Скачать презентацию Module 3 2 Transmission Media Electromagnetic Скачать презентацию Module 3 2 Transmission Media Electromagnetic

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Module 3. 2: Transmission Media • • Electromagnetic Spectrum • Unguided Transmission Media – Module 3. 2: Transmission Media • • Electromagnetic Spectrum • Unguided Transmission Media – Terrestrial Microwave – Satellite – Radio – IR – Cellular Telephony Guided Transmission Media – Twisted Pair – Coaxial cable – Optical fiber K. Salah 1

Electromagnetic Spectrum K. Salah 2 Electromagnetic Spectrum K. Salah 2

Guided Transmission Media • • • Twisted Pair Coaxial cable Optical fiber K. Salah Guided Transmission Media • • • Twisted Pair Coaxial cable Optical fiber K. Salah 3

Twisted Pair • • Most common medium • Within buildings – To private branch Twisted Pair • • Most common medium • Within buildings – To private branch exchange (PBX) • For local area networks (LAN) – 10 Mbps or 100 Mbps • Pros and Cons: – Cheap – Easy to work with – Low data rate – Short range, about 100 meters. Telephone network – Between house and local exchange (subscriber loop) K. Salah 4

Unshielded and Shielded TP • • Unshielded Twisted Pair (UTP) – Ordinary telephone wire Unshielded and Shielded TP • • Unshielded Twisted Pair (UTP) – Ordinary telephone wire – Cheapest – Easiest to install – Suffers from external EM interference Shielded Twisted Pair (STP) – Metal braid or sheathing that reduces interference – More expensive – Harder to handle (thick, heavy) – Capacity 10 -155 Mbps UTP Categories • Cat 3 – up to 16 MHz – Voice grade found in most offices • Cat 4 – up to 20 MHz • Cat 5 – up to 100 MHz – Commonly pre-installed in new office buildings RJ-11 vs. RJ-45 • • K. Salah 5 RJ-11 is a typical UTP phone connector. Has 2 pairs. RJ-45 is a UTP connector. Has 4 pairs.

Coaxial Cable • • Most versatile medium • Long distance telephone transmission – Can Coaxial Cable • • Most versatile medium • Long distance telephone transmission – Can carry 10, 000 voice calls simultaneously – Being replaced by fiber optic Television distribution – Ariel to TV – Cable TV • z Analog y Amplifiers every few km y Closer if higher frequency y Up to 500 MHz z Digital y Repeater every 1 km y Closer for higher data rates Short distance computer systems links • Transmission Characteristics Local area networks K. Salah 6

Optical Fiber • Greater capacity – Data rates of hundreds of Gbps • • Optical Fiber • Greater capacity – Data rates of hundreds of Gbps • • Smaller size & weight Lower attenuation Electromagnetic isolation Greater repeater spacing – 10 s of km at least K. Salah 7

Transmission Characteristics z Act as wave guide for 1014 to 1015 Hz y Portions Transmission Characteristics z Act as wave guide for 1014 to 1015 Hz y Portions of infrared and visible spectrum z Light Emitting Diode (LED) used in MMF y Cheaper y Wider operating temp range y Last longer z Injection Laser Diode (ILD) used in SMF y More efficient y Greater data rate z Wavelength Division Multiplexing (WDM) using light prisms. K. Salah MMF vs. SMF 8

Comparison Cable Type Cost 1 = lowest 5 = highest Typical Capacity Installation 1 Comparison Cable Type Cost 1 = lowest 5 = highest Typical Capacity Installation 1 = easy 5 = hard Max Cable Length EMI Resistance 1 = low 5 = high Coaxial. Thinnet 2 10 Mbps 2 185 meters 2 Coaxial. Thicknet 4 10 Mbps 3 500 meters 2 UTP 1 10 -100 Mbps 1 100 meters 1 STP 3 16 -155 Mbps 2 100 meters 2 Fiber-optic 5 100+ Mbps 5 Multiple kilometers 5 K. Salah 9

Wireless Transmission • • Unguided media • Directional – Focused beam – Careful alignment Wireless Transmission • • Unguided media • Directional – Focused beam – Careful alignment required • Omnidirectional – Signal spreads in all directions – Can be received by many antennae Frequencies Transmission and reception via antenna K. Salah 10 z 2 GHz to 40 GHz y Microwave y Highly directional y Point to point y Satellite z 30 MHz to 1 GHz y Omnidirectional y Broadcast radio z 3 x 1011 to 2 x 1014 y Infrared y Local pt-pt confined area

Types of Radio Propagation K. Salah 11 Types of Radio Propagation K. Salah 11

Microwave Satellite Microwave Terrestrial Microwave • • • z Satellite is relay station z Microwave Satellite Microwave Terrestrial Microwave • • • z Satellite is relay station z Satellite receives on one frequency, amplifies or repeats signal and transmits on another frequency z Requires geo-stationary orbit y Height of 35, 784 km z GEO vs. LEO z Frequency Bands: C, Ku, and Ka z Television z Long distance telephone z Private business networks Parabolic dish Focused beam Line of sight Long haul telecommunications Higher frequencies give higher data rates K. Salah 12

Wide Area: Satellite Systems • • Cover very large areas • • Dish antennas, Wide Area: Satellite Systems • • Cover very large areas • • Dish antennas, or bulky handsets Different orbit heights – GEOs (39000 Km), LEOs (2000 Km), MEOs (9000 km) – GEO is stationary. You need 3 to cover whole planet – LEO and MEO orbit the earth every one hour Optimized for one-way transmission, location positioning, GPS systems, Satellite Radio – Radio (XM, DAB) and movie (Sat. TV) broadcasting – Killed MMDS wireless TV offerings. – Future: sat. TV (eg: direct. TV) in your car • • Most two-way systems struggling or bankrupt – Expensive alternative to terrestrial cellular system (2 G) Trucking fleets, journalists in wild areas, Oil rigs K. Salah 13

LEO and MEO • • Used in GPS • 54 for LEOs to cover LEO and MEO • • Used in GPS • 54 for LEOs to cover the whole planet • Could have multiple readings for increased precision and reliability. 24 MEOs are need to cover the whole planet K. Salah 14

WLAN • Benefits of Ethernet WLAN – Cheap – Faster to deploy – Mobility WLAN • Benefits of Ethernet WLAN – Cheap – Faster to deploy – Mobility – Watch for security Ø Need for authentication Ø Need for encryption during transmission • • • What is an Access Point? • Bluetooth gives 1 Mbps. Bluetooth networks PDAs or cell phones with PCs. Operates in a short diameter (10 meters). – Operates at 2. 4 - 2. 4835 GHz – May have interference with Ethernet WLAN APs A typical diameter is a room for one AP about 40 meters Frequencies used and data rate – IEEE 802. 11 b operates at 2. 4 GHz range and gives 11 Mbps – IEEE 802. 11 a operates at 5 GHz range and gives 54 Mbps – IEEE 802. 11 g operates at 2. 4 GHz range and gives 54 Mbps K. Salah 15

Others IR (Infrared) z Modulate noncoherent infrared light z Line of sight (or reflection) Others IR (Infrared) z Modulate noncoherent infrared light z Line of sight (or reflection) z Blocked by walls z e. g. TV remote control, IRD port Broadcast Radio • • • Omnidirectional FM radio UHF and VHF television Line of sight Suffers from multipath interference – Reflections K. Salah 16

Cellular System Cellular Bands K. Salah 17 Cellular System Cellular Bands K. Salah 17