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Chapter 5

Voice Communication

Concepts and Technology

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Telephoneswitchboard

- Circa 1898

Voice

NetworkConcepts

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Voice Network Concepts

Telephone calls are connected fromsource ia circuit switching!

Circuit switching originally meant that a

physical electrical circuit was createdfrom the source to the destination!

The modern telephone system iscommonly known as the Public

Switched Telephone NetworkorPSTN

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Voice Concepts

"etting oice onto and o# of the network

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Voice $andwidth

Telephone oice bandwidth is more narrow than canactually be heard by most people!

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$asic %nfrastructure

The circuit between the central o&ce andcustomer is called the local loop

The local loop is the only remaining analogcomponent in the system!

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$asic %nfrastructure

Telephone calls are established by adeice located at the local telephonecompanies Central '&ce (C') known asa telephone switch

*ll oice tra&c destined for locationsoutside of the local +*T* must behanded o# to the +ong ,istance or

Inter-Exchange carrier(IXC) of thecustomers choice

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./TN Network 0ierarchy

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./TN Network 0ierarchy

'riginal *TT system wasorgani2ed in a 5 class hierarchy 3still a standard!

+ocal C' is lowest leel 4egional center is highest leel

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,igital Cross Connect

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Telephone Number .lans

Telephone numbers are a hierarchicaladdress method!

nited /tates telephone numbers canbe broken into three basic parts6 a threedigit area code7 a three digit echange7and a four digit subscriber number!

To make a telephone call at a minimum

the echange plus the subscribernumber must be dialed!

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/ystem /ignaling

%n addition to carrying the actual oicesignals7 the telephone system must alsocarry information about the call itself

This is referred to as system signalingor inter-oce signaling There are two approaches to system

signaling6 in band and out of band

ost home telephones use in bandsignaling across analog local loop

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Touch-Tone ,ialing

,T: ; ,ual Tone ulti-:re

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/ignaling /ystem =.rotocols

//= mapped to the '/% model

'ut-of-band signaling

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//=

- controls the structure andtransmission of both circuit-related andnon-circuit related information ia out-of-band signaling between central o&ceswitches!

- deliers the out-of-band signaling ia apacket switched network physically

separate from the circuit switchednetwork that carries the actual oicetra&c!

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Voice ,igiti2ation

The analog .'T/ system has beensupplanted in the modern telephonesystem by a combination of analog anddigital transmission technologies!

Conerting a oice conersation to digitalformat and back to analog form before itreaches its destination is completelytransparent to phone network users

There are a limited ways the electricalpulses can be aried to represent ananalog signal

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Voice ,igiti2ation

.ulse *mplitude odulation

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Voice ,igiti2ation

.ulse duration modulation

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Voice ,igiti2ation

.ulse position modulation

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Voice ,igiti2ation

,igiti2ed signal1>>>>>>> 11>>>>>> 1>1>>>>> 111>>1>>

1>>>>>>> ! ! !

*udio is sampled87>>> times persecond

?ach samplecontains8 bits

/ample /ample /ample /ample /ample

Pulse Code !odulation"PC!#

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Voice ,igiti2ation

.ulse Code odulation (.C)

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Coderdecoder (codec) ,eice that samples the analog .'T/

transmission coming in from the localloop and digiti2es it into a stream of bits

?ach codec outputs a digital signal at DBEbps

,/> ; basic unit of oice transmission

DBEbps 87>>> samplessec F 8 bits ; DB7>>> bitssec

@B ,/>s ; T1 +ine

Voice ,igiti2ation

i i i

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Voice Transmission*lternaties

*lthough the ./TN has traditionallybeen seen as the cheapest andmost e#ectie way to transmit

oice7 alternatie methods foroice transmission do eist! Vo%.

:rame 4elay *T

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Voice oer %. (Vo%.)

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:rame 4elay

Voice oer :rame 4elay

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*T

Voice oer *T

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%/,N

%/,N (%ntegrated /erices ,igitalNetwork) is a switched digital sericethat is also capable of transmittingoice and data simultaneously!

