introduction to telecommunications - westnet learning...

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Introduction to Telecommunications


Contents

Preface ............................................................................. xvii

Prerequisites ...................................................................................xviiWho Should Study This Course? ...................................................xviiKey Topics .....................................................................................xviiiCourse Objectives ..........................................................................xviiiHow Do I Use This Course? ............................................................xix

Real-World Scenarios ...............................................................xixPedagogy ..................................................................................xixKey Terms .................................................................................xix

Resources Available in Instructor-Led Settings ...............................xixWhy Choose WestNet? ....................................................................xx

Introduction ...................................................................... xxi

Course Overview .............................................................................xxi

Module 1The Public Switched Telephone Network ...........................1

Lesson 1Telecommunications History ................................................12

Invention of the Telephone .............................................................121885: American Telephone and Telegraph ......................................131893: Initial Competition ................................................................131908: Government-Approved Consolidation ..................................131934: Federal and State Regulation ..................................................141956: The Hush-a-Phone Decision ..................................................151956: The Consent Decree ...............................................................161968: Carterfone Decision ...............................................................161969: Competition From MCI .........................................................171984: Breakup and Divestiture .........................................................17

Regional Bell Operating Companies .........................................18Local Access and Transport Areas .............................................18

1988: More Freedom for the RBOCs ................................................19


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1996: Telecommunications Act .......................................................19Long Distance Service From RBOCs ..........................................19Local Service From Interexchange Carriers (IXCs) ...................20Interconnection ........................................................................20Cross-Region Competition ........................................................20Manufacturing ...........................................................................20

2004: New Rules for Unbundling Network Elements ......................21

Lesson 2Elements of the Telecommunications Business ...............................................................................25

The Players .......................................................................................25Interexchange Carriers .....................................................................26

RBOCs/Local Exchange Carriers ...............................................26Competitive Local Exchange Carriers .......................................26Competitive Access Providers ...................................................27

Regulated Competition ....................................................................28An Expanded Role for the FCC .................................................28Local Number Portability ..........................................................29Shared Platforms .......................................................................29Network Interconnection ..........................................................29Unbundled Local Loops ............................................................29Reciprocal Compensation .........................................................30Tariffs .........................................................................................30

Effects of Competition .....................................................................30Legal Struggles ...........................................................................30Price Pressure .............................................................................31Slamming ..................................................................................31

Lesson 3Local Exchange Components ...............................................34

The Telephone System Hierarchy ....................................................35Class 5 Central Office: The Local Exchange .............................37Class 4 Central Office ................................................................39Tandem Central Offices ............................................................41Class 1 Offices ...........................................................................42

Class 5 Central Office Components ................................................43Switching and Routing ..............................................................43Semipermanent Circuit Connections .......................................44IXC Point of Presence ...............................................................45Billing ........................................................................................45Customer Premises ....................................................................45

Local Exchange Calling Options ......................................................46Local Exchange Carrier Does It All ...........................................46Competitive Local Exchange Carrier Serves as Reseller ............46CLECs Switch and ILECs Wire ..................................................46CLEC Does It All ........................................................................47

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Lesson 4Central Office Switching ......................................................50

The Talking Path ..............................................................................50Evolution of Telephone Switching ..................................................52

Step-by-Step Switching and Rotary Dial Telephones ................55Crossbar Switching ....................................................................57Later Electromechanical Switching ...........................................58Digital Switches .........................................................................59DTMF Signaling .........................................................................59

How a Call is Made ..........................................................................61Dial Tone ...................................................................................61Entering a Telephone Number ..................................................61Call Routing ..............................................................................61Ringing ......................................................................................64Ending the Call .........................................................................65

Long Distance Voice Routing ...........................................................65Signaling ...........................................................................................66

In-Band vs. Out-of-Band Signaling ...............................................................66Signaling System 7 ....................................................................66

Telephone Numbering System .........................................................67The Dwindling Supply of Numbers ..........................................68Local Number Portability ..........................................................69

Assigning Telephone Numbers ........................................................71Special Area Codes ...........................................................................71Special NXX Codes ...........................................................................71

