01 TI2372 Introduction

8/2/2019 01 TI2372 Introduction

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Introduc tion to Voic e over IP for SURPASS

TI2372 VoIP for Surp ass

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Contents

1 Voice ove r IP Basics 31.1 A Voic e Network Data Network 31.2 Development and Examp les 81.3

Ga tewa ys - Phone me ets PC 11

2 Why Voice over IP 192.1 Advantage s for netw ork op erato rs 192.2 Ad va ntages for users and sub sc ribers 22

Introduc tion to Voice over IP for

SURPASS


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TI2372 VoIP fo r Surp ass

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1 Voice over IP Basics

1.1 A Voice Network Data Network

The c om munica tion networks nowadays rep resent o ne o f the m ost important p illa rs

of m od ern industria l soc ieties. It is d iffic ult to ima gine tha t only a little more than a

hundred yea rs of d eve lop ment led to this now seemingly indispensab le d evice of

mo dern life. Befo re turning to m ore d eta iled d isc ussion in the field of VoIP, using a n IP

data ne twork, we w ant to give a short overview o f the networks tha t rep resent the

present sta te a nd the opp ortunities for imp rove ment.

Generally we c an d istinguish c oa rsely two types of c om munica tion networks, that o f

netw orks ma inly used for voic e transmission (namely the ISDN/PSTN Telephone

Netw orks) and

data transmission netwo rks used to excha nge information be twe en c om puters

These d ifferent type s of ne two rks have c oexisted from the be ginning of d a ta

c om munica tion Even in the 60ties of the 20th century, the early yea rs of this new

tec hnique , da ta transmission via the a lrea dy existing Pub lic Switc hed Telep hone

Netw ork (PSTN) turned out to be unsuitab le.

So a lrea dy at tha t time insta lla tion of d ata netw orks be ga n, and the m ost succ essful

one wa s the ARPANET. It was the first step toward the eno rmo us but a t the b eg inning

of the 1980ies mo stly unnoticed c om munica tion netwo rk tha t is nowadays named

IP-Network or The Inte rnet (IP Inte rnet Protoc ol).


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Voice and Data TransmissionVoice and Data Transmission

NetworksNetworks

Requirements- real-time (critical)- small bandwidth

(narrow band)- constant bit rate

Circuit Switched Networks- fixed allocation of

bandwidth

- fixed size of channels(64 kbps)

PSTN/ISDN- Network

Voice Data

Requirements- non real-time- enormous bandwidth

(broad band)- variable bit rate

Packet Switched Networks- no allocation of

bandwidth

- flexible use ofbandwidth

IP/ATM/FR- Networks

Figure 1


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Voiceba nd Comm unication and Circuit Switched Networks

One of the mo st important req uirem ents for networks with foc us on vo ice

c om munica tion is to transmit the signa l in real time.In this light, c irc uit switc hed netwo rks c om ply best w ith th is key req uirem ent , bec ause

at the very beg inning o f communic ation a c irc uit (cha nnel) is set up to c onnec t the

subsc ribers to ea c h o ther. In other words, the c onnec tion must b e explic itly set up ,

be fore voice traffic c an b e transmitted. An ap propriate ba ndw idth is alloc ate d

exc lusively to suc h an esta b lished c irc uit as it has to be ensured, that the netwo rk is

ab le to transmit the vo ic e traffic w ithin both sma ll total de lay times and sma ll delay

variations (jitter).

Features ofFeatures of Circuit Switched NetworksCircuit Switched Networks

Appropriate for real time applications

Small and predominantly constant delay times

Connection-oriented

Fixed allocation of bandwidth (n*64 kbit/s)

Figure 2

Circuit SwitchingCircuit Switching

Traffic between Phone 2 and Phone 3

Traffic between Phone 1 and Phone 4

Phone 1

Phone 2

Phone 3

Phone 4

Switch

Switch Switch

Figure 3


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Data Comm unica tion and Pac ket Switched Network

In contrast to vo ice c ommunica tion, for da ta c om munica tion less stric t rea l-time

req uirem ents a re needed . Data transmission times c an jitte r within larger limits andthe ac cep table tota l de lay times can b e longer. On the other hand the required

bandwidth can be subjec t to c onsiderab le va ria tion. For this rea son p acket switched

netwo rks suc h as the IP-Netwo rk were introduc ed . In sp ite of a lloc ating c irc uits,

pa c kets are sent indepe ndent from ea c h other througho ut the netwo rk one at a

time. In case there a re too many pa c kets in the netw ork, c ong estions c an ap pea r in

the netw ork. Short-term overloa ds (tra ffic pea ks) c an b e susta ined by buffering the

pac kets in order to fo rwa rd them when the p ea k has passed . But if suc h an ove rloa d

situation stays uncha nged , pa c kets even can be d isc arded .

