Cisco press voice over IP first step dec 2005 ISBN 1587201569

Today, these two worlds are merging, and companies can place phone calls over their existing data network infrastructures using a technology called voice over IP VoIP.. If you work with

By Kevin Wallace

Publisher: Cisco Press Pub Date: December 07, 2005 ISBN: 1-58720-156-9

We use either a telephone or e-mail for much of our day-to-day communication Today, these two worlds are merging, and companies can place phone calls over their existing data network infrastructures using a technology called voice over IP (VoIP).

No prior experience with VoIP technology is required

Voice over IP First-Step is anyone's introduction to the world of VoIP networks The

concepts in this book are presented in plain language, so you don't need in-depth background knowledge to comprehend the technologies covered If you work with data networks, if you work with telephony networks, if you're a home user interested in how VoIP can reduce your monthly phone bill, or if the concept of VoIP simply intrigues you, this book is for you.

By Kevin Wallace

Publisher: Cisco Press Pub Date: December 07, 2005 ISBN: 1-58720-156-9

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Dedications

This book is dedicated to Vivian, my bride of 11 years

Kevin Wallace, CCIE No 7945, CCSI, CCNP, CCDP, MCSE 4,

CNE 4/5, is a full-time instructor for Thomson NETg With 16years of Cisco internetworking experience, Kevin has been anetwork design specialist for The Walt Disney World Resort and

a network manager for Eastern Kentucky University Kevin holds

a bachelor of science degree in electrical engineering from theUniversity of Kentucky Among Kevin's other publication credits

are CCDA/CCDP Flash Cards and Exam Practice Pack

(coauthored with Anthony Sequeira), CCIE Routing and

Switching Flash Cards and Exam Practice Pack (coauthored with Anthony Sequeira), and Cisco IP Telephony Flash Cards and Exam Practice Pack, all of which are available from Cisco Press Additionally, Kevin authored the Cisco Enterprise Voice over Data Design (EVoDD) 3.3 course, was a contributing author for the Cisco IP Telephony Troubleshooting (IPTT) 2.0 course, and has written for the Cisco Packet magazine Kevin also holds the

IP Telephony Design Specialist and IP Telephony Support

Specialist CQS certifications

Dave Goodwin, CCIE No 4992 (Routing & Switching and

Voice), is a customer support engineer for the Cisco TechnicalAssistance Center (TAC) He is responsible for providing

escalation support to the Cisco TAC voice teams worldwide, aswell as discovering and resolving issues in new and emergingCisco IP Communications products He also works closely withthe Cisco engineering teams and is actively involved in the fieldtrials of new products Dave has been with Cisco for seven

http://www.cisco.com/go/srnd Previously, Graham worked inthe field and at the Cisco TAC specializing in the developmentand design of packet, cell, time division multiplexing (TDM)-and voice-based systems

Todd Stone is a Unity customer solutions architect for Cisco

Systems Todd was responsible for installing the very first

versions of the product and has since become involved in thearchitectural aspects of Unity

My family's support made this book possible To my wife,

Vivian, I feel so blessed to walk through life with you To mydaughter, Sabrina, your natural sense of humor keeps us all institches, and your caring for others warms our hearts To mydaughter, Stacie, your enthusiasm for life and the way you

naturally attract new friends makes me proud to be your dad

To the instructor team at Thomson NETg, lead by Tom Warrickand Michael Watkins, working with you pushes me to be mybest and to continually grow And, as always, I acknowledge myHeavenly Father for His blessings in my life

Ever since Alexander Graham Bell invented the telephone in

1876, telephony systems have been a part of our life More

day communication (for example, e-mail) crosses an IP network(for example, the Internet) Today, these two worlds are

recently, with the advent of the Internet, much of our day-to-merging, and companies can place phone calls over their

existing data network infrastructures using a technology called

Voice over IP (VoIP)

The topic of VoIP attracts people of diverse backgrounds, fromthe private branch exchange (PBX) technician, to the networkengineer, to the home user wanting to reduce his or her

monthly phone bill This book gets all readers on the same page

by reviewing legacy telephony systems, and then it proceeds todelve into the brave new world of VoIP

When I teach VoIP courses, I use plenty of metaphors to helpanchor what can be complex concepts The format of the Cisco

Press First-Step Series allows me to talk with you and share

stories, just as if you were attending one of my classes So,expect plenty of metaphors, analogies, and even a little humor.Also, if you're like me, you learn best from examples So, I'vesprinkled multiple case studies and other examples throughoutthis book

This book is organized in a logical, step-by-step approach tobuilding a comprehensive understanding of VoIP That approach

is demonstrated in the following outline of the chapters:

