Voice Traffic Engineering Management

8/7/2019 Voice Traffic Engineering Management

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Voice TrafficVoice Traffic

Engineering &Engineering &ManagementManagement


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PSTN and PBX networks are designedPSTN and PBX networks are designedwith 2 objectives:with 2 objectives:

Maximize usage of their circuitsMaximize usage of their circuits

Minimize the cost.Minimize the cost.


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I n telecommunications, calls being handled byI n telecommunications, calls being handled by

a switching system are referred to asa switching system are referred to as traffictraffic ..A nalogous to road way traffic. Must know howA nalogous to road way traffic. Must know howmany lanes are needed, but with little waste.many lanes are needed, but with little waste.

The job of a traffic engineer is to balance theThe job of a traffic engineer is to balance thetradetrade--off between cost and service.off between cost and service.

Must be able to handle traffic sufficiently duringMust be able to handle traffic sufficiently during busy hours and no more. busy hours and no more.Designs based on historic data.Designs based on historic data.how many trunks are enough?how many trunks are enough?


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O ther questions to consider..O ther questions to consider..

How many customer service agents are needed to deliver aHow many customer service agents are needed to deliver a particular level of service in a call center. particular level of service in a call center.

How long callers have to wait with a certain number of How long callers have to wait with a certain number of agents.agents.

Both the agents and the circuits are analogous inBoth the agents and the circuits are analogous intelephony traffic engineeringtelephony traffic engineering


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Efficiency Efficiency is defined as the percent of time theis defined as the percent of time theserver is working (carrying traffic) as opposedserver is working (carrying traffic) as opposedto waiting for a call.to waiting for a call.

This is also known asThis is also known as o ccupancyo ccupancy ..

F or a given load, the more the servers, the lessF or a given load, the more the servers, the less

blocked or held calls. blocked or held calls.

The rate at which traffic arrives is seldomThe rate at which traffic arrives is seldomuniform.uniform.

P rinciples Governing Network DesignP rinciples Governing Network Design


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Principles of Network DesignPrinciples of Network Design

More servers than necessary provide good service,More servers than necessary provide good service, but at an excessive cost. but at an excessive cost.

Too few servers and both service and cost deteriorate,Too few servers and both service and cost deteriorate,resulting in loss of customers and decreased agentresulting in loss of customers and decreased agent

productivity. productivity.

The analysts job is to reach an optimum balanceThe analysts job is to reach an optimum balance between costs and service. between costs and service.


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Principles of Network DesignPrinciples of Network Design

Networks can be classified as Networks can be classified as Loss S yst em s Loss S yst em s ,,or or D elay S yst em s D elay S yst em s ..

L oss systemsL oss systems - - calls are blocked or rejectedcalls are blocked or rejectedwithout being served.without being served.

Service is measured by the % of calls blocked.Service is measured by the % of calls blocked.

Delay systems are queued calls, such as the AC DDelay systems are queued calls, such as the AC Dsystems.systems.

Service is measured by % of calls that are delayedService is measured by % of calls that are delayedwithin a certain time interval.within a certain time interval.


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Traffic Engineering F undamentalsTraffic Engineering F undamentals

To administer a telecommunications system, 3 To administer a telecommunications system, 3 variables are required:variables are required:

Grade of Service (GoS)Grade of Service (GoS)

Traffic loadTraffic loadQuantity of serversQuantity of serversK nowing 2 can determine the third.K nowing 2 can determine the third.

Systems should not be designed to handle highestSystems should not be designed to handle highest busy hour nor non busy hour nor non- -random traffic, such as thatrandom traffic, such as thatexperienced during major catastrophes or call inexperienced during major catastrophes or call incontestcontest


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Grade of Service (GoS) refers to the % of callsGrade of Service (GoS) refers to the % of calls

that encounter blockage.that encounter blockage.A s a business objective, must determine amount of A s a business objective, must determine amount of blockage that can be tolerated. blockage that can be tolerated.

