telecommunication system engineering network design procedures & traffic routing

7/29/2019 Telecommunication system engineering Network Design Procedures & Traffic Routing

1/45

Irfan Khan


2/45

Exchange placement (Toll

-

center placement):

Rather than base the placement decision on subscriber density and

their calling rates, the basic criterion is economy, the most cost-effective optimum.

Traffic matrix/Routing:

The design procedure is to construct the familiar traffic matrix,where cost ratio studies are carried out to determine whether

routing will be direct or tandem.

The tendency is to use tandem working and direct routes with

overflow

Irfan Khan


3/45

Comparison of local versus long-distance networks

Irfan Khan


4/45

We are moving away from the hierarchical concept (though slowly)

to one using more direct routes.

In Pakistan we Prefer hierarchical structure with almost three to

four levels in the hierarchy .

Irfan Khan


5/45

LINK LIMITATION

ITU-T Organization recommends that there be

, except for verylarge countries where 14 links may be acceptable

On an international connection, the

, each 4 links in tandem as follows:

1. National connection of country originating call

2. International portion

3. National connection of country terminating the call.

link in this context is defined as the connectivity from one

exchange to an adjacent exchange serving the international

connection Irfan Khan


6/45

ITU-T places this link limitation in the transmission plan to ensure

some minimum transmission quality and to provide efficient

operation of signaling ,end-to-end

LINK LIMITATION

An international connection to illustrate the nomenclature adopted and the maximum number of

links in tandem for an international connection. From ITU-T Rec.G.101 Irfan Khan


7/45

INTERNATIONAL NETWORK

International Telephone Routing Plan is contained in ITU-T Rec.

E.171. Some of its highlights are:

It is not hierarchical.

Direct traffic should be routed over final (fully provided) or high

usage circuit groups.

No more than four international circuits in tandem should be

involved between originating and terminating ISCs

Advantage should be taken of the noncoincidence of

international traffic by use of alternative routings to effect circuit

economies and provide route diversity.

The routing of transit switched traffic should be so planned to

avoid circular routings (ring-around-the-rosy). Irfan Khan


8/45

When a group consists of both terrestrial and satellite circuits,

the choice of routing should be governed by:

INTERNATIONAL NETWORK

Total delay of connectivity (


9/45

EXCHANGE LOCATION (TOLL/LONG-DISTANCE NETWORK)

Toll Areas

Assignments of toll exchanges regarding numbering &Impact of

numbering on routing a call and on accounting equipment.

Irfan Khan


10/45

Maximum size of a toll exchange

For 0.003erlangs (see next slide) per subscriber line; thus a 4000-

line toll exchange could serve just under a million subscribers

maximum

The exchange capacity should be dimensioned to the forecast

long-distance traffic load 10 years after installation.

we must have at least two levels:

1.Local area

2.Toll area.

Factors leading to more than two levels are:

Geographical size

Telephone density, usually per 100 inhabitants

Toll traffic trends

Political factors

Toll Areas

Irfan Khan


11/45

There are many choices open to the system engineer to establish

the route-plan hierarchy

Figure B is a three-level hierarchy with a four-to-five fan-out at each stage.

For a two-level hierarchy, two possibilities are suggested:

Figure C has low initial fan-out, and Figure D has a high one. The choice between C and

D may depend on traffic intensity between nodes or availability of routes

For national networks, the fan-out in Figure D may be most economical because traffic is

brought to a common point more quickly

Principal city

1

2

1

234

Low fan-out

High fan-out

Irfan Khan

Fan out:The maximum number of

devices that can be safelydriven by the output from a

logic gate or logic device

(which have only a limited

ability to drive other

devices from their output

terminals). If the fan-out is

exceeded the voltage levels

corresponding to a logic 1

and a logic 0 become more

similar and errors are more

likely.


12/45

Erlang =

Considering a group of circuits, traffic intensity in erlangs is the

number of call-seconds per second or the number of call-hoursper hour

A group of 10 circuits had a call intensity of 5 erlangs, we would

expect half of the circuits to be busy at the time of measurement.

Erlang

Calls carried x Mean holding time

Observation time period

Irfan Khan


13/45

NETWORK DESIGN PROCEDURES

The attempt to attain a final design of an optimum national

network is a major cut-and-try process.

Simple logic demands that the design must first take into account

the existing network.

Major changes in the network require a large expenditure

Technology advances are galloping along.

Ten years age of a switch might be the very outside.

Even a 5-year-old switch may have to be replaced because of

Obsolescence.