Special Information: 555 ...........................................................71Hearing-Impaired Services: 800-855 .........................................71Service Codes, or N11 Numbers ................................................71Toll-Free: 800, 888, 877, etc. .....................................................72Premium: 900 ............................................................................72700 Services ...............................................................................73Follow-Me: 500 ..........................................................................73

Lesson 5Trunks, Lines, and Loops ......................................................76

Telecommunications Terms .............................................................77Loops ................................................................................................78Lines .................................................................................................78Trunks ...............................................................................................79

Trunk Direction .........................................................................80Trunk Capacity ..........................................................................80Trunk Transmission Type .........................................................80

Analog Transmission ..........................................................80Analog Bandwidth .............................................................82Digital Transmission ..........................................................82Digital Bandwidth ..............................................................83

Channels and Multiplexing .............................................................84Multiplexing ..............................................................................84


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Pulse Code Modulation (PCM) .................................................86Types of Trunks ................................................................................89Special Access Trunks .......................................................................90

Tie Trunk ...................................................................................90Private Lines ..............................................................................91Foreign Exchange ......................................................................91Ring Down ................................................................................93Trunk Pricing .............................................................................93

Lesson 6Outside Wire Plant ...............................................................96

Transmission Media .........................................................................97Copper ..............................................................................................97

Twisted Pair ...............................................................................98Twisted Pair Cable Color Codes .......................................100

Coaxial Cable ..........................................................................102Fiber Optic Cable ............................................................................103

Wireless Transmission .............................................................106Microwave ........................................................................106Geosynchronous Satellites ...............................................106Low Earth Orbit Satellites ................................................107Cellular Phones ................................................................108

Comparing the Media .............................................................108Media Convergence .......................................................................110

Summary ...........................................................................113Quiz ..................................................................................115

Module 2Customer Premise Equipment .........................................121

Lesson 1Key Systems .......................................................................128

Key System Components ...............................................................128Cordless Key Systems .....................................................................130Limitations of Key Systems ............................................................131Hybrid Systems ...............................................................................131

Lesson 2Central Office Exchange ....................................................133

Centrex ...........................................................................................133Centrex Benefits .............................................................................134Technical Requirements for Centrex .............................................135

Distance From CO Switch .......................................................135Allocation of Call Paths ..........................................................136Customer Premises Equipment ...............................................136

IP Centrex Features ........................................................................136IP Centrex ................................................................................137

Centrex vs. PBX ..............................................................................139

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Lesson 3Private Branch Exchange ....................................................142

PBX Components ...........................................................................142Trunks ......................................................................................143Extension Lines .......................................................................144Equipment Cabinet .................................................................144Telephones and Attendant Console .......................................145Administrative Terminal .........................................................146

Making a Call on a PBX .................................................................146Calling on an IP PBX ...............................................................147

Call Routing ...................................................................................147Supplementary PBX Features .........................................................148

Direct Inward Dialing .............................................................149Direct Inward System Access ...................................................150Uniform Dialing Plan ..............................................................150

Station Set Features ........................................................................151Attendant Console Services ...........................................................153Call Accounting .............................................................................154

Authorization Codes ...............................................................155Account Codes ........................................................................155

Administration and Management Reports ....................................155Call Detail Reports .........................................................................155

Test Reports .............................................................................156Busy-Hour Studies ...................................................................156

PBX Enhancements ........................................................................156Voice Response ........................................................................156Voice Recognition ...................................................................157Call Following .........................................................................157Automatic Call Distributor .....................................................157Other Auxiliary Equipment ....................................................158Paging Equipment ...................................................................158Call Management System .......................................................158

PBX Costs and Requirements .........................................................159

Lesson 4Voice Mail Systems ............................................................163

Voice Mail Features ........................................................................163Voice Mail/PBX Integration ....................................................164Design Factors .........................................................................165Unified Messaging ...................................................................166Broadcasting ............................................................................166Voice Mail Security .................................................................166

Automated Attendants ...................................................................168

Lesson 5Systems Installation Considerations ....................................171

