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`

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`NEXT
`GENERATION
`OPTICAL
`NETWORKS
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`ee‘OpeticalTechnolo
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`
`Page 2 of 68
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`

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`Prentice Hall PTR
`UpperSaddle River, NJ 07458
`www.phptr.com
`
`Page 3 of 68
`Page 3 of 68
`
`

`

`LibraryofCongress Catalog Card Number: 2001033944
`
`Editorial/production supervision: Denna Cullen-Dolce
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`
`© 2002 Prentice Hall PTR
`Prentice-Hall, Inc.
`Upper Saddle River, NJ 07458
`
`All rights reserved. No part of this book may be
`reproduced,in any form or by any means, without
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`
`Thepublisher offers discounts on this book when ordered in bulk quantities.
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`Prentice Hall PTR
`One Lake Street
`Upper Saddle River, NJ 07458
`Phone: 800-382-3419, FAX: 201-236-714
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`
`Printed in the United States of America
`
`1098765432
`
`ISBN 0-13-028226-X
`
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`
`Page 4 of 68 age 4 of 68
`
`

`

`
`
`To ourfamily andfriends
`
`Page 5 of 68
`Page 5 of 68
`
`

`

`Contents
`
`
`
`Acknowledgments xix
`
`
`Preface xxi
`
`
`Introduction to Carrier Network Architectures 1
`
`4
`
`IP as Unifying Protocol Infrastructure 1
`The Traditional Carrier Network Architecture 2
`Achieving Long-Haul Connectivity with Optical Transmission
`Delivering Multiplexed Services 4
`Synchronous Transmission Standards 5
`Building a Complex SONET/SDH Carrier Network
`Multiplexing and Framing Standards 9
`Providing Carrier Class Network Availability 13
`Adding Versatility with Asynchronous Transfer Mode 14
`ATM Reference Model 15
`Introducing Statistical Multiplexing 16
`Transport Multiple Services across a Single Network 17
`AAL1
`18
`
`7
`
`AAL2 19
`
`AAL3/4 20
`
`AALS 20
`
`ATM Services 22
`
`vil
`
`Page 6 of 68
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`vill
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`contents
`
`PermanentVirtual Connection 23
`Switched Virtual Connection 23
`ATM VirtualConnections 23
`ATMStwitehing Operation 24
`ATMAddressing 24
`SubnetworkModel ofAddressing 25
`NSAP-Format ATM Addresses 25
`ATMAddress Common Components 25
`ATM Quality ofServsce 26
`ATM SignalingandConnectionEstablishment Overview 27
`Signaling Standards
`28
`ATM ConnectionEstablishment Procedure 28
`Connection Request Routingand Negotiation 29
`ProvidingInternetServices at theIPLayer 29
`InducingtheIPLayeron Top oftheATMLayer. 29
`UsingMultiprotocolLabelSwitchingforDeliveringIPServices ji
`ScalabilityIssues ofStandard IP Routing Protocols 31
`The ConceptofUsingLabels asForwardingInformation 3
`MPLS-Based Applications 36
`Next-Generation Carrier Networks
`38
`EliminatingIntermediateLayersintheBackbone 3?
`[PoverATMoverSONET/SDHover WDM(1) 4°
`IPoverATMover WDM (2) 41
`IP over SONET/SDHover WDM (3) 41
`
`[Pover WDM (4) 41
`Handling Fiber Capacity Exhaust 41
`Adding Intelligence to the Optical Layer 42
`Summary 44
`Recommended Reading 44
`
`Page7of68
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`Page 7 of 68
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`ff all
`
`

`

`Contents
`
`Ix
`
`Chapter 2
`
`Optical Networking Standardization 47
`
`47
`Standardization Activities and Targets
`Activities of the T1 Committee and Its T1x1 Subcommittee 48
`Optical Networking Standardization Framework (G.871) 48
`OTN Architecture (G.872) 50
`Layered Structure 50
`OCHLayer Network 51
`Optical Multiplex Section (OMS) Layer Network 52
`Optical Transmission Section (OTS) Layer Network 52
`Interlayer Adaptation 53
`Client Signal/OCH Adaptation 53
`OCH/OMSAdaptation 53
`OMS/OTSAdaptation 53
`Activities of the Institute of Electrical and Electronics Engineering (IEEE)
`10-Gbps Ethernet 54
`Resilient Packet Rings 55
`Activities of the Optical Internetworking Forum (OIF)
`OIF Mission 57
`
`57
`
`54
`
`Standard Physical Layer Interface 59
`IP-Centric Control and Signaling for Optical Paths 60
`Optical User-to-Network Interface (O-UNI) 60
`Activities of the IETF 64
`
`Summary 64
`Recommended Reading 65
`
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`