Chapter 1 , "Touring the History Museum of

Telephony"Reviews the function and purpose of public

switched telephone network (PSTN), PBX, and key systemtelephony networks The chapter covers topics such as

supervisory signaling, alert signaling, and address signaling.Near the end of Chapter 1, a case study is introduced Thescenario introduced in the case study is revisited and

expanded upon in future chapters

Chapter 2 , "Making Waves: Turning Your Voice into Zeros and Ones"Explains how the human voice can be

converted into a series of ones and zeros, and how

bandwidth can be preserved on the Wide Area Network

(WAN) by compressing voice traffic

Chapter 3 , "Paving the Pathway to a Voice over IP Network"Builds on the legacy telephony concepts

established in Chapter 1, as well as the theory of digitizingvoice covered in Chapter 2, by introducing the reader to aninitial migration step away from traditional telephony

Chapter 5 , "Speaking the Gateways'

Languages"Expands the IP telephony solution beyond a

single "cluster" to the rest of the world via gateways

Gateway protocols (for example, H.323, MGCP, and SIP) arediscussed as the potential gateway protocols of choice

Chapter 6 , "Why Quality Matters"Addresses quality of

service (QoS) issues in a VoIP network Some designersmake the mistake of simply superimposing voice traffic on adata network However, voice traffic needs high priority andhas little tolerance for delay Therefore, this chapter

introduces a plethora of QoS technologies for treating

special traffic (for example, voice) in a special way

Chapter 7 , "VoIP Supporting Roles"Introduces you to

optional, value-added IP telephony components, such asCisco Unity, which provides a unified messaging solution.Conferencing and contact center applications are also

discussed

Appendix A , "Answers to Chapter Review

Questions"Each chapter ends with a "Chapter Review

Questions" section This appendix repeats the questions andlists answers as well

Appendix B , "Next Steps: Where Do I Go From

Here?"While this book introduces you to the theory

surrounding VoIP, many readers might want to take the

next step: learning how to configure VoIP equipment Thisappendix recommends Cisco Press books and courses

offered by Cisco Learning Partners that lead not only to afurther understanding of VoIP, but also to Cisco

certifications

GlossaryThe world of VoIP requires its citizens to use oftenconfusing lingo This appendix gives clear and concise

definitions for the most important terms introduced in thebook.

If you work with data networks (perhaps to send e-mail ortransfer files), if you work with telephony networks (perhapswith a corporate PBX system), if you're a home user interested

in how VoIP can reduce your monthly phone bill, or if the

concept of VoIP simply intrigues you, this book is for you Theconcepts in this book are presented in plain language, so youdon't need in-depth background knowledge to comprehend thetechnologies presented

This book includes several features to help you digest the

materials with minimal heartburn With the solid foundationgained through this book, you can learn things about new VoIPtechnologies more easily, talk VoIP with others, or be betterprepared to begin a career in VoIP:

Chapter objectives Every chapter begins with a list of

objectives that are addressed in the chapter The objectivesare revisited in the chapter summary

Highlighted keywords and Glossary Throughout this

book, you will see terms formatted with italics These termsare particularly significant If you find you aren't familiarwith the term or at any point need a refresher, simply look

up the term in the Glossary toward the end of the book tofind a full definition

Case studies Every chapter concludes with a case study.

The case study scenario is introduced at the end of Chapter

1 and expanded upon in all remaining chapters The casestudies give you the opportunity to take what you've

learned in a chapter and put your newfound knowledge towork in a specific design scenario

Chapter summaries Every chapter concludes with a

comprehensive chapter summary that reviews chapter

objectives, ensuring complete coverage, and discusses thechapter's relationship to future content

Chapter review questions Every chapter concludes with

review questions These questions test the basic ideas andconcepts covered in each chapter You can find the answers

Nontechie headings and titles The titles and headings

throughout this book avoid the use of technical terms whenpossible, focusing instead on words that connote somethingabout the underlying concepts

If you have any comments about this book, you can submitthem through the ciscopress.com website Simply go to thewebsite, select Contact Us, and type in your message

I hope you enjoy your first step into a deeper knowledge ofVoIP, and I trust that this first step will be a giant leap in yourunderstanding of VoIP

company's voice network As a result, you avoid long-distancecharges; however, that's just the tip of the iceberg This bookintroduces you to the plethora of benefits VoIP offers

Prior to getting into the nuts and bolts of VoIP, you need to

have a firm understanding of traditional telephony networks.This chapter takes you on a tour through the history of

telephony Traditional telephony components introduced in thischapter are compared and contrasted in later chapters with

today's VoIP components, providing you with the distinctionsnecessary to begin the migration to this exciting new world oftelephony

When you pick up your home phone's handset and place a call

to a friend, many operations occur in the background This

section walks through a basic phone call step by step, assumingyou have a regular analog phone

note

Traditional analog phones are called POTS devices POTS stands for "Plain Old Telephone Service."