Signaling on the national and international networks has been

standardized on CCITT Signaling System No. 7. But every country or

administration has its own national variant of SS No.7

Factors considered for Network Design:

Irfan Khan


14/45

NETWORK DESIGN PROCEDURES

Design Process

Starting from the local exchange, there are now three bases to workfrom:

1. There are existing local areas, each of which has a toll exchange.

2. There is one or more ISCs placed at the top of the network

hierarchy.

3. There will be no more than four links in tandem on anyconnection to reach an ISC.

Irfan Khan


15/45

Class 4 exchange/ Primary center

T is a tandem exchange with a fan out of four

Four local exchanges, A, B, C, and D homing on T

The entire national geographic area will be made up of small

segments, as shown in Figure and each may be represented by a

single exchange such as T.

Design Process

Areas and exchange relationships Irfan Khan


16/45

The next step is to to and from each T.

Design Process

This information is organized and tabulated on a

Toll Traffic Matrix (Sample) (in Erlangs)

The convention used here is that values are read from the exchange in the left-hand column to the exchange in

the top row. For example, traffic from exchange 1 to exchange 5 is 23 erlangs

Irfan Khan


17/45

It is recommend that a hierarchical structure be established.

At the top of a countrys hierarchy is the international switchingcenter.

A typical hierarchical network. The

example illustrated here is the North

American network circa 1990.

Dashed lines show high-usage trunks.

Note how the two highest levels are

connected in mesh.

The earlier AT&T network in the United

States was a five-level hierarchy.

Design Process

Irfan Khan


18/45

An example of a hierarchical network with alternative

routing.

The lowest level is not shown in the

figure, that of the local exchange.

Routing structure

Design Process

The routes in the set will always betested in the same sequence

although some routes may not be

available for certain call types

The last choice route is the finalroute in the sense that no traffic

streams using this route may

overflow further.

Irfan Khan


19/45

Suppose a country had

and

could be divided into fourareas around each center.

A sample network design

We define a as a

route from which no traffic

can overflow to an alternativeroute

Irfan Khan


20/45

Irfan Khan


21/45

Irfan Khan

TRAFFIC ROUTING IN THE NATIONAL NETWORK


22/45

TRAFFIC ROUTING IN THE NATIONAL NETWORK

Objective of Routing

The objective of routing is to establish a successful connectionbetween any two exchanges in the network.

The function of traffic routing is the selection of a particularcircuit group, for a given call attempt or traffic stream, at an

exchange in the network.

The choice of a circuit group may be affected by information onthe availability of downstream elements of the network on a

quasi-real-time basis.

Irfan Khan


23/45

Network Topology

A network comprises a number of nodes (switching centers)

interconnected by circuit groups.

Direct route consists of one or more circuit groups connecting

adjacent nodes

Indirect route as a series of circuit groups connecting two nodes providingan end-to-end connection via other nodes

Network Architecture

Hierarchy of switching centers (e.g., local area, regional trunk, and

international) with each

Irfan Khan


24/45

A simplified network with circuit groups connecting pairs of nodes with one-way

and both-way (two-way) working.

Irfan Khan


25/45

Routing Scheme

There are fixed routing schemes and dynamic routing schemes

Routing patterns in a network may be fixed, in that changes in routechoices for a given type of call attempt require manual intervention.

Such changes may be time-dependent, state dependent and/or event-

dependent.

The updating of routing patterns may take place periodically or

aperiodically, predetermined, depending on the state of the network or

depending on whether calls succeed or fail. Irfan Khan


26/45

Time-Dependent Routing

With this type of routing scheme, routing patterns are altered at fixed

times during the day (or week) to allow changing traffic demands to beprovided for.

State-Dependent Routing

This is a routing scheme where routing patterns vary automatically

according to the state of the network. This is adaptive routing.

Each exchange compiles records of successful calls or outgoing trunk

group occupancies. This information is then distributed through the

network to other exchanges or passed to a centralized database.

Concept of state-dependent routing Irfan Khan


27/45

Event-Dependent Routing

Routing patterns are updated locally on the basis ofwhether calls

succeed or fail on a given route choice.

Each exchange has a list of choices, and the updating favors

those choices which succeed and discourage those which suffer

congestion.

Irfan Khan

R t S l ti


28/45

Route Selection

The action to select a definite route for a specific call.

is where the routes in a set are always

tested in sequence and the first available route is selected.

routing, the routes in a set are tested in nospecific order.

The selection can be sequential or nonsequential.

Irfan Khan


29/45

The decision to select a route can be based on :

The state of the outgoing circuit group or the states ofthe series of circuit groups in the route.

The incoming path of entry

Class of service ( Voice, data)

Type of call (Operator, Ordinary subscriber, test call etc)

Irfan Khan

Call Control Procedures


30/45

Call Control Procedures

Call control procedures define the entire set of interactive signals

necessary to establish, maintain, and release connection betweenexchanges.