`

`x
`
`contents
`
`91
`
`68
`
`77
`
`chapter 3
`Optical Networking Technology Fundamentals 67
`optical Transmission Technologies 67
`Wavelength Division Multiplexing (WDM)
`Attenuation 70
`Dispersion 71
`73
`Nonlinear Effects
`Optical Signal-to-Noise Ratio(OSNR) 74
`Optical Transmission Systems
`74
`Optical Amplifiers 74
`75
`Erbium-Doped FiberAmplifiers (EDFAs)
`Praseodynamium-Doped FiberAmplifiers (PDFAs)
`Amplifier Control 78
`DWDMSystems 79
`Wavelength Routers 83
`Electrical Wavelength Routers 85
`Hybrid Wavelength Routers 86
`Optical Wavelength Routers 87
`Data Transmission Technologies
`90
`Packet over SONET/SDH (POS)
`PPPEncapsulation 92
`Framing 94
`Interface Format 95
`Transmission Rate
`96
`Payload Scrambling 97
`PPPover SONET/SDHat OC-192c/STM-64c 98
`Paralle] Implementation 98
`Word-Oriented POS Framing 98
`Automatic Protection Switching (APS) 101
`
`Page 9 of 68
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`Contents
`
`xl
`
`APS Channel Protocol 101
`Cisco’s APS Implementation 103
`APSSwitchover Process
`105
`APS Network Layer Interaction 105
`Dynamic Packet Transport (DPT)
`105
`Encapsulation 107
`IP Data Packets 109
`
`ATM Data Packets 110
`Control Packets
`110
`Usage Packets
`112
`SRP Physical Layer Implementation 112
`Framing 112
`Interface Format 113
`
`Transmission Rate 113
`
`Packet Handling Procedures 113
`Topology Discovery 113
`Packet Processing 115
`Multicasting 116
`Packet Priority 117
`SRP Fairness Algorithm 118
`Intelligent Protection Switching 120
`IPS Messages
`121
`IPS Message Handling State Machine 124
`Node Pass-Through Mode 126
`Network Management 126
`Clocking and Synchronization 126
`Data Transmission Technology Comparison 127
`Encapsulation Overhead 127
`Framing Overhead 128
`MPLSTraffic Engineering (MPLS-TE)
`
`133
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`xil
`
`contents
`
`MPLS-TE Architecture 133
`Why MPLS-TE 133
`135
`MPLS-TE Components
`Defining the Term Traffic Trunk 137
`MPLS-TE Attributes 138
`Trunk Attributes 138
`Bandwidth 138
`Resource Class Affinity 138
`Path Selection Policy 138
`Priority/Preemption 139
`Adaptability 139
`Resilience
`139
`
`140
`Resource Attributes
`Available Bandwidth 140
`Resource Class
`140
`Administrative Weight
`Information Distribution 140
`Bandwidth Accounting 141
`OSPF Extensions
`142
`Router Address TLV 145
`Link TLV 145
`
`140
`
`IS-IS Extensions 146
`
`Router ID TLV 147
`Extended IP Reachability TLV 147
`Extended IS Reachability TLV 147
`Path Computation and Selection 148
`LSP Tunnel Setup 149
`149
`LSP Setup Procedure
`150
`LSP Setup Request
`151
`Admission Control
`.
`Explicit Routing 151
`Label Allocation and LSP Establish
`RSVP Extensions
`152
`IP Routing using MPLS-TE 153
`
`ment
`
`151
`
`a
`
`
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`

`Contents—xii
`
`MPLS-TE Protection 157
`
`Path Protection 157
`
`159
`Restoration Time
`Optimizing Path Protection 159
`Link/Node Protection 160
`Network Survivability Principles
`164
`Defining Survivability 162
`Survivability Concepts 163
`Protection 164
`
`Restoration 164
`Protection Techniques
`Protection Types 165
`1+1 Protection 165
`
`165
`
`1:1 Protection 165
`
`166
`
`1:N Protection 165
`Protection Switching Characteristics
`Protection in Ring Networks 167
`Two-Fiber UPSR 167
`169
`Two-Fiber Bidirectional Line-Switched Rings (2-Fiber BLSRs)
`Four-Fiber Bidirectional Line-Switched Rings (4-Fiber BLSR) 171
`Protection Ring Comparison 172
`MPLSRestoration 173
`Prenegotiated versus Dynamic Protection 173
`End-to-Endversus Local Restoration 174
`Protection Switching Options 174
`1+1 Protection 174
`
`1:N and N:M Protection 174
`Network Survivability Design 175
`Survivability Mechanism Categories 175
`Dedicated Protection 175
`
`Shared Protection 176
`
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`

