multiwavelength optical networks, second...

Multiwavelength Optical Networks, Second Edition

Updated and expanded, this second edition of the acclaimed Multiwavelength OpticalNetworks provides a detailed description of the structure and operation of modern opticalnetworks. It also sets out the analytical tools for network performance evaluation andoptimization for current and next generation networks, as well as the latest advances inenabling technologies.

Backbone optical networks are evolving to mesh topologies utilizing intelligent net-work elements; a new optical control plane is taking shape based on GMPLS; andsignificant advances have occurred in Fiber to the Home/Premises (the “last mile”),metropolitan area networks, protection and restoration, and IP over WDM. Each ofthese is treated in depth, together with new research on all-optical packet-switched net-works, which combine the speed of optics with the versatility of packet switching. Alsoincluded are current trends and new applications on the commercial scene (wavelengthson demand, virtual private optical networks, and bandwidth trading).

With its unique blend of coverage of modern enabling technologies, network archi-tectures, and analytical tools, the book is an invaluable resource for graduate and seniorundergraduate students in electrical engineering, computer science, and applied physics,and for practitioners and researchers in the telecommunications industry.

Thomas E. Stern is Professor Emeritus of Electrical Engineering at Columbia University,New York, and has served as department chair and technical director of Columbia’sCenter for Telecommunications Research. A Fellow of the IEEE, he holds several patentsin networking. He has also been a consultant to a number of companies, including IBM,Lucent, and Telcordia Technologies.

Georgios Ellinas is an Assistant Professor in the Department of Electrical and ComputerEngineering at the University of Cyprus, Nicosia. He has held prior positions as anAssociate Professor at City College of New York, as a Senior Network Architect atTellium Inc., and as a Senior Research Scientist at Bell Communications Research. Hehas authored numerous papers and holds several patents in the field of optical networking.

Krishna Bala is currently the CEO of Xtellus, a company that manufactures fiber opti-cal switches. Krishna was the co-founder and CTO of Tellium (NASDAQ: TELM), asuccessful optical networking company. Prior to that he was a Senior Research Scien-tist at Bell Communications Research. He holds a Ph.D. in electrical engineering fromColumbia University.

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Cambridge University Press978-0-521-88139-5 - Multiwavelength Optical Networks, Second Edition: Architectures, Design, and ControlThomas E. Stern, Georgios Ellinas and Krishna BalaFrontmatterMore information

http://www.cambridge.org/9780521881395

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Multiwavelength OpticalNetworks, Second EditionArchitectures, Design, and Control

THOMAS E. STERNColumbia University

GEORGIOS ELLINASUniversity of Cyprus, Nicosia

KRISHNA BALAXtellus






CAMBRIDGE UNIVERSITY PRESS

Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, Sao Paulo, Delhi

Cambridge University Press32 Avenue of the Americas, New York, NY 10013-2473, USA

www.cambridge.orgInformation on this title: www.cambridge.org/9780521881395

C© Cambridge University Press 2009

This publication is in copyright. Subject to statutory exceptionand to the provisions of relevant collective licensing agreements,no reproduction of any part may take place without the writtenpermission of Cambridge University Press.

First published 2009

Printed in the United States of America

A catalog record for this publication is available from the British Library.

Library of Congress Cataloging in Publication DataStern, Thomas E.Multiwavelength optical networks : architectures, design and control / Thomas E. Stern,Georgios Ellinas, Krishna Bala. – 2nd ed.

p. cm.Includes bibliographical references and index.ISBN 978-0-521-88139-5 (hbk.)1. Optical communications. 2. Computer network architectures. I. Ellinas, Georgios.II. Bala, Krishna. III. Title.TK5103.59.S74 2009621.382′7 – dc22 2008008319

ISBN 978-0-521-88139-5 hardback

Cambridge University Press has no responsibility for the persistence oraccuracy of URLs for external or third-party Internet Web sites referred toin this publication and does not guarantee that any content on such Websites is, or will remain, accurate or appropriate. Information regardingprices, travel timetables, and other factual information given in this workare correct at the time of first printing, but Cambridge University Pressdoes not guarantee the accuracy of such information thereafter.






To Monique, who has always been there for me. To our children and our grand-children (T.E.S.)

To my loving mother, Mary, and sister, Dorita, and the memory of my belovedfather, Nicos (G.E.)

To my wife, Simrat, and our children, Tegh and Amrita (K.B.)






Contents

Figures page xviiTables xxixPreface to the Second Edition xxxiAcknowledgments xxxv

1 The Big Picture 1

1.1 Why Optical Networks? 11.2 Objectives of an Optical Network Architecture 41.3 Optics versus Electronics: The Case for Transparent

Multiwavelength Networks 91.4 Optics and Electronics: The Case for Multilayered Networks 121.5 Network Hierarchies 161.6 A Little History 181.7 Overview and Road Map 22

2 The Layered Architecture and Its Resources 28

2.1 Layers and Sublayers 292.2 Network Links: Spectrum Partitioning 342.3 Optical Network Nodes: Routing, Switching, and Wavelength

Conversion 392.3.1 Static Nodes 402.3.2 Dynamic Nodes 462.3.3 Wavelength Converters 63

2.4 Network Access Stations 672.4.1 Transmitting Side 702.4.2 Receiving Side 71

2.5 Overlay Processors 742.5.1 Regeneration 762.5.2 Wavelength Interchange 76

2.6 Logical Network Overlays 772.6.1 SONET Networks 792.6.2 ATM Networks 81






viii Contents

2.6.3 IP Networks 832.6.4 MPLS and Its Extensions 84

2.7 Summary 852.8 Problems 87

3 Network Connections 91

3.1 Connection Management and Control 963.1.1 Optical Connections 1003.1.2 Logical Connections 100

3.2 Static Networks 1023.2.1 Point-to-Point and Multipoint Connections 1043.2.2 Packet Switching in the Optical Layer: The MAC Sublayer 1113.2.3 Additional Comments on Broadcast-and-Select 121

3.3 Wavelength-Routed Networks 1223.3.1 Routing and Channel Assignment 1243.3.2 Routing and Channel Assignment Examples 128

3.4 Linear Lightwave Networks: Waveband Routing 1333.4.1 Routing and Channel Assignment 1353.4.2 Multipoint Subnets in LLNs 1403.4.3 A Seven-Station Example 143

3.5 Logically-Routed Networks 1513.5.1 Point-to-Point Logical Topologies 1533.5.2 Multipoint Logical Topologies: Hypernets 156


