Pemodelan Sistem Jaringan Dan Trafik

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  • Pemodelan Sistem Jaringan dan

    TrafikTrafik

  • Kongesti Trafik

    Kongesti adalah suatu keadaan dimana semua server

    sedang dalam keadaan diduduki serempak pada satu

    waktu

    Penanganan terhadap panggilan-panggilan yang

    datang pada saat kongesti bergantung kepada sistem

    2

    datang pada saat kongesti bergantung kepada sistem

    operasi server yang ada

  • Kongesti Trafik

    1.1. Loss system (lost call cleared)Loss system (lost call cleared)

    Pada sistem ini, panggilan yang datang saat seluruh sirkit sibuk, akan

    ditolak akan dibuang dari sistem.

    Bila ada panggilan ulang (repeated call), dianggap panggilan yang

    baru.

    3

    baru.

    Sistem ini biasanya digunakan untuk menentukan jumlah saluran

    antar sentral

    SNYA

    R

  • Kongesti Trafik

    2.2. Delay System (lost call delayed)Delay System (lost call delayed)

    Panggilan yang datang saat seluruh sirkit sibuk,maka panggilan-

    panggilan tersebut akan menunggu di buffer yang disediakan sampai

    ada sirkit yang bebas.

    Sistem ini digunakan untuk komunikasi data yang tidak memerlukan

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    Sistem ini digunakan untuk komunikasi data yang tidak memerlukan

    komunikasi real time

  • Kongesti Trafik

    3.3. Overflow system (lost call held)Overflow system (lost call held)

    Panggilan-panggilan yang tidak bisa dilayani kerena seluruh group

    sirkit ke suatu arah dalam kondisi diduduki, maka diluapkan ke group

    sirkit arah lain (alternative route)

    System ini digunakan untuk mendisain suatu MEA (multi exchange

    5

    System ini digunakan untuk mendisain suatu MEA (multi exchange

    Area)

    P Q

    T

    1

    2 3

    Asal Tujuan

    Tandem

    Rute langsung(high-usage route)

    Rute alternatif

  • Grade of Service (GOS)

    Dalam loss system (sistem rugi), trafik yang dibawa

    atau dilayani oleh jaringan lebih kecil dari trafik yang

    ditawarkan sesungguhnya ke jaringan.

    Kelebihan trafik yang tidak mampu dilayani oleh Kelebihan trafik yang tidak mampu dilayani oleh

    jaringan akan ditolak atau dibuang.

    Jumlah trafik yang ditolak oleh jaringan digunakan

    sebagai indek dari kualitas pelayanan dari jaringan

    yang disebut dengan grade of service (GOS) atau B

    6

  • Grade of Service (GOS)

    Grade of Service didefinisikan sebagi perbandingan trafik yang

    hilang (ditolak) dengan trafik yang ditawarkan ke jaringan.

    SNYA

    RB =

    7

    RARB =

    AYAB =

    Dimana :

    B adalah Grade of service(GOS)

    A adalah offered traffic atau trafik yang ditawarkan ke saluran

    Y adalah carried traffic atau trafik yang dibawa/dilayani oleh saluran

    R adalah trafik yang gagal (loss traffic)

  • Probabilitas Blocking didefinisikan sebagai probabilitas seluruh saluran

    (server) dalam sistem sedang sibuk.

    Jika seluruh saluran sibuk, tidak ada trafik yang bisa dilayani oleh sistem

    dan panggilan yang datang akan ditolak.

    Dalam sistem loss probabilitas blocking sama dengan GOS, dikarenakan

    lamanya holding time call yang hilang dianggap sama dengan holding time lamanya holding time call yang hilang dianggap sama dengan holding time

    call yang terlayani

    Perbedaan mendasar antara GOS dan probabilitas blocking adalah :

    GOS diukur dari titik pelanggan,diamati panggilan yang ditolak. Sedangkan probabilitas

    blocking diukur dari titik network atau switching, dimana diamati server-server (saluran)

    yang sibuk dalam system switching.

    GOS disebut juga dengan Call congestion atau loss probability dan probabilitas blocking

    disebut dengan time congestion.

    8

  • Call Rates

    In a loss system each call is either loss or carried

    Thus, there are three types of call rates:

    Offered traffic

    Carried traffic

    Loss traffic

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    Loss traffic

  • Call Rates

    carried traffic (Y)Offered traffic (A)SN

    10

    loss traffic (R)

  • Carried traffic (Y)

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  • Grade of Service (GOS)

    Grade of Service is comparison between lost

    traffic and offered traffic in network.

    GOS = orRB = YAB =

    15

    GOS = or

    Smaller GOS is better services.

    ARB =

    AYAB =

  • Exercise

    16

  • Probability of Blocking

    Definition of Probabilitas Blocking is

    probability all line (server) in system is busy.