`al xiv Contents
`
`189
`
`Restoration
`
`176
`
`Restoration Time 176
`Survivability Mechanism Comparison 178
`Multilayer Survivability 180
`Survivability Design Trendsfor Optical Networks
`Eliminating SONET/SDHandATM 180
`Putting Intelligence into the Optical Core 181
`Summary 182
`Recommended Reading 183
`Optical Transmission Technologies 193
`Optical Transmission Systems
`183
`Data Transmission Technologies
`184
`Packet over SONETYSDH 184
`Dynamic Packet Transport (.DPT) 184
`MPLS TrafficEngineering (MPLS-TE) 184
`Network Survivability Principles 185
`
`Existing and Future Optical Control Planes 187
`Overlay Control Plane
`189
`Static[Pp Optical OverlayModel
`189
`IPServicefi"“frastructure 189
`Adaptation 19]
`Two-LaierArchitectsreT,mplementation 192
`Mulp;
`‘
`aVeleneth Transmission 194
`“dwide),Management 197
`taticOptical Contro] Plane
`199
`S =infstructureImplementation 198
`Mal] Point-to-Point Backbones or Backbone Inter©?
`
`S
`
`‘
`
`.
`
`erase
`
`anectio™
`
`7
`
`Page 13 of 68
`iaacme
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`

`Contents
`
`XV
`
`Large-Scale Hierarchical Backbones 200
`POP Aggregation 204
`Switched POP Aggregation 204
`Point-to-Point POP Aggregation 206
`DPT Fiber Ring POP Aggregation 207
`Optical Transport Infrastructure Implementation 208
`DWDMSystem Building Blocks 208
`Transponders 210
`WDM Network Design 211
`Topology 211
`Channel Spacing 212
`Maximum Line Rate 213
`Optical Power Budget 213
`Restoration 215
`
`Optical Protection 216
`Optical Line Protection 216
`Optical Channel Protection 218
`Optical Multiplex Section Protection 219
`Service Layer Restoration 221
`Automatic Protection Switching 221
`Intelligent Protection Switching 222
`IP Restoration 223
`Application-Based Restoration 223
`Layer 3 Route Convergence 224
`Load balancing 224
`MPLS-TEFast Reroute 225
`Dynamic IP Optical Overlay Control Plane 226
`Wavelength Routing Overlay Model 227
`Architecture and Elements 228
`Wavelength Routing Control Plane 231
`Lightpath Provisioning 234
`Lightpath Attributes 236
`Centralized Lightpath Routing 236
`
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`

`

`xvi__contents
`
`DistributedLightpath Routing 237
`Optical UNI Signaling 239
`Wavelength Conversion 240
`Restoration 240
`Protection Strategy 241
`Prenegotiated Protection 241
`On-DemandProtection 243
`QoS Levels 243
`Advanced Protection Concepts 243
`Local Protection 243
`Hierarchical Protection 243
`Integrated IP Optical Peer Control Plane 244
`Applicability Considerations 245
`Advantages 245
`Comparing WRs and LSRs 245
`Comparing LSPs andLightpaths 246
`MPLmS Model 247
`Architecture and Elements 248
`MPLmSControl Plane 249
`Lightpath Provisioning 252
`Optical Routing 252
`Topology Discovery 253
`Optical Link State Advertisement 254
`Optical LSA Objects 254
`Constrained-Based Routing 256
`Lightpath (OpticalLSP) Signaling 257
`et ofNested LSPs 257
`Ptical LSP Setup 258
`RSVp Setup Procedure 258
`:
`Optical LSp Setup in an OTN without Wavelength Conv
`S8tegation 261
`
`‘
`
`|
`
`|
`
`4
`rersio"
`
`Page 15 of 68
`
`
`aammm aa
`
`