4 Enabling Technology 165

4.1 Evolution of Transmission and Switching Technology 1664.2 Overview of the Optical Connection 1674.3 Optical Fibers 168

4.3.1 Principles of Guided-Wave Propagation 1684.3.2 Optical Fiber Technology: Transmission Impairments 1744.3.3 Solitons 1874.3.4 Photonic Crystal Fibers 188

4.4 Amplifiers 1904.4.1 Erbium-Doped Fiber Amplifiers 1914.4.2 Raman Amplifiers 1984.4.3 Semiconductor Optical Amplifiers 2014.4.4 Amplification Trends in Metro Optical Networks: Amplets 204

4.5 Optical Transmitters 2054.5.1 Lasers 2054.5.2 Vertical Cavity Surface Emitting Lasers 2114.5.3 Modulation Technology 212






Contents ix

4.6 Optical Receivers in Intensity-Modulated Direct-DetectionSystems 2174.6.1 Photodetectors 2174.6.2 Front-End Amplifier: Signal-to-Noise Ratio 2194.6.3 Digital Signal Detection: Noise, Interference, and Bit

Error Rate 2214.6.4 Analog Systems: Carrier-to-Noise Ratio 227

4.7 The End-to-End Transmission Channel 2284.7.1 Modulation Formats 2294.7.2 Forward Error Correction 2314.7.3 Equalization 233

4.8 Coherent Optical Systems 2344.9 Performance Impairments in a Network Environment 235

4.9.1 Cross-Talk 2354.9.2 Signal Power Divergence 2394.9.3 Chirp-Induced Penalty 2404.9.4 Optical Filter Concatenation: Distortion-Induced Penalty 2404.9.5 Polarization Mode Dispersion Impact on

System Performance 2414.10 Optical and Photonic Device Technology 241

4.10.1 Couplers and Switches 2424.10.2 Reciprocity 2554.10.3 Nonreciprocal Devices 2574.10.4 Optical Filtering Technology 2574.10.5 Multiwavelength Switch Technology 266

4.11 Wavelength Conversion and Signal Regeneration 2744.11.1 All-Optical Wavelength Conversion 2754.11.2 Opaque Wavelength Conversion and Signal Regeneration 278

4.12 Optical Switch Architectures 2814.12.1 Space Switches 2814.12.2 Wavelength-Selective Switches 288

4.13 Performance Evaluation: Methodology and Case Studies 2974.13.1 Physical-Layer Simulation: Three-Step Approach 2984.13.2 WDM Network Simulation Case Studies 301

4.14 Problems 311

5 Static Multipoint Networks 324

5.1 Shared Media: The Broadcast Star 3245.2 Representative Multiplexing and Multiple-Access Schemes 327

5.2.1 Time-Wavelength-Division Multiplexing/MultipleAccess 328

5.2.2 Subcarriers 3365.2.3 Code Division Multiple Access 352






x Contents

5.3 Traffic Constraints in Shared-Channel Networks 3675.3.1 Balanced Traffic 3705.3.2 Unbalanced Traffic 370

5.4 Capacity Allocation for Dedicated Connections 3715.4.1 Fixed-Frame Scheduling for Stream Traffic 3715.4.2 Fixed-Frame Scheduling for Packet Traffic 383

5.5 Demand-Assigned Connections 3895.5.1 Blocking Calculations in WDMA Networks 3905.5.2 Blocking in Combined Time-Wavelength-Division

Networks 3955.6 Packet Switching in the Optical Layer 399

5.6.1 Uncontrolled Scheduling: Random Access 4015.6.2 Scheduling with Loss 4035.6.3 Lossless Scheduling: Reservations 4055.6.4 Perfect Scheduling 4075.6.5 Dynamic versus Fixed Capacity Allocation 408

5.7 The Passive Optical Network 4095.7.1 ATM and Fixed-Frame PONs 4125.7.2 Ethernet-Based PONs 4145.7.3 WDM PONs 4165.7.4 Optical-Wireless Access 4205.7.5 Recent Trends 422


6 Wavelength/Waveband-Routed Networks 432

6.1 Introduction 4326.2 Physical Topologies 4346.3 Wavelength-Routed Networks: Static Routing

and Channel Assignment 4426.3.1 Flow Bounds: Matching the Physical

and Logical Topologies 4446.3.2 Nonblocking Stations 4486.3.3 RCA as a Graph Coloring Problem 4496.3.4 Rings 4526.3.5 Ring Decomposition of General Mesh Networks 4586.3.6 Multistar Wavelength-Routed Networks 4626.3.7 RCA as an Optimization Problem 4646.3.8 Heuristics for Static RCA 474

6.4 Wavelength-Routed Networks: Dynamic Routingand Channel Assignment 4846.4.1 Some Basic Routing and Channel Assignment Algorithms 484






Contents xi

6.4.2 Case Study: Bidirectional Rings 4916.4.3 Performance of Dynamic Routing Rules on Meshes 4946.4.4 Case Study: An Interconnected Ring 4956.4.5 Routing Multicast Connections in WRNs 497

6.5 Linear Lightwave Networks: Static Routing Rules 5076.5.1 Routing of Optical Paths 5096.5.2 Optical Connections: λ-Channel Assignment 5166.5.3 Significance of Nonblocking Access Stations in LLNs 5186.5.4 Local Access to LLNs 5196.5.5 Routing Waveband and Channel Assignment on the

Petersen Network 5216.5.6 Channel Assignment 5286.5.7 Multistar Linear Lightwave Networks 540

6.6 Linear Lightwave Networks: Dynamic Routing Rules 5446.6.1 Point-to-Point Connections 5446.6.2 Routing Multicast Connections in LLNs 558

6.7 Problems 568

7 Logically-Routed Networks 576

7.1 Introduction: Why Logically-Routed Networks? 5767.1.1 Multitier Networks: Grooming 581

7.2 Point-to-Point Logical Topologies: Multihop Networks 5857.2.1 ShuffleNets 5877.2.2 Families of Dense Logical Topologies 589

7.3 Multihop Network Design 5917.3.1 Logical-Layer Design 5917.3.2 Physical-Layer Design 5947.3.3 Traffic Grooming in Point-to-Point

Logical Topologies 5977.4 Multipoint Logical Topologies: Hypernets 607

7.4.1 Capacity of a Multipoint Subnet 6117.4.2 Families of Dense Hypernets 6137.4.3 Kautz Hypernets 6157.4.4 Hypernet versus Multihop 6287.4.5 Multicast Virtual Connections 631

