telecommunications switching systems 2

7/29/2019 Telecommunications Switching Systems 2

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TelecommunicationSwitching Systems

and NetworksCS/EEE/INSTR C414

Telecommunications

The word telecommunicationwas adaptedfrom the French word tlcommunication.

It is a compound of the Greek prefix telemeaning 'far off', and the Latincommunicare, meaning 'to share'.

The French word tlcommunicationwascoined in 1904 by French engineer andnovelist douard Estauni.


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Telecommunications has been definedas a technology concerned withcommunicating from a distance.

It includes mechanical and electricalcommunication becausetelecommunications has evolved from

mechanical to electrical.

Telecommunications

BidirectionalUnidirectional Mass

Communication

Press

Radio

TV

Post Telegraph

Telex Telephone

Data Networks Cellular Services


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Telecommunication is an important part of modernsociety and world economy. In 2008, estimates placedthe telecommunication industry's revenue at $3.85trillion.

GDP world (2008) = $60 trillion.

Just estimate the significance of telecom industry inworld economy.

India GDP - 2% of Worlds GDP (2008),

Indian Telecom sector contributes 5.6% (2009) to GDP(India).

Telecommunication Services have an essentialimpact on the development of a community.

Looking at Teledensity (Telephone Density:Number of telephones per 100 inhabitants) of acountry, one can estimate its level of technicaland economic development.

A teledensity greater than 100 means there aremore telephones than people.


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Teledensity in India

Teledensity: 31.5% (Oct 2008)

Teledensity: 38.88% (May 2009)

Teledensity: 52.74% (March 2010)

Projected teledensity: 500 million by2010.

Actual Teledensity: 621.28 Million in 2010.

Services dependent onTelecommunications

Banking, ATMs

Aviation, Railways (Ticket Booking)

Sales, Purchases, and Orders handling.

Credit card Payments.

Travel and Tourism.

Public Services.


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Basic elements

A telecommunication system consists of threebasic elements: Terminals, TransmissionSystems, and Switching.

Often telecommunication systems are two-waybetween entities/subscribers, and a singledevice acts as both a transmitter and receiver ortransceiver.

For example, a mobile phone is a transceiver.

In telephone conversation the one whoinitiates the call is referred to as thecalling subscriber (Source) and the onefor whom the call is destined is the calledsubscriber (Destination).

Terminals Instruments (Rotary or TouchTone)


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Signaling

In order to draw attention of calledsubscriber, some form of signaling isrequired.

E.g. If the called subscriber is engaged, asuitable indication should be given to thecalling subscriber by means of signaling.

Subscriber line signaling

Inter- and Intra- Exchange Signaling

Transmission Systems

Conducting Media

Non-conducting Media

Wireless Media

A channel is the transmission mediumused to send multiple streams ofinformation.


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Point to point link

Telecommunicationover a phone line iscalled point-to-pointcommunicationbecause it is betweenone transmitter andone receiver.

Switch

SwitchingOffices/Systems Central Offices Telephone Exchanges -Wire Centers.

Saving Copper Wires

CO


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Network

A collection of transmitters, receivers ortransceivers that communicate with eachother is known as a network.

Networks with point-to-point links amongall the entities fully connectednetworks.

Links that run between the switchingsystems are called trunks, and those thatrun to the subscriber premises are knowas subscriber lines.


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The analog network hierarchy

Bell system hierarchy (pre-1984)

Consists of five levels

Regional center, sectional center, primarycenter, toll center, end office (centraloffice).

Network Hierarchy

Regional center

Sec tional center Sect ional center

Primary center Primary Center

Toll center Toll Center

End OfficeEnd Office

International Gateway Exchange


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Class1

The class 1 office - Regional Center (RC).

Regional centers served three purposes :

(a) "last resort" for final setup of calls when routes betweencenters lower in the hierarchy were not available

(b) authority to block portions of the network within theregion in case of emergencies or network congestion

(c) international overseas gateways.

Class 2 The class 2 office - Sectional Center (SC).

The sectional center typically connected major tollcenters within one or two states or provinces - interstateor interprovincial connections for long-distance calls.

At various times, there were between 50 and 75 active

class 2 offices in the network.


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Class 3

The class 3 office - Primary Center (PC).

Calls being made beyond the limits of a smallgeographical area.

High usage trunks to complete connection between tollcenters.

The primary center never served dial tone to the user.

The number of primary centers in the network fluctuatedfrom time to time, ranging between 150 and 230.

Class 4 The class 4 office is the Toll Center (TC), Toll Point (TP),

or Intermediate Point (IP).

