Showing papers presented at "International Conference on Transparent Optical Networks in 2006"

The Influence of Dense Fog on Optical Wireless Systems, Analysed by Measurements in Graz for Improving the Link-Reliability

Abstract: Free Space Optics (FSO) has gained considerable importance in this decade of demand for high bandwidth transmission capabilities. FSO can provide a feasible solution for the last mile access problem, but the availability and reliability issues have prevented it from gaining mass acceptance. Thus, a thorough investigation is required into the atmospheric attenuators and their impact on terrestrial FSO. In this work, we present our results about light attenuation at 950 and 850 nm wavelengths in continental city fog conditions with peak values up to 120 dB/km and compare them with the attenuation under dense maritime conditions with peak values up to 480 dB/km. The shown measurements are mainly important for predicting the reliability of FSO links.

Dispersion Optimised Impairment Constraint Based Routing and Wavelength Assignment Algorithms for All-Optical Networks

Abstract: Current methods in the area of Impairment Constraint Based Routing Algorithms (ICBRA) lack the capabilities to support information regarding dispersion management. The inclination towards higher bit-rates and heterogeneous optical networks in the future challenges the popular assumption that chromatic dispersion (CD) is adequately compensated on a per-link basis. Recognising the importance of dispersion management, this paper proposes algorithms which apply metrics that contain dispersion information to both the routing and wavelength assignment sub-problems. To the best of our knowledge, this is the first attempt to include dispersion information within the wavelength assignment sub-problem. The newly proposed algorithm is named Dispersion Optimised Impairment Constraint-based RWA (DOIC). The performance is compared to existing routing and wavelength techniques under two scenarios: 40 Gb/s and mixed 10 Gb/s 40 Gb/s services. Two physical impairments under investigation are Chromatic Dispersion (CD) and Optical Signal to Noise Ratio (OSNR).

Reliable Optical Wireless Links within UAV Swarms

Abstract: Unmanned Aerial Vehicles (UAV) flying in swarm formations carrying a variety of sensors for monitoring and surveillance is in fact a future application for both civil and military use. Different requirements of guidance and control of UAV were already identified; however, the communication facilities between mobile platforms and air-to-ground links are restricted to low bit rate radio based technology. In the near term data rates in the area of 100 Mbit/s to 1 Gbit/s will be needed to handle multiple sensor information in real-time and in parallel. Thus, UAV equipped with Free Space Optics (FSO) will emerge as a challenging new needs for large data transfer in real time. With data rate capabilities of up to 2.5 Gbit/s the FSO surpass all possible microwave and RF solutions.

Optimum Planning of GMPLS Transport Networks

Abstract: The rapid increase in the number of wavelengths per fiber has significantly increased the size of the Optical Crossconnect (OXC) in WDM transport networks. To maintain the scalability of the OXC at a reasonable level, various Multi-Granular OXC (MG-OXC) architectures have been proposed. Motivated by the fact that the MG-OXC constitutes only the optical segment of the Generalized Multi-Protocol Label Switching (GMPLS)-based transport node architecture, we first propose a novel node architecture that handles the whole traffic hierarchy defined in GMPLS. Second, incorporating the proposed architecture with our novel contributions, namely (1) bifurcation of multi-granularity traffic demands; (2) traffic flow grouping strategies at all granularity levels, requires defining a new transport planning problem, which we call the Routing and Multi-Granular Paths Assignment (RMGPA) problem. The RMGPA problem is formulated as a Mixed Integer Linear Programming (MILP) model with the objective of minimizing the overall network weighted port count.