    If all line is busy ( use ), no traffif can serve by

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    If all line is busy ( use ), no traffif can serve by

    system and arrival call will be blocking.

  • GOS vs probability blocking

    GOS ( grade of services ) calculate from user side, estimate by call block.

    probabilitas blocking calculate from network switching side, estimate by server or line busy ini

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    switching side, estimate by server or line busy ini system switching.

    GOS is Call congestion or loss probability and probability blocking is time congestion.

  • More examples

    A group of 20 subscribers generate 50 calls with an

    average holding time of 3 minutes, what is the

    average traffic per subscriber?

    Traffic = (50 calls)*(3min)*(1 hour/60 min)

    = 2.5 Erlangs

    19

    = 2.5 Erlangs

    = 2.5 / 20 or 0.125 Erlangs per subscriber.

    Individual (residential) calling rates are quite low and

    may be expressed in milli-Erlangs, i.e. 0.125 Erlangs

    = 125 milli-Erlangs.

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  • Traffic Model Choice

    Traffic model choice is use to calculate capacity

    needed, and get GOS what we want.

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  • Pemilihan Model Trafik

    In Traffic model choice, we have to considere this

    parameters :

    Arrival rate pattern

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    Arrival rate pattern

    Traffic blocking

    The number of traffic source

    holding time

  • Traffic Arrival Pattern and

    Arrival Probability Distribution

    Main Traffic Arrival Pattern are :

    smooth call arrival pattern

    peak call arrival pattern

    30

    peak call arrival pattern

    random call arrival pattern

  • smooth call arrival pattern

    Smooth or hypo-exponential traffic happen when traffic variation is not to big. holding time and interarrival time can be prediction.

    31

  • Peaked Call Arrival Pattern

    32

  • Random Call Arrival Pattern

    33

  • Blocked Calls

    C=carried trafficTrunk

    F=first attemp O=offered

    Block call will be effect on model choice because

    different block call is different traffic load.

    34

    C=carried traffic

    Call held

    Calls cleared Call delayed

  • Blocked Calls

    There type of block call are :

    Lost Calls Held (LCH)

    Lost Calls Cleared (LCC)

    35

    Lost Calls Cleared (LCC)

    Lost Calls Delayed (LCD)

    Lost Calls Retried (LCR)

  • Types of Blocking Models

    Blocked Calls Cleared (BCCBCC)

    Blocked calls leave system and do not return

    Good approximation for calls in 1st choice trunk group

    36

  • Types of Blocking Models

    Blocked Calls Held (BCHBCH)

    Blocked calls remain in the system for the amount

    of time it would have normally stayed for

    If a server frees up, the call picks up in the middle

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    If a server frees up, the call picks up in the middle

    and continues

    Not a good model of real world behaviour

    (mathematical approximation only)

    Tries to approximate call reattempt efforts

  • Types of Blocking Models

    Blocked Calls Wait (BCWBCW)

    Blocked calls enter a queue until a server is

    available

    When a server becomes available, the calls

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    When a server becomes available, the calls

    holding time begins

  • Source #1

    Offered Traffic

    Source #2

    1 3

    10 minutes

    Total Traffic Offered:

    TO = 0.4 E + 0.3 E

    T = 0.7 E

    2 sources

    Blocked Calls Cleared (BCC)

    39

    Offered Traffic 2 4 TO = 0.7 E

    Only one server

    Traffic

    Carried

    1st call arrives and is served

    1

    2nd call arrives but

    server already busy

    22nd call is cleared

    1

    3rd call arrives and is served

    3

    4th call arrives and is served

    4

    Total Traffic Carried:

    TC = 0.5 E

  • Source #1

    Offered Traffic

    Source #2

    1 3

    10 minutes

    Total Traffic Offered:

    TO = 0.4 E + 0.3 E

    T = 0.7 E

    2 sources

    Blocked Calls Held (BCH)

    40

    Offered Traffic 2 4 TO = 0.7 E

    Traffic

    Carried 1 21 2 3 4

    Only one server1st call arrives and is served

    2nd call arrives but server busy

    2nd call is served

    3rd call arrives and is served

    4th call arrives and is served

    Total Traffic Carried:

    TC = 0.6 E

    2nd call is held until server free

  • Source #1

    Offered Traffic

    Source #2

    1 3

    10 minutes

    Total Traffic Offered:

    TO = 0.4 E + 0.3 E

    T = 0.7 E

    2 sources

    Blocked Calls Wait (BCW)

    41

    Offered Traffic 2 4 TO = 0.7 E

    Only one server

    Traffic

    Carried

    1st call arrives and is served

    1

    2nd call arrives but server busy

    2

    2nd call waits until s