Telecommunications Switching Systems 2
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Transcript of 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