traffic forecasting & network planning - lec 04

8/8/2019 Traffic Forecasting & Network Planning - Lec 04

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Traffic Forecasting & Network

Planning

Lec 04

Kamran Nadeem

[email protected]


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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

traffic forecasting & network planning - lec 04

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