Voice ove r Pac ket (VoPac ket) and in particular Voice o ver IP wa s initially reg arded

as not fea sib le b ec ause o f the follow ing set o f p rob lem s:

tota l delay time (caused by Pac ketizing a nd Routing)

considerab le va ria tion of the de lay

risk of too m uc h pac ket loss


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Features of PacketFeatures of Packet Switched NetworksSwitched Networks

hardly appropriate for real-time applications

highly variable delays (depending on the load level)

for the most part connectionless

flexible use of bandwidth

Figure 4

PacketPacket SwitchingSwitching

PC Client 2

PC Client 1 Server a

Server b

Traffic bw. PC 2 and Server a

Traffic bw. PC 1 and Server b

Router

Router Router

Figure 5


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1.2 Development and Examples

1.2.1 A p hone call from PC to PC

The m ore p ow erful both Persona l Computers and Routers in the IP Netw ork have

bec om e, the c loser the netw orks have c om e to sa tisfying Voice ove r IP solutions.

In Feb rua ry 1995 for the very first time softwa re w as b roug ht on to the ma rket, tha t

a llow s voice c om munica tion with the help of tw o Persona l Comp uters. As

prerequisite, ea ch PC just had to b e equipp ed with sound c ard , loud spe aker,

microp hone and of c ourse a LAN card for the IP c onnec tion . This wa s the beg inning

of the story, even though the quality of the spe ec h wa s not tha t high.

But soo n other com panies launc hed the ir solutions for phone c a lls over IP netwo rksand the q uestion of c om patibility of the d ifferent solutions soon ap pea red .

In Janua ry 1996 the Internet Eng ineers Task Force IETF pub lished the Rea l-Time

Transport Protoc ol RTP which was designe d to support the t ransmission o f rea l-time

c ritica l information suc h as voice and video ove r the IP netw ork.

Also in the year 1996 the ITU-T (Inte rnat iona l Telec ommunic a tion Union -

Telec om munica tion Sec to r) pub lished the H.323 sta ndard , that inc ludes the RTP as

protocol used for transmission. Moreover, this standard covers and defines protocols

need ed for c all set up .

VoiceVoice overover IPIP -- HistoryHistory

Februar 1995: first VoIP-solution on the market(Fa. VocalTec/IL)

January 1996: IETF standardizes RTP (RFC1889)

May 1996: ITU-T adopts H.323

Figure 6


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VoIP PC

VoIPVoIP PCPC--toto--PCPC

IP-Netz,z.B. LAN VoIP PC

or IP-Phone or IP-Phone

Figure 7

Nowa da ys this kind of c ommunicat ion is wide ly-sprea d for instanc e in loc al

enterprise ne tworks. In doing so, a c om pany utilizes its LAN for bo th d a ta and vo ice

services. Often the func tionality of softw are a nd hardw are c omponents is integ rated

in IP-Phones, which a re d irec tly connec ted to the IP-network. In this wa y the

c onventional enterprise telep hone netwo rk c an be ab and oned .

Utilizing the PC to PC com munica tion more g ene ra lly, it is even p ossible to b ring

about c hea p long d istanc e c a lls, as the a cc ess fee is indep end ent from the d istanc e

of the c alled pa rty and very often it is indepe ndent from the c all duration (flat rate),

to o

To avoid expensive internat iona l long d ista nc e-c onnec tions via the PSTN, it is possible

to bypa ss it w ith a c onnec tion via the glob a l internet, which is c harged (in PSTN

terms) like a loca l c a ll on ly. By running a pprop riate softwa re on the PC, the

esta b lished c onnec tion, for insta nce b etw een a PC in Germany a nd a PC in Ind ia ,

c an be used to transmit voic e.