`

`Contents
`
`xvii
`
`Using MPLmSin the Overlay Model 262
`Restoration 263
`
`Summary 263
`
`Recommended Reading 264
`Static IP Optical Overlay Control Plane 264
`Dynamic IP Optical Overlay Control Plane 265
`Integrated IP Optical Peer Control Plane 265
`
`Chapter 5
`
`
`
`Optical Networking Applications and Case Examples 267
`
`Optical End-to-End Networking Design Trends
`Service POP 268
`
`267
`
`Metro Solutions 272
`
`IP and Optical Metro Evolution 273
`Core Solutions 276
`
`IP and Optical Core Evolution 277
`Conclusions 278
`
`Case Example A: Next-Generation Storage Networks 279
`Application Requirements 283
`CommonSolutions 283
`
`Case Example B: Next-Generation Internet Service Provider 285
`Application Requirements 285
`Common Solutions 286
`
`Case Example C: Next-Generation Carrier
`Application Requirements 294
`Common Solutions 294
`
`293
`
`summary 300
`Recommended Reading 301
`
`Page 16 of 68
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`
`

`

`ai
`
`xviil Contents
`
`Glossary 303
`
`Notes 311
`
`Index 317
`
`—
`
`—~\
`
`age 17of68
`
`Page 17 of 68
`
`a.
`
`

`

`—-eee
`
`
`
`Introduction to Carrier Network
`Architectures
`
`In the first chapter, we give an overview about existing and possible future
`Carrier Network Architectures. We will explain the traditional architectural ele-
`ments and describe the basic concepts and requirementsofthese architectures in
`order to put each ofthe different elementsandits functionality into context. We
`do not go deep into the details ofall used technologies, but rather point out the
`most important basics to provide the reader with just the necessary level of
`knowledge to understand the moredetailed discussions of next-generation opti-
`cal networks throughout therest of the book.
`
`IP as Unifying Protocol Infrastructure
`Theexplosive growth ofInternet/intranettraffic is making its mark on the exist-
`ing transport infrastructure. An unprecedentedshift has occurred in traffic con-
`tent, pattern, and behavior. It has transformed the design of multiservice
`networks and created a commercial demandfor Internet Protocol (IP) networks
`that operate in excess of 1 Gigabit per second. A change in usage patterns from
`connection-oriented, fixed configured services to dynamic, connectionless IP
`services is currently underway. According to several studies, telephone company
`revenue will grow significantly, with data services—particularly IP—accounting
`for most of this increase. For public carriers, IP is critical for future revenue
`growth.
`
`:
`
`Page 18 of 68
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`
`

`

`Pend
`
`Exponential growth in IP traff, ech
`growth ofInternet and enterprise file is 2504),
`enhanced IP services based on Voice a Networ} ‘
`ties, and cost-effective, high-bandvi
`IP
`A
`ot—_poP=]
`scriber Line (DSL),cable modem,and viel nei
`From the networking perspective, IP i. = technocy ty
`and all transport technologies. Even epde © onl te
`technologies such as Asynchronous TrangferMs Solution
`tems and applications to map IP traffic onto e (ANY)a
`forms a commonand standardizedinterface : ackbop, cin Me
`technologies that are used to deliver the isles Svicewt
`enables operators to adapt quickly to rapidlyhae UCa stanlea
`ofnew technologies, and increasing competition gingMarkera
`An intelligent networkis onethatis able to separa
`:
`Such an intelligent network will recognize individ_
`leg fron {
`:&
`Users ang
`authenticate them asvalid users of the network, enable
`them to she
`and deliver the appropriate level ofperformance to the applicat
`Consideringthat the service providers’ business oftlymyi
`services, such as dial access and Frame Relay, ATM has ini
`way is to form an IP + ATM networkinfrastructure. An IPsAl\-
`infrastructure combinesthe application layervisibility ofIPandten:
`agement capabilities ofATM,all onasingle platform.This ensls-
`viders to provision services such as dial access and FrameRelay,is¥
`generation VoIP andintegrated access services from a unified netw-
`ture without compromising Quality of Service (QoS).
`
`.
`The Traditional Carrier NetworkArchitecture
`kinds ofnet
`Service providers have been using a mix ofvarious
`kinds
`nerwo™ P
`ogies for building up their national or international cam®tin
`1-1). In doing so, they had to cope with several constrain’ef bal
`eeches?wr
`networking technology introduced by the service
`in
`many networks, still handles—theissues ofone oF ™°"
`
`Page 19 of 68
`Page 19 of 68
`
`
`
`

