Switching systems-lecture3.ppt

8/16/2019 Switching systems-lecture3.ppt

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Dar es Salaam institute of Technology(DIT)

ETU 07420

Switching Systems

Ally, J

[email protected]


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Traffic Engineering and NetworkPlanning


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Introduction The t!a""ic is #e"ine# as the ccu$ancy " the se!%e!. The &asic $u!$se " the t!a""ic enginee!ing is t #ete!mine the

cn#itins un#e! which a#e'uate se!%ice is $!%i#e# t su&sc!i&e!swhile ma(ing ecnmical use " the !esu!ces $!%i#ing the se!%ice.

The "unctins $e!"!me# &y the telecmmunicatin netw!( #e$en#s nthe a$$licatins it han#les.

Sme maj! "unctins a!e switching, !uting, "lw cnt!l, secu!ity,

"ailu!e mnit!ing, t!a""ic mnit!ing, accunta&ility inte!netw!(ing an#netw!( management. T!a""ic enginee!ing $!%i#es the &asis "! analysis an# #esign "

telecmmunicatin netw!(s ! m#el. The #e%el$e# m#el is ca$a&le t $!%i#e &est accessa&ility an#

g!eate! utili)atin " thei! lines an# t!un(s. Als the #esign is t $!%i#e cst e""ecti%eness " %a!ius si)es an#

cn"igu!atin " netw!(s. The t!a""ic enginee!ing als #ete!mines the a&ility " a telecm netw!(

t ca!!y a gi%en t!a""ic at a $a!ticula! lss $!&a&ility.


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Trafic Statistics *alling !ate+ This is the a%e!age num&e! " !e'uests "! cnnectin that

a!e ma#e $e! unit time.

The calling !ate - is als !e"e!!e# as a%e!age a!!i%al !ate. The a%e!age

calling !ate is measu!e# in calls $e! hu!.

/l#ing time+ The a%e!age hl#ing time ! se!%ice time h1 is the a%e!age

#u!atin " ccu$ancy " a t!a""ic $ath &y a call. The !eci$!cal " the

a%e!age hl#ing time !e"e!!e# t as se!%ice !ate in calls $e! hu! is

gi%en as+

Dist!i&utin " #estinatins+ 3um&e! " calls !ecei%ing at a echange may

&e #estine# t its wn echange ! !emte# echange ! a "!eign

echange.

Use! &eha%i!+ The statistical $!$e!ties " the switching system a!e a

"unctin " the &eha%i! " use!s wh encunte! call &lc(ing. A%e!age ccu$ancy+ I" the a%e!age num&e! " calls t an# "!m a te!minal

#u!ing a $e!i# T secn#s is n1 an# the a%e!age hl#ing time is h1

secn#s, the a%e!age ccu$ancy " the te!minal is gi%en &y


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Trafic Pattern Parameters 5usy hu!+ T!a#itinally, a telecmmunicatin "acility is enginee!e# n

the intensity " t!a""ic #u!ing the &usy hu! in the &usy sessin. 5usy hu!+ *ntinuus 60 minutes inte!%al "! which the t!a""ic %lume ! the

num&e! " call attem$ts is g!eatest. ea( &usy hu!+ It is the &usy hu! each #ay %a!ies "!m #ay t #ay, %e! a

num&e! " #ays. Time cnsistent &usy hu!+ The 8 hu! $e!i# sta!ting at the same time each #ay

"! which the a%e!age t!a""ic %lume ! the num&e! " call attem$ts is g!eatest%e! the #ays un#e! cnsi#e!atin.

*all cm$letin !ate **9+ 5ase# n the status " the calle# su&sc!i&e!! the #esign " switching system the call attem$te# may &e success"ul! nt.

5usy hu! call attem$ts+ It is an im$!tant $a!amete! in #eci#ing the$!cessing ca$acity " an echange. It is #e"ine# as the num&e! " callattem$ts in a &usy hu!.

5usy hu! calling !ate+ It is a use"ul $a!amete! in #esigning a lcal ""icet han#le the $ea( hu! t!a""ic. It is #e"ine# as the a%e!age num&e! "calls !iginate# &y a su&sc!i&e! #u!ing the &usy hu!.

Day:t:#ay hu! t!a""ic !ati+ It is #e"ine# as the !ati " &usy hu! calling!ate t the a%e!age calling !ate "! that #ay. It is n!mally 6 ! 7 "! !u!ala!eas an# %e! 20 "! city echanges.