Latency Constrained Aggregation in Sensor Networks

Abstract: Summary form only given. A sensor network is a network of sensor nodes which may exchange data through wireless communication. A particular feature of sensor networks is that they are highly energy constrained due to their use of batteries. We investigate data aggregation as a possible way to save energy consumption: nodes may delay data in order to aggregate them into a single packet before forwarding them towards some central node (or nodes). Latency constraints restrict the delay allowed for data arriving at the central node. These two ingredients, data aggregation and latency constraints, give rise to a large variety of optimization problems depending on how transmission energy and time are related to size of packets sent and transmission distance, how transmission paths are chosen, if latency is data or node dependent or not, if we work off- or on-line, in a centralized setting or in a distributed setting, etc. In this paper we investigate a first, basic data aggregation problem in which transmission energy and -time depend only on the pair of nodes involved in the transmission, and not on packet size. We assume unique transmission paths that form a tree rooted into the central node. The objective we have chosen is to minimize the maximum energy consumption over all nodes. Already this simple model gives rise to interesting and challenging algorithmic problems. We prove that the off-line version of the sensor problem is strongly NP-hard and we design a 2-approximation algorithm. Almost all real life sensor networks are managed in an on-line fashion by simple distributed algorithms in the nodes. We consider distributed on-line models both if the nodes are synchronized and non-synchronized and we apply competitive analysis into the quality of algorithms for them

Multilevel Digital Pulse Interval Modulation Scheme for Optical Wireless Communications

Abstract: In this paper a new pulse time modulation technique known as Multilevel-Digital Pulse Interval Modulation (MDPIM) is introduced and its properties are presented. Expressions for the pulse train, bandwidth, transmission rate and capacity are given. The performance of MDPIM is compared with other pulse modulation techniques. Also system block diagram and signal simulation are presented.

2D Photonic Crystal Cavity-Based WDM Multiplexer

Abstract: We designed an innovative frequency multiplexer based on contra-directional coupling and standing-wave resonators within a photonic crystal (PhC) structure. Three add-drop filters were cascaded, and the lattice periods of the PhC strips containing the cavities were changed to tune the dropped frequencies, with a very high degree of freedom. Each filter has a 1 nm bandwidth around 1550 nm and the three channels are 10 nm spaced. The variation of the local lattice period is very small, and the mismatch between the two adjacent structures does not affect the beam travelling the bus channel. The PhC structure was analyzed by using the plane wave expansion method and the device performance was investigated with the finite-difference time-domain technique. The transmittance of each drop channel is about 74%, with a non-uniformity between channels smaller than 5%. The overall longitudinal dimension of the multiplexer is less than 20 µ m, so that the device is ultra-compact.

Mathematical Modelling and Comparisons of Four Heuristic Optimization Algorithms for WCDMA Radio Network Planning

Abstract: In order to obtain accurate and reliable network planning and optimization results. The characteristics of WCDMA networks such as power control, soft handover (SHO) and the strong couplings between coverage and capacity have to be modelled accurately. These characteristics lead to unprecedented complexity of WCDMA radio network planning and optimisation that has not been seen in previous cellular networks. In this paper, we will present mathematical models that consider the characteristics of WCDMA radio networks. We will also present and compare the performance of four optimisation algorithms based on meta-heuristics that can be used to find solutions for practical WCDMA radio network planning and optimisation.

Expenditures Study for Network Operators

Abstract: One of the most important concerns of networks operators is the expenditures of their networks. The expenditures of any company can be split in two types: Capital Expenditures (CapEx) and Operational Expenditures (OpEx). The former deals with the costs of the infrastructure such as the network infrastructure, the buildings, the installations, bought equipment, etc. The latter deals with the cost related with the use of the network, i. e., network maintenance, network planning, service provisioning, fault reparation, etc. This paper will present the framework for the study of the Total Cost of the network Ownership (TCO). A more detailed description on the business, network planning and accounting/billing processes will be presented.

Highly Birefringent Photonic Crystal Fibre with Enhanced Sensitivity to Hydrostatic Pressure

Abstract: We present three constructions of birefringent photonic crystal fibres with increased sensitivity to hydrostatic pressure. The enhancement of sensitivity was obtained by enlarging diameters of several cladding air-holes or by introducing two air channels located symmetrically in the solid part of the cladding. We used nodal based finite elements method to calculate pressure-induced deformations and stress distribution in the fiber cross-section and hybrid edge/nodal finite elements method with perfectly matched layer to calculate propagation constants of the fiber modes. We calculated the spectral dependence of the phase modal birefringence and its susceptibility to hydrostatic pressure. Our results show that the sensitivity to pressure can be increased several times by optimizing the fiber geometry.