When you pick up the handset of your phone, you hear a dial tone in the receiver, and you can press keys on the touchtone

keypad to dial digits However, on close inspection of your

phone, you notice that there doesn't seem to be a battery in thephone, and it's not being powered from an alternating current(AC) wall outlet So, the question is, "Where is the phone

getting its power?" The answer is the phone company The

telephone switch at the phone company's central office (CO)

applies -48 volts of direct current (DC) across the wires comingout of the telephone wall jack That voltage enables the phone

to dial digits or even illuminate the keypad (in case you need todial in the dark), for example

note

The telephone jack in the wall of your home (assuming you live in North America) is an RJ-11 jack, where RJ means Registered Jack This RJ-11 jack has up to six conductors, although a phone that has only a single line

You dial your friend's phone number of 555-1212 The tonescreated from the digits you dial travel over a pair of wires

leaving your phone, into your RJ-11 wall jack, and back to thetelephone switch at your local CO These two wires leaving your

phone are called the tip and ring wires.

note

Did you ever notice that in the movies or on television, almost all phone numbers begin with 555? That's because originally, there were no residential or business seven- digit phone numbers in the North American Dial Plan beginning with 555 (Although some numbers outside the 555-0100 through 555-0199 range are now released for actual assignment.) Examples include 555-1212 for the Brady Bunch's home and 555-0267 for the Townsend

Agency in Charlie's Angels (It doesn't work I tried.) The

producers don't want to create another situation like the one caused by the song "Jenny." Remember, eight six seven five three oh nine.

The names tip and ring come from the plug used by the

operators of yesteryear to interconnect calls As you can see in

Figure 1-1, the plug used by these operators resembles theplug you might use to connect your headphones to your homestereo equipment There are three conductors on this plug Theconductor (that is, wire) connected to the tip of the plug is

called the tip, and the conductor connected to the ring in themiddle of the plug is called the ring

The tip and ring wires take on a new name after they leave yourhome The connection from your home to the local CO is calledthe local loop When your dialed digits, carried over the localloop, reach your local CO, the local loop connects into a phone

switch As the name suggests, a phone switch is responsible for

interconnecting the endpoints (that is, the phones) that make

up a phone call The phone switch can recognize the digits youdialed by listening to the tones generated by your telephonykeypad, or by interpreting pulses generated by a rotary phone.The phone switch can then determine to where your call should

be forwarded, based on those dialed digits If your friend livesjust across town, perhaps your friend's phone connects into thesame CO that your home phone connects to If that's the case,then the phone switch sends ringing voltage over the local loopconnecting to your friend's home If your friend does not livenearby, then the phone switch might need to forward your call

to a phone switch in a different CO A connection from one

phone switch to the other is called an interoffice trunk

Your friend's phone begins to ring, and he picks it up Your

friend's local CO telephone switch notices that he picked up hisphone's handset and stops sending ringing voltage At this

point, you and your friend can begin to talk with one another

This chapter digs deeper into the inner workings of the phone

occurred to make the phone call possible When you heard thedial tone and your friend heard his phone ringing, that was

information signaling When you dialed digits, that was address signaling

Figure 1-2 illustrates some of the components that make up atraditional telephony network

Figure 1-2 Components of a Telephony Network

The list that follows defines the traditional telephony networkcomponents illustrated in Figure 1-2:

trunk typically transports multiple simultaneous

conversations

The preceding example considered a phone switch located inyour local CO However, for businesses, that is not always thecase Businesses might have their own phone switches Thenext few lessons in this chapter compare and contrast thesevarious types of phone switches, beginning with phone switchesthat make up the public switched telephone network (PSTN)

The Public Switched Telephone Network: The Phone System That You Grew Up With

The telephone that Alexander Graham Bell invented in 1876 didnot have a touchtone keypad Nor did it have a rotary dial Infact, for decades after the invention of the telephone, manycallers could not directly dial the person they wanted to speakwith They first had to speak with an operator and ask the

operator to connect them with the desired party

You have probably seen this scene played out on the Andy

Griffith Show Andy picks up the receiver on his phone in the

sheriff's office and asks Sara to connect him with Floyd's BarberShop Andy didn't have the option of dialing Floyd directly

This was standard operation for the phone system until a

Kansas City undertaker became fed up Back in 1889, an

undertaker named Almond Brown Strowger was losing businessbecause the local Bell Telephone operator had a brother-in-lawwho was a competing undertaker So, when someone called theoperator wanting to speak with an undertaker, guess who theywere connected with? That's right, the Bell Telephone operator'sbrother-in-law

note

Different accounts of the story suggest relationships between the operator and the competing undertaker other than brother-in-law/sister-in-law (such as cousin or

spouse) However, the various versions of the story do depict a close family relationship between the operator and the competing undertaker.