A call going between two end offices not directlyconnected together, or whose direct trunks are busy, isrouted through the toll center.

This toll center may also be called the tandem office


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Class 5

The class 5 office is the local exchange or end office.

It delivers dial tone to the customer.

The end office, also called a branch exchange, is theclosest connection to the end customer.

Switching Hierarchy

P

T

T S

S

P

T

P

R

P

T

T


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In modern times only the terms Class 4 and Class 5 aremuch used, as any tandem office is referred to as aClass 4.

This change was prompted in great part by changes inthe power of switches and the relative cost oftransmission, both of which tended to flatten the switchhierarchy.

North American Network(showing alternate routing capability)

End user(originating)

Class 5(end office)

Class 4(Toll Ctr)

Class 3(Primary Ctr)

Class 2(Sectional Ctr)

Class 1(Regional Ctr)

1

23

High UsageTrunks

1

2

1

1

2

Backbone network

Direct Inter-Officetrunks

End user(terminating)

Traffic always routed through lowest available level network


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Bell system hierarchy

A combination of hierarchical and meshnetwork for better reliability

High usage trunks,

alternate routing paths.

tandem switches within a exchange area.

International Telecommunication Union(ITU)

Two main bodies

ITU-Telecommunications (Formerly CCITT Consultative Committee International Telegraph andTelephone, Now, ITU-T)

Establishes recommendations for telephone,telegraph and data communications

ITU-Radio (Formerly Consultative CommitteeInternational Radio, Now, ITU-R)

Coordinating the use of radio spectrum


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Role of ITU-T & ITU-R?

Standardization

Open Standards are needed to enable theinterconnections of systems, equipmentand networks of different manufacturers,vendors and operators.


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Coding of audio G.711 and G.72x series

Coding of still images JPEG T.80 and JPEG 2000 T.800 series Coding of video coding H.262/MPEG2-Video and H.264/MPEG-4 Fax standards T.2 T.4, T.30, T.37, T.38 H.323 family of standards for multimedia and VoIP IMSI (International Mobile Subscriber Identity) codes used in SIM

cards E.212 ISDN and PSTN/3G videoconferencing systems, H.320 and H.324 ISDN (Integrated Services Digital Network) Q.931 OSI (Open Systems Interconnection) Passive optical networks (PON) G.983, G.984 Public telecommunication numbering plan, E.164 Signaling System 7 Q.7xx series Standards relating to Quality of Service (QoS)

Synchronous Digital Hierarchy (SDH) G.707 G.803 Wavelength-division multiplexing (WDM) X.25 (x)DSL (Digital Subscriber Line) series of standards for broadband

telecoms

Few Standards by ITU:

Why you need

STANDARDS?


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Standards

Enable competition products cost effective, lowcost services to telecom users

Leads to economics of scale in manufacturingand engineering decrease cost increaseacceptance.

Make international services available.

Make users and network operators vendor

independent and improve availability of thesystems.

Political interests often lead to differentstandards in Europe, Japan and America.

International standards are threat to localindustries of big countries but

opportunities for small countries.


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Standard Organizations

Authorities that approve official standards.

Players in telecom business

Interested Parties

Equipment

Manufacturers

ServiceUsers

NetworkOperators

Academic

Experts

Govt. Officials

National Standard Authorities Approve Official National standards

SFS: Finnish Standards Institute ANSI: American National Standards Institute DIN: Deutche Industrie-Normen BSI: British Standards Institute

DIN

SFS BSI

ANSI


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Other

Organizations

European Organizations ETSI: European Telecommunications Standard

Institute

CEPT: European Conference of Posts andTelecommunications Administrations(Conference Europeenne des Administrationsdes Posts et des Telecommunications)

CEN/CENELEC: European Committee forElectrotechnical Standardization/EuropeanCommittee for standardization


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American Organizations

Institute of electrical and ElectronicsEngineers (IEEE)

Electronic Industries Association (EIA)

Federal Communications Commission(FCC)

Global Organizations International Telecommunications Union (ITU)

International Standards Organization/International Electrotechnical Commission(ISO/IEC).

CCITT ITU-T (Comite Consultatif Internationalde Telegraphique et Telephonique) InternationalTelegraph and Telephone Consultative

Committee. CCIR ITU-R (Comite Consultatif International

des Radiocommunications) International RadioConsultative Committee.


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Other Organizations

Internet Engineering Task Force (IETF)

Asynchronous Transfer Mode Forum(ATM Forum)

Network Management Forum

telecommunications switching systems 2

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