TN 325: TELE-TRAFFIC ENGINEERING

Dimensioning of
Telecommunication
Networks
Why network dimensioning?
 “The purpose of dimensioning of
telecommunications network is to ensure
that the expected needs will be met in an
economical way both for subscribers and
operators.”
Network Planning
 Network planning includes designing,
optimising, and operating
telecommunication networks.
 During the process of Network Planning
and Design, estimates are made of the
expected traffic intensity and traffic load
that the network must support
Network Planning Cont..
 If a network of a similar nature already
exists, traffic measurements of such a
network can be used to calculate the
exact traffic load.
 If there are no similar networks, then the
network planner must use
telecommunications forecasting methods
to estimate the expected traffic intensity.
Network Planning Cont..
 The network planning process begins with
the acquisition of external information.
This includes:
 forecasts of how the new
network/service will operate;
 The economic information concerning
costs
 the technical details of the network’s
capabilities
Stages of the planning process:

 Stages of the planning process:

– Topological design
– Network-synthesis problem
 •Traffic routing
 Dimensioning
– Network-realization (circuit-routing)
problem
Traffic Forecast
 To properly dimension the network we
need to estimate the traffic offered
 If the network is already operating,
– the current traffic is most precisely
estimated by making traffic measurements
 Otherwise, the estimation should be
based on other information, e.g.
– estimations on characteristic traffic
generated by a subscriber
Traffic Forecast Cont..
– estimations on the number of
subscribers
 Long time-span of network investments
– it is not enough to estimate only the
current traffic
– forecasts of future traffic are also needed
Traffic Forecast Cont..
 Purpose
– provide a basis for decisions on
investments in network
 Forecast periods
– time aspect important (reliability)
– need for forecast periods of different
lengths
Traffic Forecasting Procedure
 The forecasting process involves several steps

meza
Traffic Forecasting Methods
 Trend methods
– linear extrapolation
– nr of subscribers increased yearly by
about 200 in the past 5 years
3 * 200 = 600 new subscribers in the next
3-year period
– not suitable if growth is exponential
Traffic Forecasting Methods Cont..
 Statistical demand analysis
– network operator seeks to map out
those factors that underlie the earlier
development
– changes that can be expected during the
forecasting period are then collated
 Assessment methods
– analogy method: situations or objects
with similar preconditions will develop
similarly
Traffic Forecasting Methods Cont..
 Traffic forecast defines
– the estimated traffic growth in the
network over the planning period
 Starting point:
– current traffic volume during busy hour
(measured/estimated)
 Other affecting factors:
– changes in the number of subscribers
–change in traffic per subscriber
(characteristic traffic)
Traffic Forecasting Methods Cont..
Final result (that is, the forecast):
The final result of the traffic forecast is
given by a traffic matrix
– traffic matrix describing the traffic
interest between exchanges (traffic
areas)
Traffic Matrix
 To specify the traffic demand in an area
with K exchanges we should know K2 traffic
values Aij(i; j = 1…….K), as given in the
traffic matrix shown in Table 1.
 The traffic matrix assumes we know the
location areas of exchanges.
Traffic Matrix Cont..
 Let us assume we know the actual traffic
matrix and that we have a forecast for
future
 row sums O(i) and column sums T(i), i.e. the
total incoming and outgoing traffic for each
exchange.
 The total incoming traffic is equal to the total
outgoing traffic.
Traffic Matrix Cont..
 Table 1: Traffic Matrix
Traffic Matrix Cont..
 The traffic matrix has the following
elements:
Aij = is the traffic from i to j.
Aii = is the internal traffic in exchange i.
Ai = is the total outgoing (originating) traffic
from i.
Aj = is the total incoming (terminating) traffic
to j.
Traffic Matrix Cont..
 Problem:
– easily grows too big: 600 exchanges Þ
360,000 elements!
 Solution: hierarchical representation
– higher level: traffic between traffic areas
– lower level: traffic between exchanges
within one traffic area
Example 1
Data:
– There are 1000 private subscribers and
10 companies with their own PBX’s in the
area of a local exchange.
– The characteristic traffic generated by a
private subscriber and a company are
estimated to be 0.025 erlang and 0.200
erlang, respectively.
Example 1 Cont..
 Questions:
– What is the total traffic intensity a
generated by all these subscribers?
– What is the call arrival rate λ assumed
that the mean holding time is 3 minutes?
 Answers:
– a = 1000 * 0.025 + 10 * 0.200 = 25 + 2
= 27 erlangs
– h = 3min
– λ = a/h = 27/3 calls/min = 9 calls/min
Example 2
 Data:
– In a 5-year forecasting period the number
of new subscribers is estimated to grow
linearly with rate 100 subscribers/year.
– The characteristic traffic generated by a
private subscriber is assumed to grow to
value 0.040 erlang.
– The total nr of companies with their own
PBX is estimated to be 20 at the end of
the forecasting period.
Example 2 Cont..
 Question:
– What is the estimated total traffic
intensity a at the end of the forecasting
period?
 Answer:
– a = (1000 + 5*100)* 0.040 + 20 * 0.200
= 60 + 4 = 64 erlangs
Example 3
 Data:
– Assume that there are three similar local
exchanges.
– Assume further that one half of the traffic
generated by a local exchange is local
traffic and the other half is directed
uniformly to the two other exchanges.
Example 3 Cont..
 Question:
– Construct the traffic
matrix T describing the
traffic interest between
the exchanges at the
end of the forecasting
period.
 Answer:
– T(i,i) = 64/2 = 32 erlangs
– T(i,j) = 64/4 = 16 erlangs
Traffic dimensioning