7.5 Hypernet Design 6327.5.1 Logical-Layer Design 6327.5.2 Physical-Layer Design 6347.5.3 Traffic Grooming in Multipoint Logical

Topologies 6377.5.4 Multistar Realizations 639







xii Contents

8 Survivability: Protection and Restoration 647

8.1 Objectives of Protection and Restoration 6488.2 Current Fault Protection and Restoration Techniques in

the Logical Layer 6508.2.1 Point-to-Point Systems 6508.2.2 SONET Self-Healing Rings 6548.2.3 SONET Self-Healing Ring Interconnection Techniques 6578.2.4 Architectures with Arbitrary Mesh Topologies 663

8.3 Optical-Layer Protection: Point-to-Point and Ring Architectures 6698.3.1 Point-to-Point Systems 6698.3.2 Self-Healing Optical Rings 672

8.4 Optical-Layer Protection: Mesh Architectures 6778.4.1 Shared Optical Layer Line-Based Protection 6798.4.2 Optical Path-Based Protection 6928.4.3 Segment Protection 7008.4.4 Survivability Techniques for Multicast Connections 702


9 Optical Control Plane 714

9.1 Introduction to the Optical Control Plane 7169.1.1 Control-Plane Architecture 7199.1.2 Control-Plane Interfaces 7199.1.3 Control-Plane Functions 721

9.2 Overview of Multiprotocol Label Switching 7229.2.1 Packet Transport through an MPLS Network 7229.2.2 MPLS Protocol Stack 7279.2.3 MPLS Applications 728

9.3 Overview of Generalized Multiprotocol Label Switching 7299.3.1 Link Management in GMPLS 7319.3.2 Routing in GMPLS 7349.3.3 Signaling in GMPLS 742

9.4 Conclusions 751

10 Optical Packet-Switched Networks 756

10.1 Optical Packet-Switched Network Architectures 75810.1.1 Unbuffered Networks 75910.1.2 Deflection Routing 76410.1.3 Performance Analysis of Deflection Routing 76610.1.4 Buffering: Time Domain Contention Resolution 77010.1.5 Buffering and Wavelength Conversion: Time/Wavelength

Domain Contention Resolution 778






Contents xiii

10.1.6 Comparison of Contention Resolution Techniques forAsynchronous OPS Networks 782

10.1.7 Hybrid Electronic and Optical Buffering 78410.2 OPS Enabling Technologies 787

10.2.1 Packet Synchronization 78810.2.2 All-Optical 2R or 3R Regeneration 78810.2.3 Optical Switching 78810.2.4 Wavelength Conversion 78910.2.5 Optical Header Processing 78910.2.6 Optical Buffering 789

10.3 OPS Network Testbed Implementations 79110.3.1 CORD Testbed 79110.3.2 KEOPS Testbed 79310.3.3 WASPNET Testbed 796

10.4 Optical Burst Switching 79810.4.1 Just Enough Time Protocol 80110.4.2 Just In Time Protocol 80310.4.3 Contention Resolution in OBS Networks 806

10.5 Optical Label Switching 80810.5.1 All-Optical Label Swapping 80910.5.2 Contention Resolution Techniques 81110.5.3 OLS Network Implementations 811

10.6 Conclusions 82010.7 Problems 822

11 Current Trends in Multiwavelength Optical Networking 828

11.1 Business Drivers and Economics 82811.1.1 Cost Issues for WDM Point-to-Point Systems 83111.1.2 Cost Issues for WDM Rings 83211.1.3 Cost Issues for WDM Cross-Connect Networks 83311.1.4 Open versus Closed WDM Installations 835

11.2 Multiwavelength Optical Network Testbeds 83811.2.1 Optical Networks Technology Consortium 83811.2.2 All-Optical Network Consortium 83911.2.3 European Multiwavelength Optical Network Trials 83911.2.4 Multiwavelength Optical Network 84011.2.5 National Transparent Optical Networks Consortium 84011.2.6 The Importance of the Testbeds in Driving the

Telecommunications Infrastructure 84011.3 Metropolitan Area Networks 841

11.3.1 Metro Network Unique Characteristics 84111.3.2 Defining the Metropolitan Networking Domain 842






xiv Contents

11.3.3 Metro Network Evolution 84411.3.4 Metro Networking State of the Art 847

11.4 Long-Haul and Ultra Long-Haul Networks 85411.4.1 Current Considerations in Wide Area

Network Architectures 85411.4.2 Some Recent Commercial Network Deployments 856

11.5 New Applications and Services 85811.5.1 Wavelength-on-Demand 85811.5.2 Virtual Private Optical Networks 85811.5.3 Bandwidth Trading 859

11.6 Conclusions 861

A Graph Theory 869

A.1 Graphs 869A.1.1 Cycle Double Covers 872A.1.2 Eulerian Graphs 872A.1.3 Planar Graphs 873A.1.4 Matchings in Graphs 873A.1.5 Graph Coloring 874A.1.6 Digraphs 875A.1.7 Moore Bounds 875A.1.8 Max Flow–Min Cut 876

A.2 Hypergraphs 877A.2.1 Undirected Hypergraphs 877A.2.2 Directed Hypergraphs 878

B Fixed Scheduling Algorithm 879

B.1 Column/Row–Expansion Algorithm 880B.2 Decomposition into Permutation Matrices 883B.3 Column/Row–Compression Algorithm 883

C Markov Chains and Queues 884

C.1 Random Processes 884C.2 Markov Processes 885C.3 Queues 887

C.3.1 The M |M |1 Queue 888C.3.2 The M |G |1 Queue 888C.3.3 Little’s Formula 889






Contents xv

D A Limiting-Cut Heuristic 890

D.1 The Multicommodity Flow Problem and Limiting Cuts 890D.2 A Heuristic 891

D.2.1 Swap (X, Y ) 891D.2.2 Limcut 892

E An Algorithm for Minimum-Interference Routingin Linear Lightwave Networks 893

E.1 The Image Network 893E.2 The Min-Int Algorithm 894E.3 Minimum Interference 895

