1. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني

2. Transmission media (wires and no wires) Transmission media:  Guided media, the waves are guided along a physical path; examples of guided media are twisted pair, coaxial cable, and optical fiber.  Unguided media, also called wireless, provide a means for transmitting electromagnetic waves but do not guide them; examples are propagation through air, vacuum, and seawater.

3. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني  Guided Transmission Media  Magnetic Media  Twisted Pair  Coaxial Cable  Fiber Optics

4. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني  Magnetic Media One of the most common ways to transport data from one computer to another is to write them onto magnetic tape or removable media (e.g., recordable DVDs), physically transport the tape or disks to the destination machine, and read them back in again. A. PC => recordable DVD => another PC; B.Ultrium tape: 200 gigabytes; A box (60X60X60 cm) can hold about 1000 of these tapes =>200 terabytes or 1600 terabits (24 hours by Federal Express, 1600 terabits/86400 sec = 19Gbps => if one hour away => 400Gbps. C.Cost less than 5000 USD for 200 TB => less than 3 cents for 1GB

5. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني  Twisted Pair (Copper Wires) (a) Category 3 UTP. (b) Category 5 UTP.

6. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني  A coaxial cable (Copper Wires) A coaxial cable.

7. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني  Fiber Optics (a) Three examples of a light ray from inside a silica fiber impinging on the air/silica boundary at different angles. (b) Light trapped by total internal reflection.

8. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني  Transmission of Light through Fiber Attenuation of light through fiber in the infrared region.

9. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني  Fiber Cables (a) Side view of a single fiber. (b) End view of a sheath with three fibers.

10. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني  Fiber Cables (2) A comparison of semiconductor diodes and LEDs as light sources.

11. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني  Optical Fiber vs. Copper Wire Comparison of the properties of wires and fiber:

12. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني  Unguided Transmission Media  The Electromagnetic Spectrum  Radio Transmission  Microwave Transmission  Infrared and Millimeter Waves  Lightwave Transmission

13. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني  The Electromagnetic Spectrum The electromagnetic spectrum and its uses for communication.

14. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني  Radio Transmission (a) In the VLF, LF, and MF bands, radio waves follow the curvature of the earth. (b) In the HF band, they bounce off the ionosphere.

15. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني  Microwave Transmission Microwaves have much bandwidth and are widely used indoors (WiFi) and outdoors (3G, satellites) – Signal is attenuated/reflected by everyday objects – Strength varies with mobility due multipath fading, etc.

16. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني  Infrared and Millimeter Waves infrared and millimeter waves: are widely used for short-range communication. The remote controls used on televisions, VCRs, and stereos all use infrared communication.

17. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني  Lightwave Transmission Convection currents can interfere with laser communication systems. A bidirectional system with two lasers is pictured here.

18. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني  Wireless vs. Wires/Fiber Wireless : + Easy and inexpensive to deploy + Naturally supports mobility + Naturally supports broadcast Transmissions interfere and must be managed Signal strengths hence data rates vary greatly Wires/Fiber : + Easy to engineer a fixed data rate over point-to-point links Can be expensive to deploy, esp. over distances Doesn’t readily support mobility or broadcast