the ambient environment, whereas the buried shielded sections remain largely stable for month-long time periods. It follows that the temporal variations of the differential group delay for any given channel constitute a distinct statistical distribution with its own channel-specific mean value. The impact of these observations on outage statistics is analyzed, and the implications for future optoelectronic fiber-based transmission are discussed

/pdf/polarization-mode-dispersion-of-installed-fibers-582kkow2ng.pdf

Polarization Mode Dispersion of Installed Fibers

A detailed survey of approaches reducing energy consumption of core networks is presented in this paper. We consider a multilayer architecture, in which the optical layer can be realized either with a Wavelength Division Multiplexing (WDM) network or an Elastic Optical Network (EON). We focus on the design and operation stages, i.e., deciding which devices to install in the network during the former step, and choosing which devices to put into sleep mode during the latter one. A taxonomy for classifying the surveyed approaches is provided in order to compare the works covering energy efficiency in core networks (in terms of both optimal formulations and heuristic solutions). Moreover, our work provides a global view of the traffic assumptions, the topologies, and the power consumption models in the literature. The need of further investigations in this field clearly emerges. We envision future works targeting: (1) more effective standardization efforts to practically realize sleep modes; (2) the evaluation of the impact of sleep mode on the device lifetime; (3) the extensive adoption of new paradigms like Software Defined Networking (SDN) and EON; and (4) a radical improvement in the testbed implementations.

/pdf/a-survey-on-energy-aware-design-and-operation-of-core-35z5q51rug.pdf

A Survey on Energy-Aware Design and Operation of Core Networks

In this paper, we present a dynamic energy efficient routing and spectrum assignment algorithm with regenerator placement (RP) capability for elastic optical networks. In this algorithm, a virtual graph is considered for a given network topology graph, whereby the cost functions of virtual graph is computed according to the energy consumption of the corresponding links and intermediates routers. Furthermore, the arrived connection request is served by finding the most energy-efficient path among the possible candidate paths. Then, the quality of transmission (QoT) of the selected path is evaluated in terms of bit error rate. If the estimated QoT is higher than a predetermined threshold, the designated path is assigned to the incoming request, otherwise, the RP algorithm is utilized to place a regenerator at the most energy-efficient position. In addition, the demanded transmission rate and required QoT are fulfilled by assessing different modulation formats and selecting appropriate modulation format in terms of power consumption and blocking probability (BP). We evaluate the proposed algorithms through extensive numerical simulations. The results of simulations reveal that the proposed algorithms have better performance than other existing schemes in terms of network total energy consumption and acceptable BP.

Energy Efficient Routing and Spectrum Assignment With Regenerator Placement in Elastic Optical Networks

Routers and switches are major contributors to the energy consumption of modern networks. Today, many energy efficiency metrics for these high-capacity devices are coarse-grained, i.e., based upon a single energy per bit value given at peak load or averaged over several specific loads. In this paper, we develop a new power model and a vendor-agnostic methodology that permits quantifying the energy efficiency of Internet equipment at a more fundamental level, i.e., at the granularity of per-packet processing, and per-byte store and forward packet handling operations. We demonstrate the efficacy of the proposed technique by applying it to various types of routers and switches. We describe how our technique can be used to accurately estimate the network-wide energy footprint incurred when accessing different applications. We offer our method as a valuable framework against which the energy efficiency of current and future generation of load-proportional Internet equipment can be benchmarked.

Modeling Energy Consumption in High-Capacity Routers and Switches

Optical systems and technologies have been radically changing the telecommunication networks for past 15 years; today wavelength division multiplexing (WDM) technology, optical amplifiers, and simple optical switching elements like optical add-drop multiplexers (OADMs) are used in the backbone networks of all operators worldwide. Optical systems nowadays provide the basis for cost-effective transmission of large amounts of bandwidth over the Internet, and will enable its future growth and the spreading of new applications and services. This paper summarizes the main trends in optical networking and investigates potential future application areas. Optical system technology has become so pervasive in network design that it needs to be considered in the context of provisioning new applications and services. Therefore, the analysis is not limited to the aspects of physical transmission, but also takes into account recent developments in integrated network design as well as network control and management. The following sections describe the key functionalities of future optical network architectures, and the key findings of the theoretical analysis are supported by the results of a field trial of advanced transmission technology

Evolution of Terrestrial Optical System and Core Network Architecture

Reasonably accurate reference power consumption values are required for any work that evaluates power consumption in telecommunication networks. Many existing works provide or use optimal power rating (W/Gbps) values, i.e. the power rating achieved for the maximum capacity of the system, with the shared relative overhead thus being the smallest. In this paper, we evaluate how power rating values are influenced by practical equipment filling levels for core IP-over-WDM equipment. We show that, over the equipment's lifetime, for IP/MPLS routers it is reasonable to almost double the optimal power rating value under real-life equipment filling conditions. For Optical Line Amplifiers a correction factor of 1.5 is appropriate, and for WDM terminals the required correction is almost negligible, i.e. 1.1. Furthermore, power measurements on IP routers and Optical Line Amplifiers show that their power consumption marginally depends on traffic load.

/pdf/evaluation-of-power-rating-of-core-network-equipment-in-3yvyt1m148.pdf

Evaluation of power rating of core network equipment in practical deployments

Orange Labs organized a 6 month field trial to characterize states of polarization (SOP) variations with time on representative links of the future 40 Gbit/s deployment and to enable specifying the adaptation speed needed by optical polarization mode dispersion compensators (OPMDC). The SOP variations speed can reach more than 50°/1ms which seems not fully compatible with OPMDC specifications.

http://ieeexplore.ieee.org/iel5/5273784/5286960/05287313.pdf

Fast SOP variation measurement on WDM systems are the OPMDC fast enough

For incumbent operators, PMD may be an issue for 10 Gbit/s WDM ULH transmission systems; solutions studied in France Telecom R&D div. and implemented in field are discussed.

Design trade-off for high PMD routes in installed transmission systems

We report on the impact of PMD in a 8/spl times/170 Gbit/s DWDM transmission experiment over 430 km field installed SSMF with and without PMD compensation. Stable performance is only achieved when using PMDC.

Suzanne Salaun

Papers

Evaluation of power rating of core network equipment in practical deployments

Fast SOP variation measurement on WDM systems are the OPMDC fast enough

Design trade-off for high PMD routes in installed transmission systems

PMD tolerance of 8/spl times/170 Gbit/s field transmission experiment over 430 km SSMF with and without PMDC

Demonstration of simultaneous OSNR and CD monitoring using asynchronous delay tap sampling on an 800 km WDM test bed