-Telecomm-switching.ppt

8/13/2019 -Telecomm-switching.ppt

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Telecommunication

Telecommunication is theassisted transmission ofsignals over a distance forthe purpose of

communication.


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SwitchingThe equipments and

techniques forenabling any stationin a communicationssystem to beconnected with anyother station..


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SwitchingSwitching is an essentialcomponent of telephone,telegraph, data-processing, and othertechnologiesSwitching may beperformed byelectronic,optical, orelectromechanicaldevices.


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Telecomm

ComponentsSubscriber

Devices attached to networkLocal Loop

Subscriber loopConnection to network

ExchangeSwitching centersEnd offices

TrunksBranches between exchangesMultiplexed


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Switching

Any subscriber line can request aconnection to any other line ortrunk.The Switching Network mustallow for these connections to be

established and removed.


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General Principles ofSwitching

Mass communication:communication from few tomany, requires:

one way communication path

Point-to-point communication:from one communicator toanother, requires:

Both-way communications and

rapid reconfiguration oftransmission path


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Point to point lines

If we could have point to point lines between aand all receivers, then we would not need swit


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Imagine point to point

lines between all pairs ofpeople:

# of people #of lines

2133

1045

1004950

10000.5 million

In general, for n people, # of lines


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Need for Switching


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.Lines or wires from everybody'shouse go into the switch When a call is placed, the switchcreates a temporary link

between these lines.


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Switch

As

if

AbidUmar

Amir

Khalid

Mubashir

Z

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Amir

Kha

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Zia

Mubashir


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TYPICAL CONNECTIVITY

OF A SUBSCRIBER

Subscrib

er Office

D

P

DC

MDF

TELEPHONE

EXCHANGE

OUTSIDE

PLANT/COPPER

NETWORK

INSIDE PLA NT/CENTRAL

OFFICE


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Telephony Equipment

Telephone Set

PABX

Advanced features and call routingTens to hundreds of telephonehandsets

Central Office (CO) or Exchange


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CO Stages in

EquipmentManual switching: All telephone lines terminate in a jack, patch cord used to connectparties

Automatic switching:

Electromechanicalstep-by-step switching (Strowgerswitch)cross-bar switching (common control)

Computer-controlled switching


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Basic Call Progress

On Hook


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Basic Call Progress

Off Hook


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Basic Call Progress --

Dialing


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Basic Call Progress --

Switching


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Basic Call Process --

Ringing


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Analog Signaling

Supervisory SignalingLoop Start

Almost All TelephonesCurrent Flow Sensed

Ground StartMomentary Ring Lead


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Loop Start


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Normal Signal Flow


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Switching Systems


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.To get attention of the operator

was a small hand- cranked ACgenerator or magneto atsubscriber end

Produced about 90 V ac, at 20

Hz frequency.


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Classification of switchingsystem

manual

trowger or step-by-step Crossbar

Electomechanical

Space division switching

Space switch Time switCombin

Digital A

Time division

Electroic(Stored program cont

Automatic

Switching System


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Strowger Switch A step by step (SXS) systemperforming switching in two

dimensions (horizontal andvertical)Switching action is a direct resultof the dial pulses generated by

the rotary telephone set.Example a 10,000 lines SXScentral office switch.


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Strowger Switch

OperationWhen a caller goes off-hook, current isdetected in the sub. Loop and preselector switch become active.

The preselector switch advances to a level thatseizes an idle line and sends a dial tone to thesubscriber.

In step by step, the talk path is established asdigits are dialed.

Say party now dials 5831.When 5 is dialed, the resulting electrical pulsescauses the electromechanical relay of aselector switch to step in the vertical direction toa level equal to 5.


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Strowger Switch

OperationThe wiper then advances step bystep, in the horizontal direction,

until it seizes an idle lineavailable on the next selectorswitch.

An 8 is dialed, and the procedure

is repeated.The connection is furtheradvanced to final destination.


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Strowger Switch

OperationThe final selector is capable ofhandling last two digits

When 3,1 are dialed, the final selectorswitch is advances vertically to thethird level and horizontally to the firstposition.The called party at 5831 is tested for abusy condition and the ring potential isapplied if the party is idle.Once the party answers, the lines arefurther supervised till the termination

of the call.


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Strowger Switch--

Example


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Negative StepperProperties

High maintenance costSlow mechanical operation

Slow signalingCant take full advantage of CCS7and other electronic signalingsystems

Big and bulkyDigital switches use ~1/50th the floorspace of steppers; ~1/10th the floorspace of crossbar switches .


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Common Control

SwitchIn common control signaling, thedialed digits are collected andstored until all the digits aredialed.The digits necessary to

determine the talk pathsconnections within the callerscentral office are handled locallyand remaining digits are

retransmitted to the next officeinvolved in the call.