System Power Considerations ........................................................171DC Power .................................................................................172AC Power .................................................................................172


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System Grounding .........................................................................174The National Electric Code .....................................................174Reasons for Grounding ...........................................................174

Overvoltage Protection ....................................................175Voltage Stabilization ........................................................175Provide a Path for Overcurrent Devices ...........................175

Approved Grounds ..................................................................175Multiple Approved Grounds ............................................176

Ground Reference Points ........................................................177Line Power Conductor Identification .....................................179

System Environmental Concerns ..................................................179Heat Dissipation ......................................................................179Temperature and Humidity ....................................................179Air Purity .................................................................................180RFI Noise .................................................................................180ESD ..........................................................................................181

Summary ...........................................................................186Quiz ..................................................................................188

Module 3Telephony Services ..........................................................191

Lesson 1Analog Voice Services ........................................................199

Voice Billing Options .....................................................................199Flat Rate ...................................................................................200Measured Service .....................................................................200Local Measured Service ...........................................................200Mileage-Sensitive Rates ...........................................................200

Enhanced Voice Services ................................................................200Call Waiting ............................................................................201Call Forwarding .......................................................................201Conferencing ...........................................................................203Call Hold .................................................................................203Voice Mail ...............................................................................203Speed Calling ...........................................................................204Distinctive Ringing .................................................................204Call Pickup ..............................................................................204Hunting ...................................................................................204

Custom Local Area Signaling Services ...........................................205Caller ID ..................................................................................205Anonymous Call Blocking ......................................................205Continuous Redial ..................................................................206Callback ...................................................................................206Call Rejection ..........................................................................206Priority Call .............................................................................206Preferred Interexchange Carrier ..............................................206Call Trace .................................................................................207

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Operator Assistance ........................................................................207Directory Listings ...........................................................................207Package Deals .................................................................................208

Internet Call Waiting ..............................................................208

Lesson 2Signaling Basics .................................................................211

Supervisory Signals .........................................................................212Loop Start ................................................................................212Ground Start ............................................................................214E&M .........................................................................................215Emulated Tie Trunks ...............................................................216Wink Start ...............................................................................216Digital Signaling ......................................................................217

Address Signals ...............................................................................218Dial Pulse Signaling .................................................................218Dual Tone Multifrequency Signaling ......................................221

Alerting Signals ..............................................................................221Control Signals ...............................................................................221In-Band vs. Out-of-Band Signaling ................................................222

Lesson 3Digital Line Services ...........................................................226

The Significance of Digital Communications ................................226T1 Lines ..........................................................................................227

T1 Bandwidth ..........................................................................227The Digital Signal Hierarchy ...................................................228Digital Voice Transmission .....................................................228Digital Data Transmission .......................................................229Subscriber Line Carrier ............................................................229

Integrated Services Digital Network ...............................................230How ISDN Works ....................................................................230Basic Rate Interface .................................................................230Primary Rate Interface .............................................................231

Channel Bonding and Non-Facility Associated Signaling .............232Digital Transmission Methods .......................................................234ISDN Voice Features .......................................................................236Required Hardware .........................................................................237

NT1: Network Termination, Type 1 .................................238NT2: Network Termination, Type 2 .................................238TA: Terminal Adapter .......................................................238TE1, TE2: Terminal Equipment, Types 1 and 2 ...............238R, S, T, and U Interfaces ...................................................238

Synchronous Optical Network ................................................239How SONET Rings Work .........................................................240

Digital Subscriber Line ...................................................................241


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Lesson 4Connecting to the Internet ................................................246

The Internet Hierarchy ..................................................................246Tier 1 .......................................................................................247Tier 2 .......................................................................................247Autonomous Systems ..............................................................247

Network Access Points ...................................................................247How the Hierarchy Works .............................................................248Internet Service Providers ..............................................................248Single-User Dial-Up Access .............................................................249Connecting a Business to an ISP ....................................................250

Non-Dedicated Access .............................................................251Dedicated Access .....................................................................252

Components of a Dedicated Connection ......................................252Common Carrier Connection .................................................253Channel Service Unit/Data Service Unit .................................254Broadband Modem ..................................................................254Router ......................................................................................254Getting an Internet Address ....................................................255