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Units o Telephone Trafic

T!a""ic intensity is measu!e# in tw ways. They a!e E!langs

an# *ent call secn#s **S.

E!langs+ The inte!natinal unit " t!a""ic is the E!langs. Ase!%e! is sai# t ha%e 8 e!lang " t!a""ic i" it is ccu$ie# "!the enti!e $e!i# " &se!%atin. ;!e sim$ly, ne e!lang!e$!esents ne ci!cuit ccu$ie# "! ne hu!.

It is name# a"te! the Danish ;athematician, Agne! .

The t!a""ic intensity is the !ati " the $e!i# "! which these!%e! is ccu$ie# t the ttal $e!i# " &se!%atin ismeasu!e# in e!langs.


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Example:I" a g!u$ " 20 t!un( ca!!ies 80 e!langs an# the a%e!age call #u!atin is

? minutes, calculate a a%e!age num&e! " calls in $!g!ess & ttal

num&e! " calls !iginating $e! hu!.

! the $!esent #ay netw!(s which su$$!t %ice, #ata an# manythe! se!%ices, e!lang is &ette! measu!e t !e$!esent t!a""ic intensity.


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Units o Telephone Trafic *ent call secn#s **S+ It is !e"e!!e# as hun#!e#

call secn#s. **S as a measu!e " t!a""ic intensity is

%ali# nly in tele$hne ci!cuits.

**S !e$!esents a call time $!#uct. This is use# as a

measu!e " the amunt " t!a""ic e$!esse# in units "800 secn#s. Smetimes call secn#s *S an# call

minutes *; a!e als use# as a measu!e " t!a""ic

intensity.

The !elatin &etween e!lang an# **S is gi%en &y


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Example *nsi#e! a g!u$ " 8200 su&sc!i&e!s which gene!ate 600

calls #u!ing the &usy hu!. The a%e!age hl#ing time is2.2 minutes. hat is the ""e!e# t!a""ic in e!langs, **S

an# *;.


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Grade o Service (GOS) The g!a#e " se!%ice !e"e!s t the $!$!tin " unsuccess"ul calls

!elati%e t the ttal num&e! " calls. BCS is #e"ine# as the !ati " lst t!a""ic t ""e!e# t!a""ic.

The smalle! the %alue " g!a#e " se!%ice, the &ette! is the se!%ice. The!ecmmen#e# BCS is 0.002, i.e. 2 call $e! 8000 ""e!e# may lst. In a

system, with e'ual n. " se!%e!s an# su&sc!i&e!s, BCS is e'ual t )e!. BCS is a$$lie# t a te!minal t te!minal cnnectin. 5ut usually a

switching cent!e is &!(en int "llwing cm$nents An inte!nal call su&sc!i&e! t switching ""ice An utging call t the t!un( netw!( switching ""ice t t!un(

The t!un( netw!( t!un( t t!un( A te!minating call switching ""ice t su&sc!i&e!.

The!e a!e tw $ssi&ilities " call &lc(ing, which a!e st system an#aiting system.


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Example Du!ing a &usy hu!, 8400 calls we!e ""e!e# t a g!u$ "

t!un(s an# 84 calls we!e lst. The a%e!age call #u!atin

has ? minutes. in# a T!a""ic ""e!e# & T!a""ic ca!!ie# c

BCS an# # The ttal #u!atin " $e!i# " cngestin.


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loc!in" Pro#a#ilit$ and%on"estion The %alue " the &lc(ing $!&a&ility is ne as$ect " the tele$hnecm$any1s g!a#e " se!%ice.

The &asic #i""e!ence &etween BCS an# &lc(ing $!&a&ility is that BCS is a

measu!e "!m su&sc!i&e! $int " %iew whe!eas the &lc(ing $!&a&ility is ameasu!e "!m the netw!( ! switching $int " %iew.

5ase# n the num&e! " !ejecte# calls, BCS is calculate#, whe!eas &y&se!%ing the &usy se!%e!s in the switching system, &lc(ing $!&a&ility will&e calculate#.

The &lc(ing $!&a&ility, 5 is #e"ine# as the $!&a&ility that all the se!%e!s in

a system a!e &usy. *ngestin the!y #eals with the $!&a&ility that the ""e!e# t!a""ic la#ecee#s sme %alue. Thus, #u!ing cngestin, n new calls can &eacce$te#.

The!e a!e tw ways " s$eci"ying cngestin, which time cngestin an# callcngestin.

