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Introduction to Telecommunications
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
Introduction to Telecommunications
iv
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
Contents
v
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
Introduction to Telecommunications
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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
Contents
vii
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
Contents
ix
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
Introduction to Telecommunications
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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
Contents
xi
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
Contents
xiii
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
Introduction to Telecommunications
xiv
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
xv
Summary ...........................................................................440Quiz ..................................................................................441Course Quiz ......................................................................449
Glossary ............................................................................459
Index ................................................................................479