1. Presentation on Transmission Media for Trunks

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

3. 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

4. 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

5. 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

6. 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

7. 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

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

9. 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

10. 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.

11. 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

12. 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.
3-30k(VLF,G), K(LF,G), 0.3-3M (MF,S), 3-30M (HF,S, ), M(VHF, S/LOS, VHF TV, FM RADIO), 0.3-3G(UHF, LOS, UHF TV,CELLULAR, PAGING, SAT), 3-30G(SHF, LOS, SAT), G(EHF, LOS, RADAR/SAT)

13. 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

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

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

16. 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 The TAT-l (Transatlantic) Cable System, developed by AT&T, spanned a distance of 2200 nautical miles

17. 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

18. 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

19. 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

20. 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

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

22. 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

23. 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

24. 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

25. 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

26. 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)

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

28. 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

29. 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

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

31. 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

32. 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

33. 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