I f the GoS is too high (zero blockage), many circuitsI f the GoS is too high (zero blockage), many circuits

will be underutilized.will be underutilized.Too low means too many busy signals encountered.Too low means too many busy signals encountered.Most business situations call for between 1% and 5 %Most business situations call for between 1% and 5 %

blockage. blockage.


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Tr affic Lo ad Tr affic Lo ad is the amount of traffic during busyis the amount of traffic during busyhour.hour.

Bu s y Ho u r Bu s y Ho u r The A verage Busy Hour ( A BH) is the average of the busyThe A verage Busy Hour ( A BH) is the average of the busyhour over a several day period.hour over a several day period.

Used to determine the capacity needs.Used to determine the capacity needs.

I f the busy hour of each day varies, the average is called theI f the busy hour of each day varies, the average is called theA verage Bouncing Busy Hour ( A BBH).A verage Bouncing Busy Hour ( A BBH).


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Busy Hour Busy Hour A t the busy hour, more blockage will occur,A t the busy hour, more blockage will occur,

I t is not feasible to design circuits to handle the absolute peaks.I t is not feasible to design circuits to handle the absolute peaks.Therefore, some blockage is expected.Therefore, some blockage is expected.

I f some seasons have busier times than others, the studyI f some seasons have busier times than others, the studyshould be taken then.should be taken then.

Between the holidays or registration week at a college.Between the holidays or registration week at a college.

A common definition for seasonal busy hour is the averageA common definition for seasonal busy hour is the averageamount of traffic during the 10 highest days of the year.amount of traffic during the 10 highest days of the year.


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Traffic L oad can be distinguished betweenTraffic L oad can be distinguished betweenO ffe r ed l o ad O ffe r ed l o ad vsvs Ca rr ied l o ad Ca rr ied l o ad . .

C arried LoadC arried Load is what is shown on Billing Reportsis what is shown on Billing ReportsT alk t ime.T alk t ime.

O ffered LoadO ffered Load also includes setup times.also includes setup times.

Talk Time + Setup TimeTalk Time + Setup TimeC all setup time is the time used to signaling time andC all setup time is the time used to signaling time andringing, as the circuit is occupied during that time, butringing, as the circuit is occupied during that time, butno billing is recorded.no billing is recorded.


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Engineers useEngineers use O ffered L o ad (talk + setup)O ffered L o ad (talk + setup) totoengineer aengineer a Circuit Gr o up.Circuit Gr o up.

The Traffic L oad is the amount of trafficThe Traffic L oad is the amount of trafficduring busy hour.during busy hour.

O nce engineers know the Traffic L oad and theO nce engineers know the Traffic L oad and therequired service level (amount of acceptablerequired service level (amount of acceptable

blockage, also called GoS), the number of blockage, also called GoS), the number of circuits required could be found by looking atcircuits required could be found by looking ata traffic design table.a traffic design table.

There are several type of traffic design tables, for There are several type of traffic design tables, for

specific characteristics.specific characteristics.


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Traffic Design TablesTraffic Design Tables

3 types of tables are used, depending on the3 types of tables are used, depending on thegiven situation. Each table uses a differentgiven situation. Each table uses a differentdistribution theoremdistribution theorem

E r lang A t able E r lang A t able and assumes Block C allsand assumes Block C alls H eld H eld (BC H), which assumes that callers immediately(BC H), which assumes that callers immediatelyredial upon receiving a busy.redial upon receiving a busy.E r lang B t able E r lang B t able and assumes Block callsand assumes Block calls Cleared Cleared

(BCC

), which assumes the caller either waits(BCC

), which assumes the caller either waitslonger to redial or does not redial.longer to redial or does not redial.E r lang C t able E r lang C t able and assumes Block calledand assumes Block called D elayed D elayed (BC D), in which the calls are queued until a circuit(BC D), in which the calls are queued until a circuit

becomes available. becomes available.


