6 telecommunications traffic

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Telecommunications Traffic

Tcom 142 Lecture No. 61st Sem SY 2009-2010


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Introduction Trunkis any entity tat !ill carry one call

"ay#e an international circuit !it a len$t of tousands of

kilometers or a fe! meters of !ire #et!een s!itces in tesame tele%one e&can$e Trunkin$is te arran$ement of trunks and s!itces

!itin a tele%one e&can$e

Num#er of trunks to #e %ro'ided de%endson te traffic to #e carried( sufficient for#usiest time)%eak traffic load


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*usy +our Num#er and duration of %one calls 'aries in a random manner

,de%endin$ on su#scri#er cate$ories and time of day !en te callsare made.

esult of tis !ill #e a 'aryin$ load on te e/ui%ment. continuous one-our %eriod durin$ !ic traffic in a %art of te

net!ork is at its most intensi'e is called #usy our. Tis our mayoccur at different times of day ,or ni$t de%endin$ on !iccate$ory of su#scri#ers is dominant.


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imensionin$ imensionin$ te route is to determine te

num#er of trunks re/uired on a route or

connection #et!een e&can$es 1imensionin$ %ro#lem te #asic %ro#lem of

determinin$ te si3e of a telecommunicationssystem is $i'en te offered traffic0 andte s%ecified $rade of ser'ice * find tenum#er of trunks N tat is re/uired

Traffic to #e andled ,i.e. usa$e determinesnum#er of trunks to #e %ro'ided %articularlydurin$ te #usiest time of day


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+oldin$ Time 5a%acity of an e&can$e cannot #e e&%ressed

ust as te num#er of %ossi#le simultaneous

calls. T 5ontrol e/ui%ment used in te call set-u%

%rocedure is en$a$ed to a $reater or less e&tentdurin$ a t!enty-four-our %eriod.

Tis is due to 'ariations in te mean oldin$time ,call set-u% time 7 con'ersation time 7disconnection time


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Traffic Intensity Te unit of traffic flo! in any %articular %art

of a net!ork is named erlan$,8 in onour

of te anis matematician $ner raru%8rlan$ ,1:;:-1929 !o de'elo%ed #asicteories of te relationsi%s #et!een te

tree teletraffic factors Traffic intensitycan #e defined as te

a'era$e num#er of calls in %ro$ress


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Traffic Intensity Traffic carried #y a $rou% of trunks is te %roduct

of te a'era$e num#er of call arri'als %er unit oftime T and te a'era$e call oldin$ time

< 5)T!ere < traffic in erlan$s 5 < a'era$e num#er of call arri'als durin$ time T < a'era$e call oldin$ time

8&am%le In a local e&can$e te total num#er ofcalls durin$ one our !as 1:00. Te mean oldin$time !as = minutes. >e o#tain a traffic intensityof < 1:00 ? =)60 < 90 erlan$s


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Traffic @at Asa$e Asa$e is defined #y t!o ,2 %arameters

callin$ rate - num#er of times a route or traffic

%at is used %er unit %eriod ,call intensity %ertraffic %at durin$ te #usy our oldin$ time B duration of occu%ancy of a traffic

%at #y a call

Traffic %atis a cannel time slot fre/uency#and line trunk s!itc or circuit o'er !icindi'idual communications %ass in se/uence


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Traffic 5once%ts In addition to te term traffic intensity

tere are tree different traffic

conce%ts traffic carried ,c ,e/ui'alent to te traffic

intensity(

traffic offered ,o( and traffic lost ,l


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Crade of Ser'ice In a tele%one e&can$e teoretically %ossi#le for

e'ery su#scri#er to make simultaneous calls cost ofmeetin$ tis demand is %roi#iti'e %ro#a#ility of it

a%%enin$ is ne$li$i#le 5on$estionis situation !erein all trunks in a $rou%of trunks are #usy no furter calls can #e acce%ted

In messa$eBs!itced system calls tat arri'e durin$con$estion !ait in a /ueue until an out$oin$ trunk

#ecomes free( delayed #ut not lost. Suc systems arecalled /ueuin$ systemsor delay systems In circuit-s!itced system all attem%ts to make calls

o'er a con$ested $rou% of trunks are unsuccessful(called lost-call systems


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Lost-5all System In lost-call systems te actual traffic carried is less

tan te traffic offered to te systemTraffic carried = traffic offered traffic lost

