CE 4228 DATA COMMUNICATIONS AND NETWORKING Transmission Media

Transmission Media – Outline Guided media Twisted pair Coaxial cable Optical fiber Unguided media Antenna Propagation

Transmission Media – Design Key concerns are data rate and distance Bandwidth Higher bandwidth gives higher data rate Transmission impairments Attenuation Interference Number of receivers In guided media More multi-point receivers introduce more attenuation

Transmission Media – Guided Twisted pair Coaxial cable Optical fiber

Twisted Pair (a) Category 3 UTP (b) Category 5 UTP

Twisted Pair – Rationale

Twisted Pair – Applications Most common medium Telephone networks Between house and local exchange Subscriber loop Within buildings To private branch exchange or PBX Local area networks

Twisted Pair – Characteristics Analog Amplifiers every 5 to 6 km Digital Use either analog or digital signals Repeater every 2 or 3 km Limited distance Limited bandwidth Limited data rate Susceptible to interference and noise

Twisted Pair – UTP/STP UTP Unshielded twisted pair Ordinary telephone wire Cheapest Easiest to install Suffer from external EM interference STP Shielded twisted pair Metal braid or sheathing that reduces interference More expensive Thick, heavy Harder to handle

Twisted Pair – UTP Category 3 Up to 16 MHz Voice grade found in most offices Twist length of 7.5 cm to 10 cm Category 4 Up to 20 MHz Category 5 Up to 100 MHz Commonly pre-installed in new office buildings Twist length 0.6 cm to 0.85 cm Category 5e Enhanced Category 6 Category 7

Twisted Pair – Categories

TelephoneCategory 3Category 5eCategory 6

Twisted Pair – Category 6 UTP

Twisted Pair – Categories/Classes Category 3 Class C Category 5 Class D Category 5E Category 6 Class E Category 7 Class F Bandwidth16 MHz100 MHz 200 MHz600 MHz Cable TypeUTPUTP/FTP SSTP Link Cost

Twisted Pair – Comparison Attenuation (dB per 100 m)Near-end Crosstalk (dB) Frequency (MHz) Category 3 UTP Category 5 UTP 150-ohm STP Category 3 UTP Category 5 UTP 150-ohm STP — — — — ——21.4——31.3

Twisted Pair – Summary Cheap Easy to work with Low data rate Short range

Coaxial Cable 75-ohm cable is widely used Impedance easily matched with 300- ohm antenna 50-ohm cable is sometimes used when intended for digital transmission from the start

Coaxial Cable – Applications Most versatile medium Television distribution Aerial to TV Cable TV Long distance telephone transmission Can carry 10,000 voice calls simultaneously Being replaced by fiber optic Short distance computer systems links Local area networks

Coaxial Cable – Characteristics Analog Amplifiers every few km, closer if higher frequency Up to 500 MHz Digital Repeater every 1 km, closer for higher data rates 500 Mbps or higher For comparison 6 MHz/TV channel 1.4 Mbps for CD

Optical Fiber

Optical Fiber – Applications Long-haul trunks Metropolitan trunks Rural exchange trunks Subscriber loops LANs

Optical Fiber – FTTH

Optical Fiber – Characteristics Act as wave guide for to Hz Portions of infrared and visible spectrum Theoretical bandwidth of 50 Tbps Practical data rate of 2 Gbps Speed/distance limited by dispersion Two types of light source LED Light emitting diode ILD Injection laser diode Wavelength division multiplexing

Optical Fiber – Light Source

Optical Fiber – Modes

Optical Fiber – Dispersion

Define the following D = dispersion rate in s/km Pulse width increased/distance Depend on types of fiber R = bit rate in bps L = length of fiber in km Sending … L×D ≤ T/2 → R×L ≤ 1/2D Hence, R×L must be less than 10 Mbps × km for a step-index fiber 1 Gbps × km for a graded-index fiber 200 Gbps × km for a single-mode fiber

Wavelength range (nm) Frequency range (THz) Band label Fiber typeApplication 820 to to 333 MultimodeLAN 1280 to to 222SSingle modeVarious 1528 to to 192CSingle modeWDM 1561 to to 185LSingle modeWDM Optical Fiber – Frequency Range

Optical Fiber – Frequency Band

Optical Fiber – Benefits Greater capacity Data rates of hundreds of Gbps Smaller size & weight Lower attenuation Electromagnetic isolation Can be operated for communications and control networks in close proximity to electrical circuits without problems Greater repeater spacing 10 km or more