Time cngestin is the $e!centage " time that all se!%e!s in a g!u$ a!e&usy.

*all cngestin is the $!$!tin " calls a!ising that # nt "in# a "!ee se!%e!. In gene!al BCS is calle# call cngestin ! lss $!&a&ility an# the &lc(ing

$!&a&ility is calle# time cngestin.


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&odelin" o Trafic T analy)e the statistical cha!acte!istics " a switching system,

t!a""ic "lw an# se!%ice time, it is necessa!y t ha%e a mathematicalm#el " the t!a""ic ""e!e# t telecmmunicatin systems.

The m#el is a mathematical e$!essin " $hysical 'uantity t!e$!esents the &eha%i! " the 'uantity un#e! cnsi#e!atin.

Als the m#el $!%i#es an analytical slutins t a telet!a""ic$!&lems.

As the switching system may &e !e$!esente# in #i""e!ent ways,

#i""e!ent m#els a!e $ssi&le. De$en#ing n the $a!ticula! system an# $a!ticula! ci!cumstance, asuita&le m#el can &e selecte#.

In $!actice, the "acilities " the switching systems a!e sha!e# &ymany use!s. This a!!angement may int!#uce the $ssi&ility " callsetu$ ina&ility #ue t lac( " a%aila&le "acilities.

I" a su&sc!i&e! "in#s n a%aila&le se!%e! "! his call attem$t, he willwait in a line 'ueue ! lea%e imme#iately. This $henmenn may&e !ega!#e# as a 'ueueing system.

The mathematical #esc!i$tin " the 'ueueing system cha!acte!icsis calle# a 'ueueing m#el.


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Telephone 'etor! Or"aniation A telecmmunicatin netw!( cntains a la!ge num&e! "

lin(s jining #i""e!ent lcatins, which a!e (nwn as the

n#es " the netw!(.

T $!%i#e e""icient cmmunicatin, a tele$hne netw!(shul# inclu#e %a!ius t!ansmissin system "! eam$le,te!!est!ial, mic!wa%e, $tical satellite cmmunicatins,

switching system t i#entity an# cnnect calling an# calle#su&sc!i&e! an# t echange in"!matin &etweensu&sc!i&e! an# switching systems ! &etweeninte!echanges, a g# signaling system !e'ui!e#.

Tele$hne netw!(s !e'ui!e ce!tain "!m " $!ce#u!e t!ute a $a!ticula! call t the #estinatin "! e""ecti%e an#cst e""ecti%e cmmunicatin. S, the tele$hne netw!(shul# &e im$lemente# with a g# !uting $lan.


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'etor! &ana"ement The &asic gal " the netw!( management is t maintain

e""icient $e!atins #u!ing e'ui$ment "ailu!es an# t!a""ic

%e!la#s. A %ital "unctin " netw!( management is cnt!lling the

"lw " call !e'uests #u!ing netw!( %e!la#.

! the e""ecti%e netw!( management the stu#y " %a!iusse!%ices $!%i#e# &y the netw!(, ""e!e# la# " thenetw!(, classi"icatin " the netw!( &ase# n se!%ices""e!e#, inte!cnnectin " #i""e!ent ty$es " netw!(s an#

netw!( $lanning is im$!tant.

5ase# n the #ata a%aila&le "! the a&%e "act!s, thenetw!( management is &ecme u$#ate#.


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'etor! Plannin"

The $lanning " telecmmunicatin systemcm$!ising a netw!( " switching cente!s

inclu#es %a!ius $lans.

!m initiating the netw!( t the etensin "

the netw!( &ase# n the inc!ease# la#,

netw!( $lanning $lays a %ital !le.


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'etor! services The ca$a&ilities "ten cllecti%ely !e"e!!e# t as intelligenceF within

the netw!( a!e liste# &elw. De$en#ing u$n the a$$licatins the

netw!( is t han#le the inte!cnnecti%ity with the! netw!(s. Switching: The $!cess " inte!cnnecting incming calls ! #ata t

the a$$!$!iate utging channel calle# #estinatin is !e"e!!e#switching.

Routing: The a&ility " the netw!( t select a $ath t cnnect

calling an# calle# su&sc!i&e! "! tele$hne cn%e!satins !$!%i#ing $ath "! #ata t!ans"e! &etween su!ce an# #estinatin is!e"e!!e# as !uting.