`

`ae es
`
`ii.©|
`
`all
`
`n
`
`< Nal
`
`ic volumesis associated with
`“ONtinue
`‘
`twork
`e intranet networ usage, rapid ‘
`oice over IP (VoIP) and multicagy %
`width residential connectiy} Via
`8 Capa
`,, and wireless technologies,
`ital Si,
`tive, IP is the only protocol that ry
`Sven end-to-end solutions baseq on Ver ay
`susTransfer Mode (ATM)rely on ont
`P traffic onto backbonecircuits. Thetefpe
`ed interface between services andthe es
`liver the services. Such a standardizeden,
`ly to rapidly changing markets,the introduct,
`sing competition.
`thatis able to separate servicesfrom technolo,
`ill recognize individual users and applicati,
`s of the network, enable them to select serie:
`| of performance to the applications.
`providers’ business of todayis a mix ofdiffer
`d Frame Relay, ATM hasto beintegrated.(
`| network infrastructure. An IP+ATM new
`dlication layer visibility ofIP andthe traf
`all on a single platform.This enables se™™
`h as dial access and Frame Relay, as wel .
`d access services from a unified network #
`ality of Service (QoS).
`
`€twork Architecture
`‘ing a mix ofvarious kindsof networ fe
`1onal or international carrier neret
`Cope with several constraints anden
`duced by the service provider - gle
`the issues of one or more ofthes?
`
`;
`
`c
`
`in
`
`-
`
`~the
`
`;
`
`Page 20 of 68
`Page 20 of 68
`
`

`

`
`
`chapter» INTRODUCTIONTO CARRIER NETWORK ARCHITECTUppos
`
`9
`
`y.
`Exponential growth in IP trafficvolumesis 4SsOciated
`growth of Internet and enterprise intranet network iss
`enhanced IP services based on Voice over IP (VoIP) an- rapid tng
`ties, and cost-effective, high-bandwidthresidential connectstigsk
`scriberLine (DSL),cable modem,and wireless technologies ViaDigit
`From the networkingperspective, IP is the only Protocol ‘
`ib
`and all transport technologies. Even end-to-end solutions } at
`|
`technologies such as Asynchronous Transfer Mode(ATM)
`ased on bat,
`tems and applications to map IPtraffic onto backbone circuits he
`forms a commonand standardizedinterface betweenservices anth rb
`technologies that are used to deliver the services. Such a standatie
`enables operatorsto adapt quickly to rapidly changing markets, the eae
`ofnew technologies, and increasing competition.
`:
`An intelligent network is one that is able to separate services from tects
`Such an intelligent network will recognize individual users and appli
`authenticate them as valid users of the network, enable them to select senixs
`and deliver the appropriate level of performanceto theapplications.
`Considering that the service providers’ business of today is a mix ofdie
`services, such as dial access and Frame Relay, ATM hasto be integrated a
`way is to form an IP + ATM network infrastructure. An IP+ATMos
`infrastructure combines the applicationlayervisibilityofIPandthe=
`agement capabilities ofATM,all onasingle platform.This enables
`viders to provision services such as dial access and FrameRelay kad
`generation VoIP andintegrated access services from a unified net?
`ture without compromising Quality of Service (QoS).
`
`TheTraditional Carrier Network Architecture aitod
`Serviceproviders have been using a mix ofvarious kinds0 7 ks
`ogies forbuilding up their national or international aneandalee
`1-1). In doingso, they had to cope with several constraintsef hand age
`networking technology introduced by the service provase“o
`many networks,still handles—theissues ofone of ™°
`
`Page 21 of 68
`Page 21 of 68
`
`df
`
`

`

`The Traditional Carrier Network Architecture
`
`3
`
`
`
`IP
`
`arn
`
`Fa __
`
`Data/internetServices
`
`ory
`
`Statistical Multiplexing
`Multiservice Integration
`
`SONET/SDH
`
`wn
`
`|
`
`titeralien
`
`Optical/WDM
`
`i> |
`
`Capacity
`
`Figure 1-1
`The traditional network architecture consists of multiple layers
`As a consequence,a traditional service provider network architecture is built
`of multiple layers. The optical/Wavelength Division Multiplexing (WDM)
`layer forms the physical transport medium providing sheer bandwidth; in the
`past, this layer did not have too muchrouting intelligence. To allocate band-
`width in a proper way, the Synchronous Optical Network (SONET)/Synchro-
`nous Digital Hierarchy (SDH)layer is used in manytraditional networks. It
`offers mechanisms for efficient bandwidth utilization plusintelligent protection
`mechanismsbutdoes notallow intelligent routing. The ATM layer abovegives
`additional possibilities for statistical multiplexing while allowing multiservice
`integration at the same time. This basically enhancesefficient utilization of the
`layers below (the SONET/SDH and the optical/WDM layer). ATM also
`defines routing mechanismsintendedto optimizetraffic delivery throughoutthe
`network in termsof the different ATM service offerings.
`If service providers do not offer any IP services, the three-layer infrastructure
`described so far is more than sufficient. Because IP-based applications enforced
`IP service offerings, several mechanismsevolved integrating IP with the infra-
`structure described so far, ranging from pure overlay methods to very advanced
`integration models such as Multiprotocol Label Switching (MPLS).
`This layered network architecture grew and changedastheservices provided
`and sold by the providers changed and networking technology evolved. To
`understand this dramatic change in the architecture of today’s networks fully,
`
`Page 22 of 68
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`