%/,N $4% ($asic 4ate %nterface) sericeo#ers two DBEbps channels!

'ne of these channels is used for data

while the other is used tosimultaneously transmit oice!

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%/,N

/imultaneous oicedata with %/,N

Gi l V i

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Gireless VoiceTransmission

$efore cell phones7 people who needed mobile-communications installed radio telephonesintheir cars

The radio-telephone system had one central

antenna tower per city7 and perhaps $%channelsaailable on that tower

sing a central antennameant that thephone in your car needed a powerful

transmitter -- big enough to transmit B> or 5>miles (about => km)! %t also meant that notmany people could use radio telephones --there Hust were not enough channels!

Gi l V i

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Gireless VoiceTransmissionThe genius of the cellular system is

the diision of a city into small cells!This allows etensie &re'uency

reuseacross a city7 so that millions ofpeople can use cell phonessimultaneously!

* good way to understand the

sophistication of a cell phone is tocompare it to a C$ radio or a walkie-talkie!

Gi l V i

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Gireless VoiceTransmission $oth walkie-talkies and C$ radios are hal&-

duplexdeices Two people communicating on a C$ radio

or on walkie-talkies are using the same

fre

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Gireless VoiceTransmission Channels- * walkie-talkie typically has one

channel7 and a C$ radio has B> channels! * typicalcell phone can communicate on 17DDB channels ormoreI

(ange- * walkie-talkie can transmit about 1 mile(1!D km) using a >!@5-watt transmitter! * C$ radio7because it has much higher power7 can transmitabout 5 miles (8 km) using a 5-watt transmitter! Cellphones operate within cells7 and they can switchcells as they moe around! Cells gie cell phonesincredible range! /omeone using a cell phone candrie hundreds of miles and maintain a conersationthe entire time because of the cellular approach!

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Cells3 /erice proiderchops up serice area into1> s

$ecause cell phones andbase stations use low-power transmitters7 thesame fre

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Cell)

Cell%

Cell

*

Cell+

Cells hae D sides each cell issurrounded by D other cells

* single cell in an analog cell-phonesystem uses one-seenth of theaailable duple oice channels so ithas a uni

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Therefore7 each cell has about %*/oice channelsaailable! %n otherwords7 in any cell7 5D people can betalking on their cell phone at one time!

?ach carrier in each city also runs onecentral o&ce called the !obile

Telephone Switching 0ce(T/')!

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Cellular /tandards

1re'uency di/ision multiple access(:,*) puts each call on a separate &re'uency

Time di/ision multiple access(T,*) assigns each call a certain portion of timeon a

designated fre

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Cellular /tandards - :,*

:,* separates the spectrum into distinctoice channels by splitting it into uni&ormchunks o& bandwidthlike radio stations

?ach station sends its signal at a di#erent

fre

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Cellular /tandards - T,*

*TTand

T-obile

*ka ,-*./

T,* achiees more than one conersation per fre

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Cellular /tandards - C,*

C,*attempts to maimi2e the number of calls transmittedwithin a limited bandwidth by using a spread spectrumtransmission techni

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Gireless ,ata /erice"enerations .re-" Technologies (aka >")

?nhanced .aging and two-way tet messaging (pagers) .riate .acket 4adio (proprietary modem)

1" Circuit-switched analog cellular (*./) %ntroduced in !/! in 198A by *TTO Cellular ,igital .acket 4adio (C,.,) *TT - serice ended in @>>BO

@" Time ,iision ultiple *ccess (T,*) *TT and T-obileO Code ,iision ultiple *ccess (C,*) Veri2on and /printO

@!5" "eneral .acket 4adio /erice (".4/) *TT and T-obileO

$ased on T,* standard

14TTVeri2on and /printO $ased on C,* standard

A" ?nhanced ,ata for "/ ?olution (?,"?) *TT and T-obileO ?olution ,ata 'ptimi2ed or ?olution ,ata 'nly (?,') Veri2on and

/printO

/ee tableon page19A

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1" Cellular

2d/anced !obile Phone Ser/ice (2!PS) 2nalogcellular systems 'perate in the 8>>02 fre

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1" Cellular

Cellular 3igital Packet (adio "C3P3# used unused bandwidth normally used by

*./ mobile phones between 8>> and 9>>

02! /peeds up to 19!@ kbits were possible!The serice was discontinued in conHunction

with the retirement of the parent *./

serice!

