Скачать презентацию Chapter 4 Transmission Media Overview Guided Скачать презентацию Chapter 4 Transmission Media Overview Guided

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Chapter 4 Transmission Media Overview • Guided – wire (twisted pair, coaxial cable, optical Chapter 4 Transmission Media Overview • Guided – wire (twisted pair, coaxial cable, optical fiber) • Unguided – wireless (broadcast radio, terrestrial microwave, satellite) • Characteristics & quality of data transmission is determined by medium & signal • For guided medium, the medium itself is more important in determining the transmission limitations • For unguided medium, the bandwidth produced by the antenna is more important • Key concerns are data rate and distance in the design of trans. sys. 3/16/2018 Spring, 2003 EE 4272

Design Factors • Bandwidth: Ø Higher bandwidth (HZ) gives higher data rate (bps) • Design Factors • Bandwidth: Ø Higher bandwidth (HZ) gives higher data rate (bps) • Transmission impairments: e. g. Attenuation Limits the transmission distance Ø Twisted pair -> coaxial cable -> optical fiber Ø • Interference: from competing signals in overlapping frequency bands can distort or wipe out a signal. • Number of receivers: In guided media Ø Point-to-point link or share link with multiple attachment: each attachment introduce some attenuation & distortion on the line, limiting distance and/or data rate 3/16/2018 Spring, 2003 EE 4272

Electromagnetic Spectrum for Telecom 3/16/2018 Spring, 2003 EE 4272 Electromagnetic Spectrum for Telecom 3/16/2018 Spring, 2003 EE 4272

Guided Transmission Media • Twisted Pair • Coaxial cable • Optical fiber 3/16/2018 Spring, Guided Transmission Media • Twisted Pair • Coaxial cable • Optical fiber 3/16/2018 Spring, 2003 EE 4272

Twisted Pair & Applications • Most common medium: least expensive • Telephone network Ø Twisted Pair & Applications • Most common medium: least expensive • Telephone network Ø Between house and local exchange (subscriber loop) • Within buildings Ø To private branch exchange (PBX) • For local area networks (LAN) Ø 10 Mbps or 100 Mbps 3/16/2018 Spring, 2003 EE 4272

Twisted Pair - Transmission Characteristics • Pros and Cons Cheap; Easy to work with Twisted Pair - Transmission Characteristics • Pros and Cons Cheap; Easy to work with Ø Low data rate; Short distance <- bigger attenuation Ø • • • Analog Signal: Amplifiers every 5 km to 6 km Digital Transmission: repeater every 2 km or 3 km Limited distance Limited bandwidth (1 MHz) Limited data rate (100 Mbp) Susceptible to interference and noise 3/16/2018 Spring, 2003 EE 4272

Unshielded and Shielded TP • Unshielded Twisted Pair (UTP) Ordinary telephone wire Ø Cheapest Unshielded and Shielded TP • Unshielded Twisted Pair (UTP) Ordinary telephone wire Ø Cheapest Ø Easiest to install Ø Suffers from external EM interference Ø • Shielded Twisted Pair (STP) Metal braid or sheathing that reduces interference Ø More expensive Ø Harder to handle (thick, heavy) Ø 3/16/2018 Spring, 2003 EE 4272

UTP Categories • Cat 3 up to 16 MHz Ø Voice-grade cable found in UTP Categories • Cat 3 up to 16 MHz Ø Voice-grade cable found in most offices Ø Twist length of 7. 5 cm to 10 cm Ø • Cat 4 Ø up to 20 MHz • Cat 5 up to 100 MHz Ø Commonly pre-installed in new office buildings Ø Twist length 0. 6 cm to 0. 85 cm Ø 3/16/2018 Spring, 2003 EE 4272

Coaxial Cable 3/16/2018 Spring, 2003 EE 4272 Coaxial Cable 3/16/2018 Spring, 2003 EE 4272

Applications & Transmission Characteristics Applications: • Television distribution : Cable TV • Long distance Applications & Transmission Characteristics Applications: • Television distribution : Cable TV • Long distance telephone transmission Can carry 10, 000 voice calls simultaneously (via FDM) Ø Being replaced by fiber optic Ø • Short distance links between computer devices Transmission Characteristics: • Analog Amplifiers every few km; Closer if higher frequency Ø Up to 500 MHz Ø • Digital: Repeater every 1 km; Closer for higher data rates 3/16/2018 Spring, 2003 EE 4272

