1. 1 Chapter Three The Media – Conducted and Wireless

2. 2 Introduction The world of computer would not exist if there were no medium( وسط ناقل ) by which to transfer data The two major categories of media include: –Conducted media –Wireless media Chapter Three - The Media - Conducted and Wireless

3. 3 Twisted Pair Wire ( Conducted media ) One or more pairs of single conductor( موصل ) wires that have been twisted around each other Twisted pair wire is classified by category. Twisted pair is currently Category 1 through Category 7, although Categories 2 and 4 are nearly obsolete( مهمل ) two important laws from physics: –(1) A current passing through a wire creates a magnetic field around that wire –(2) a magnetic field passing over a wire induces a current in that wire. Therefore, a current or signal in one wire can produce an unwanted current or signal, called crosstalk, in a second wire. Chapter Three - The Media - Conducted and Wireless

4. 4 Twisted Pair Wire Chapter Three - The Media - Conducted and Wireless Twisting the wires helps to eliminate electromagnetic interference between the two wires Shielding can further help to eliminate interference

5. 5 Chapter Three - The Media - Conducted and Wireless If the two wires run parallel to each other the chance for crosstalk increases. If the two wires cross each other at perpendicular angles the chance for crosstalk decreases.

6. 6 Twisted Pair Wire Chapter Three - The Media - Conducted and Wireless

7. 7

8. 8 Coaxial Cable ( Conducted media ) A single wire wrapped in a foam insulation( عازلة مادة ) surrounded by a braided metal shield to block electromagnetic signals from entering the cable and produce noise, then covered in a plastic jacket. Cable comes in various thicknesses Baseband coaxial technology uses digital signaling in which the cable carries only one channel of digital data Broadband coaxial technology transmits analog signals and is capable of supporting multiple channels of data simultaneously Chapter Three - The Media - Conducted and Wireless

9. 9 Coaxial Cable Chapter Three - The Media - Conducted and Wireless

10. 10 Coaxial Cable Chapter Three - The Media - Conducted and Wireless

11. 11 Fiber Optic Cable ( Conducted media ) A thin glass cable approximately a little thicker than a human hair surrounded by a plastic coating and packaged into an insulated( معزول ) cable A photo diode or laser generates pulses of light which travel down the fiber optic cable and are received by a photo receptor Chapter Three - The Media - Conducted and Wireless

12. How does a thin glass cable transmit data? –A light source, called a photo diode, is placed at the transmitting end and quickly switched on and off to produce light pulses. –These light pulses travel down the glass cable and are detected by an optic sensor called a photo receptor on the receiving end. –The light source can be either a simple and inexpensive light-emitting diode (LED), laser. –The laser is much more expensive than the LED, and it can produce much higher data transmission rates. Fiber optic cable advantages: –providing high-speed, low-error data transmission rates. –Small noise as the light pulses bounce around inside the glass cable, this noise is significantly less than noise generated in twisted pair wires or coaxial cables –More secure than twisted pair wires or coaxial cables, it is impossible to wiretap. Without physically break into the line

13. 13 Chapter Three - The Media - Conducted and Wireless fiber-optic cable has two small disadvantages: Light pulses can travel in one direction only. Thus, to support a two-way transmission of data, two fiber- optic cables are necessary. Its higher cost than twisted pair wires or coaxial cables

14. 14 Fiber Optic Cable Fiber optic cable is capable of supporting millions of bits per second for 1000s of meters Thick cable (62.5/125 microns) causes more ray( شعاع ) collisions, so you have to transmit slower. This is step index multimode fiber. Typically use LED for light source, shorter distance transmissions Thin cable (8.3/125 microns) – very little reflection, fast transmission, typically uses a laser, longer transmission distances; known as single mode fiber Chapter Three - The Media - Conducted and Wireless