F Synopsis of the SONET Standard 896

G A Looping Algorithm 900

Acronyms 903

Index 915






Figures

1.1 Multilayered network. page 61.2 Physical picture of the network. 81.3 Layered view of an optical network. 131.4 Alternative network approaches. 151.5 Hierarchical network. 171.6 Road map. 242.1 Layered view of optical network connections. 292.2 A typical connection. 322.3 Client server associations in an optical transport network. 332.4 Fiber resources. 342.5 Wavelength and waveband partitioning of the optical spectrum. 352.6 Network picture based on spectrum partitioning. 382.7 Tree physical topologies. 412.8 Directional coupler. 422.9 A 16 × 16 star coupler. 43

2.10 Static routing node. 442.11 Directed star. 452.12 Space switch connection matrices. 462.13 Unidirectional ring. 472.14 Crossbar switch. 482.15 Clos switch. 492.16 Recursion for Benes switch. 492.17 An 8 × 8 Benes switch. 502.18 Generalized optical switch. 532.19 δ–σ linear divider-combiner. 542.20 A node without loopback connections. 552.21 Three-stage realization of a waveband-space switch. 562.22 Multiwaveband directional coupler. 572.23 WADM–NAS combination. 582.24 Wavelength conversion as a linear operation. 642.25 Wavelength interchanger. 652.26 Wavelength-interchanging switch. 652.27 WIXC implementation. 662.28 Wavelength-routed network. 67






xviii Figures

2.29 Network access station. 682.30 Example of a logical connection between two NASs. 692.31 Optical transmitter. 702.32 Optical receivers. 722.33 Heterodyne receiver and spectra. 732.34 Overlay processor. 752.35 Logically routed network. 782.36 SONET DCS. 812.37 ATM cell format. 822.38 ATM switch connections. 832.39 TCP/IP and OSI. 842.40 Taxonomy of multiwavelength networks. 86

3.1 End systems: full connectivity. 923.2 Star physical topology. 923.3 Bidirectional ring physical topology. 933.4 The control plane in an optical network. 983.5 Connection management system. 993.6 Star coupler example. 1053.7 Time-shared medium. 1063.8 A TDM/TDMA schedule. 1083.9 TDM/T-WDMA. 110

3.10 CSMA/CD. 1143.11 CSMA/CD collision. 1153.12 NAS equipped for packet switching. 1163.13 Packet switching in the optical layer. 1183.14 MAC protocol in the layered architecture. 1203.15 Wavelength-routed star network. 1233.16 Channel assignment example. 1253.17 Nonblocking access link. 1293.18 Bidirectional ring: single access fiber pair. 1303.19 Bidirectional ring: two access fiber pairs. 1323.20 A mesh network. 1333.21 Inseparability. 1363.22 Two violations of DSC. 1373.23 Inadvertent violation of DSC. 1373.24 Avoidance of DSC violations. 1383.25 Color clash. 1393.26 Seven stations on a mesh. 1413.27 Tree embedded in mesh. 1423.28 Multistar network. 1443.29 Embedded star on a bidirectional ring. 1463.30 Seven-node hypernet. 1483.31 Assumed channel spacings. 1503.32 A logical switching node in an optical network. 152






Figures xix

3.33 Eight-node ShuffleNet. 1543.34 ShuffleNet embedding. 1553.35 Details of ShuffleNet node. 1573.36 Twenty-two node hypernet. 1593.37 Hypernet embedding. 1604.1 A point-to-point optical connection. 1674.2 Refractive index profiles for fibers. 1694.3 Snell’s law. 1694.4 Ray propagation in a step-index fiber. 1704.5 Ray propagation in a graded-index fiber. 1714.6 Cylindrical coordinates. 1734.7 Commercial fiber cables. 1754.8 Attenuation as a function of wavelength. 1764.9 Broadening of pulses due to dispersion. 178

4.10 Dispersion coefficients as a function of frequency. 1794.11 Limitations due to nonlinear effects in multiwavelength systems. 1864.12 Soliton. 1884.13 Three types of microstructured fibers. 1894.14 Basic erbium-doped fiber amplifier structures. 1924.15 Energy levels in EDFA. 1924.16 EDFA gain profile. 1944.17 Illustration of noise figure. 1964.18 Raman gain coefficient in bulk silica as a function of frequency shift. 1984.19 Hybrid distributed-discrete amplification. 2004.20 Signal and pump power in hybrid system. 2004.21 Fabry–Perot laser. 2064.22 Single-frequency lasers. 2084.23 Laser array. 2104.24 Typical VCSEL structure. 2114.25 Pulse and accompanying chirp. 2134.26 Mach–Zehnder interferometer. 2154.27 Typical structure of an EA-DFB transmitter. 2164.28 Absorption and chirp (linewidth enhancement factor) parameters

versus reverse bias voltage for a typical EA-DFB transmitter. 2164.29 Photodiode. 2174.30 Transimpedance amplifier. 2194.31 Binary receiver. 2214.32 Typical waveforms in an IM/DD system. 2224.33 Eye diagram. 2234.34 Ideal detection. 2254.35 BER as a function of Q. 2264.36 Transmission channel processing operations. 2284.37 Modulation formats. 2294.38 FEC encoding/decoding functions. 232






xx Figures

4.39 Transversal decision-directed equalizer. 2334.40 Heterodyne receiver. 2344.41 Types of cross-talk. 2374.42 Power penalty with homodyne cross-talk. 2384.43 Controllable directional coupler. 2454.44 Mach–Zehnder switch. 2464.45 Two-stage Mach–Zehnder switch. 2474.46 Y-branch switch. 2484.47 Gate array switch. 2494.48 Laser-activated bubble switch element. 2504.49 2D mechanical switch using micromachined mirrors. 2514.50 3D MEMS switch. 2524.51 3D gimbaled mirror. 2534.52 Liquid crystal holographic switch. 2544.53 Two hologram N × N liquid crystal holographic switch. 2554.54 Illustration of reciprocity. 2564.55 Optical isolator. 2584.56 Fabry–Perot filter and its spectral response. 2604.57 MI filter. 2624.58 MI filter array. 2634.59 FBG used as a drop filter. 2644.60 A Mach–Zehnder WADM. 2644.61 Arrayed waveguide grating. 2664.62 Acousto-optic tunable filter. 2674.63 Liquid crystal MWS. 2694.64 A MEMS-based WADM. 2704.65 An MI filter-based WADM. 2724.66 Wavelength-dilated switch. 2734.67 Optoelectronic wavelength converter. 2754.68 Performance of a difference frequency converter. 2774.69 Opaque conversion and regeneration. 2784.70 SA-based regenerator. 2794.71 Nonlinear Mach–Zehnder regenerator. 2794.72 Nonlinear optical loop mirror regenerator. 2804.73 Optical crossbar switch. 2824.74 Path-independent loss crossbar switch. 2824.75 Circuit layout for 8 × 8 optical crossbar switch. 2844.76 Router/selector. 2854.77 Benes switch. 2854.78 Orders of cross-talk. 2864.79 Enhanced performance switch. 2874.80 Space dilation. 2884.81 OADMs in a network. 289