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Common Control

SwitchClear separation between controland switching network of manual

switching reestablishedControl apparatus only used toset up and terminate callsGeneral principle of commoncontrol switches still used inelectronic switching today


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Crossbar switch

Introduced in 1917The switches are electromechanicallyactivated and rely on moving parts.

The switch contains sets of contactpoints or cross-points with three to sixindividual contacts per set.Magnets cause vertical and

horizontal bars to cross each otherand make coordinates determined bythe numbers dialed.Each switch typically has either 100

or 200 crosspoints.


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Electronic Switching

Systems ESS No. 1:

Computer control/stored program control(SPC)

Analog Relay switching, using sealedcontact reed switchesCan handle 10000 to 70000 lines .

ESS No.2

Capable of handling 1000 to 10,000 lines Attractiveness lies in providing reliableservices to smaller communities at aneconomical cost.

Also fully operational at a remote site

Up gradation from DTL to RTL increasingthe speed and reducing the size of controlcircuitry,


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Electronic SwitchingSystems

ESS No.3Bipolar LSI ROMs for micro programcontrol.SPC executed from a unique set ofmicroinstructions stored in ROMDesigned for small offices and small citiesof 100 to 100 subscribers.

ESS No. 4:First all-electronic exchange with digitaltechnology employed in its computerizedcontrol and switching matrix.Over 10,00 trunks can be handled using acombination of TDM and SDM.


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Electronic Switching

SystemsESS No.5

Most advanced and versatile

Capable of serving 100,00 to 1,000subscribers.Relies heavily on LSISoftware technology incorporated

to permit rapid addition of newtechnology with the advancementsin hardware.Some facilities:

Call forwarding, Call waiting,call within, Speed call, Threeway calling, Caller ID etc.


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Origins of digitalswitching

Stored Program Control Switches(1970+)

i.e. Digital SwitchesUtilize a CPU for controlling mostswitching

operations Few moving parts More maintenance free and efficient Allow significant flexibility of service

(programs can be stored and executedfor each subscriber : Call blocking Repeat last call Reminder calls Call diversion


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DLU

DAS

LTG

SN

CP

CCG

MB

SYP

C7/SS7POW

ERSUPPLY

ACCESS SWITCHINGNETWORK

POWERSUPPLYSYSTEM

CONTROL

SIGNALLING

TYPICAL SWITCH


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A digital exchange ( Nortel DMS-100 ) used by anoperator to offer local and long distanceservices
http://en.wikipedia.org/wiki/Nortelhttp://en.wikipedia.org/wiki/DMS-100http://en.wikipedia.org/wiki/DMS-100http://en.wikipedia.org/wiki/DMS-100http://en.wikipedia.org/wiki/DMS-100http://en.wikipedia.org/wiki/Nortel


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DLU

DAS

LTG

SN

CP

CCG

MB

SYP

C7/SS7POW

ERSUPPLY

ACCESS SWITCHINGNETWORK

POWERSUPPLYSYSTEM

CONTROL

SIGNALLING

TYPICAL SWITCH


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Switching TechnologyCircuit Switching (CS)

Need a connection establishment

between end nodes.Connection is maintained untilone of end nodes terminates.Connection is dedicated to thecommunication between twonodes.Reduces the number and thetotal length of the linksExample : Public Switch

Telephone Network (PSTN)


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Switching TechnologyPacket Switching (Virtual Circuitand Datagram)

Data are transmitted in short messagescalled packets .

A connection between the two end-nodesis not maintained.

A node-to-node link can be dynamicallyshared by many packets.Example : Public Data Network (PDN)likes X.25, Frame Relay.

Message Switching (MS)Cell Switching (ATM)


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NationalTelecommunications

NetworkPrimary Center (LocalNetwork/Primary Trunk Switching

Centers)

Secondary Center (Trunknetwork/Regional TandemSwitching Centers)

Tertiary Center (NationalTandem Exchanges/TertiaryTrunk Switching Centers)


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TerminologyNorth American

1 Customers Loop

2 Central Office3 End Office4 Class 5 Office

5 Inter Office Trunk6 Junctor7 Toll Office8 Toll Network

British

1 LocalNetwork/AccessNetwork

2 Exchange3 Local Exchange

5 Junction6 Trunk7 Trunk exchange

8 Trunk Network


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RegulationsDifferent countries have useddifferent methods to regulate thetelecommunication business. Inmost countries thetelecommunication monopoly hasbeen controlled by stateownership like PTA in Pakistan.


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StandardsInternational Communications Union (ITU)

The work of ITU is carried out through two

main bodies:

1) The ITU Telecommunication Sector (ITU-T)Its duties include the study of technicalquestions, operating methods and tariffs fortelephony, telegraphy and data

communications2) The ITU Radio Communication Sector (ITU-

R)It studies all technical and operating questionsrelating to radio communications includingpoint to point communications, mobile

services and broadcasting. Associated with itis the International Frequency RegistrationBoard (IFRB), which regulates the assignmentof radio frequencies to prevent interferencebetween different transmissions

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