CHAPTER 5 Teletraffic Eng

8/13/2019 CHAPTER 5 Teletraffic Eng

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TELETRAFFIC

ENGINEERING


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Traffic engineering is the mathematical modeling ofdemand on a telecommunications network, and thenumber of lines needed to meet those needs.

The techniques of traffic engineering can be appliedto networks of all kinds, including the PSTN (publicswitched telephone network), LANs (local area

networks), WANs (wide area networks), cellulartelephone networks, and the Internet.


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The measurement of traffic in a public switched

telephone network (PSTN) allows network operatorsto determine and maintain the quality ofservice (QoS) and in particular the grade of service(GoS) that they promise their subscribers.


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A flow of telephone calls within atelephone exchange .

OR

From one Exchange to anotherExchange

SO

The study of this behaviors is calledTeletraffic


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WHAT IS ERLANG?

Erlang defined as the traffic carried by agroup of trunks.

(careful with units, all times in hours)

Erlang = 1 Call

hour / hour1 Erlang = 1 hour (60 minutes) of traffic

)( timeholding hour busy

Calls Erlang

Unit must be

same


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EXAMPLE 1

A call established at 2 am between a centralcomputer and a data terminal. Assuming acontinuous connection and data transferred at 34kbit/s what is the traffic if the call is terminated at

2:45am?


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WHAT IS CCS?

Centum call secondAlso known the hundred call secondIs a unit of telecommunications traffic density that isthe equivalent of one call in a specific channel for

100 seconds in an hour.CCS = Hundred call seconds.

Erlang

hour

361

min601

sec60min1sec100

sec1001 CCS


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How does the Erlang unit correspond to ccs?

Percentage of time a terminal is busy is equivalent tothe traffic generated by that terminal in Erlangs, orAverage number of circuits in a group busy at any time.


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A subscriber makes three phone calls of 3 minutes, 4 minutesand 2 minutes duration in a one hour period. Calculate thesubscriber traffic in Erlangs and CCS.


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The average traffic density (occupancy) duringany one hour period and writes in Erlang (E)units.

WhereA= Traffic intensity

h=The average holding time of a callC=The average number of callrequested/hourT=1 hour / 60 minutes / 3,600 seconds

T

Ch A


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Consider a PSTN which receives 240 calls/hr. Eachcall lasts an average of 5 minutes. What is theoutgoing traffic intensity to the public network.


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Given traffic intensity of 90 E and holding time for a call is 3minutes. Find call intensity.


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Busy hour is that continuous 60 minutes timespan of the day during which the highestusage occurs.

Busy hour


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At stage of all the trunks in a group oftrunks are busy cannot accept any furthercalls is called congestion orWhen the level of network traffic nears,reaches or exceeds the design maximum,the network is said to be congested.

)(sec1 ond hour GoS congestionTime


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Is a measure of the probability that apercentage of the offered traffic will beblocked or delayed.

offered call of Nolost call of No

Gos

A

A A

offered Trafficlost TrafficGoS

..

0

0

Where; A = offered traffic A0 = carried traffic A-A0 = lost traffic


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The total length of time that a call makes useof a trunk or channel.measured in seconds.


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This is the traffic which would be carried if nocalls were rejected due to lack of capacity .

Aoffered = Acarried + Areject

Offered traffic = Avg no.of calls X Avg call holding time


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the traffic intensity actually handled by the group

Acarried = Aoffered - Areject

Traffic carried = Traffic Offered Traffic Lost


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Rejected calls occur as a result of heavy trafficloads (congestion) on the system and can result inthe call either being delayed or lost.

Areject = Aoffered - Acarried


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1200 calls are offered to a channel and 6calls are lost. Duration of a call is 3 minutes.Find:

i. Offered traffic, Aii. Carried trafficiii. Lost trafficiv. GoS, Bv. Congestion time


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On average, during the busy hour, acompany makes 120 outgoing calls ofaverage duration 2 minutes. It receives 200

incoming calls of average duration 3 minutes.Find:

i. Outgoing traffic

ii. Incoming trafficiii. Total traffic


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Traffic to be offered at peak hours is 600 calls.The average call is 3 minutes and 20 calls werefailing. Calculate :

i. Offered traffic in Erlang unitii. Carrying traffic in Erlang unit


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.Calculate the G.O.S of a switching centerwhich has busy hour offered traffic of 200Ewhen the average call duration is 3 minutes

and 40 calls are lost during this hour.


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Telekom Malaysia Berhad is offeringtelecommunication service to its customers.The traffic being offered in its transmissionmedia is 120E in a duration of 6 minutes 15

second. While the traffic being carried is 110E.Calculate:

i. the number of call being offered in the line.ii. the number of call being carried in the line.iii. the number of call being lost due to congest.iv. the traffic loss due to congestion.v. grade of service

CHAPTER 5 Teletraffic Eng

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