Figures xxi

4.82 Parallel and serial OADM architectures with capability for mwavelength add/drops. 290

4.83 Functional diagram of an OADM based on wavebands andwavelengths. 290

4.84 Typical B&S OADM architecture. Assumes (1+1) protection. 2924.85 Typical 4 × 4 ROADM based on 4 × 1 wavelength selective switch

and B&S-type of architecture. 2924.86 Transparent OXC. 2934.87 Opaque O-E-O OXC. 2944.88 Opaque O-O-O OXC. 2944.89 Hybrid waveband/wavelength switch. 2974.90 Wavelength-domain simulation. 2994.91 WADM chain. 3024.92 WADM structure and simulation model. 3024.93 Simulation results for the WADM chain. 3034.94 Ring interconnect network architecture. Worst-case paths between

A and B are indicated. 3044.95 Histogram of all cross-talk terms accumulated at receiver B for the

worst-case path of Figure 4.94. 3064.96 Cross-talk-induced Q penalty in dB versus dominant cross-talk term

power level. 3074.97 Q-channel performance for the worst-case path of Figure 4.94

assuming OC-192 bit rate and EA-modulated transmitters. 3084.98 A DWDM metro network deployment scenario. All rings represent

typical SONET OC-12/48/192 designs. DWDM is deployed onlybetween the superhub nodes (dark squares) in ring (solid) or possiblemesh (dotted) configurations. 309

4.99 DWDM metro network case study based on the network deploymentscenario presented in Figure 4.98. Nodes represent only superhubstations with typical distances (not shown to scale). 309

4.100 Simulation results for path A-F-D in Figure 4.99 comparingQ-channel performance with and without EDC. 311

5.1 Star networks. 3255.2 A 3 × 3 example. 3305.3 TDM/T-WDMA channel allocation schedules. 3315.4 Illustrating channel reuse in an FT-TR system. 3325.5 Illustrating optical spectral efficiency. 3345.6 SCMA example. 3375.7 Transmitting and receiving stations equipped for SCMA. 3375.8 Subcarrier spectra. 3405.9 Effect of OBI. 342

5.10 TDM/T-SCMA. 3465.11 SCM/SCMA. 349






xxii Figures

5.12 SCM/WDMA/SCMA. 3505.13 SCM/WDMA/SCMA example. 3515.14 Block diagram of a direct-detection CDMA system. 3545.15 Waveforms for a direct-detection CDMA system. 3565.16 Orthogonal optical codes. 3575.17 Parallel CDMA transceiver structure. 3595.18 CDMA with all-optical processing. 3595.19 Multidimensional codes. 3615.20 FBG encoder for FFH-CDMA. 3615.21 A 3D CDMA system. 3635.22 Realization of coherent optical CDMA. 3645.23 Shared-channel broadcast medium. 3675.24 Normalized traffic matrices. 3705.25 CASs for systems with a full complement of channels. 3765.26 CASs for Examples 4, 5, 6, and 7. 3785.27 Heterogeneous traffic scheduling. 3795.28 Logical multicast CAS. 3825.29 Single-server queue. 3855.30 Throughput versus traffic intensity. 3875.31 Markov chain model for demand-assigned traffic. 3915.32 Comparison of Engset and Erlang models. 3935.33 Normalized throughput versus traffic intensity. 3945.34 Normalized throughput versus traffic intensity. 3955.35 Matching time slots. 3965.36 Framed system blocking probabilities. 3975.37 Illustrating rearrangeability. 3985.38 Slotted ALOHA. 4035.39 Tell-and-go protocol. 4045.40 Lossless scheduling. 4065.41 Queues for perfect scheduling. 4075.42 Passive optical network. 4105.43 BPON frame. 4125.44 Transmission scenario in a BPON system. 4135.45 PON equipped for decentralized control. 4165.46 LARNet. 4175.47 RITE-Net. 4185.48 WDM PON. 4195.49 Integrated system for dual services. 4215.50 Dual services testbed. 4215.51 DWDM/TDM PON. 423

6.1 Number of vertices in known maximal graphs. 4356.2 Thirty-eight-vertex graph. 4356.3 Tessellations of the plane. 4366.4 Undirected deBruijn and Kautz graphs. 437






Figures xxiii

6.5 Construction for �dmin. 438

6.6 Plot of �dmin as a function of N . 438

6.7 Internodal distances in random networks. 4396.8 Recursive grid. 4406.9 Hierarchical Petersen graph. 441

6.10 Limiting cuts for four networks. 4476.11 Three-node network. 4496.12 Illustrating RCA in a wavelength-routed network. 4516.13 A four-fiber SPRING. 4536.14 A two-fiber SPRING. 4546.15 Bidirectional ring. 4556.16 Five-node WDM ring. 4586.17 Ring decomposition. 4596.18 Bridged ring overlay. 4626.19 A multistar network. 4626.20 Layered view of RCA. 4656.21 External traffic in flow conservation equations. 4676.22 Wavelength savings by increasing fibers. 4766.23 Mean values of N λ versus α. 4776.24 Minimum values of N λ versus α. 4786.25 Flow chart of the Monte Carlo algorithm. 4816.26 Time trace of Monte Carlo algorithm. 4836.27 An example of SPD routing. 4886.28 Blocking on an 11-node WDM ring. 4906.29 Gain in blocking; 11-node WDM ring, simulation. 4916.30 Fairness ratio; 11-node WDM ring, simulation. 4926.31 Fairness ratio improvement versus interchanger density; 11-node