Flow control: ;anaging the !ate at which t!a""ic ente!s a netw!(. Anetw!( withut e""ecti%e "lw cnt!l $!ce#u!es &ecmes %e!yine""icient.

Security: The!e a!e tw ways " $!%i#ing secu!ity " the netw!(. T inc!ease the secu!ity " $e!atin in $!esence " "aults. !e%enting unauth!i)e# access t the netw!( an# the #ata it

ca!!ies.


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'etor! services(*) Signaling: A signaling system lin( the %a!iety " switching system,

t!ansmissin system an# su&sc!i&e! e'ui$ments in a telecmmunicatinnetw!( t ena&le the netw!( t "unctin as a whle.

Traffic management: The a&ility " the netw!( t (ee$ t!ac( " t!a""icle%els. T!a""ic management is use"ul &th in sh!t te!m an# lng te!m&ases. Cn a sh!t te!m &asis, it can &e use# t su$$!t #ynamic !utingan# "lw cnt!l. C%e! a lng te!m it can &e use# in netw!( #esign ti#enti"y $a!ts " the netw!( whe!e ca$acity may &e $!#ucti%elyinc!ease# ! #ec!ease#.

Accountability: This inclu#es cha!ging, &illing, accunting an#in%ent!y cnt!l. This is the a&ility " the netw!( t t!ac( the use!s "the netw!(.

Administration: It is !elate# t the a&ility " the netw!( t i#enti"y thela# " a netw!( an# $!%i#ing c!!es$n#ing u$g!a#itin " $a!ts,etentin " netw!(s "acility. It als i#entities the sales st!ategy,in%estment $lanning etc.

Inter networking: It is the a&ility " the netw!( t $e!"!m the "unctinsnee#e# t cmmunicate with an# ac!ss the! netw!(s. This inclu#es$!%i#ing !utes "! t!a""ic c!ssing th!ugh, int an# ut " the netw!(,an# allcating !esu!ces such as &u""e!s an# lin( ca$acity t t!a""ic!iginating the! netw!(s.


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'etor! +evels All the a&%e "unctins an# sme the! se!%ice !elate# "unctins a!e

usually classi"ie# ! g!u$e# int #i""e!ent le%els.

This g!u$ing ease the netw!( an# the cnce!ne# netw!( enginee!st ca!!yut the "unctins e""iciently.


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,arious 'etor!in" Plans A natinal telecmmunicatin netw!( is la!ge an# cm$le. The!e"!e ce!tain $lans a!e nee#e# t g%e!n the #esign " netw!(. The $lans a!e in#e$en#ent an# a!e a""ecte# &y the $!e#icte# !

$lanne# g!wth !ate " the telecmmunicatin system. ;!e s$eci"ic netw!( $lanning a!e +

Routing lans Numbering lans !harging lan Transmission lan Signaling lan "rade of ser#ice Network control and network administration$

The chice " a $lan "! a telecmmunicatin system gene!ally in%l%escm$a!isn " the ecnmics " %a!ius $ssi&le $lans.

It als in%l%es cm$a!isn " the ecnmy " %a!ius $ssi&le $lansan# in%l%es a ce!tain amunt " human ju#gment.


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T$pes o 'etor!s The!e a!e in gene!al th!ee netw!(s which can &e use# "! any

se!%ices %ice ! #ata t!ans"e!.

Public switched network: It allws access t the en# ""ice,cnnects th!ugh the lng:#istance netw!(, an# #eli%e!s t the en#$int. The gal " the netw!( hie!a!chies is t cm$lete the call inthe least amunt " time an# the sh!test !ute $ssi&le.

Pri#ate networks: ;any cm$anies, #e$en#ing n thei! si)e an#nee#, c!eate ! &uil# thei! wn netw!(s. I" thei! netw!(s a!eun#e!utili)e#, they may gi%e thei! netw!( "! hi!e ! lease. Thesenetw!(s em$ly mitu!e " technlgies.

%ybrid networks: T $!%i#e a se!%ice, i" an !gani)atin uses &th$!i%ate an# $u&lic netw!(s, the netw!( is !e"e!!e# as hy&!i#netw!(. 3!mally, the high:en# usage se!%ices a!e cnnecte# %ia$!i%ate "acilities, the lwe! %lume lcatins use the switche#netw!(.