Optical Fiber - Transmission Characteristics • Optical Fiber: transmit a signal-encoded beam of light Optical Fiber - Transmission Characteristics • Optical Fiber: transmit a signal-encoded beam of light by means of total internal reflection • Act as waveguide for freq. of 1014 to 1015 Hz Ø Portions of infrared and visible spectrum • Three Transmission Modes: Ø Step-index multimode; Graded-index multimode; Single-mode • Two Type of Light Sources: Ø Light Emitting Diode (LED) v Cheaper; Ø Wider operating temp range; Last longer Injection Laser Diode (ILD): More efficient; Greater data rate • WDM: multiple beams of light at different freq. are transmitted on the same fiber. This is a form of FDM. 3/16/2018 Spring, 2003 EE 4272

Optical Fiber Transmission Modes 3/16/2018 Spring, 2003 EE 4272 Optical Fiber Transmission Modes 3/16/2018 Spring, 2003 EE 4272

Optical Fiber - Properties & Applications Properties: • Greater capacity: in the unit of Optical Fiber - Properties & Applications Properties: • Greater capacity: in the unit of Gbps, Tbps • Smaller size & lighter weight • Lower Attenuation • EM Isolation: not affected by external EM interference • Greater Repeater Spacing: every hundreds of km Applications: • Long-haul trunks ; Metropolitan trunks; LANs • Rural exchange trunks • Subscriber loops 3/16/2018 Spring, 2003 EE 4272

Wireless Transmission • Unguided media • Transmission & reception via antenna • Directional Focused Wireless Transmission • Unguided media • Transmission & reception via antenna • Directional Focused beam Ø Careful alignment required Ø • Omnidirectional Signal spreads in all directions Ø Can be received by many antennae Ø 3/16/2018 Spring, 2003 EE 4272

3 Frequency Ranges • 30 MHz to 1 GHz: Suitable to Omnidirectional app. Ø 3 Frequency Ranges • 30 MHz to 1 GHz: Suitable to Omnidirectional app. Ø Refer to as broadcast radio range Ø • 2 GHz to 40 GHz: Microwave frequency Highly directional beams are possible Ø Suitable to point- to-point transmission Ø Can also be used for satellite comm. Ø • 3 x 1011 to 2 x 1014 Infrared portion of the spectrum Ø Local apps. Within confined areas, e. g. a single room Ø 3/16/2018 Spring, 2003 EE 4272

Terrestrial Microwave • Physical Description: the most common type of antenna is the parabolic Terrestrial Microwave • Physical Description: the most common type of antenna is the parabolic “dish” • Focuses a narrow beam: to achieve line-of-sight trans. to the receiving antenna • Apps. : Long haul telecommunications • Higher frequencies give higher data rates Ø common freq : 2 – 40 GHZ 3/16/2018 Spring, 2003 EE 4272

Satellite Microwave • Satellite is a microwave relay station • Satellite receives on one Satellite Microwave • Satellite is a microwave relay station • Satellite receives on one frequency, amplifies or repeats signal and transmits on another frequency • Requires geo-stationary orbit Ø Height of 35, 784 km • Applications: Television Ø Long distance telephone Ø Private business networks Ø 3/16/2018 Spring, 2003 EE 4272

Broadcast Radio • Omnidirectional • Freq: 30 MHZ to 1 GHZ FM radio Ø Broadcast Radio • Omnidirectional • Freq: 30 MHZ to 1 GHZ FM radio Ø UHF and VHF television Ø • Trans. is limited to the line of sight • Suffers from multipath interference 3/16/2018 Spring, 2003 EE 4272

Infrared • Transceivers modulate noncoherent infrared light • Two parties must be within line Infrared • Transceivers modulate noncoherent infrared light • Two parties must be within line of sight (or reflection) • Blocked by walls • e. g. TV remote control 3/16/2018 Spring, 2003 EE 4272