Overview of Telecommunication Networks-I

Objectives In this chapter, we will learn to: Describe the growth of telecommunications technology since the early 20 th century Facilities provided to subscribers,Administration and Maintenance personnel. Concepts of local and Trunk Networks Call routing Functions of a typical Telephone Exchange. conclusion

Evolution of Telecommunication Technology Today’s telecommunication technologies have evolved from the earliest smoke signals to almost instant global transmission of large amounts of data.

Early Signaling and Telegraphy Semaphore - a type of signaling, in which visual cues represent letters or words. Morse code - the transmission of a series of short and long pulses (dots and dashes) that represented characters. Duplexing - simultaneously transmitting a signal in both directions along the same wire. Multiplexing - simultaneously transmitting of an indeterminate number of multiple signals over one circuit.

Early Signaling and Telegraphy Western Union Telegraph Company was founded – Over two thousand telegraph offices operated across the United States.

Telephone Technology

Evolution Of Telephone Exchanges (1) Manual Exchange (2) Automatic Exchange: Strowger, Cross bar (3) Electronic Exchange

Chronological Development of Electronic Exchanges 1965No.1 ESSLocalBell labs,USA 1973MetacontaLocalLMT,France 1975ProteoLocal &TransitProteo,Italy 1976No.4 ESSTransitBell labs,USA 1978AXELocalEricsson,Sweden 1981E-10BLocal& Transit CIT,ALCATEL,FRANCE 1984CDOTLocal&TransitECIL,ITI 1990EWSDLocal&TransitSeimens, Germany

DIGITAL EXCHANGES- CAPACITY MODELCAPACITY LINES (IN 1000) CAPACITY TRUNKS (IN 1000) TRAFFIC EARLANGS BHCA CDOT E-10B AXE OCB EWSD ESS FETEX

ADVANTAGES OF ELECTRONIC EXCHANGES ELECTRO MECHANICAL EXCHANGES ELECTRONIC EXCHANGES Limited flexibilityHighly flexible Partial availability hence blocking Full availability hence non-blocking Swg speed is in milli seconds In micro seconds Lot of swg noiceAlmost noiceless Long testing timeShort testing time Preventive Mtce is necessary Remedial Mtce is very easy

Facilities extended from Electronic exchanges 1. Hot Line (With and with out Time-out) 2. Reminder Call/ Alarm Services 3. Subscriber Controlled Call Restriction Services. 4. Queuing Service 5. Priority Subscriber 6. Distinctive Ringing for Long Distance Calls 7. Call forwarding 8. Call waiting 9. Conference call 10. CLIP(Calling Line Identification Presentation)

Constraints of electronic exchanges Total protection from dust Stable power supply Temperature & Humidity control PCB Repair And Faster obsolescence

Telephone Network

Basic Diagram for Telephone Exchange Battery-A Battery-B Eng /Alt Power Plant Switch Room OMC MDF Extnl. plant

MDF

External plant of an exchange MDF WILL HAVE TWO SIDES- LINE SIDE and EXCHANGE SIDE ON LINE SIDE,100pr ARE TERMINATED PER TAG BLOCK ON EXCHANGE SIDE, NUMBER OF PAIRS VARIES AS PER SWITCH’S TECHNOLOGY

PILLARS One exchange can have any number of pillars that are necessitated based on the topography of that exchange external plant U/G cables that connect the MDF and pillars are called as Primary cables. U/G cables that connect the pillar and the DPs in that pillar area are called as Distribution cables.

DP A DP’s capacity can be 1,2,5,10,20 or 50 pairs. Each DP is given a 4 digit number, in which the first 2 digits indicate the pillar number in which that DP is working. Through a Drop wire,the connection is extended into customer premises.

Types of Telephone Calls Local Call(Intra exge call): Origination and Destination subscribers are in same exge Outgoing Call: Destination Subscriber is outside the exge Incoming Call: Origination Subscribers is outside the exge Transit Call: Both subscribers are outside the exge

Local & Trunk N/W

LOCAL & TRUNK CALLS A call is called a local call if the calling and called subscribers are within the same SDCA. Inter SDCA calls are called as Trunk calls,which generally pass through the TAX exchange.

SPC Exchange

Main sub-systems of Electronic exchange Terminal equipment Switching network Switching processor Switching peripherals Signalling interfaces Data processing peripherals

BASICS OF SWITCHING It must be possible for every telephone in the world to be connected to every other telephone, through some type of switch.

Customer Premise Equipment (CPE) Customer Premise Equipment (CPE) is the term used to denote the station equipment the customer uses to interface with the PSTN. It is a generally used term and covers any equipment the customer uses when calling on the PSTN. There are many services available on the PSTN and many different varieties of CPE.

SPACE DIVISION SWG Space division switching where each call is allocated a physical path through a sequence of switches in the exchange. This is an analogue technique. It is relatively old, and no new installations use this technique

TIME DIVISION SWG Time division switching, where each side of a call is allocated a time slot every 125  s into which the 8 bit PCM coded sample is inserted at each switch point. The call is not allocated a path through the exchange, but only a sequence of time slots. All new exchanges since about 1980 use this technique.

Time Division switching

RSU CONCEPT In some cases a telephone is not connected directly into an exchange, but instead all the telephones in an area or business estate are connected back to a Remote Subscriber Unit (RSU) or concentrator, which in turn is connected to an exchange by means of a Mbit/s, 32 channel PCM link. The concentrator does no switching, this is all done in the Main exchange, even for a call between neighbours. The main saving here is in the cost of underground cabling.

RSU

Wireless Technology Telegraphs and telephones are examples of wireline, or wire-bound technology, because they rely on physically connected wires to transmit and receive signals. Wireless technology - relies on the atmosphere to transmit and receive signals.

Wireless Technology Examples of wireless technology –Phones –Radios –Televisions –Satellite communications

Wireless Technology Wireless Technology is used for Inter exchanges through UHF VHF Micro Wave Satellite Wireless Technology is used for Intra exchanges (Wireless in Local Loop) through GSM CDMA VSAT

Wireless Technology for Satellite Geosynchronous - means that satellites orbit the earth at the same rate as the earth turns. Uplink - a broadcast from an earth-based transmitter to an orbiting satellite. At the satellite, a transponder receives the uplink, then transmits the signals to another earth-based location in a downlink.

Wireless Technology

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