Photonic Crystal Sensors

Abstract: The paper deals with the possibility of using photonic crystals for sensing purpose. The optical properties of photonic crystals allow to realize sensing devices characterized by a high degree of compactness and a good resolution of the quantity to detect. A particular attention is devoted to force/pressure sensors and the design of a PhC microcavity pressure sensor is reported.

Recent Developments in WDM-PON Technology

Abstract: Considerable research is being conducted to exploit the potential of novel WDM-PONs exhibiting individual, data and protocol agnostic virtual point-to-point (p2p) links for each ONU. The research focuses on the deployment of uniform building blocks throughout the entire access network and on upgrading the channel data rate efficiently towards 10 Gb/s. This contribution gives an overview of basic principles of WDM-PONs, discusses merits and drawbacks of related approaches and highlights important requirements for key components such as injection-locked Fabry-Perot lasers, (R) SOAs, SLEDs and athermal AWGs.

Shared Risk Resource Groups and Survivability in Multilayer Networks

Abstract: Failure resilience is a desired feature of the Internet. Most traditional restoration architectures are designed assuming single failure cases, which is not adequate in present day multilayer networks. Multiple link failure models, such as Shared Risk Link Groups (SRLG), Shared Risk Node Groups (SRNG), and more generally Shared Risk Resource Groups (SRRG), are becoming critical in survivable network design. These shared risk models have been unified through the notion of colored graphs. In this paper we provide an efficient MILP formulation for the minimum color path problem which is related to finding a path of maximum reliability in a multilayer network and is thus essential issue of network survivability.

Optimization of The Shortest-Path Routing with Equal-Cost Multi-Path Load Balancing

Abstract: In this paper we address the problem of routing optimization in IP networks. We assume that traffic is routed along the shortest paths computed with respect to administrative link metrics. Metrics are distributed in a network by open shortest path first (OSPF) or a similar routing protocol. If it happens that the shortest path is not unique then equal-cost multi-path (ECMP) load balancing principle is applied. It means that the demand traffic destined to specific node is split among all the shortest paths to that node. The problem considered here is to determine the shortest-path routing pattern satisfying traffic demands, and to find appropriate link metrics while link capacities are not exceeded. Besides that many traffic engineering criterias can be used as objective function of the problem, we assume that the residual capacity volume is maximized. In this paper we formulate the problem as a mixed integer programme (MIP) and propose some combinatorial separation cuts for the problem and give an effective method for deriving such cuts.

Semiconductor Optical Amplifiers for Advanced Optical Applications

Abstract: We present different types of Semiconductor Optical amplifier, each specifically optimised for a particular optical application. Especially, we focus our attention on which key device parameters are desirable for applications such as in-line optical amplification, or all-optical signal processing. We start from the device design characteristics, focussing on the challenges involved in making leading-edge semiconductor material. We then present a range of SOA?s developed at CIP for specific applications, concentrating on the key features of each design. Finally, we, show results from several examples of advanced applications from booster amplification to non linear applications.

Optical Wavelength and Waveband Converters

Abstract: Wavelength conversion has been acknowledged as one of the most significant optical processing functions and various papers have been involved with investigating methods of translating very high bit-rate data into other wavelengths. This paper will give an overview of the recent advances in the area, with emphasis on methods that can be used as both wavelength and waveband converters, which can be used at higher bit rates without any configuration changes and are integratable and hence compact solutions. Four-wave mixing in SOAs is one of these techniques and we will elaborate on particulars of this technique. Switch architectures that benefit from wavelength and waveband conversion are presented.

The Modelling of MMI Devices

Abstract: Multimode interference (MMI) structures have found wide application as low-order couplers, splitters, combiners, switches and multiplexers. Recent advances in MMI devices have led to ultra-short MMI couplers, segmented MMI structures and cascaded MMI switches. This paper reviews the modeling techniques applicable to MMI structures. The paper covers analytical, semi-analytical and numerical approaches to the analysis and design of these newer MMI devices.