 Basic task in traffic dimensioning:

Dimensioning a new network determines the
minimum capacity requirements that will still
allow the Teletraffic Grade of Service (GoS)
requirements to be met
 Telecommunications system from the traffic
point of view:
Traffic dimensioning Cont..
 To do this, dimensioning involves planning
for peak-hour traffic, i.e. that hour during
the day during which traffic intensity is at
its peak
 The dimensioning process involves
determining the network topology,
routing plan, traffic matrix and GoS
requirements.
Traffic dimensioning Cont..
 These information are used to determine
the maximum handling capacity, and the
maximum number of channels required
between switches
Traffic dimensioning Cont..
 General rule:
– Dimensioning should be based on peak
traffic not on average traffic
 However,
– Revenues are based on average traffic
 For dimensioning (of telephone
networks), peak traffic is defined via the
concept of busy hour:
Simplified traffic dimensioning
in a telephone network
 Assume
– fixed topology and routing
– given traffic matrix
– given GoS requirement
 Dimensioning of network nodes:
Determine the required call handling
capacity
– max number of call establishments the
node can handle in a time unit
Simplified traffic dimensioning
in a telephone network Cont..
 Dimensioning of links:
Determine the required number of
channels
– max number of ongoing calls on the link
Dimensioning rule
 To get the required Grade of Service (the
average time a customer waits before
service should be less than the average
service time) …… Keep the traffic load
less than 50%
 A dimensioning rule is that the planner
must ensure that the traffic load should
never approach a load of 100 percent.
Dimensioning rule Cont..
 To calculate the correct dimensioning to
comply with the above rule, the planner
must take on-going measurements of the
network’s traffic, and continuously
maintain and upgrade resources to meet
the changing requirements.
 Another reason for overprovisioning is
to make sure that traffic can be rerouted
in case a failure occurs in the network
Dimensioning rule Cont..

Remember
 If you want a less stringent requirement,
still remember the safety margin
…Don’t let the total traffic load approach
to 100%
 Otherwise you’ll see an explosion!
Example 4
Example 4 Cont..
 Assumptions:
– 3 local exchanges completely connected
to each other
– Traffic matrix T describing the busy hour
traffic interest (in erlangs) given below
– Fixed (direct) routing: calls are routed
along shortest paths.
– Mean holding time h = 3 min.
Example 4 Cont..
 Task:
– Determine the call handling capacity
needed in different network nodes
according to the GoS requirement ρ <
50%.

Given: ρ = λ/µ
Example 4 Cont..
 Node 1:
– call requests from own area:
[T(1,1)+ T(1,2) +T(1,3)]/h=90/3=30 calls/min
– call requests from area 2:
T(2,1)/h = 30/3 = 10 calls/min
– call requests from area 3:
T(3,1)/h = 30/3 = 10 calls/min
– total call request arrival rate:
λ(1) = 30+10+10 = 50 calls/min
Example 4 Cont..
– required call handling capacity:
ρ(1) = λ(1)/µ(1) = 0.5
µ(1) = 2*λ(1) = 100 calls/min
 Node 2:
– total call request arrival rate:
λ(2)=[T(2,1)+T(2,2)+ T(2,3)+
T(1,2)+T(3,2)]/h
= (75+15+15)/3 = 35 calls/min
– required call handling capacity:
Example 4 Cont..
 Node 3:
– total call request arrival rate :
λ(3) = [T(3,1) + T(3,2) + T(3,3)
+ T(1,3)+T(2,3)]/h
= (75+15+15)/3 = 35 calls/min
– required call handling capacity:
µ(3) = 2*λ(3) = 70 calls/min
Traffic classes
 Networks should match offered service
to source requirements (corresponds to
utility functions)
 Traffic classes encompass both user
requirements and network service offerings
 Example: telnet requires low bandwidth
and low delay
◦ network should provide a low-delay service
◦ or, telnet belongs to the low-delay traffic class
Traffic Classes
 Basic classes
guaranteed service
best effort
Guaranteed Service
 Guaranteed service (Sensitive traffic) is
traffic the operator has an expectation to
deliver on time. This includes VoIP, online
gaming, video conferencing, and web
browsing.
 Traffic management schemes are typically
tailored in such a way that the quality of
service of these selected uses is
guaranteed, or at least prioritized over
other classes of traffic
Best- effort
 Best effort traffic is all other kinds of non-
detrimental traffic. This is traffic that the
ISP deems isn't sensitive to Quality of
Service metrics (jitter, packet loss,
latency).
 A typical example would be peer-to-peer
and email applications. Traffic management
schemes are generally tailored so best-
effort traffic gets what is left after
sensitive traffic.
GS vs. BE
 Degree of synchrony
time scale at which peer endpoints interact
GS are typically synchronous or interactive
 interact on the timescale of a round trip
time
 e.g. telephone conversation or telnet
BE are typically asynchronous or non-interactive
 interact on longer time scales
 e.g. Email
GS vs. BE Cont..
 Sensitivity to time and delay
GS apps are real-time
performance depends on wall clock
BE apps are typically indifferent to real
time
automatically scale back during overload
Note:
 Compared to network engineering, which
adds resources such as links, routers and
switches into the network, traffic
engineering targets changing traffic paths
on the existing network to alleviate traffic
congestion or accommodate more traffic
demand.
Reading Assignment
 Networks of Queues
 What is Queues network
 Open queuing network
 Closed queuing network
 Networks of Queues Applications