` Chapter 1» INTRODUCTION TO CARRIER NETWORK Arc} TEC™
`
`TURES
`
`Th
`
`thy
`
`.
`
`*
`
`the functions and features of each of these layers wil]
`OW be discus
`chapter in more detail.
`Achieving Long-Haul Connectivity with Optical 7;
`ANSMiggi,
`Optical fiber as a transport medium offers a tremen
`will look into optical transmission details in greater detail in
`nt Ofcq
`.
`the folloy
`ters, but for the moment,we will try to keep it simple.
`nig the,
`Because of the fibers’ transmission capabilities, a
`modulated
`,..
`which is usually inserted by a laser, can be transmitted several ki] Ptical tiny
`it has to be recovered. With technologies available today(lasers sonehed.
`the signal has to be recovered every 40 to 80 km. The typical bit ln :
`with advanced modulation techniques today allow data to be sentat ag
`wavelength (optical frequency) and can be expected to Bo even higher =
`nology evolves.If multiple frequencies are used in parallel overone fbe, (ui
`generally is called WDM), the transmission capacity perfiber can be seid
`today into the Tb range.
`By deploying these technologies, service providers caneasily build opti
`networks with tremendous transmission capacity, ranging from several Ghp:
`Tbps, forming the basis for the current and next-generation backbone «i:
`networks.
`
`Delivering Multiplexed Services
`In the past,service providers typically delivered telephony services eet
`tomers. For this, they used nonsynchronous hierarchies called ang
`DigitalHierarchies (PDHs) to carry the low-bit-rate signals rep, i
`the customer's voice or data connections. PDH networks Bere! Pa
`tions. To begin with, the highest multiplexing rate is iiinaamount
`In addition, the transportefficiency is low because there is a a ous
`capacity required for accommodating delays betweenthea a
`ofthe network equipment. Furthermore, interoperability iis is de
`dorsis difficult because only multiplexing—not the trans™
`the standards.
`
`Page 23 of 68
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`The Traditional Carrier Network Architecture
`
`5
`
`Synchronous Transmission Standards
`SONETand SDH overcome the drawbacks of PDH networks and enable ser-
`vice providers also to provision high-bit-rate connections above 155 Mbps.
`These connections are typically required for today’s increasing data transport
`needs. SONET and SDH allowed service providers to build a Time Division
`Multiplexing (TDM) network ontop oftheir physical fiber plant. Although
`SONETis the North American synchronous TDM standard, SDH is the
`TDMstandard commonly used in Europe and Japan. Because SDH canbe seen
`as a global standard (and SONETbeing a subset of SDH), interoperability at
`certain levels is ensured, as will be outlined in more detail later. In addition to
`the summary in this chapter, the Nortel whitepaper “SONET 101” [NORT-1],
`the Bellcore standard GR-253 [BELL-1], and the International Telecommuni-
`cation Union (ITU) T recommendation G.707 [ITU-3] can be consultedforall
`the details on SONET/SDH.
`Both SONETand SDHdefine a digital multiplexing hierarchy and should
`ensure compatibility of equipment and implement synchronous networking.
`The basic functionality is that client signals of different service types, such as
`E0, E1, DSO, T1, ATM,andothers, are mapped into appropriate payloads that
`are then multiplexed into synchronousoptical signals.
`Both SONET and SDH accommodate nonsynchronous TDM hierarchies.
`SONETincludes the North American hierarchy, which is based on the DS1
`signal, combining 24 DSOs (56-Kbps channels) into one 1.54-Mb stream. SDH
`integrates the European hierarchy, which is based on the E1 signal, combining
`32 E0s (64-Kbps channels) into one E1 at a speed of 2.048 Mbps, as can be
`seen from Table 1-1.
`
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`6
`
`Chapter 1» INTRODUCTION TO CARRIER NETWorRK ARCHITEon JRES
`
`Table 1-1
`
`The North American and European TOM Hierarchies
`
`
`
`
`‘sew[sm|Oxo
`
`SONET, which was developed first, specifies a basic transmission mi
`51.84 Mbps, called the synchronous transport signal 1 (STS-1). The sila
`optical signal is called OC-Z (optical carrier 1). To ensure that both SONFT
`and SDH match into a common multiplexing hierarchy, SDH defines its hax
`level, the synchronous transport module 1 (STM-1), at 155.52 Mbps, whichis
`three times the SONETbase level. The optical line rates of both hierarchiesix
`shown in Table 1-2.
`
`Table 1-2
`
`interface Rates of the SONET/SDH Multiplexing Hierarchy
`
`
`
`Page 25 of 68 ge 25 of 68
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`

