Telecom Networks: Physical Media and Cables

Practical Work No. 7

Topic: Media Guided - Part 2

1. What are the physical media used in telecommunications networks that are mentioned in the text?
2. In reference to copper wires, what are the main variants that exist?
3. What are some of the major disadvantages of bare wire lines?
4. How are UTP cables used? Features of these cables provide each one of their technical characteristics.
5. What are underground multipair cables? What is their utility, and how is their isolation?
6. What are aerial multipair cables and what is their use?
7. What is Coaxial Cable? Depict it graphically.
8. What is referred to as the characteristic impedance of coaxial cables? What are the normal values of the characteristic impedance?
9. What is referred to as attenuation and what is its unit?
10. How are multi-conductor coaxial cables used?
11. Deepen research on the advantages of optical fiber. Research online about how to place fiber optic cables in the ocean.
12. (Empty question)
13. How is multimode subdivided?
14. What are the losses caused by fiber optic cables?
15. What is referred to as an optoelectronic system and what are its main elements?
16. What are the accessories of a fiber optic cabling installation? Explain each of them.

Coaxial Cable

Cable used for computer networks as well as cable television. The name comes from its structure: a metal shield surrounding a central wire. The shielding protects the signal wire inside against electrical interference.

Characteristic Impedance

Impedance features of these cables is a very important parameter. It can be calculated as the ratio between applied voltage and the current adsorbed by a cable of infinite length.

This value, characteristic of coaxial cables, is determined by the ratio of the diameters of the inner and outer conductors and the dielectric insulating material between these conductors.

Attenuation

Attenuation is the loss of power at a certain frequency. It is expressed in decibels per kilometer of cable. The attenuation of these cables depends on factors including temperature. Increasing this increases the resistivity of the conductors.

Multi-Conductor Coaxial Cables

Optical Fiber

An optical fiber is a long, thin filament of transparent dielectric material, usually glass or plastic, with a diameter approximately equal to that of a hair (50 to 125 microns). It is given a special coating with certain characteristics to transmit light signals over long distances.

A fiber optic cable is composed of the following parts, as indicated in Figure 01:

• Core: This is the optical fiber itself, a thin strand of glass through which light travels.
• Cladding: One or more layers surrounding the fiber, made of a material with a refractive index lower than that of the optical fiber. This causes light rays to be reflected by the principle of total internal reflection back to the core, preventing light loss.
• Coating: A plastic coating that protects the fiber and the middle layer from moisture and damage.

Optical fibers come in two types:

• Multimode fibers: Transmit many signals per fiber (used in computer networks, local area networks).
• Singlemode fibers: Transmit a single signal over the fiber (used in telephones and cable television). Singlemode fibers have very thin cores (about 9 microns in diameter) and transmit infrared laser light (wavelength = 1300-1550 nm). Multimode fibers have larger cores (about 62.5 microns in diameter) and transmit infrared light (wavelength = 850-1300 nm) from light-emitting diodes (LEDs).