pemodelan sistem jaringan dan trafik
DESCRIPTION
antenaTRANSCRIPT
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Pemodelan Sistem Jaringan dan
TrafikTrafik
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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
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datang pada saat kongesti bergantung kepada sistem
operasi server yang ada
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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.
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baru.
Sistem ini biasanya digunakan untuk menentukan jumlah saluran
antar sentral
SNYA
R
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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
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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
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System ini digunakan untuk mendisain suatu MEA (multi exchange
Area)
P Q
T
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2 3
Asal Tujuan
Tandem
Rute langsung(high-usage route)
Rute alternatif
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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
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Grade of Service (GOS)
Grade of Service didefinisikan sebagi perbandingan trafik yang
hilang (ditolak) dengan trafik yang ditawarkan ke jaringan.
SNYA
RB =
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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)
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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.
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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
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Call Rates
carried traffic (Y)Offered traffic (A)SN
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loss traffic (R)
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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 =
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GOS = or
Smaller GOS is better services.
ARB =
AYAB =
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Exercise
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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.
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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.
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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
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= 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
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Traffic Arrival Pattern and
Arrival Probability Distribution
Main Traffic Arrival Pattern are :
smooth call arrival pattern
peak call arrival pattern
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peak call arrival pattern
random call arrival pattern
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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.
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Peaked Call Arrival Pattern
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Random Call Arrival Pattern
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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.
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C=carried traffic
Call held
Calls cleared Call delayed
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Blocked Calls
There type of block call are :
Lost Calls Held (LCH)
Lost Calls Cleared (LCC)
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Lost Calls Cleared (LCC)
Lost Calls Delayed (LCD)
Lost Calls Retried (LCR)
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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
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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
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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
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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)
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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
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Total Traffic Carried:
TC = 0.5 E
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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)
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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
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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)
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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 server free
2nd call served1 2
3rd call arrives, waits, and
is served
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4th call arrives, waits, and
is served
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Total Traffic Carried:
TC = 0.7 E
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Lost model
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Traffic Model
Erlang B,
Extended Erlang B, and
Erlang C. Other commonly adopted traffic models are
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Engset,
Poisson,
EART/EARC, and
Neal-Wilkerson.
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Comparison of Model Traffic
Model Traffic SourceArrival
Pattern Blocking callHolding
Times
Poisson Infinite Random Held Exponential
Erlang B Infinite Random Cleared Exponential
Extended Erlang B Infinite Random Retried Exponential
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Extended Erlang B Infinite Random Retried Exponential
Erlang C Infinite Random Delayed Exponential
Engset Finite Smooth Cleared Exponential
EART/EARC Infinite Peaked Cleared Exponential
Neal-Wilkerson Infinite Peaked Held Exponential
Crommelin Infinite Random Delayed Constant
Binomial Finite Random Held Exponential
Delay Finite Random Delayed Exponential
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Comparison Traffic Model
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Application of Erlang B Traffic Model
Designing public phone systems where:
blockage is very low and hence retries are uncommon (and can be neglected), or
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uncommon (and can be neglected), or
blockage may be high, but blocked calls overflow to some other facility (modeled separately)
Grade of Service, non-USA Telcos
Grade of service in commercial (low blockage) networks
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Application of PoissonTraffic Model
Grade of Service, USA Telcos
Grade of service in commercial networks
PBX trunk sizing in large offices
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Application of Erlang C Traffic Model
Calculating staffing levels (i.e.. required
agents) for customer call centers
Auto-Attendants, Auto Call Distributors (ACDs)
Latency in data transmission circuits
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Latency in data transmission circuits
Bank Teller, Supermarket, etc. lines
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Application of EngsetTraffic Model
Designing private phone systems (PBXs)
where:
blockage is very low and hence retries are
uncommon (and can be neglected), or
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uncommon (and can be neglected), or
blockage may be high, but blocked calls overflow
to some other facility (e.g. public phone system)
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Application of BinomialTraffic Model
Designing private phone systems (PBXs)
where:
Office size (sources) is small
Where there is no overflow
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Where there is no overflow
Networked servers (e.g. Fax Servers, Modem
Pools,)
Help Desk phone traffic.