@ro%ortion of calls lost or delayed due to con$estionis a measure of te ser'ice %ro'ided called $rade ofser'ice2 *

B= Number of calls lostNumber of calls offered

lso B= Traffic lost Traffic offered

< %ro%ortion of te time for !ic con$estion e&ists < %ro#a#ility of con$estion < %ro#a#ility tat a call !ill #e lost due to con$estion


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8&am%le 1urin$ te #usy our 1200 calls !ere offered to a

$rou% of trunks and si& calls !ere lost. Te

a'era$e call duration !as = minutes. Dind2. Te traffic offered

=. Te traffic carried

4. Te traffic lostE. Te $rade of ser'ice

6. Te total duration of te %eriods of con$estion


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8&am%le 2


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Crade of Ser'ice If traffic0erlan$s is offered to a $rou% of trunks a'in$

a $rade of ser'ice * te traffic lostisABand tetraffic carriedisA (1-B)erlan$s

CFS is normally s%ecified for traffic at te #usy our(lar$er CFS te !orse is te ser'ice $i'en

Too lar$e CFS B users make many unsuccessful calls andare dissatisfied( too small CFS B unnecessary

e&%enditure incurred on e/ui%ment rarely used In %ractice #usy-our CFS can 'ary from 1 in 1000 forcea% trunks inside an e&can$e to 1 in 100 for inter-e&can$e connections and 1 in 10 for e&%ensi'einternational routes


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Crade of Ser'ice Te .eference 1ata for .adio 8n$ineers

states tat te CFS %ro'ided #y a

%articular $rou% of trunks or circuits ofs%ecified si3e and carryin$ a s%ecifiedtraffic intensity is te %ro#a#ility tat a

call offered to te $rou% !ill finda'aila#le trunks already occu%ied onfirst attem%t.


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Dactors affectin$ Crade of

Ser'ice Tis %ro#a#ility de%ends on a num#er of

factors te most im%ortant of !ic are

te distri#ution in time and duration of offeredtraffic e.$. random or %eriodic arri'al and constantor e&%onentially distri#uted oldin$ time

te num#er of traffic sources B limited or i$,infinite

te a'aila#ility of trunks in $rou% to traffic sourcesB full or restricted a'aila#ility and

te manner in !ic lost calls are GandledH


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Traffic Sources

Dor infinite traffic sources cases te %ro#a#ility of call arri'al is constant and does

not de%end on te state of occu%ancy of tesystem also im%lies an infinite num#er of call arri'als

eac !it infinitely small oldin$ time

Dinite traffic sources Num#er of sources is com%arati'ely small in

com%arison to te num#er of circuits


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'aila#ility

S!itces are de'ices !it lines and trunks(#etter terms for descri#in$ a s!itc are

GinletsH and GoutletsH Dull a'aila#ilityis !en eac inlet as access

to any outlet Limited a'aila#ilityis !en not all te free

outlets can #e reaced #y inlets Dull a'aila#ility is more desira#le #ut more

e&%ensi'e for lar$er s!itces


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Limited 'aila#ility

Switch with Limited Availability


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Dull 'aila#ility

Switch with Full Availability


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+andlin$ of Lost 5alls

In con'entional tele%one traffic teory tree metods areconsidered for andlin$ or dis%ensin$ of lost calls1. lost calls eld ,L5+

assumes tat te tele%one user !ill immediately reattem%t is call onrecei%t of con$estion si$nal and !ill continue to redial

assumed tat lost calls are eld or !aitin$ at te users tele%one furter assumes tat suc lost calls e&tend te a'era$e oldin$ time

teoretically ,a'era$e oldin$ time is 3ero and all te time is !aitin$time

2. lost calls cleared ,L55 assumes tat user !ill an$ u% and !ait some time inter'al #efore

reattem%tin$ suc calls is assumed to disa%%ear from te system( reattem%t ,after

te delay is considered a ne! call 8rlan$ formula is #ased on tis criterion

=. lost calls delayed ,L5 assumes tat te user is automatically %ut in /ueue

6 telecommunications traffic

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