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Sources of traffic usage informationSources of traffic usage information

Many PBX systems provide traffic usage data.Many PBX systems provide traffic usage data.Most L EC s can perform aMost L EC s can perform a b usy studyb usy study on selectedon selectedtrunk groups.trunk groups.

shows the number of items that callers attempted andshows the number of items that callers attempted andencountered a busy.encountered a busy.I f no busies are logged, too many trunks have beenI f no busies are logged, too many trunks have beenassigned.assigned.

C all A ccounting SystemC all A ccounting System a P C connected to aa PC connected to aSMDR port of the switch provides info.SMDR port of the switch provides info.

I t can then exported and parsed to a spreadsheet as in theI t can then exported and parsed to a spreadsheet as in thenext figure.next figure.

No call setup time info is provided in this report. No call setup time info is provided in this report.


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Traffic Usage is measured in CC S or Erlangs.Traffic Usage is measured in CC S or Erlangs.

Erlang equals 1 hour of traffic usage.Erlang equals 1 hour of traffic usage.C an be converted to minutes by multiplying by 6 0.C an be converted to minutes by multiplying by 6 0.

CC S (C enti* C all Seconds) is used for smaller CC S (C enti* C all Seconds) is used for smaller increments of measurement.increments of measurement.

1 CC S is worth 100 seconds.1 CC S is worth 100 seconds.C is the Roman Numeral for 100C is the Roman Numeral for 100


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1 Erlang=6

0 minutes=3 6

00 seconds=3 6

CC

S,1 Erlang=6

0 minutes=3 6

00 seconds=3 6

CC

S,1 CC S=1. 67 minutes.1 CC S=1. 67 minutes.

The typical resident generates about 3The typical resident generates about 3 --5 CC S5 CC S per call and the typical business is about per call and the typical business is aboutdouble that.double that.

K nowing desired GoS and traffic load, theK nowing desired GoS and traffic load, thenumber of circuits is found using traffic tables.number of circuits is found using traffic tables.


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Example: using the first type of table, we state that 1% blocking is acceptable, andExample: using the first type of table, we state that 1% blocking is acceptable, and4 Erlangs of traffic are measured during the A BBH, 10 trunks are needed. If 4 Erlangs of traffic are measured during the A BBH, 10 trunks are needed. If 5 % blocking is acceptable, only 8 trunks are needed.5 % blocking is acceptable, only 8 trunks are needed.

Remember, 4 Erlangs = 4 hours of traffic (not necessarily via 1 circuit)Remember, 4 Erlangs = 4 hours of traffic (not necessarily via 1 circuit)


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Busy signals from blocked calls can be returned inBusy signals from blocked calls can be returned inone of 2 ways when considering a PBX:one of 2 ways when considering a PBX:

By the carrier By the carrier By the AC D, which can be throttled, controlling theBy the AC D, which can be throttled, controlling thenumber of calls coming into the call center.number of calls coming into the call center.

If calls in queue > 3 0 and agents logged on 2If calls in queue > 3 0 and agents logged on 2

minutes, then busy.minutes, then busy.The key question is will the caller call back or goThe key question is will the caller call back or gosomewhere else? depends on their motivation andsomewhere else? depends on their motivation andalternatives.alternatives.

Some AC Ds can capture the A N I and return a busy signal.Some AC Ds can capture the A N I and return a busy signal.The A N I is stored in a database, so knowledge of whether The A N I is stored in a database, so knowledge of whether or not they call back can be known.or not they call back can be known.


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SMDR (Station Message Detailed Report)


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Av aya Definity G-3 PBX


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A ll too many times, PBX are trunked improperly due to poor planning.

O ften management wants zero busy signals, so over trunking and excessive costs are incurred. However,when planning is used, you are often working with

incomplete data, shooting at a moving target.A ssumptions are based on History, which may beincorrect assumptions and history may not repeatitself. Therefore, frequent measurements should be

performed and adjustments made accordingly. Muststay alert to factors that could change the pattern,such as business activities, number of employees,internal work flow, acquisitions, etc..

Voice Traffic Engineering Management

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