How eve r, as eve rybo dy knows from surfing the internet, delays c an oc c ur during

such a telephone call. In this wa y the c oherence of a n internet p hone c all c an

suffer, and in worse c ases the received speec h can bec om e incomp rehensib le.


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Advantages ofAdvantages of VoIPVoIP

A unique Network:

less investment, less techniquesless efforts for maintainence

Cost-effective:Charging can be independent from the distanceCharging can be independent from the duration

Figure 8


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1.3 Gateways - Phone meets PC

At the b eg inning o f the VoIP deve lop me nt the foc us wa s on c onnec tions from PC toPC. For insta nc e, on one ha nd this kind o f solution a llow s the sta ff to c a ll ea c h other

within the c om panys LAN doma in, but on the other hand in the ea rly da ys of VoIP

no o p tion to c om munica te with the PSTN wa s g iven.

But this important p rob lem w as c lear right from the very be ginning . Finally the

prob lem w as solved b y the deve lop me nt of VoIP Med ia Gatew ays. VoIP Med ia

Ga tew ays a llow VoIP netw orks to c onnec t to the PSTN network. Ac ting a s a kind of

interpreter, VoIP Med ia Ga tew ays ma ke phone c a lls possib le b etw een PCs loc a ted

in a p ac ket switc hed IP netwo rk and POTS/ ISDN-te lephones loc a ted in the c irc uit

switc hed PSTN. They a re able to forward voice traffic rec eived from the c ircuit

switched tec hnique a t the pa c ket switched tec hnique a nd vice versa.

A ve ry suc c essful offer in this c ontext was to sta rt long -dista nc e c a lls from the PC.

Contrary to the PC to PC method, ord inary subsc ribers a re a va ilab le, too. For

examp le, at hom e a nd a broad even friends without internet ac c ess c an b e

c onta c ted in a c heap a nd easy way. However, generally such a c all might not have

the same qua lity tha t is usua lly p rovided by the PSTN.


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VoIPVoIP MediaMedia GatewaysGateways

allow access for subscribers connected to external networks

act as a kind of interpreter,

for example between IP and PSTN networks

calls from the (cheaper) data network can be forwarded atthe PSTN

Figure 9

VoIP PC

VoIPVoIP PCPC--toto--PhonePhone

IP-Network

MG

PSTN-Network

PSTN-Telephone

VoIPMedia

Gateway

Figure 10


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The introd uc tion of the VoIP Med ia Ga tew ays a lso paved the wa y for two PSTN

telephones to b e c onnec ted via a n IP netwo rk (Phone to Phone). After the

liberaliza tion and deregulation o f the te lec om munica tion market ac ross most of the

wo rld, IP network operators c an, with little effo rt, enter this new ma rket easily byp lac ing at lea st two VoIP Med ia Ga tew ays at the borders of their IP netw ork. This

VoIP scena rio is ma inly used for internat iona l ca lls from Phone to Phone.

Typica lly, for inte rna tiona l c onnec tions, a t ransla tion of the na tiona l signa ling

protoc ols used in the PSTN is nec essary. Therefore spec ial (tha t means expensive)

switc hes must usua lly be used to c onnec t two c ountry spec ific PSTN netwo rks.

VoIP gives small operators the chance to bypass this huge investment, which would

not bec ome a ca sh cow for them anyway.

MG

VoIPVoIP PhonePhone--toto--PhonePhone

IP-Network

MGPSTN-Network

PSTN Telephone

PSTN-Network

PSTN Telephone

Figure 11


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1.3.1 Gatekeeper - More Functiona lity

To esta b lish a VoIP connec tion g enera lly a m inimum of two terminlsl is suffic ient. Thisc an be rea lized by two VoIP-PCs, two IP-phones, two G atew ays or any c om bina tion

of the a bove.

How eve r, by a dd ing spec ia l servers, ca ll set up and release c an b e c ontrolled

c entrally a nd supp lementa ry fea tures and functionalities c an be imp leme nted .

In te rms of the H.323 standard such a server is nam ed Ga tekeeper, othe r p roto c ol

suites use different names.

