INTRODUCTION TO TELECOMMUNICATION

1. INTRODUCTION TO TELECOMMUNICATION SHAKEEL AHMAD

2. ALREADY STUDIED • SIGNALS BASICS • PCM

3. TODAY ON 21-02-2004 Transmission Media for Trunks

4. Media Types • Open Wire Pairs • Twisted Pair Wires • Coaxial Cable • Microwave Links • Submarine Cables • Satellite Communications • Optical Fiber

5. Open Wire Pairs • Used in early years of telephony, more of history now. • A pair consists of two open wires suspended on telephone poles. • The wires are separated by approximately 1 ft to minimize capacitance. • Glass insulators mounted on wooden crossbeams of the telephone pole suspend the wires between poles

6. Open Wire Pairs • Open wire is usually made of steel, coated with copper • Steel is used for the strength necessary to withstand varying weather conditions and to withstand the suspension weight of the wire between poles • Distance between repaeters upto 50kms • No. of channels over a single pair – 12

7. Open Wire Pairs • Frequency range up to 160kHz • Disadvantages: • Bulky and unsightly • Affected by weather conditions i.e. large leakage with insulators • Severe cross-talk • High radiation at the high frequencies

8. Twisted-Pair Wires • Insulated Pairs of copper wire bundled together • Individual pairs of wires twisted together to minimize crosstalk • Cables can contain several hundreds of twisted pairs in different gages. • Laid in cities underground

9. Twisted-Pair Wires • Suffer from cross-talk because of pairs being bound closely. • Due to the small diameter of the wires, resistance contributes significantly to signal loss

10. Twisted-Pair Wires • Repeaters required every 3 to 6.5 km • Used for short haul trunks • Voice channels over a single pair 12-120 • Frequency range up to 1MHz

11. Coaxial Cable • Coax is manufactured with a hollow cylindrical copper tube used for the shield • Insulating material (dielectric ) separates the conductive tube from the copper center conductor • Frequency Range 3-60 MHz • Radiation losses and adjacent channel interference are virtually eliminated by coaxial shielding

12. Coaxial Cable • Highly suited for Long haul trunk circuits such as inter-city or interstate routes. • Several individual coaxial tubes are often bound together with insulating material and steel reinforcement to produce a high capacity trunk cable • Repeaters spacing 3-65kms • Each coaxial tube can carry several thousands of voice channels.

13. The Bell System's L5 coaxial carrier • A long-haul trunk that includes 22 coaxial tubes bound together to form a single cable. • Total of 108,000 simultaneous two-way voice conversations can be carried by the cable. • Ten tubes carry108,000 voice channels in one direction, and 10 tubes are for the opposite direction. • Overall system frequency 58Mhz

14. Microwave Links • An alternative to coaxial cables for high-capacity long-haul trunks are microwave radio links • Repeater spacing 30-50kms • Work on line of sight, therefore repeaters antennas are typically put on towers, hilltops, and huge skyscrapers. • Frequency range 3-7 GHz approx.

15. Microwave Links • Affected by weather conditions such as rain resulting in fading • Can cause radio interference • High velocity of propagation minimizing the time delay • No. of channels in thousands per route

16. Microwave Links • Advantages • Fewer repeaters are necessary for amplifying signals • Underground facilities are not necessary • Multiple channels can be transmitted over a single link

17. Microwave Links Advantages • Minimal delay times • Minimal cross talk • Fewer repeaters mean increased reliability and less maintenance

18. Submarine Cables • Submarine cables are coaxial cables specially designed to withstand the rugged oceanic floor conditions throughout the world • First voice-grade cable was laid across the Atlantic Ocean floor in 1956. The TAT-l (Transatlantic) Cable System, developed by AT&T, spanned a distance of 2200 nautical miles

19. Submarine Cables • Construction of the cable includes several layers of insulation and armored steel reinforcement surrounding the conductor to protect it from corrosion, temperature changes, and leakage • Repeaters are constructed in a similar manner to prevent the damage of internal circuitry

20. Submarine Cables • Important factors • The cable must be protected from saltwater corrosion and leakage • Suboceanic terrain conditions and ocean depth must be considered • Temperature and pressure changes from sea level to ocean floor must be determined

21. Submarine Cables Important factors • The weight of cable material and rate of descent to the oceanic floor are critical parameters. • Off-coast trenches must be dug in shallow waters to bury and protect the cable from fishing trawlers and anchors

22. Submarine Cables • Electrical circuits must be environmentally tested at temperature extremes exceeding those of the ocean floor • Repeater units must be x-ray tested for faulty welds and leaks • Performance tests must be exercised constantly while laying cable to determine immediately the location of a fault

23. Submarine Cables • First generation laid in 1950s • 48 voice channels • Repeaters at 39 nautical miles • Overall bandwidth 164 kHz

24. Submarine Cables • Latest generation • Overall bandwidth 28Mhz • 4000 Voice channels • Now fiber optic cables being installed with half the size, one third the weight and double the capacity of existing coaxial cable

25. Satellite Communications • First satellite Intelsat I (called Early Bird) was designed to handle 240 voice channels (in 1965) • Telephone and television broadcast signals are beamed up to the satellite from an earth through the use of a large, highly directive microwave dish antenna that is synchronized to the position of the satellite

26. Satellite Communications • A device called a transponder is used on board the satellite to receive the weak microwave signal, amplify and condition it, and retransmit the signal back to another earth station in a different location on earth

27. Satellite Communications • To prevent the transponder's strong transmitted signal from interfering with the earth station's weak received signal, most commercial satellite links separate, transmit, and receive carrier frequencies by about 2 GHz

28. Satellite Communications • Earth stations typically transmit their signals to satellites on carrier frequencies in the 6-GHz band, ranging from 5.92 to 6.43Ghz (the up-link frequency). • The satellite's transponder down-converts these signals to a 4-GHz band, ranging from 3.7 to 4.2 GHz. (the down-link frequencies)

29. Satellite Communications • Geo-synchronous or geo-stationary satellites positioned at approximately 22,300 miles above the equator

30. Satellite Communications • At an altitude of 22,300 miles, 40% of the Earth is exposed. The satellite's antenna is designed to emit a radiation pattern that covers this entire exposed portion

31. Satellite Communications • Satellites positioned in geo-synchronous orbit, 120° apart from each other, can cover the entire surface of the earth • Subject to long delays

32. Satellite Communications • Much lower cost per channel than submarine cable for transatlantic communications • 600 channels per transponders, 12 transponders per sartellite

33. Optical Fiber • Material composition types (cladding & core) • Glass cladding and glass core • Plastic cladding and glass core • Plastic cladding and plastic core • Special protection required, the extent of which depends upon application used. • No. of voice channels in thousands

34. Optical Fiber • Not subject to interference or tapping making it secure as well • Modern day requirements of several gigabits per sec can be accommodated • Repeaters spacing possible over 100 km because of less loss • Optic fiber Cables substantially lighter than copper cables with same capacity

35. Optical Fiber • Optic fiber cable has a longer life span than copper because it is more resistant to corrosion • Interfacing cost is higher for electronic facilities which are to be converted into optics. • Difficult to splice • Remote powering is a problem, sometimes metallic conductors are bundled in the cable for the purpose

36. Thank You