WDM ring with 32 wavelengths. 4936.32 Simulation and asymptotic analysis; 195-node interconnected WDM

rings. 4966.33 Blocking improvement with wavelength interchange; 195-node

interconnected WDM rings. 4976.34 Fairness ratio improvement with wavelength interchange; 195-node

interconnected WDM rings. 4986.35 Fairness ratio improvement versus interchanger density; 195-node

interconnected WDM ring, 32 wavelengths. 4996.36 Multicast connection in a transparent network. 5006.37 A P×P split-and-deliver switch. 5016.38 A P×P multicast-capable optical cross-connect based on a

split-and-deliver switch. 5026.39 A P×P multicast-capable optical cross-connect based on splitter

sharing. 5036.40 Multicasting in a network with sparse splitting capabilities. 506






xxiv Figures

6.41 Petersen network. 5096.42 Structure of a nonblocking access station for an LLN. 5106.43 Optical paths. 5126.44 Optical connection hypergraph. 5186.45 Local access subnets on the Petersen network. 5206.46 Embedded star on tree TA. 5236.47 Waveband assignments: W = 5. 5266.48 Connection interference graph. 5296.49 Connection interference graph for Equation (6.60). 5306.50 Optical connection hypergraph. 5346.51 Fixed-frame scheduling for four LCs. 5346.52 Directed hypernet GKH (2, 8, 4, 4). 5426.53 Color clash. 5476.54 Illustrating inseparability. 5486.55 Illustrating Min-Int. 5506.56 Random network. 5516.57 Max Reuse versus Min Reuse channel allocation. 5526.58 k-SP routing. 5536.59 k-SP versus Min-Int routing. 5546.60 Blocking in networks with multifiber links. 5556.61 Blocking in networks with multiple wavebands. 5566.62 Example of a multicast connection. 5596.63 Example of a tree decomposition using MBFS-1. 5626.64 Example of a tree decomposition using MBFS-4. 5636.65 Illustrating routing on a tree. 5646.66 Blocking probability for multicast connections. 568

7.1 Why logically-routed networks? 5777.2 A schematic of a point-to-point LRN. 5797.3 Two-tier architecture. 5827.4 The architecture of a grooming node with optical bypass. 5847.5 ShuffleNet: δ = 3, k = 2, N = 18. 5877.6 Maximum throughput per node for ShuffleNet. 5887.7 deBruijn and Kautz digraphs. 5907.8 A traffic matrix and matched LCG. 5937.9 ShuffleNet on Atlantis. 595

7.10 Benefit of traffic grooming. 5987.11 A node in a SONET over WDM ring. 5997.12 Advantage of grooming static traffic in SONET over WDM rings. 6017.13 Construction of an auxiliary graph for grooming. 6057.14 Layered view of a hypernet. 6087.15 Hypernets. 6097.16 Illustrating fan-out in hypergraphs. 6137.17 Shuffle hypernet. 6147.18 Orders of K H (2, D, r ). 616






Figures xxv

7.19 Duality construction. 6187.20 Directed hypergraph construction via duality. 6197.21 Directed hypergraph construction via edge grouping. 6207.22 Tripartite representation of G K H (2, 42, 3, 28). 6227.23 Routing header. 6247.24 Comparison of hypernets and multihop networks. 6287.25 Multicast tree in DK H (1, 4, 2). 6317.26 Multicast-capable logical-grooming switch. 6388.1 Path versus line protection. 6518.2 (1 + 1) SONET protection. 6528.3 (1:1) SONET protection. 6538.4 (1:N) SONET protection. 6548.5 Single- and dual-access ring interconnection configurations. 6588.6 Two-fiber UPSR-to-UPSR ring interconnection. 6608.7 BLSR-to-BLSR ring interconnection. 6618.8 BLSR-to-UPSR ring interconnection. 6628.9 (1 + 1) Protection in the optical layer. 670

8.10 (1:1) Protection in the optical layer. 6718.11 (1:N) Protection in the optical layer. 6718.12 (1 + 1) Optical protection and (1:N) electronic protection for

a WDM system. 6728.13 Four-fiber WDM SPRING architecture. 6738.14 Four-fiber WDM SPRING surviving a link failure. 6748.15 Four-fiber WDM SPRING surviving a node failure. 6758.16 Two-fiber WDM SPRING architecture. 6768.17 A taxonomy of survivability schemes. 6778.18 Rerouting around a failed link. 6828.19 Directed cycles in a planar graph. 6838.20 Directed cycles in a nonplanar graph: K5. 6838.21 Face traversal for a planar national network. 6848.22 Orientable CDC of the ARPANet. 6868.23 Seven-node planar network with default protection switch settings. 6878.24 Seven-node planar network after a link failure. 6878.25 Failure recovery using the p-cycle approach. 6888.26 Generalized loopback example. 6918.27 (1+1) dedicated protection architecture. 6928.28 (1:3) shared protection in a mesh network. 6938.29 Spanning trees used in optical path protection. 6978.30 Shared risk groups. 6988.31 SRG classification. 6998.32 SLSP protection scheme. 7018.33 Examples of different types of islands centered on node 22. 7028.34 Examples of segment and path-pair protection of multicast sessions. 7038.35 Example illustrating the arc-disjoint and MC-CR algorithms. 704






xxvi Figures

9.1 A mesh optical network. 7159.2 Example of an optical node architecture. 7169.3 Provisioning a connection between two routers through

an optical network. 7179.4 Control plane architecture. 7209.5 Control plane interfaces. 7219.6 MPLS header format and MPLS packet format. 7249.7 Two LSPs in an MPLS packet-switched network. 7259.8 Label stacking. 7279.9 MPLS protocol stack. 728

9.10 Link bundling illustration. 7409.11 LSP hierarchy in GMPLS. 7419.12 User-Network Interface. 7439.13 Provisioning in GMPLS. 7449.14 Path and Resv message flows in RSVP for

resource reservation. 7469.15 RSVP message format. 7479.16 Protection signaling using GMPLS RSVP-TE. 75110.1 Optical packet-switching node. 76010.2 A generic OPS node architecture for an unslotted network. 76110.3 A generic OPS node architecture for a slotted network. 76110.4 An FDL-based synchronizer. 76210.5 A generic packet format for a slotted network. 76210.6 Optical packet contention. 76410.7 Petersen network graph. 76610.8 Paths from A to D. 76610.9 Input buffered optical packet switch with WSXC. 77110.10 Input buffered optical packet switch using multiple space

switch planes. 77210.11 FDL input buffer. 77210.12 Example of head-of-the-line (HOL) blocking. 77310.13 Feed-forward delay line architecture. 77310.14 Feedback delay line architecture. 77410.15 Dump-and-insert buffer architecture. 77510.16 Typical packet sequence in DI buffers for a 4 × 4 optical switch. 77610.17 Generic node architecture with TOWCs at the input lines. 77910.18 Details of output buffers for TOWC switch. 78010.19 Packet-loss probability versus number of FDLs with and without

wavelength conversion. 78010.20 Generic node architecture with TOWCs that are shared among