One of the mo st imp ortant ta sks of a Ga tekeeper is the address resolution.

Telepho ne numb ers or a lias names must b e c onve rted into the IP address a lloc a ted

to the c alled pa rtys terminal eq uipm ent.

Moreover cha rging c an b e p erformed and resourc es like the availab le b and width

c an b e c ontrolled.

Fea tures tha t a re p resent in eve ry priva te b ranc h exchange (PBX) c an be

imp leme nted in a Ga tekeep er as ad ditiona l fea tures.

After improving the func tionality step by step , VoIP is fina lly able to c ompete with

c irc uit switc hed solutions. Since 1998 comp lete solutions suc h a s IP based c a ll centers

or IP PBX have been ava ilab le on the m arket.

GatekeeperGatekeeper

centralized control of call set up and release

supplementary functionality:- address resolution- control of bandwidth resources- charging

Features:

- knocking- to act as a broker- etc.

Figure 12


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VoIP PC

VoIPVoIP GatekeeperGatekeeper

IP-Network,e.g. LAN

VoIP PC

Gatekeeper

hiQ 20 (H.323)

Figure 13


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1.3.2 Qua lity of Servic e

As an essentia l but silent p rerequisite, the VoIP solutions disc ussed previously req uirean IP netw ork that is ab le to hand le voice tra ffic in real-time. But this only can b e

true, if

the d ista nce for voice t ra ffic to b e transmitted is not to o long

the involved ne twork eleme nts wo rk at high speed

the required bandwidth is available any time

In p articular the last p rereq uisite is d ifficult to fulfill. Without taking add itiona l steps

usua lly this is only possible if there is considerab ly more b andwidth ava ilab le in thenetwo rk than is nee ded a t a ny particular po int in time. This me ans over-provisioning is

a must. If not , the q ua lity of a voice transmission w ill dep end solely on the ac tua l

loa d in the network and good luck.

RealReal--timetime requirements for datarequirements for data

networknetwork

short distances

high-speed network elements (Router, Switches)

necessary bandwidth must be available

Solutions: I) Over ProvisioningII) QoS-Mechanisms

(IntServ, DiffServ, MPLS)

Figure 14


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CharacteristicCharacteristic ofof

VoiceVoice andand Data TrafficData TrafficV o i c e t r a f f i c p r o f i l e ( s c h e m a t i c )

0

0 , 2 5

0 ,5

0 , 7 5

1

1 , 2 5

1 5 913

17

21

25

29

33

37

41

45

49

53

T i m e

Volume

D a t a t r a f f i c p r o f i l e (s c h e m a t i c )

0

0 , 2 5

0 , 5

0 , 7 5

1

1 , 2 5

1 5 913

17

21

25

29

33

37

41

45

49

53

T i m e

Volume

Figure 15

Over-provisioning is diffic ult. There c an be c onsiderab le time dep end ent va ria tions

the d ema nd for ba ndw idth in the IP netwo rk bec ause of the d ata traffic . Apa rt from

this, ove r-provisioning is very expensive, as over a long period of time the use o f the

netw ork c apac ity is relatively low .

In rec ent yea rs, new te c hniques have be en d eveloped in order to m ake sure that

enough b and width for voic e traffic c an b e p rovided any time by the netwo rk

without too muc h over-p rovisioning. These tec hniques p rovide wha t is c a lled Qua lity

of Servic e (QoS). The most importa nt ones a re RSVP (Resource Reserva tion Protoc ol),

IntServ and DiffServ (Inte grated and Different iated Servic es) and last b ut no t leastMPLS (Multi Proto c ol Label Switching).