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'etor! %lasses 5ase# n the se!%ices+

8. The u&lic Switche# tele$hne 3etw!( ST3G"!tele$hny. 2. The $u&lic switche# teleg!a$h netw!(G"! tele

?. Data netw!(sG"! %ice an# #ata

4. *ellula! !a#i netw!(G"! m&ile cmmunicatin

H. S$ecial se!%ice netw!(sGt meet s$eciali)e#

#eman#s.

;aj! telecmmunicatin netw!(s+

8. ST3 ! CTS 2. Data netw!(s

?. ISD3.


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-outin" Plan 9uting $lanning !e"e!s t the $!ce#u!es that

#ete!mine which $ath in a netw!( a!e assigne# t$a!ticula! cnnectins.

The switching cente!s may use "ie# !utes t each#estinatin.

A#a$ti%e !uting may &e em$lye# in which eachechange may use #i""e!ent !utes "! the same#estinatin, #e$en#ing u$n t!a""ic cn#itins.

! e""ecti%e !uting " a call, sme "!m "

inte!cnnectin " switching echanges a!e !e'ui!e#.


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asic Topolo"ies The th!ee &asic t$lgies a!e ;esh, sta! an# mie# ! hie!a!chical

;esh:cnnecte# netw!(+ This is als calle# "ully cnnecte# t$lgy. The

a#%antage " mesh netw!( is that each statin has a #e#icate# cnnectin

t the! statins. This t$lgy ""e!s the highest !elia&ility an# secu!ity. Themesh t$lgy !e'ui!es 33 82 cnnectins. ! 800 statins, 4=H0 lin(s

!e'ui!e#.

Sta! t$lgy+ It is an alte!nati%e t the mesh a!!angement. In sta! netw!(,

the num&e! " lines is e'ual t the num&e! " statins. It nee#s la!ge!, an#m!e $we!"ul t!un( cent!e. As nly ne la!ge! cent!e is !e'ui!e#, sta!

a!!angement $!e"e!a&le. 3te that the echange a!ea in#icates that all the

calls in that a!ea a!e cnsi#e!e# t &e lcal calls.

/ie!a!chical netw!(s+ ;any sta! netw!(s may &e inte! cnnecte# &y using

an a##itinal tan#em echange, lea#ing t tw le%el sta! netw!(. An !#e!ly

cnst!uctin " multile%el sta! netw!(s lea#s t hie!a!chical netw!(s.

/ie!a!chical netw!(s a!e ca$a&le " han#ling hea%y t!a""ic with minimal

num&e! " t!un( g!u$s.


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'um#erin" Plan The num&e!ing $lan is use# t i#enti"y the su&sc!i&e!s

cnnecte# in a telecmmunicatin netw!(.

The main &jecti%e " num&e!ing $lan &y any natin ist stan#a!#i)e the num&e! length whe!e%e! $!acticalacc!#ing t **ITT !ecmmen#atins.

Cthe! &jecti%es inclu#es+

T meet the challenges " the changing telecmen%i!nment

T meet su&sc!i&e! nee#s "! a meaning"ul an# use!"!ien#ly scheme

T !ese!%e num&e!ing ca$acity t meet theun#e"ine# "utu!e nee#s.


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ITU -ecommendations in'um#erin" Recommendation E$&'(: It $!%i#es the num&e! st!uctu!e an#

"unctinality "! th!ee categ!ies " num&e!s use# "! inte!natinal

$u&lic telecmmunicatin. The th!ee categ!ies " num&e!s a!e+ National telehone ser#ices: An inte!natinal $u&lic

telecmmunicatin num&e! "! geg!a$hic a!eas is als !e"e!!e# tas the natinal signi"icant num&e! 3S3. 3S3 cnsists " thecunt!y c#e **, natinal #estinatin c#e 3D* an# the

su&sc!i&e! num&e! S3. "lobal telehone ser#ices: An inte!natinal $u&lic

telecmmunicatin num&e! "! gl&al tele$hne se!%ice cnsists "a th!ee #igit cunt!y c#e an# gl&al su&sc!i&e! num&e!. Thecunt!y c#e is always in the >KK ! =KK !ange.

International networks: An inte!natinal $u&lic telecmmunicatinnum&e! "! inte!natinal netw!(s cnsists " th!ee #igit cunt!yc#e, a netw!( i#enti"icatin c#e an# a su&sc!i&e! num&e!. Thecunt!y c#e is always in the >KK !ange. The i#enti"icatin c#e isne t "u! #igits.