input lines. 78110.21 Node architectures for different contention resolution schemes:

single-wavelength delay line, multiwavelength delay line, wavelength






Figures xxvii

conversion, and wavelength conversion with multiwavelengthbuffering. 783

10.22 Switch architecture with electronic bufferingand wavelength conversion. 784

10.23 All-optical buffering and switching architecture. 79010.24 Physical implementation of the CRO device. 79210.25 CORD testbed. 79210.26 Packet format for the KEOPS project. 79410.27 Proposed unicast node architecture for the KEOPS project. 79410.28 Proposed multicast/broadcast node architecture

for the KEOPS project. 79510.29 SLOB architecture. Each stage is a photonic switch element (PSE). 79610.30 WASPNET optical packet switch. 79710.31 Optical packet switching and Optical burst switching. 79910.32 OBS architecture concept. 80010.33 Just enough time (JET) protocol. 80210.34 Just in time (JIT) protocol. 80410.35 Segmentation of a burst. 80710.36 Packet-loss probability versus load for different contention resolution

policies in OBS. 80810.37 OLS network. 80910.38 All-optical processor for OLS. 81010.39 OLS subcarrier transmission system. 81210.40 OLS network node. 81310.41 Network node architecture for an OLS testbed demonstration. 81410.42 FSK/IM orthogonal labeling scheme used in the STOLAS project. 81410.43 Optical router and optical label swapper used in the STOLAS project. 81510.44 Architecture of the edge-router in OPSnet. 81610.45 Architecture of the core-router in OPSnet. 81710.46 Core node configuration for label swapping and packet switching. 81910.47 OCSS technique. 81910.48 Experimental setup for multihop packet transmission

and multirate payload. 82010.49 K3,3 network. 82211.1 Six Central Offices, including two hubs, with capacity exhaust. 83111.2 Application of WDM point-to-point systems to alleviate

capacity exhaust. 83211.3 Six Central Offices, including two hubs, with capacity exhaust. 83311.4 Economic case for WDM rings. 83411.5 Node in Central Office: Electronic cross-connect. 83511.6 Economic case for WDM optical cross-connect. 83611.7 Open WDM network architecture: Opaque network. 83711.8 Integrated closed WDM network architecture. 83711.9 Current legacy SONET/SDH design in U.S. metropolitan regions. 842






xxviii Figures

11.10 Metro WDM interconnected-ring simulation case study. 84411.11 Typical ILEC metro network in the 2004 time frame. 84511.12 Typical view of a superhub in the ILEC metro network of

Figure 11.11 (2004 time frame). 84611.13 Typical view of a current superhub in an ILEC metro network. 84711.14 Typical deployment of 10 GbE technology in the metro environment. 84811.15 Typical metro network ring architectures. 85011.16 Typical vendor generic WADM node architecture for the metro

network application space of Figure 11.15. 85111.17 Metro network case study. 85311.18 Wavelength-brokering operational model. 86011.19 Infrastructure swapping. 86011.20 Multicarrier recovery. 861A.1 A maximal independent set. 870A.2 The complete graph K5. 870A.3 The complete bipartite graph K3,3. 871A.4 Orientable cycle double cover for K3,3. 872A.5 Multigraphs: Non-Eulerian and Eulerian. 873A.6 Maximum matching of a bipartite multigraph. 874A.7 A diclique. 876A.8 A cut. 877B.1 Example of decomposition of an NQDS matrix. 881B.2 Example of fixed-frame scheduling. 882C.1 Two-state chain. 886C.2 Birth–death process. 887C.3 A queue. 888E.1 Image network. 894F.1 SONET STS-1 frame and overhead channels. 897F.2 Creating an OC-N signal. 898F.3 Structure of a concatenated SONET frame. 898

G.1 Looping, first step. 901G.2 Final switch settings. 901






Tables

3.1 Tree routing on mesh 1493.2 Seven-station comparisons 1503.3 Wavelength assignments for ShuffleNet on a ring 1565.1 SCM/WDMA/SCMA example 3515.2 Multicast connections 3826.1 Orders of some graphs 4376.2 Comparative performance of three RCA heuristics 4806.3 Routing table 5176.4 Waveband routing in the Petersen graph: W = 3 5246.5 Waveband routing in the Petersen graph: W = 5 5276.6 Comparison of performance of various configurations of the

Petersen network 5386.7 Sizes of trees generated with the MBFS-d algorithm 5677.1 ShuffleNet routing on Atlantis 5967.2 Relative costs for different ring networks 6027.3 Kautz hypergraphs 6157.4 Performance of K H (2, D∗, r ) 6277.5 Performance comparison of DK H (d, D, s) to multihop networks 6307.6 Hypernet trees on Atlantis 636






Preface to the Second Edition

The first edition of this book was published when optical networks were just emergingfrom the laboratory, mostly in the form of government-sponsored testbeds. Since thenthere have been fundamental changes in many aspects of optical networking, drivenby the move from the laboratory to commercial deployment and by the twists andturns of the world economy. The investment climate in which optical networks havedeveloped has had two major swings as of this writing. During the technology bubble thatbegan at the end of the 20th century, investment in research, product development, andnetwork deployment increased enormously. The activities during this time of euphoriaproduced advances in the technology base that would not have been possible withoutthe extraordinary momentum of that period. At the same time, commercial networkdeployment provided a reality check. Some ideas that were pursued in the late 1990sdropped by the wayside because they did not meet the test of commercial viability, andnew ones came along to take their place. When the bubble burst after less than a decadeof “irrational exuberance,” the pendulum swung the other way. Investors and executiveswho a short time earlier thought the sky was the limit now wondered if demand wouldever materialize for all of the fiber capacity in the ground. At this writing a more reasonedapproach has taken hold; that seemingly elusive demand has materialized and, hopefully,a more rational and sustainable growth period will ensue.

This is the context for the second edition. It is designed to build on the foundationslaid out in the first edition while reflecting the new developments of the past 9 years:a maturing underlying technology, new tools for network control, and a recognition ofthe latest directions of optical network deployment and research. These new directionsinclude cost-effective metropolitan area network architectures tailored to the strengths ofcurrent optical transmission and switching equipment, passive optical networks to bringhigh-speed access to the end user, hybrid optical/electronic architectures supporting themerging of multiwavelength and Internet technologies, and networks of the future basedon all-optical packet switching.

