Overview of Telecom Networks-01

Overview of Telecommunication Networks-I

Objectives

In this chapter, we will learn to:• Describe the growth of telecommunications

technology since the early 20th 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

• 1856 - Western Union Telegraph Company was founded.

• 1861 – Over two thousand telegraph offices operated across the United States.

Telephone Technology

Telephone Technology

Chronological Development of Electronic Exchanges

1965 No.1 ESS Local Bell labs,USA

1973 Metaconta Local LMT,France

1975 Proteo Local &Transit

Proteo,Italy

1976 No.4 ESS Transit Bell labs,USA

1978 AXE Local Ericsson,Sweden

1981 E-10B Local&

Transit

CIT,ALCATEL,FRANCE

1990 EWSD Local&Transit

Seimens,

Germany

DIGITAL EXCHANGES-CAPACITY

MODEL CAPACITY

LINES (IN 1000)

CAPACITY

TRUNKS (IN 1000)

TRAFFIC

EARLANGS

CALLS ATTEMPTED PER SECOND

E-10B 30 4 2400 25

AXE10 64 60 26000 800000

OCB283 200 60 25000 800000

EWSD 250 60 25200 1000000

5ESS 250 60 26000 1000000

FETEX 240 60 24000 180000

ADVANTAGES OF ELECTRONIC EXCHANGES

ELECTRO MECHANICAL EXCHANGES

ELECTRONIC EXCHANGES

Limited flexibility Highly flexible

Partial availability hence blocking

Full availability hence non-blocking

Swg speed is in milli seconds

In micro seconds

Lot of swg noice Almost noiceless

Long testing time Short testing time

Preventive Mtce is necessary

Remedial Mtce is very easy

Constraints of electronic exchanges

• Total protection from dust

• Stable power supply

• Temperature & Humidity control

• PCB Repair

• And Faster obsolescence

Telephone Network

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.

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 125s 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 2.048 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

• 1894- Italian physicist Guglielmo Marconi a method of transmitting electromagnetic signals through the air. – His invention relied on an induction coil.

Wireless Technology

• Induction coil is made by winding wire in a either one or multiple layers around a metal rod to form a coil then applying a charge

• Charged wire induces an electromagnetic field that generates voltage

• Marconi connected an induction coil to a telegraph key. Each time the key was pressed the coil discharged a voltage through the air between to brass surfaces

• Metal filings in a glass cylinder became charged and cohered. The length of time they cohered translated into short and long pulses.

• Pulses were relayed to a Morse code printer.

• Marconi invention used the same type of signals sent and received by a telegraph.

Wireless Technology

• Vacuum tube - a sealed container made of glass, metal, or ceramic, that contains, in a vacuum, a charged plate that transmits current to a filament.

• Audion - patented in 1907by DeForest, is a type of vacuum tube that contains an additional electrode in the middle of the positive and negative electrodes. – Boosts or amplifies a signal.

– First instants of signal amplification and it formed the basis for all subsequent radio and television advances.

• 1912- Edwin Armstrong improved the Audion. He discovered that by feeding the signal back the tube the power of the Audion could be increased.

Wireless Technology

• Continued experimentation resulted in the invention of Frequency modulation.

• Frequency modulation is technology used in FM radio and other forms of wireless technology.

• In Frequency modulation one wave containing the information to be transmitted (for example, on a classical FM radio station, a violin concerto) is combined with another wave, called a carrier wave, whose frequency is constant.

– Frequency is the number of times each second that a sine wave completes a full cycle.

Wireless Technology

• The advent of FM radio afforded the best clarity of all wireless technologies then available.

• Walkie-Talkies use frequency modulation

• 1946- Bell Laboratories connect the first wireless car phone to the St. Louis network.

• 1962- Telstar Satellite successfully transmitted television and telephone conversation across the Atlantic for the first time.

Wireless Technology

• 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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