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VoiceVoice andand DataData inin one networkone network

Data Traffic (schematic)

0

0,25

0,5

0,75

1

1,25

1 4 710

13

16

19

22

25

28

31

34

37

40

43

46

49

52

55

Time (arbitrary units)

TrafficVolume

(arbitraryunits)

Profile of Voice Traffic (schematic)

0

0,25

0,5

0,75

1

1,25

1 4 710

13

16

19

22

25

28

31

34

37

40

43

46

49

52

55


TrafficVolume

(arbitraryunit)

Voice Traffic + Data Traffic

0

0,25

0,5

0,75

1

1,25

1 4 710

13

16

19

22

25

28

31

34

37

40

43

46

49

52

55


TrafficVolume

(arbitraryunits)

Capacity limit overflow,Several Packets

(Voice? Data?)get delay

Figure 16

The b asic c onc ep t is true fo r all of them : In orde r to red uce interferenc e w ith the rea l-

time traffic, variation in the hardly determinab le vo lume of d ata traffic m ust b e (as

fa r as possible) avoided . With the use o f Qua lity of Servic e tec hniques a voice

quality for VoIP sc ena rios c an be a c hieved c om pa rab le to that rea lized in the PSTN

network.


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2 Why Voice over IP

2.1 Advantages for network operators

Throug hout the wo rld , c ircuit switched telep hone netw orks fac ilita te highly reliab le

voice c ommunicat ion w ithin go od qua lity. In this c onte xt, ce rta inly the question

arises as to why operato rs would wa nt to turn awa y from a lrea dy insta lled and

proven circuit switched techniques, and instead turn towards voice transmission via

pa c ket switched netwo rks.

A selec tion of rea sons are g iven below:

Advantages ofAdvantages of VoIPVoIP

forfor network operatorsnetwork operators

more efficient use of the network- silence detection- compression

low costs- a unique network

(Administration, Operation, Maintainence)

high innovation pace- open interfaces allow seamless and quick integration of

innovations from different manufactureres (betweenGatekeeper and transmission technique)

Integration of voice and data services (Multimedia)

Figure 17

2.1.1 More e ffic ient use of the networks

In c irc uit switched netw orks a fixed bandwidth is a lloc a ted to a c onnec tion. For

examp le, in a PSTN netw ork the voic e-c hannel is transported a s a b idirec tiona l

b itstream of 64kbit/s tha t is a lloc a ted to e ac h c onnec tion reg ard less of whethe r the

person is spea king or not. Thus as long as suc h a c onnec tion is held 128 kbit/ s a re in

use, mea ning 128 x 60=7680 kbit a re transmitte d per minute ( or 960 kiloByte perminute respec tively). For a five m inute c a ll this p iles up to 4800 kiloByte . Contrary to


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the PSTN sc ena rio, in a p ac ket switched netw ork this va lue c an b e reduc ed

considerably:

Silenc e detec tionTypica l pho ne c a lls wa ste a lot o f the a lloc a ted c apa c ity, as usually one subsc riber

listens to wha t his counte rpart him is ta lking to. In spite of the fac t tha t b andw id th is

a lloc a ted in both d irec tions, information is mo re o r less transmitte d unidirec tiona lly

only. By the use of a voice ac tivity de tec tion, the b its c onta ining informa tion ca n be

sep arated from the ones without a ny mea ning (i.e. ba ckground noise). Bec ause

there is no need to t ransmit bits without a c tua l informat ion, the a c tua l tra ffic in the

netwo rk ca n be red uced by a bo ut the half. For the example of a five minute c all

that means the a mount of voice traffic that m ust b e sent through the network c an

be red uced from about 4.7 MB to about 2.4 MB. This estimation does not take into

ac count the p hases in which bo th parties are silent.

Compression

Shortly afte r digitaliza tion wa s introd uc ed to the te lep hone netw orks, the bandwidth

for a single c onnec tion was sa tndardised a t 64 kb it/ s for a single c onnec tion. The

rea son for that was the a nc ient c ontem po rary state o f the a rt in teleco mmunic ation

tec hnique that wa s not a ble to keep a go od qua lity when using less ba ndw idth.

After seve ra l years of intensive stud ies, new ly d eve lop ed a lgo rithms and tec hniques

were a ble to reduc e the b and width need ed for high q uality voic e c all. However, the

PSTN co uld no t ta ke an advanta ge o f this improvem ents, since the w hole system is

strong ly based on 64 kbit/ s-channels. Only new networks like the GSM m ob ilenetw ork, utilize the newly developed com pression algo rithms (and even then, only

on the rad io interfac e e.g. 13kb it/ s for voice).

In a pac ket switched netw ork, cha nnels of p red efined size d o no t exist a t a ll.Therefore c om pression a lgo rithms c an save c onsiderab le ba ndwidth espec ia lly in an

IP network environment.

