traffic forecasting & network planning - lec 04
TRANSCRIPT
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Traffic Forecasting & Network
Planning
Lec 04
Kamran Nadeem
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Traffic Intensity (1)
a = T, where
= number of carried connections per time unit (arrival rate, call rate)
T = mean duration of a connection or holding time
Traffic intensity is a bare number, but in order to emphasize
the context, one often writes as its unit erlang (E, erl) Traffic intensity describes the mean number of simultaneous
call in progress
Instead of a "connection" we may consider reservation of
any resource (trunk, modem etc)
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Traffic Intensity (2)
Example
In a local switch the number of calls in an hour is 1800
The mean holding time of a call is 3 min
What is the intensity?
Typical traffic intensities per a single source are (fraction of
time they are being used)
private subscriber 0.01 - 0.04 erlang business subscriber 0.03 - 0.06 erlang
PBX 0.1 - 0.6 erlang
A load of 90 erlang is created by a population of some 2250
- 9000 private subscribers.
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Traffic Variations (2)
Non-predictive Variations
Short term
Call arrivals
Holding times
Long term
Variations in profiles Probabilistic nature of traffic
Variations due to external events
Natural disasters
Ordinary theoretic traffic models are based on short term
random variables (most predictive)
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Traffic Variations (3)
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Busy Hour (1)
For dimensioning we need an estimated traffic load
Telephone networks use busy hour for dimensioning
Busy hour
Continuous 1-hour duration when traffic is maximum
What is the busy hour for a single day X?
What is the busy hour for a whole month?
ITU has two major definitions
Average Daily Peak Hour (ADPH)
Time Consistent Busy Hour (TCBH)
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Busy Hour (2)
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Busy Hour (3)
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Telephone Traffic Model
Telephone traffic consists of calls
a call occupies one channel from each of the links along its route call characterization: holding time (in time units)
Modeling of offered traffic: call arrival process (at which moments new calls arrive)
holding time distribution (how long they take)
Link model: a pure loss system a server corresponds to a channel
the service rate depends on the average holding time
the number of servers, n, depends on the link capacity
when all channels are occupied, call admission control rejects newcalls so that they will be blocked and lost
Modelling of carried traffic: traffic process tells the number of ongoing calls = the number of
occupied channels
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Telephone Traffic Process
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Packet-level Model - Data Traffic
Data traffic consists of packets
packets compete with each other for the processing and transmissionresources (statistical multiplexing)
packet characterization: length (in data units)
Modeling of offered traffic: packet arrival process (at which moments new packets arrive)
packet length distribution (how long they are)
Link model: a single server queuing system the service rate depends on the link capacity and the average
packet length
when the link is busy, new packets are buffered, if possible, otherwisethey are lost
Modeling of carried traffic: traffic process tells the number of packets in the system (including
both the packet in transmission and the packets waiting in the buffer)
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Packet-level Process (1)
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Packet-level Process (2)
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Data Traffic at Flow Level
In a longer time scale, data traffic may be thought to
consist of flows
A single flow is described as a continuous bit stream with
a possibly varying rate (and not as discrete packets)
Flow classification: Elastic flows
transmission rate adapts to traffic conditions in the network by a
congestion control mechanism
e.g. transfers of digital documents (HTTP,FTP,...) using TCP
Streaming flows
transmission rate independent of traffic conditions in the network
e.g. real time voice, audio and video transmissions using UDP
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Flow Level Model - Elastic
Elastic traffic consists of adaptive TCP flows
flow characterization: size (in data units) the transfer rate and the duration of an elastic flow are not fixed but
depend on the network state dynamically
Modeling of offered traffic: flow arrival process (at which moments new flows arrive)
flow size distribution (how large they are)
Link model: a sharing system due to lack of admission control, no flows are rejected
the service rate depends on the link capacity and the average flowsize
in the model, the adaptation of the transmission rate is immediate,and the link capacity is shared evenly (fairly) among all competingflows
Modeling of carried traffic:
traffic process tells the number of flows in the system
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Elastic Traffic Process
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Flow Level Model - CBR
Streaming CBR traffic consists of UDP flows with constant
bit rate flow characterization: bit rate and duration
Modeling of offered traffic: flow arrival process (at which moments new flows arrive)
flow duration distribution (how long they last)
Link model: an infinite system due to lack of admission control, no flows are rejected
the service rate depends on the average flow duration
transmission rate and flow duration are insensitive to the networkstate
no buffering in the flow level model: when the total transmission rateof the flows exceeds the link capacity, bits are lost (uniformly from allflows)
Modeling of carried traffic: traffic process tells the number of flows in the system, and, as well,
the total bit rate
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Assignment 01
Your task is to research how PTCL models its
voice and data traffic
Write the paper in your own words
Do not copy/paste from the internet or any other
resource
Give extensive references
Deadline: Sunday, November 14, 2010
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The End