Summary ...........................................................................258Quiz ..................................................................................259

Module 4Internet Telephony ..........................................................263

Lesson 1The TCP/IP Protocol Suite ..................................................273

TCP/IP Protocol Layers and the OSI Model ...................................273The OSI Stack ..........................................................................274The TCP/IP Model Layers ........................................................274

Network Interface Layer Protocols ...................................275Internetwork Layer Protocols ...........................................275Transport Layer Protocols ................................................276Application Layer Protocols .............................................277

Communication Using TCP/IP ......................................................278Application Layer ...........................................................................278

Transport Layer .......................................................................279Network Layer .........................................................................279Network Interface Layer ..........................................................279Destination Station .................................................................280

Lesson 2IP, UDP, and TCP ...............................................................283

Overview of IP ................................................................................284Best-Effort Service ....................................................................285Multiplexing Protocols ............................................................285IP Packet Encapsulation ..........................................................286

IP Addresses ....................................................................................286

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Class A Address ........................................................................287Class B Address ........................................................................287Class C Address .......................................................................287Class D Address .......................................................................288Class E Address ........................................................................288Dotted Decimal Notation ........................................................288Getting an IP Network Address ...............................................289

Public Networks ...............................................................289Private Networks ..............................................................289

UDP and TCP .................................................................................291Demultiplexing Based on Port Number ..................................291Types of Port Numbers ............................................................293Well-Known Port Numbers .....................................................293Ports and Addressing ...............................................................294

Lesson 3Packet Telephony ..............................................................299

How Packet Telephony Works .......................................................300Packet Telephony Standards ..........................................................301Packet Telephony Architectures .....................................................303

IP Trunks Between Sites ..........................................................303IP Trunks and Telephones .......................................................305

Call Processing on IP Telephones and Trunks .................307LAN-Based PBX Systems ..........................................................308Internet VoIP Service ...............................................................308

Summary ...........................................................................312Quiz ..................................................................................313

Module 5Convergence and VoIP ....................................................317

Lesson 1Overview of Telecommunications Standards ......................319

ITU-T Protocols ..............................................................................319Commercial Telecom Standards .............................................320Codecs .....................................................................................320Multimedia Call Control and Signaling .................................321

H.32x–Multimedia over Data Networks ..........................321Call Setup, Signaling, and Control Protocols ..................321Supplementary Packet Telephony Services ......................323

ISDN Protocols ........................................................................323ISDN Switching and Signaling Protocols ................................324Terminal Protocols ..................................................................324Data Communications Over the Voice Network ....................325Packet Data Network Protocols ...............................................325

IEEE .................................................................................................326ANSI ................................................................................................326Telcordia .........................................................................................327


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EIA and TIA ....................................................................................328IETF .................................................................................................329

RFCs .........................................................................................329Internet Standards ...................................................................329BCP ..........................................................................................329

Lesson 2General QoS Concepts ......................................................333

Network Requirements for Convergence .......................................333Converged Network Architecture ..................................................334

A Hybrid Approach to Convergence .......................................334Parallel WAN Paths for QoS ....................................................335Application-Level QoS .............................................................336

Voice Quality ..................................................................................336The QoS Parameters .......................................................................336

Bandwidth ...............................................................................338Throughput .............................................................................338Delay ........................................................................................339

Encoding, Decoding, and Compression ..........................340Packetization ....................................................................340

Jitter .........................................................................................341Jitter Buffers ......................................................................341Measuring Jitter ................................................................342

Wander ....................................................................................343Packet Loss ..............................................................................343Availability ..............................................................................344Security ....................................................................................345

Lesson 3Admission Control and Traffic Shaping ..............................349

Admission Control .........................................................................349Traffic Shaping ...............................................................................351

Traffic Smoothing ...................................................................352Traffic Burst Shaping ...............................................................353

Network Admission Policies ...........................................................353Admission Control and Traffic Shaping Applications ...................355

Lesson 4Traffic Prioritization ............................................................359