15. 15 Fiber Optic Cable Chapter Three - The Media - Conducted and Wireless

16. 16 Fiber Optic Cable Fiber optic cable is susceptible( عرضة ) to reflection (where the light source bounces around inside the cable) and refraction( الانكسار ) (where the light source passes out of the core and into the surrounding cladding( الكسوة )) Thus, fiber optic cable is not perfect either. Noise is still a potential problem Chapter Three - The Media - Conducted and Wireless

17. 17 Fiber Optic Cable Chapter Three - The Media - Conducted and Wireless

18. 18 Fiber Optic Cable It is very common to mix fiber with twisted pair in LANs Chapter Three - The Media - Conducted and Wireless

19. 19 Chapter Three - The Media - Conducted and Wireless

20. 20 Wireless Media Radio, satellite transmissions, and infrared light are all different forms of electromagnetic waves that are used to transmit data Technically speaking – in wireless transmissions, space is the medium Note in the following figure how each source occupies a different set of frequencies Chapter Three - The Media - Conducted and Wireless

21. 21 Chapter Three - The Media - Conducted and Wireless

22. 22 Terrestrial( أرضي ) Microwave Transmission systems transmit tightly focused beams of radio signals from one ground-based microwave transmission antenna to another. Land-based, line-of-sight transmission Approximately 20-30 miles between towers Transmits data at hundred of millions of bits per second Signals will not pass through solid objects Popular with telephone companies and business to business transmissions might be less expensive in the long run than leasing a high- speed telephone line with monthly payment. once the system is purchased and installed, no telephone service fees are necessary. Chapter Three - The Media - Conducted and Wireless

23. Terrestrial( أرضي ) Microwave Many microwave antennas are located on top of free-standing towers, The higher the tower, the farther the possible transmission distance. Another factor that limits transmission distance is the number of objects that might obstruct the path of transmission signals. Buildings, hills, forests, and even heavy rain and snowfall all interfere with the transmission of microwave signals. Disadvantages: –loss of signal strength and interference from other signals, –in addition to the costs of either leasing the service or installing and maintaining the antennas.

24. 24 Chapter Three - The Media - Conducted and Wireless

25. 25 Chapter Three - The Media - Conducted and Wireless Often the microwave antennas are on towers or buildings

26. 26 Satellite Microwave Similar to terrestrial microwave except the signal travels from a ground station on earth to a satellite and back to another ground station Can also transmit signals from one satellite to another Satellites can be classified by how far out into orbit each one is (LEO, MEO, GEO, and HEO) Chapter Three - The Media - Conducted and Wireless

27. 27 Satellite Microwave Chapter Three - The Media - Conducted and Wireless

28. 28 Satellite Microwave LEO – Low Earth Orbit – 100 to 1000 miles out. Used for wireless e-mail, special mobile telephones, pagers, spying, videoconferencing MEO – Middle Earth Orbit – 1000 to 22,300 miles. Used for GPS (global positioning systems) and government GEO – Geosynchronous( المتزامن مع الأرض ) Earth Orbit – 22,300 miles. Always over the same position on earth (and always over the equator( خط الاستواء )). Used for weather, television, government operations HEO - highly elliptical orbit, which is used by governments for spying and by scientific agencies for observing celestial bodies( السماوية الأجرام ). –It follows an elliptical pattern. When the satellite is at its perigee (closest point to the Earth), it takes photographs of the Earth. When the satellite reaches its apogee (farthest point from the Earth), it transmits the data to the ground station. At its apogee, the satellite can also photograph objects in space. Chapter Three - The Media - Conducted and Wireless

29. Satellite Microwave

30. 30 Satellite Microwave Satellite microwave can also be classified by its configuration: –Bulk carrier configuration the satellite system and all its assigned frequencies are devoted to one user. transmitting large amounts of data in a very short time, used for large application. entire satellite system by one user. For example, a telephone company use a bulk carrier satellite system to transmit thousands of long-distance telephone calls. –Multiplexed configuration (Multiple users ) The ground station accepts input from multiple sources. –Single-user earth station configuration. each user employs his or her own ground station to transmit data to the satellite Chapter Three - The Media - Conducted and Wireless