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ITU -ecommendations in'um#erin" (*) Recommendation E$&)*: This #e"ines a stan#a!# way t

w!ite tele$hne num&e!s, email a##!esses an# we&

a##!esses. It !ecmmen#s hw t use hy$hen :, s$ace , ! $e!i# L . a!e use# t in#icate #igits that a!esmetimes nt #ialle#, is use# t in#icate alte!natenum&e!s an# L is use# in we& a##!esses.

Recommendation E$&'): This !ecmmen#atin#esc!i&es that the !iginating cunt!y must analy)e amaimum " se%en #igits " the E.864 inte!natinalnum&e!. hen a num&e! is &eing analy)e#, it will &e #neacc!#ing t this !ecmmen#atins.

Als, the inte!natinal num&e!ing $lan ! w!l# num&e!ing$lan has &een #e"ine# in !ecmmen#atins E.860 M E.868an# E.862.


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International 'um#erin" Plan This $lan has t &e im$lemente# i!!es$ecti%e " a cunt!y1s natinal

num&e!ing $lane an# im$lemente# in acc!#ance t the

!ecmmen#atins " ITU.

ith sme stan#a!# inte!natinal "!amew!(, su&sc!i&e!s "!m #i""e!ent

cunt!ies can call each the!.

This $lan ma(es it $ssi&le t access all cunt!ies with the same

cunt!y c#e any whe!e in the w!l#.

! the inte!natinal num&e!ing $lan, the w!l# has &een #i%i#e# int

nine geg!a$hical a!ea.

The gene!al !ule is that within each gl&al !egin each cunt!y c#e

sta!ts with the same #igit.


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.orld 'um#erin" /ones

An inte!natinal tele$hne num&e! sta!ts with ne t th!ee #igit cunt!y c#e

"llwe# &y = t 82 su&sc!i&e! num&e!. The #ialing $!ce#u!e is that theinte!natinal $!e"i 001 shul# &e #iale# "i!st "llwe# &y the tele$hne num&e!.


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'ational 'um#erin" Plan Each cunt!y #eci#es "! itsel" what (in# " num&e!ing $lan it can ha%e. A

num&e!ing $lan may &e $en, semi $en ! clse#. 3atinal num&e!ing $lan is the ne that each cunt!y #eci#es what !ules t

"llw when issuing tele$hne num&e!s. An $en num&e!ing $lane ! nn:uni"!m num&e!ing scheme allws %a!iatins

in the num&e! " #igits t &e use# t i#enti"y the su&sc!i&e!. This $lan is use#in cunt!ies e'ui$$e# etensi%ely with nn:#i!ect! st!wge! switching system.This scheme is almst etinct nt nw eisting.

A clse# num&e!ing $lan ! uni"!m num&e!ing $lan !e"e!s t a num&e!ing

$lan which nly allws tele$hne num&e!s " a $!e#ete!mine# length. S$ecialse!%ices tll "!ee, $!emium !ate, etc. a!e usually eclu#e# "!m this !ule. A semi:$en $lan $e!mits num&e! lengths t #i""e! &y almst ne ! tw #igits.

T#ay, this scheme is the mst cmmn an# is use# in many cunt!iesinclu#ing In#ia, Swe#en, Swit)e!lan# an# U.


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%har"in" Plan The initial csts a!e c%e!e# $a!tly "!m installatin cha!ges an#

$a!tly "!m !ental. The $e!ating csts " the tele$hne echangea!e !ec%e!e# th!ugh !ental an# call cha!ges.

Acc!#ing t the g%e!nment $licy, the !ental may &e le%ie# n amnthly, &imnthly ! &y sme the! m#es.

The 'uantity " e'ui$ments use#, !uting echanges, switchingsystems, lines ca!!ying %ice#ata an# human in%l%ement inesta&lishing a cnnectin &etween su&sc!i&e!s #i""e!s with !es$ect tthe #istance &etween the su&sc!i&e!s, the time at which the call is

ma#e at &usy hu! ! "" $ea( hu!, the a!ea &usiness !!esi#ential etc.

The cha!ging meth#s "! in#i%i#ual calls "all un#e! tw &!a#categ!ies. Du!atin in#e$en#ent cha!ging Du!atin #e$en#ent cha!ging

T!a#itinally, cha!ges "! lng #istance calls ha%e &een $!$!tinalt #istance multi$lie# with #u!atin.

The lcal calls within a num&e!ing a!ea a!e usually cha!ge# n a#u!atin in#e$en#ent &asis.


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Thanks!

Technology changes but communication lasts.

Switching systems-lecture3.ppt

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