802.1Q VLAN Standard ..................................................................359The VLAN Tag .........................................................................359802.1Q as an Architecture .......................................................361802.1Q Protocols .....................................................................361

802.1p Traffic Prioritization Standard ...........................................362Priority Tags and Traffic Classes .............................................362How 802.1p Prioritizes Traffic .................................................363Mapping 802.1p Traffic Prioritization to IP and ATM Networks .364

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Lesson 5H.323 Standard for Packet Multimedia ..............................368

Overview of the H.323 Standard ....................................................368Version 1: Videophone ...........................................................369Version 2: Packet-Based Multimedia .......................................369Version 3: Under Development ..............................................369

Other Standards of the H.323 Family ............................................369Fundamental H.323 Network Components ..................................370

Terminals .................................................................................370MCUs .......................................................................................370Gateways .................................................................................371Gatekeepers .............................................................................372

MGCP .............................................................................................373MGCP Network Components .................................................373

MG ....................................................................................374MGC .................................................................................375

The H.323 Protocols and Their Effect on Voice Stream QoS .........375H.323 Protocols .......................................................................375Audio Codecs ..........................................................................376

Silence Suppression ..........................................................377G.711 Companding Algorithms ......................................377MOS ..................................................................................378Audio Codec Delays .........................................................379DSPs ..................................................................................379DSP Delays ........................................................................380

RTP ..........................................................................................380Time Stamping .................................................................380Sequencing .......................................................................381

eRTCP ......................................................................................381RAS: H.225 ...............................................................................381Call Signaling: H.225 ..............................................................382Control Signaling: H.245 ........................................................382H.323 Protocol Limitations .....................................................382Document Conferencing: T.120 Series ...................................382

Integration with the Digital PSTN .................................................383ISDN/VoIP Integration ............................................................383Adding SS7 to VoIP .................................................................384

Network Infrastructure Requirements ...........................................385

Lesson 6H.323 Call Processing ........................................................389

H.323 Call Progression Phases .......................................................389Gatekeeper Discovery and Registration: H.225 RAS ...............390Call Setup and Signaling: H.225 .............................................391Control Signaling: H.245 ........................................................394Call Termination: H.245/H.225 ..............................................396

H.323v2 fastStart ............................................................................397SIP ...................................................................................................398SS7 to ITSP Call Progression ...........................................................399


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Lesson 7Session Initiation Protocol ..................................................405

SIP ...................................................................................................405SIP Messages ...................................................................................407

Request Messages ....................................................................407SIP Addresses ....................................................................408Request Message Format ..................................................408

Response Messages ..................................................................409Response Message Format ................................................410

SIP Servers .......................................................................................410Proxy .......................................................................................410Redirect ....................................................................................411Registrar ...................................................................................411

SIP Clients ......................................................................................411SDP .................................................................................................411Creating a SIP Session ....................................................................413

Lesson 8Approaches to IP Network QoS .........................................417

IP Header Features ..........................................................................417ToS Field ..................................................................................417IP Precedence ...........................................................................418

DiffServ ...........................................................................................418DSCP Code Points ...................................................................418PHB ..........................................................................................419

Standard PHBs ..................................................................419Custom PHBs ....................................................................420

DiffServ Domains ....................................................................420IntServ ............................................................................................420

RSVP ........................................................................................420CBQ ................................................................................................421COPS ...............................................................................................422MPLS ...............................................................................................424Policy Routing ................................................................................426PQ ...................................................................................................426RED .................................................................................................426Traffic Shaping ...............................................................................426WFQ ...............................................................................................427WRED .............................................................................................427

Lesson 9CO Softswitches ................................................................430

What is a Softswitch? .....................................................................430Softswitches in Telecomm .............................................................431Leveraging Legacy Networks ..........................................................432Who is Using Softswitches? ...........................................................432Local Voice Switching ....................................................................433Toll Bypass ......................................................................................436Features and Benefits of Softswitch Systems ..................................437

Contents

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Summary ...........................................................................440Quiz ..................................................................................441Course Quiz ......................................................................449

Glossary ............................................................................459

Index ................................................................................479

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