`

`The Traditional Carrier Network Architecture
`
`7
`
`Building a Complex SONET/SDHCarrier Network
`A typical SONET/SDH networkbasically consists of four different network
`elements:
`
`1. Add/Drop Multiplexer (ADM)
`2. Terminal Multiplexer (TM)
`3. Digital Cross-Connect (DXC)
`4. Regenerator
`All of these elements are interconnected using the service provider's fiber
`plant and form a typical SONET/SDHnetwork, as shown in Figure 1-2.
`ADMsused for ring networks and TMsused in linear topologies may be
`interconnected directly with darkfiber. If the distance between two multiplexers
`exceeds approximately 40 km,a regenerator mustbe placed in between the mul-
`tiplexers. The regenerator ensures proper transmission through regenerating the
`optical signal, which has been degraded during optical transmission across the
`fiber.
`
`
`
`IP Router
`
`Trunk Interfaces
`
`Eg
`
`
`A typical SONET/SDH network consists of multiple multiplexers forming rings
`Figure1-2
`orlinear links, which are interconnected with digital cross-connects
`
`Page 26 of 68
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`

` Chapter 1» INTRODUCTION TO CARRIER NeTWorK ARCHITECT,
`
`.
`
`ES
`
`fi
`
`.
`
`=
`
`Multiplexers are equipped with two types of interface
`interfaces. Trunk interfaces are used to interconnect i 5
`faces can range from OC-3/STM-1 to OC-192/sTyy
`current SONET/SDH_recommendations. Tributary en as
`“Pcifigg My
`attach client equipment, such as IP routers, AT sane ate a
`switches, to the multiplexers. The range of available tribue OF wil
`multiplexer typically starts at the hierarchy leve|
`- itera
`of the mult;
`face and goes down to DS-0 or E11 interfaces.
`REPStrun “
`To be able to switch a connection from a ring network segme
`|
`onto a point-to-point segment, DXCsare used. For example -"anhe,
`DXCis placed between ring A,ring B, andthelinear segment Ps igure
`plexer from each segment is attached to the DXC, using thik. Ma
`interfaces. Depending on whatlevel of the TDM hierarchy connect tbs,
`be cross-connected, a certain type ofDXC and the appropriate tina, nt
`to be used. Ifconnections at DS1/E1level are to be CLOSS-connected im
`tributaries must be used to attach the multiplexers to the DXc, and a Dt
`capable of switching at DS1/E1level must be selected,
`A networkreference model is specified by the SONET/
`SDHstandirs:
`define a proper structure forall of the mechanis
`ms in this complex networks
`nario. Threelayers are defined (Figure 1-3). Each network elementmaybens
`ofonly one or moreofthese layers, accordingtoits tasks andits requirement
`Thelowestlayer, called section layer (within SONET)or regeneratorsen
`layer (within SDH), incorporates optical transmission and signal regenentix
`All network elements are part of this layer. Moreover, regenerators areoa
`ofthis layer, because they simply regenerate the optical signals along vw!
`distance interconnections.
`
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`