Two types of call control procedures are:

1. Progressive Call Control

Progressive call control uses link-by-link Signaling to pass

supervisory controls sequentially from one exchange to the next

In the irreversible case, call control is always passed

downstream toward the destination exchange.

Call control is reversible when it can be passed backwards

(maximum one node), toward the originating exchange. Irfan Khan


31/45

2.Originating Call Control

Originating call control requires that the originating exchange

maintain control of the call setup until a connection betweenoriginating and terminating exchanges has been completed.

Irfan Khan

Applications


32/45

Applications

Automatic Alternative Routing

One type of progressive (irreversible) routing is automatic alternativerouting (AAR).

There are two principal types of this routing available:

1. When there is a choice of direct circuit groups between the twoexchanges.

2. When there is a choice of direct and indirect routes between the two

exchanges.

Irfan Khan


33/45

Automatic Rerouting (Crankback)

Automatic rerouting is a routing facility enabling connection of call

attempts encountering congestion during the initial call setup phase.

If a signal indicating congestion is received from exchange B,

subsequent to the seizure of an outgoing trunk from exchange A,

the call can be rerouted at exchange A.

Blocking from B to D activates signal S1 to A. Blocking from D to F

activates signal S2 to A. Irfan Khan


34/45

Load Sharing

Each outgoing routing pattern (A, B, C, D) may include alternative

routing options.

Routing schemes can be developed to ensure that call

attempts are offered to route choices according to apreplanned distribution.

Irfan Khan

Dynamic Routing Examples


35/45

Dynamic Routing Examples

Example State-Dependent Routing

A centralized routing processor is employed to select optimum routing

patterns on the basis of actual occupancy levels of the circuit groupsand exchanges in the network which are monitored on a periodic basis.

This routing technique inherently incorporates fundamental principles of

network management in determining routing patterns. These include: Avoiding occupied circuit groups.

Not using overloaded exchanges for transit.

In overload circumstances, restriction of routing direction connections.

Irfan Khan


36/45

Example of Time-Dependent Routing.

For each originating and terminating exchange pair, a particular route

pattern is planned depending on the time of day and the day of the

week.

This type of routing takes advantage of idle circuit capacity in other

possible routes between originating and terminating exchanges which

may exist due to noncoincident busy hours.

Irfan Khan

E l f E D d R i


37/45

Example of Event-Dependent Routing

This type of routing scheme routes traffic away from congested

linksby retaining routing choices where calls are successful.

It is simple, adapts quickly to changing traffic patterns, and

requires only local information.

In a fully connected network, calls between each originating and

terminating exchange pair try the direct route with a two-link

alternative path selected dynamically.

Irfan Khan


38/45

Irfan Khan


39/45

The long-distance network is entirely four-wire. As the network

is extended, delay becomes more of a problem.

Propagation

Processing time

Echo in telephone systems is the return of a talkers voice. Echo is

a reflection of voice.

The cause of echo is impedance mismatches that might be

present any place in the electrical telephone connection.

Two factors determine the degree of annoyance of echo: its

and its

Delay has two components:

Irfan Khan


40/45

Singing is the result of sustained oscillations due to positivefeedback in telephone amplifiers or amplifying circuits

Circuits that sing are unusable and promptly overload multiplex

equipment, particularly FDM equipment.

Singing may be regarded as echo that is completely out of

control.

This can occur at the frequency at which the circuit is resonant.

Irfan Khan


41/45

The mismatch is usually between the two-wire side and the hybrid,

where the balancing transformer provides the other side of the match.

Impedance match is described by a term called return loss. The higherthe return loss value, the better the match.

Irfan Khan


42/45

We relate return loss, measured in dB, to the impedancesof the

two-wire line we callLand the balancing network N by:

If the balancing network (N) perfectly matches the impedance of

the two-wire line (L), then ZN = ZLand return loss would be infinite.

We use the term balance return loss ( ITU-T Rec. G.122 ) and classify

it as two types:

1. Balance return loss from the point of view of echo (Echo return

loss). This is the return loss measured between the frequencies 300

and 3400 Hz.

2. Balance return loss from the point of view of stability. This is the

return loss measured between 0 and 4000 Hz. Irfan Khan


43/45

Improved return loss at the term set (hybrid).

Adding loss on the four-wire side (or on the two-wire side). Reducing the gain of the individual four-wire amplifiers.

Echo paths in a four-wire circuit Irfan Khan


44/45

Delay is measured in one-way or round-trip propagation time

measured in milliseconds.

Practice in North America .where echo delay is less than that, then echo can be controlled

by adding loss.

Irfan Khan


45/45

telecommunication system engineering network design procedures & traffic routing

Documents