Telecomm switching

8/14/2019 Telecomm switching

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TELECOMMUNICATION

SWITCHING

TANVIR AHMAD KHAN NIAZI


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Telecommunication

Telecommunication is the assisted

transmission of signals over adistance for the purpose of

communication.


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Switching

The equipments andtechniques for enabling any

station in a communicationssystem to be connected with

any other station..


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Switching

Switching is an essential

component of telephone,

telegraph, data-processing, andother technologies

Switching may be performed by

electronic,optical, orelectromechanical devices.


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Telecomm ComponentsTelecomm Components Subscriber

Devices attached to network Local Loop

Subscriber loop

Connection to network Exchange

Switching centers End offices

Trunks

Branches between exchanges Multiplexed


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Switching

Any subscriber line can request a connection

to any other line or trunk.

The Switching Network must allow for theseconnections to be established and removed.


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General Principles of

Switching

Mass communication: communication from

few to many, requires: one way communication path

Point-to-point communication: from one

communicator to another, requires: Both-way communications and rapid

reconfiguration of transmission path


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Point to point lines

If we could have point to point lines between all sendersand all receivers, then we would not need switching.


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Imagine point to point lines

between all pairs of people:

# of people # of lines

2 1

3 3

10 45

100 4950

1000 0.5 million

In general, for n people, # of lines = n(n-1)/2


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Need for Switching


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.

Lines or wires from everybody's house go

into the switch

When a call is placed, the switch creates atemporary link between these lines.


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Switch

Asif

Abid

Umar

Amir

Khalid

Mubashir

Zia

Amir

Khalid

Zia

Mubashir


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TYPICAL CONNECTIVITY OF A

SUBSCRIBER

Subscriber

OfficeD

P

D

C MDFTELEPHONE

EXCHANGE

OUTSIDE PLANT/COPPER

NETWORKINSIDE PLANT/CENTRAL OFFICE


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Telephony Equipment

Telephone Set

PABX Advanced features and call routing

Tens to hundreds of telephone handsets

Central Office (CO) or Exchange


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CO Stages in Equipment

Manual switching:

All telephone lines terminate in a jack, patch

cord used to connect parties

Automatic switching: Electromechanical

step-by-step switching (Strowger switch)

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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Basic Call Process -- Talking


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Analog Signaling Supervisory

Signaling

Loop Start Almost All Telephones

Current Flow Sensed

Ground Start Momentary 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 AC generator or magneto

at subscriber end

Produced about 90 V ac, at 20 Hz

frequency.


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Classification of switching system

m a n u a l

S t r o w g e r o r s t e p - b y - s t e p C r o s s b a r

E l e c t o m e c h a n i c a l

S p a c e d i v i s i o n s w i t c h i n g

S p a c e s w i t c h T i m e s w i t c h C o m b i n a t i o n s w i t c h

D i g i t a l A n a l o g

T i m e d i v i s i o n s w i t c h i n g

E l e c t r o i c

( S t o r e d p r o g r a m c o n t r o l )

A u t o m a t i c

S w i t c h i n g S y s t e m


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Strowger Switch

A step by step (SXS) system performingswitching in two dimensions (horizontal andvertical)

Switching action is a direct result of the dialpulses generated by the rotary telephone set.

Example a 10,000 lines SXS central officeswitch.


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Strowger Switch Operation

When a caller goes off-hook, current is detected in the sub. Loopandpreselectorswitch become active.

Thepreselectorswitch advances to a level that seizes an idleline and sends a dial tone to the subscriber.

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

Say party now dials 5831. When 5 is dialed, the resulting electrical pulses causes the

electromechanical relay of a selector switch to step in the verticaldirection to a level equal to 5.


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The wiper then advances step by step, in thehorizontal direction, until it seizes an idle lineavailable on the next selector switch.

An 8 is dialed, and the procedure is repeated. The connection is further advanced to final

destination.


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The final selectoris capable of handling last twodigits

When 3,1 are dialed, the final selector switch is

advances vertically to the third level and horizontallyto the first position. The called party at 5831 is tested for a busy

condition and the ring potential is applied if the partyis idle.

Once the party answers, the lines are furthersupervised till the termination of the call.


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Strowger Switch--Example


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Negative Stepper Properties

High maintenance cost

Slow mechanical operation

Slow signaling Cant take full advantage of CCS7 and other

electronic signaling systems

Big and bulky Digital switches use ~1/50th the floor space of

steppers; ~1/10th the floor space of crossbarswitches.


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Common Control Switch

In common control signaling, the dialed digits

are collected and stored until all the digits are

dialed.