directly, without a meddling operator This frustration led to hisinvention of the first telephone switch This switch, through aseries of mechanical relays, could interpret a caller's dialed

digits and form a pathway between the calling party's phoneand the called party's phone The Strowger Switch, also known

as the Step-by-Step Switch, was adopted by AT&T in 1924 andwas in widespread use in the United States into the 1980s

Today's CO telephone switches are digital, as opposed to themechanical Strowger Switch, and these switches are connected

do not have an available trunk between themselves)

Long-Haul Network Long-haul networks typically

interconnect local exchanges (for example, Class 5 offices)with long-distance offices

Private Branch Exchanges: How Big Businesses Talk

I used to work on the telephone system at a university, and theuniversity had about 6000 telephones on campus How much doyou think it would cost for each one of those phones to have adirect connection back to the local CO? In those days (the early90s), a business line had a recurring monthly charge of

approximately $40 That comes out to $240,000 every monthfor local phone service for those 6000 phones! There must be amore economical approach

One such approach was for the university to have its own phoneswitch That's right A private entity such as a business or

university can have its internal phones connect to its own phoneswitch instead of the local CO That private phone switch thenconnects to the local CO over a series of trunks (analog and/ordigital, which are discussed Chapter 3, "Paving the Pathway to aVoice over IP Network") The good news is that 6000 trunk

connections back to the local CO were not required becausestatistically speaking, all 6000 phones would never be in use atexactly the same time In fact, based on traffic studies (a topiccovered in Chapter 2, "Making Waves: Turning Your Voice intoZeros and Ones"), we needed approximately 210 trunk lines(that is, voice paths) interconnecting the university's phone

switch with the local CO, as illustrated in Figure 1-3

Figure 1-3 University Telephone System

Smaller businesses only needing to support 30 to 40 phonesmight not be able to justify the purchase of a PBX system andinstead might rely on another option called a key system Like aPBX, a key system can act as a phone switch for phones withinthe organization and provide trunk lines back to the local CO forcall destinations outside of the business

The distinction between a classic key system and a PBX is morethan simply the number of supported phones In a PBX

environment, callers typically dial a 9 on the telephone keypad

to access an outside line In other words, after they dial a 9,they get a second dial tone This second dial tone comes fromthe local CO

In a key system environment, because the number of lines

(that is, trunk connections) going back to the local CO is

relatively small, these lines are directly accessible from the keysystem's key phones For example, you might be using a keyphone with five line buttons If you want to call outside of thelocal business, instead of dialing a 9 to access an outside line,you can press an available line button right on the key phone

You might have been visiting a car lot, as an example, and

heard over the booming intercom, "Kevin, you have a call online three Kevin, please pick up line three." In that instance,Kevin could go to one of the key system's key phones, and

press the line three button to access the call

However, if you have been in the market for PBXs or key

systems lately, you have probably realized that the line betweenthe two is starting to blur More and more key systems are

starting to feel very PBX-like For example, these days, you

might need to dial a 9 to access an outside line on your key

system These phone switches that have characteristics of both

PBXs and key systems are sometimes called hybrid phone switches.

Earlier in this chapter, you considered an end-to-end telephonecall between you and a friend In passing, you learned that

various types of "signaling" occurred during that phone call Thefollowing sections examine the various types of signaling:

when a phone receives an incoming call Supervisor signalingincludes:

sitting there, waiting for the circuit to close After the handsetgoes off-hook, however, the tip and ring circuit is closed, andcurrent can begin to flow through that circuit When the

telephone switch at the CO sees this current begin to flow, itknows that the phone has gone off-hook, and the telephoneswitch sends a dial tone to the caller, indicating that they canbegin dialing digits This type of supervisory signaling is called

loop start signaling

Loop start signaling has an issue with glare Did you ever pick

up the phone to call someone, but you didn't hear any dial toneand instead discovered that someone was on the other end ofthe line? If so, you experienced glare Glare occurs when youbeat the signaling and pick up your handset before your phonerings What's really spooky is when the person you were about

to call is the person on the other end of the line!

Glare may not be a major concern in a home environment, butwhat about a line connecting to a company's PBX system?

Because the lines connected to a PBX experience a significantlyhigher call volume than you do on your home phone (unlessyou have teenagers), the probability of glare occurring with aPBX using loop start signaling is much higher than the

probability of glare occurring on your home phone Therefore,you often find another type of signaling used on PBX systems,and also on pay phones That other type of signaling is ground start, and the good news is that ground start signaling preventsglare

Ground Start Signaling

With ground start signaling, the phone switch monitors the

voltage potential on the "ring" lead of a line, and when the ring