31. 31 Chapter Three - The Media - Conducted and Wireless

32. 32 Infrared Transmissions Transmissions that use a focused ray of light in the infrared frequency range Very common with remote control devices, but can also be used for device-to-device transfers, such as PDA to computer Chapter Three - The Media - Conducted and Wireless

33. 33 Bluetooth is a wireless technology that uses low power, short- range radio frequencies to communicate between two or more devices. Bluetooth is a specification for short-range, point-to- point or point-to-multipoint voice and data transfer Bluetooth can transmit through solid, non-metal objects Thus, a device that is transmitting Bluetooth signals can be carried in a pocket or briefcase. Its typical link range is from 10 cm to 10 m, but can be extended to 100 m by increasing the power Chapter Three - The Media - Conducted and Wireless

34. 34 Bluetooth Bluetooth will enable users to connect to a wide range of computing and telecommunication devices without the need of connecting cables Typical uses include phones, pagers, modems, LAN access devices, headsets, notebooks, desktop computers, and PDAs Chapter Three - The Media - Conducted and Wireless

35. Bluetooth To appreciate the potential power of Bluetooth technology, consider examples: You can automatically synchronize all e-mail messages between your PDA and your desktop/laptop computer; as you approach your car, your PDA will tell the car to unlock its doors and change the radio to your favorite station; as you walk up to the front door of your house, your PDA will instruct your house to unlock the front door, turn on the lights, and turn on an entertainment system, and as you sit in a business meeting, your PDA/laptop will wirelessly transmit your slide presentation to a projector and your notes to each participant ’ s PDA/laptop.

36. 36 Wireless LAN (IEEE 802.11) This technology transmits data between workstations and local area networks using high-speed radio frequencies access point is the connection into the wired portion of the local area network. Current technologies allow up to 54 Mbps (theoretical) data transfer at distances up to hundreds of feet) IEEE 802.11n. supporting a 100-Mbps signal between wireless devices and uses multiple antennas to support multiple independent data streams. All protocols—802.11a, 802.11b, 802.11g, and 802.11n—are now called Wi-Fi. Chapter Three - The Media - Conducted and Wireless

37. 37 Free Space Optics Uses lasers, or, in some cases, infrared transmitting devices, to transmit data between two buildings over short distances, such as across the street. Data transfer speeds can be as high as 1.25 Gbps, higher in the future. Lasers lose their strength when transmitting through fog. Thus, if the fog is thick, transmission distances can be cut down to less than 50 meters Line of sight between buildings Typically short distances, such as across the street Newer auto-tracking systems keep lasers aligned when buildings shake from wind and traffic Chapter Three - The Media - Conducted and Wireless

38. ZigBee relatively new wireless technology supported by the IEEE 802.15.4 standard. It has been designed for data transmission between smaller, often embedded, devices that require low data transfer rates (20 – 250 Kbps) and low power consumption. For example, home and building automation (heating, cooling, security, lighting, and smoke detectors), industrial control, automatic meter reading, and medical sensing and monitoring. power consumption is so low that some suppliers claim that their ZigBee-equipped devices will last multiple years on the original battery. Bluetooth is best at replacing cables for short distances, while ZigBee will be good at sending low-speed signals over short to medium distances.

39. 39 Media Selection Criteria Cost Speed Distance and expandability Environment Security Chapter Three - The Media - Conducted and Wireless

40. 40 Media Selection Criteria - Cost Different types of cost –Initial cost – what does a particular type of medium cost to purchase? To install? –Maintenance / support cost ROI (return on investment) price/performance ratio – if one medium is cheaper to purchase and install but is not cost effective, where is the savings? Chapter Three - The Media - Conducted and Wireless

41. 41 Media Selection Criteria - Speed Two different forms of speed: –Propagation speed – the time to send the first bit across the medium. This speed depends upon the medium. Airwaves and fiber are speed of light. Copper wire is two thirds the speed of light –Data transfer speed – the time to transmit the rest of the bits in the message. This speed is measured in bits per second Chapter Three - The Media - Conducted and Wireless