The digits necessary to determine the talk

paths connections within the callers central

office are handled locally and remaining

digits are retransmitted to the next officeinvolved in the call.


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Common Control Switch

Clear separation between control andswitching network of manual switchingreestablished

Control apparatus only used to set up andterminate calls

General principle of common control switchesstill used in electronic switching today


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Crossbar switch

Introduced in 1917 The switches are electromechanically activated

and rely on moving parts.

The switch contains sets of contact points orcross-

points with three to six individual contacts per set.

Magnets cause vertical and horizontal bars to cross

each other and make coordinates determined by

the 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 sealed contact reed

switches Can handle 10000 to 70000 lines.

ESS No.2 Capable of handling 1000 to 10,000 lines Attractiveness lies in providing reliable services to smaller

communities at an economical cost. Also fully operational at a remote site Up gradation from DTL to RTL increasing the speed and

reducing the size of control circuitry,


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ESS No.3 Bipolar LSI ROMs for micro program control. SPC executed from a unique set of microinstructions stored

in ROM Designed for small offices and small cities of 100 to 100

subscribers.

ESS No. 4: First all-electronic exchange with digital technology

employed in its computerized control and switching matrix. Over 10,00 trunks can be handled using a combination of

TDM and SDM.


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ESS No.5 Most advanced and versatile Capable of serving 100,00 to 1,000 subscribers.

Relies heavily on LSI Software technology incorporated to permit rapid

addition of new technology with theadvancements in hardware.

Some facilities:Call forwarding, Call waiting, call within,

Speed call, Three way calling, Caller ID etc.

O f


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Origins of digital switching

Stored Program Control Switches (1970+)

i.e. Digital Switches

Utilize a CPU for controlling most switchingoperations Few moving parts

More maintenance free and efficient

Allow significant flexibility of service (programs can bestored and executed for each subscriber : Call blocking

Repeat last call

Reminder calls

Call diversion


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DLU

DAS

LTG

SN CP

CCG

MB

SYP

C7/SS7POWER

SUPPLY

ACCESS SWITCHING

NETWORK

POWER

SUPPLY

SYSTEM

CONTROL

SIGNALLING

TYPICAL SWITCH


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A digital exchange (NortelDMS-100) used by an operator to

offer local and long distance services
http://en.wikipedia.org/wiki/Nortelhttp://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/SS7POWER

SUPPLY

ACCESS SWITCHING

NETWORK

POWER

SUPPLY

SYSTEM

CONTROL

SIGNALLING

TYPICAL SWITCH


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Switching Technology

Circuit Switching (CS) Need a connection establishment between end

nodes.

Connection is maintained until one of endnodes terminates. Connection is dedicated to the communication

between two nodes.

Reduces the number and the total length ofthe links Example : Public Switch Telephone Network

(PSTN)


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Switching Technology

Packet Switching (Virtual Circuit andDatagram) Data are transmitted in short messages calledpackets. A connection between the two end-nodes is not

maintained. A node-to-node link can be dynamically shared by many

packets. Example : Public Data Network (PDN) likes X.25, Frame

Relay.

Message Switching (MS)Cell Switching (ATM)

N ti l T l i ti


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National Telecommunications

Network

Primary Center (Local Network/Primary TrunkSwitching Centers)

Secondary Center (Trunk network/RegionalTandem Switching Centers)

Tertiary Center (National TandemExchanges/Tertiary Trunk Switching Centers)


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Terminology

North American

1 Customers Loop

2 Central Office

3 End Office

4 Class 5 Office

5 Inter Office Trunk

6 Junctor7 Toll Office

8 Toll Network

British

1 Local Network/Access

Network

2 Exchange

3 Local Exchange

5 Junction

6 Trunk

7 Trunk exchange

8 Trunk Network


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Regulations

Different countries have used different

methods to regulate the telecommunication

business. In most countries the

telecommunication monopoly has beencontrolled by state ownership like PTA in

Pakistan.


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Standards

International Communications Union (ITU)

The work of ITU is carried out through two main bodies:

5)

The ITU Telecommunication Sector (ITU-T)Its duties include the study of technical questions, operatingmethods and tariffs for telephony, telegraphy and datacommunications

7) The ITU Radio Communication Sector (ITU-R)

It studies all technical and operating questions relating to radio

communications including point to point communications,mobile services and broadcasting. Associated with it is theInternational Frequency Registration Board (IFRB), whichregulates the assignment of radio frequencies to preventinterference between different transmissions


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Thanks

Documents

Telecomm switching