Physical Mediums
- 2. Physical Links • In lower level, a network can consist of two or more computers directly connected by some physical medium, such as coaxial, twisted pair or an optical cable. • This physical medium is called as links. • Transmission medium is also defined as, a medium that can carry information from a source to a destination.
- 3. Physical Links Contd… • Transmission media is classified into two categories, Guided (Wired) Unguided (Wireless)
- 4. Guided Media – Provide a conduit from one device to another device. • Coaxial • Twisted Pair • Fiber optic – Here coaxial and twisted pair cables accept and transport signal in the form of electrical signals. – Fiber optic cable accepts and transport signals in the form of light. Physical Links Contd…
- 5. Twisted Pair: • Consist of two conductors (metallic), each with its own plastic insulation. – One wire is used to carry the signals to the receiver. – Another one for ground reference. • Interference and cross talk may affect both the wires and make unwanted noise. Physical Links Contd…
- 6. • Twisting the cable makes it probable that both wires are equally affected by external influences (noise or crosstalk). • The receiver calculates the difference between the two, receives no unwanted signals. The unwanted signals are mostly canceled out. • the number of twists per unit of length (e.g., inch) has some effect on the quality of the cable. Types, – Shielded – Unshielded Physical Links Contd…
- 8. Applications: – Telephone Network – Local Area Network (10BaseT, 100BaseT) Coaxial Cable: • Carries signals of higher frequencies than twisted pair. • Coaxial has central core conductor of solid copper wire enclosed in an insulating sheath. • The outer metallic wrapping serves both as a shield against noise and as the second conductor, which completes the circuit. • This outer conductor is also enclosed in an insulating sheath Physical Links Contd…
- 9. Physical Links Contd… Coaxial Cable
- 10. Categories of Coaxial cable Applications • Cable TV • Traditional LAN Physical Links Contd… Category Use RG-59 Cable TV RG-58 Thin Ethernet RG-11 Thick Ethernet
- 11. Fiber Optic Cable Made of glass or plastic; signals are transmitted as light pulses from an LED or laser Light is also a form of electromagnetic energy Speed depends on density of medium it is traveling through; fastest when in a vacuum, 186,000 miles/second Propagation Modes, • Single Mode • Multi Mode Physical Links Contd…
- 15. Single Mode
- 16. Advantages of Fiber Optics – Higher bandwidth than twisted-pair and coaxial cable; not limited by medium, but by equipment used to generate and receive signals – Noise resistance – Less signal attenuation – More resistant to corrosive materials – Lightweight – Greater security Physical Links Contd…
- 17. • Unguided Medium Physical Links Contd…