As in the first edition, the emphasis of this book is on concepts and methodologies thatwill stand the test of time. The first three chapters provide a qualitative foundation forwhat follows, presenting an overview of optical networking (Chapter 1), the multiwave-length network architecture and its supporting components (Chapter 2), and a high-levelview of the different network structures considered throughout the book (Chapter 3). Amore detailed picture is provided in the remaining chapters, with a survey of enablingtechnology (Chapter 4) and in-depth studies of the three basic network structures: static






xxxii Preface to the Second Edition

multipoint networks (Chapter 5), wavelength/waveband routed networks (Chapter 6),and optical/electronic (logically routed) networks (Chapter 7). The remaining chapterscomplete the networking picture: survivability (Chapter 8), network control (Chapter 9),optical packet switching (Chapter 10), and current trends (Chapter 11).

The first three chapters are suitable for the reader who wishes to gain an understandingof multiwavelength networks without delving deeply into the analytical tools for net-work design and the physical underpinnings of the optical technology. These beginningchapters, together with Chapter 11, would be suitable for a short undergraduate coursefor electrical engineers and computer science majors.

The first seven chapters provide a largely generic framework for understanding net-work architectures, performance, and design in an abstract setting. An exception isChapter 4, which surveys enabling technology from theory to practice, thereby provid-ing the necessary background concerning the physical limitations and possibilities ofthe network technology. The material through Chapter 7, together with selected materialfrom the remaining chapters (depending on the reader’s orientation), can form the basisof a comprehensive graduate course, introducing the student to the latest developmentsin the field and suggesting a host of different research directions.

The networking developments since the publication of the first edition have served toreorient and expand our treatment in significant ways.

� Recognizing the importance of current activity in the “last mile” (fiber to thehome/premises), and in metropolitan area networks, we have added a new sectionon passive optical networks (PONs) in Chapter 5,1 and we have included new materialin Chapters 4 and 11 to connect our generic networking approach to recent metronetwork developments.

� Chapter 4 was substantially expanded and updated to provide a glimpse of the im-pressive new trends in photonic and electro-optic technology. Some of the new and/orexpanded topics are photonic crystal fibers, Raman amplification, supercontinuumgeneration, amplification trends in metro networks, and forward error correction andequalization to improve transmission performance. There are also new and expandedsections on wavelength conversion and signal regeneration with emphasis on all-optical techniques, and a new section on microelectromechanical system (MEMS)devices. The treatment of optical switch architectures has been significantly enlargedwith a focus on cost-effective architectures and opacity versus transparency. Moreemphasis is placed on the effects of signal impairments, including a new section onperformance impairments in a network environment. Also, new case studies are in-cluded that illustrate methodologies for evaluating the performance of metropolitanarea networks.

� Chapter 8, on survivability, protection, and restoration, was extensively updated, con-sistent with the growing importance of optical layer fault management in current

1 It is interesting to note that the PON, epitomized by the broadcast star, was the first structure that demonstratedthe possibilities of optical networking in the 1980s. However, it was largely ignored for large-scale networkdeployment until recently, when it has again come into its own as the vehicle of choice for extending opticalnetworks to the end user.






Preface to the Second Edition xxxiii

networks. It contains recent work on the subject, including shared line-based protectionin mesh networks, path-based protection, ring-based protection, segment protection,the treatment of shared risk groups, and recovery of multicast connections.

� Chapter 9, describing the control plane, was added to present the latest developments inoptical network control. It describes the control plane architecture as it has developedthrough the recent activities of several standards organizations. The chapter offers adetailed discussion of Multiprotocol Label-Switching (MPLS) and Generalized MPLS(GMPLS) as it applies to optical networks.

� Chapter 10, on optical packet-switched networks, was added to provide an introductionto this emergent field.2 It provides a window on a cutting-edge research area that hasthe potential to offer the next breakthroughs in optical networking.

� Chapter 11, on current networking trends (replacing the original Chapter 9), is acompletely updated description of the current networking environment. This includesa historical perspective describing the pioneering network testbeds, business drivers,and current trends in metro, long-haul, and ultra long-haul netwoks. Included alsoare some new applications that have emerged on the commercial scene, such aswavelengths on demand, virtual private optical networks, and bandwidth trading.

� This edition places increased emphasis on the practical aspects of hybrid (i.e., elec-tronic/optical and wavelength/waveband) architectures. This includes the importanceof grooming, which is required to pack electronically multiplexed channels efficientlyinto an optical wavelength channel, and to pack wavelength channels into wavebands.Also, the existence of transparent (purely optical) and opaque (electronic/optical) alter-natives to network design is stressed throughout. These practical aspects of networkinghave become important as optical networks have found their place in the real world.

Exercises are provided for most of the chapters, and many of them suggest avenues forfuture study. The book is meant to offer several different alternatives for study dependingon the interest of the reader, be it understanding the current state of the field; acquiringthe analytical tools for network performance evaluation, optimization, and design; orperforming research on next-generation networks.

2 Although the idea of using packet switching in optical networks is not new, it has attracted renewed interestas the technology for purely optical packet processing has developed over the past few years, and theadvantages of merging Internet and WDM technology have become apparent.






Acknowledgments

The first edition of this book had its origins in 1990, when we organized a small groupwithin the Center for Telecommunications Research (CTR) at Columbia University, toinvestigate lightwave networks. Among the many colleagues, students, and friends whocontributed in various ways to the first edition, there are several who have continuedto interact with us in the preparation of the second edition. We specifically express ourthanks to Eric Bouillet, Aklilu Hailemariam, Gang Liu, and G.-K. Chang. Special thanksgo to Ioannis Roudas for useful discussions and comments. Mischa Schwartz, who wassingled out as our guiding spirit in the first edition, is still an indefatigable contributorto communication networking and a continuing inspiration to us.

We are especially indebted to Neophytos Antoniades for coauthoring Chapters 4 and11 of the second edition. His understanding of the role of physical layer simulation andthe evolution of optical networks in the metropolitan area domain provided invaluableadditions to this edition.

We also express our thanks to Phil Meyler at Cambridge University Press for hissupport and encouragement, and to Anna Littlewood at Cambridge and Barbara Walthallat Aptara for their help in putting everything together.

Finally, Thomas Stern expresses his profound gratitude to his wife, Monique, for hereverlasting support; Georgios Ellinas is deeply grateful to his mother, Mary, and sister,Dorita, for their unyielding support and understanding during this endeavor; and KrishnaBala is greatly indebted to his wife, Simrat, and children, Tegh and Amrita, for theirpatience and support.






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