Ultrafast All-optical Self Clock Extraction Based on Two Inline Symmetric Mach-Zehnder Switches

Abstract: In this paper, we report a novel ultrafast all-optical self clock extraction module (CEM) based on two inline symmetric Mach-Zehnder switches. In the proposed CEM, incoming data packet is used as the control signal to set/reset the imbalance/balance states of the SMZs for extracting the clock pulse. CEM offers fast clock extraction response and high on/off contrast ratio between extracted clock pulse and residual signals. Simulation results show that contrast ratio of more than 20 dB at low input energy (1 fJ) and small required processing time in 100 Gb/s transmission are achievable.

10 Gb/s and 40 Gb/s Multi-Wavelength Conversion Based on Nonlinear Effects in HNLF

Abstract: We present experimental results and numerical simulations of multi-wavelength conversion of 10 Gb/s NRZ signals based on 2-pumps four-wave mixing, 10 Gb/s and 40 Gb/s RZ signals derived from supercontinuum (SC) generated in highly nonlinear fibre (HNLF). High quality SC with bandwidth exceeding 50 nm was generated when the HNLF was pumped with 25 dBm average power. Sliced SC can be used as a source for all-optical multicasting.

Optical Network Components Based on Microring Resonators

Abstract: In the last years much effort has been made to arrive at optical integrated circuits with high complexity and advanced functionality for application in optical networks. For this aim high index contrast structures, like optical microresonators, are employed that allow for a large number of functional elements within a given chip area: VLSI photonics. Experimental results of work performed at MESA+ will be reported including a microresonator-based, ultra-compact reconfigurable optical add-drop multiplexer operating at 40 Gbit/s and fabricated in SiON technology. In addition a discussion will be given of new challenges and possible solutions.

Availability of Translucent Networks Based on WSS Nodes, Comparison with Opaque Networks

Abstract: In this paper, we compare port unavailability relating to translucent and opaque optical networks. Translucent networks are based on unprotected and protected WSS (Wavelength-Selective Switch) nodes architectures. For opaque networks, standard nodes architectures are used. For the translucent networks, three representative conditions in terms of traveled kilometers and number of traversed nodes are described. This study reveals that, translucent networks are more interesting than opaque ones when the WSS nodes are protected; for the nodes architectures, the traffic matrix, and the failure rates considered in this study, translucent networks are on average 16% more available than opaque networks. When the WSS nodes are not protected, opaque networks are more advantageous for all ULH conditions. The difference is emphasized with the increase of the WSS failure rate which was increased from 2000 to 10000 FIT.

Comparison of Conventional and Offset Time-Emulated Optical Burst Switching Architectures

Abstract: Optical Burst Switching (OBS) control architecture considers two different models for management of offset-times in the network. A conventional OBS introduces an offset time (OT) between a control packet and a corresponding burst in soft-way by delaying the transmission of the burst in respect to the control packet in the edge node. Another idea for an OBS operation comes from Optical Packet Switching (OPS) world and it intends to emulate OT by means of an additional fiber span (FS) introduced in the data path at the input port of core node. Although the conventional OBS has attracted lots of attention, in this paper we highlight that it possesses many difficulties that can be avoided easily in OT-emulated OBS.

Traffic Grooming in Bidirectional WDM Ring Networks

Abstract: We study the minimization of ADMs (Add-Drop Multiplexers) in Optical WDM Networks with Bidirectional Ring topology considering symmetric shortest path routing and all-to-all unitary requests. We insist on the statement of the problem, which had not been clearly stated before in the bidirectional case. Optimal solutions had not been found up to date. In particular, we study the case C = 2 and C = 3 (giving either optimal constructions or near-optimal solutions) and the case C = k(k+ 1)/2 (giving optimal decompositions for specific congruence classes of N). We state a general Lower Bound for all the values of C and N, and we improve this Lower Bound for C = 2 and C = 3 (when N = 4t+ 3). We also include some comments about the simulation of the problem using Linear Programming.