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@" 3 ,igital Cellular

3igital Cellular o#erssigniQcantcapacity increases compared to *./analog cellular systems!

Carriers hae steadily moed to digitalcellular systems!

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@" 3 ,igital Cellular

Call is digiti4ed at the telephone handset and sentin a digital format to the tower

,igital conersations can be compressedwhich allowsbetween three to 1> digital cell-phone calls to occupythe space of a singleanalog call!

ore calls to share the common bandwidth in a cellconcurrently

Luality is greatly improed $etter e

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@!5" 3 Cellular

"eneral .acket 4adio /erices (".4/) *TT and T-obileO $ased on T,* model

Gireless7 packet-based communication serice

ntil recently was the standard @!5" protocol used in mostsmartphones

nlike a circuit-switched oice connection7 this is a packet-switched7Palways onP connection that remains actie as long as the phone is

within range of the serice! %t allows smartphones to do things likerun applications remotely oer a network7 interface with the

%nternet7 participate in instant messenger sessions7 act as a wirelessmodem for a computer and transmit and receie e-mails

Theoretical data transfer rate of S@>> Ebps (5DEbps actual) /ome smartphones in the nited /tates still use this

protocol7 though newer7 faster protocols are aailable

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@!5" 3 Cellular

14TT $ased on C,* model

,ata transfer rate of 1>>Ebps

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A" 3 ,igital Cellular

5technology is intended for thetrue multimedia cell phone --typically called JsmartphonesK

:eatures increased bandwidth andtransfer rates to accommodateGeb-based applications and

phone-based audio and ideo Qles!

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Enhanced 3ata 5S! En/ironment "E35E#!?,"? can transmit data at more than threetimes the rate of ".4/ (A8B Ebps)

any smartphones in the nited /tates are

now using ?,"? protocol sed by *TT and T-obile

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E/30 "C3!2 $666# ,ata transmission rates6

@!B bits with 4e! >

up to A!1 bits with 4e! * (B")

sed by Veri2on and /print

Gireless ,ata /erices

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Gireless ,ata /erices -"/

'riginally7 the acronym "/ stood for 5roupe Sp7cial !obile7a group formed by the Con&erence o& European Posts andTelegraphs "CEPT#in 198@ to research the merits of a ?uropeanstandard for mobile telecommunications!

Commercial serice using the "/ system did not actually startuntil 1991! %nstead of using analog serice!

5lobal System &or !obile communications "5S!#is aninternational standard! %f you trael in ?urope and many otherparts of the world7 "/ is the only type of cellular sericeaailable!

/erice layer that oerlies T3!2 (original draft was for C,*7

howeer endors carriers werent willing to standardi2e on apatented technology)

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B" - ,igital Cellular

$eing deeloped to accommodate the Lo/ and ratere

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Coerage aps

Veri2on /print

*TT technology

T-obile

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.riate $ranch ?change

* .$F is really Hust a priately owned7smaller ersion of the switch intelephone company central o&ces thatcontrol circuit switching for the general

public! ,epending on the re

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.$F

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.$F

Call *ccounting /ystems may be installed withthe .$F

Computer Telephony

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Computer Telephony%ntegration

CTI or seeks to integrate the computerand the telephone to enable increasedproductiity not otherwise possible byusing the two deices in a non-

integrated fashion! CT% is not a single application7 but an

eer-widening array of possibilities

spawned by the integration of telephonyand computing!

Computer Telephony

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Computer Telephony

%ntegration

,esktop CT%

Computer Telephony

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Computer Telephony%ntegration

Client /erer CT%

Documents

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