Quicker introduc tion of Innovations

In a VoIP netw ork, different func tions a re imp lemente d in diverse a nd sep arated

netw ork elements. For examp le, while the switching of the pa c kets is exec uted by

routers, the log ica l c ont rol of the c a ll as we ll as add itional servic es a re c ent ra lized in

servers (Ga tekeeper, etc ). Communica tion amo ng the d iverse equipment is rea lized

via sta nda rd ized interfac es. Thus they c an be up grad ed , mo d ified , renewe d o r

rep lac ed indepe ndently from ea c h othe r. For instance , to introd uce a new service,

the servers on ly must be m od ified , the route rs a re no t touc hed a t a ll. If routers a re

rep lac ed by mo re pow erful ones, then the servers and their servic es rem ian

unaffec ted. Imp rovements c an b e implemented in a much q uic ker and c heap er

wa y. Moreover, tha nks to o pen interfac es, netwo rk elements from d ifferent vend ors

c an b e c ombined. Add itiona lly, this fac t lea ds to more c ompe tition am ong the

vendors, which c an ultimate ly results in low er prices.


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2.1.2 New Opportunities

Operators of data services offer voice services

With the introd uc tion o f VoIP, Op erato rs which have previously spec ia lized in da ta

servic es c an now offer voice servic es, too . VoIP op ens the doo r to the luc ra tive

telec om munica tion market without investing in a c irc uit switched netw ork.

Op erato rs offering b roa dba nd acc ess (xDSL, c ab le mod em , pow erline) to the IP

netw ork c an offe r in p ara llel VoIP for their subsc ribers even though they d o not own a

PSTN netw orks ac c ess infrastruc ture (Loc al Exchanges, Ac c ess Networks).

Operators of voic e service s offer data services

The vo lume of d a ta c om munica tion has been increased rap id ly in the last yea rs. It isestima ted tha t if this trend c ont inues, the vo lume o f da ta traffic will soo n surpa ss tha t

of vo ic e traffic. Op erato rs of vo ic e servic es c an prepare fo r these c ha lleng es by a

step by migrating from c irc uit switc hed netw orks to pac ket switc hed netw orks.

Integration of voice and d ata - multimedia

In a c onvergent voice d ata network, apa rt from the p ure voice and the p ure d ata

servic es, servic es c om bining vo ice a nd d a ta c an also b e o ffered . And these a re not

just telephone c onferenc es launc hed and c ontrolled from an internet web pa ge . In

suc h a netw ork multimed ia services like vide o te lep hony, vide o c onferenc ing , video

stream ing or tele-lea rning c an b e o ffered . Com mo n to all these services is bo th the

rea l time c riteria and the enormous need for band width.


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2.2 Advantages for users and subsc ribers

There a re several advanta ges for users gene ra ted by a Vo IP:

AdvantagesAdvantages for usersfor users andand

subscriberssubscribers

unique Infrastructure (one communication technique)

only one network access

new innovative services (Click-to-Call, etc.)

Figure 18

Unique infrastructure

Private households and companies may ease internal networking by use of VoIP.

Instea d of op erating a da ta netwo rk (LAN) and a telephone e xc hang e in pa rallel,

one netw ork is suffic ient fo r both: telephony and d a ta netw orking.

Only one network ac cess

If the access to the voice network is realised with VoIP, voice transmission uses same

line then d a ta transmission. A spec ial c ab ling for a c c ess of PSTN is not nec essary a ny

long er. Furthermore maybe one provide r c an offe r both servic es.

New innovative services (Clic k to Call, etc.)

With c om bining voice and da ta services within one single netwo rk, also c om plete ly

new servic es c an b e o ffered. Eg. c ustom ers c an a dministrate c a lls via the internet.They a lso c an d irec tly sta rt their c a lls autom atica lly via the internet (eg. w ake-up

c a lls from weather servic es). Com panies, which p resent p rod uc ts in the internet ma y

imp rove their servic e b y plac ing a but ton o n their we bsite, which a llow s the

c ustom er direc tly to c a ll the c om pany via p ressing this button (Clic k to Ca ll).

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