Transparent Ring Interconnection using Multi-Wavelength Processing Switches

Abstract: Summary form only given. The talk will introduce the activities of the IST EU FP6 STREP project TRIUMPH (transparent ring interconnection using multi-wavelength photonic switches). It will focus on the use of advanced optical signal regeneration subsystems that enable novel optical networking concepts such as transparent ring interconnection at high bit rates (up to 160 Gb/s). The presentation will aim to reveal the possible configurations and associated performance of an optical cross connect that will offer multiwavelength regeneration and WDM to OTDM and OTDM to WDM conversion.

How to Transform a Multilayer Network into a Colored Graph

Abstract: Along with GMPLS new network survivability issues arose, and new models and tools were needed to cope with them. In this context the notion of Shared Risk Resource Group have been proposed, and then the colored graph model to answer these needs. In this work the basic definitions about colored graphs are reminded. Then the question of the transformation of a multilayer network into a colored graph is studied, since the way in which it is done can have a great impact on the quality of the solutions of some essential optimization problems in survivability issues, such as the shortest path problem, or the disjoint paths problem.

Evaluation of Packet Delay in OBS Edge Nodes

Abstract: In OBS networks, packets are aggregated into bursts in the edge nodes and then send through the all-optical network to the destination node. Most of the delay phenomenon (variable delay) occurs in the edge node, which is an important issue for the QoS provisioning. The paper characterizes the packet delay in the edge node, which is mainly determined by the burst assembly, transmission queuing as well as the characteristic of the incoming IP traffic.

Analysis of the Slotted Non-persistent CSMA Protocol with Poissonian Packet Size Using a Semi-Markov Graph Representation

Abstract: In this paper, we analyze the slotted non-persistent CSMA protocol when the packet size follows a poissonian distribution. To that purpose, we use a semi-Markov representation of the protocol and derive a closed form for the saturation throughput. The method can apply to a very large family of protocols and therefore unifies lots of results. The new formula for non-persistent CSMA with non unitary packet size present many interesting aspects.

Reconfigurable Add/Drop Multiplexer Design to Implement Flexibility in Optical Networks

Abstract: Reconfigurable Optical Add-Drop Multiplexer (ROADM) is a key network element enabling flexible handling of wavelengths. Its architecture allows for remote traffic provisioning at the wavelength level in network node, better utilization of transmission bandwidth, operation cost reduction, simplification of network design and implementation. In this talk we present recent results on the investigation of ROADM architecture, components and technologies. The study considers physical and networking aspects including modeling and simulations for optimization of the switching node.

Optical Amplifiers for Modern Networks

Abstract: Recent trends in optical networks, such as Reconfigurable Optical Add Drop Multiplexing (ROADM) and optical cross connects, require advanced optical amplifiers based on both Erbium Doped Fibre Amplifiers (EDFAs) and Raman technology. To address the dynamic nature of modern networks, EDFAs should provide broadband variable gain operation, flexible mid-stage access, fast transient response to dynamic events, and advanced spectral monitoring and control to adjust to changing spectral conditions in the network. An important supplement to EDFA technology is the use of Distributed Raman Amplification (DRA) to achieve transmission over multi-span Ultra Long Haul (ULH) links in all optical networks, as well as very high loss repeaterless links.

Study of the Impact of Burst Assembly Algorithms in Optical Burst Switched Networks with Self-Similar Input Traffic

Abstract: This work investigates the impact of burst assembly algorithms applied at the edge routers of optical burst switched (OBS) networks in terms of the self-similarity level observed at the output traffic in presence of self similar input traffic. The algorithms under consideration are based on of time and burst size criteria, while both static and adaptive approaches are examined. This study is based on existing and new models developed in the OPNET simulation platform. In order to quantitatively assess the self-similarity level of the input and output traffic at the edge nodes, various Hurst parameter estimators have been applied. The performance impact of the burst assembly algorithms in terms of burst assembly delay and its jitter is also assessed. Our study has shown that the burst assembly mechanism at the OBS edge routers reduces the self-similarity level of the output traffic and that this reduction depends on the parameters of the algorithm. Our results reveal that the proposed adaptive burst assembly algorithm performs better comparing to its non-adaptive counterpart.