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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
ia
Amir
Kha
lid
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/Nortel8/13/2019 -Telecomm-switching.ppt
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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