`The Traditional Carrier Network Architecture
`
`9
`
`Path Layer (SONET)
`
`Multiplex Section Layer (SDH)
`
`Path Layer (SDH) LIne Layer (SONET)
`
`FD Section Layer (SONET)
`Regenerator Section
`
`|
`
`Regenerator Section
`Layer (SDH)
`
`Figure 1-3=SONET/SDH network reference model introduces three functionallayers
`
`Regenerator
`
`The secondlayeris called the line layer (SONET) or multiplex section layer
`(SDH). At this layer, several low-speed signals are multiplexed to and demulti-
`plexed out of the high-bit-rate signal of the trunk interfaces. Multiplexers and
`DXCsare part ofthis layer.
`Thethird layer is responsible for end-to-end connection delivery andis called
`thepath layer (SONET and SDH).Theclient equipmentterminating the end-
`points of connectionsis part ofthis layer.
`Certain control information is required at each layer for signaling, perfor-
`mance monitoring, or protection switching. This control information is carried
`in the overhead ofeach layer. Thus, a multiplexer is adding some path overhead
`(POH)to the signal coming from thetributary interface. It multiplexes multiple
`signals together and addsthe section overhead (SONET)or multiplex section
`overhead (SDH). Finally, before sending it out to the next network element,it
`adds the line overhead (LOH) within SONETorthe regeneratorsection over-
`head (RSOH)within SDH.
`
`Multiplexing and Framing Standards
`A widevariety of signals can be transported across a SONET/SDHinfrastruc-
`ture. A signal inserted or extracted througha tributary interface is mapped into
`an appropriate container. This containeris called virtual tributary (VT) within
`
`Page 28 of 68
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`40 Chapter1» INTRODUCTIONTOCARRIERNETWORKARCHITECTUR
`
`:
`
`ES
`
`|
`
`hy
`
`aay.
`SONETand virtual container (VC) within SDH. In
`itself, the container also includes the POH informationst tod.
`connectivity.
`' “"Suring enda,
`Howsignals are multiplexed and mappedis specified in
`th,
`recommendations. The mapping and multiplexing scheme a SONET
`tant signal ratesis outlined in Figure 1-4. Pleas
`moa.
`OF the
`e keep in mind
`Most IM,
`complete picture ofboth the SONETand SDH multiplexing a .Ihy
`SDH
`SONET
`Interfaces
`
` STM-4
`
`Figure1-4
`
`SONET and SDH multiplexing hierarchy
`
`Within SONET, four VT1.5s and three VT2s are
`then com 360
`VT group (VTG) at the DS1 level. Seven VTGs afe 1DSM
`mappedinto the basic building block the STS-1, which seertott js not i
`Because the first optical interface specified (the OC-1 ope conse
`monly used in practice, the first optical SONET ee the yrGs"
`OC-3 interface running at 155 Mbps. Thus, after mappin’
`STS-1, three STS-1s are mapped into an OC-3interface ined ost
`Within SDH,four VC-11s and three VC12s are CON 9. a!
`transport unit group (TUG-2)at the F1 level. Seve?
`
`
`
`Page 29 of 68
`age 29 of 68
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`

`

`The Traditional Carrier Network Architecture
`
`11
`
`the E3 level. As opposed to
`bined together and mapped into a VC-3 at
`SONET, SDHalso allows a high-bit-rate signal at 34 Mpbsto be mapped into
`a VC-3. Thefirst specified optical interface within SDH is the STM-1 interface
`running at 155 Mbps(equivalent to the OC-3 interface of SONET). A VC-3
`itself can be mapped in twodifferent ways into an STM-1 interface. It can be
`mapped into a TUG-3, and three TUG-3s can be combined into a VC-4, which
`is then mappedinto an STM-1interface. The secondpossibility is to map three
`VC-3s directly into an STM-1 interface.
`The basic building block of SONET is the STS-1, and the basic building
`block of SDH is the STM-1 frame. A high-level logical picture of the frame
`structure of both the STS-1 and STM-1is shown in Figure 1-5. Keep in mind
`that the STS-1 frame is used for a 51.84-Mbpsinterface, and the STM-1 frame
`is used for a 155-Mpbsinterface. Thus, the STM-1 frame has three times the
`columns of the STS-1 frame. From a functional point of view, the structures of
`the two frames are mostlikely the same.
`The first columnsof the frame are used for carrying the overheadofthe first
`two SONET/SDHlayers, the section overhead (SOH) and LOH,asdefined in
`SONET, or the RSOH and the multiplex section overhead (MSOH), as
`defined in SDH. The remaining columnsare used for the payload carrying the
`multiplexed containers. As already mentioned, the overhead ofthe third layer
`(the POH)is carried within each container.
`The payload pointers, which are part of the LOH (SONET) or MSOH
`(SDH), are the key function in both synchronoushierarchies. The VTs and VCs
`possibly may not be synchronous with the STS/STM-Frame.Ideally, SONET/
`SDHnetworks are synchronous, butin practice, there are always small clocking
`differences, and these have to be accommodated. As a consequence, the VTs and
`VCs are mapped into the STS/STM-frameatslightly varying boundaries. The
`payload pointers then are used to maintain a fixed relationship between the
`STS/STM-frame boundaries and the position of the containers mapped into
`the payload.
`
`Page 30 of 68
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