Guided Media – Characteristics Frequency Range Typical Attenuation Typical DelayRepeater Spacing Twisted pair (with loading) 0 to 3.5 kHz0.2 1 kHz 50 µs/km2 km Twisted pairs (multi-pair cables) 0 to 1 MHz0.7 1 kHz 5 µs/km2 km Coaxial cable0 to 500 MHz7 10 MHz 4 µs/km1 to 9 km Optical fiber186 to 370 THz0.2 to 0.5 dB/km 5 µs/km40 km

Guided Media – Characteristics

Guided Media – Attenuation

Electromagnetic Spectrum

Wireless – Frequency Band

Radio 10 kHz to 1 GHz Omnidirectional Broadcast radio Infrared 3×10 11 to 2×10 14 Hz Local Microwave 1 GHz to 40 GHz Highly directional Point to point Satellite

Wireless – ISM Band Industrial, scientific, medical Unlicensed usage Low power only, to avoid interference Garage door openers, cordless phones, wireless mice, wireless LANs, Bluetooth

Wireless Unguided transmission media Several reasons of usages Mobility Accessibility Modern wireless digital communications began in Hawaii, where conventional landline system was inadequate

Antenna Transmissions Radio frequency energy from transmitter Converted to electromagnetic energy by antenna Radiated into surrounding environment Receptions Electromagnetic energy impinging on antenna Converted to radio frequency electrical energy Fed to receiver Same antenna often used for both

Antenna – Radiation Pattern Power radiated in all directions Not same performance in all directions Isotropic antenna is theoretical point in space Radiate in all directions equally Give spherical radiation pattern

Antenna – Parabolic Reflective Used for terrestrial and satellite microwave Parabola is locus of point equidistant from a line and a point not on that line Fixed point is focus Line is directrix Revolve parabola about axis to get paraboloid Cross section parallel to axis gives parabola Cross section perpendicular to axis gives circle

Antenna – Parabolic Reflective Source placed at focus will produce waves reflected from parabola in parallel to axis Creates theoretical parallel beam of light/sound/radio On reception, signal is concentrated at focus, where detector is placed

Antenna – Parabolic Reflective

Antenna – Gain Measure of directionality of antenna Power output in particular direction compared with that produced by isotropic antenna Measured in dB Result in loss in power in another direction Effective area relates to size and shape Related to gain

Terrestrial Microwave Parabolic dish Focused beam Line of sight Higher frequencies give higher data rates Long haul telecommunications A microwave tower every 50 km

Satellite Satellite is relay station Satellite receives on one frequency, amplifies or repeats signal and transmits on another frequency Inherently broadcast media Can be deployed almost instantly Military Cost of transmitting is independent of the distance

Satellite Geostationary orbit Height of 35,784 km Relatively large propagation delay Typical value is 270 msec 3 μsec/km for terrestrial microwave 5 μsec/km for coaxial cable or optical fiber Television Long distance telephone Private business networks

Satellite – Frequency Band

Satellite – Altitude

Satellite – Point to Point Link

Satellite – Broadcast Link

Satellite – VSAT

Broadcast Radio Omnidirectional FM radio UHF and VHF television Line of sight Suffer from multipath interference Reflections

Infrared Modulate noncoherent infrared light Line of sight or reflection Blocked by walls TV remote control, IrDA port Point to point

Cellular System Replace high power transmitter/receiver systems Use lower power, shorter range, more transmitters Area divided into cells Adjacent cells on different frequencies to avoid crosstalk Frequency reuse Hexagonal cells Most resemble to circular shape Can be packed without hole

Cellular System – Cells

Cellular System – Design Factor Fading Time variation of received signal, caused by changes in transmission paths Multiple access FDMA TDMA CDMA Handoff Base station location

Cellular System – Signal Strength

Wireless – Propagation Signal travels along three routes Ground wave Sky wave Line of sight

Wireless – Ground Wave Frequency less than 2 MHz Follow contour of the earth AM radio

Wireless – Sky Wave Frequency of 2-30 MHz BBC world, Voice of America, amateur radio Signal reflected, or actually refracted, from ionosphere layer

Wireless – Line of Sight Frequency above 30 MHz May be further than optical line of sight due to refraction

Wireless – Refraction Velocity of electromagnetic wave is a function of density of material 3×10 8 m/s in vacuum, less in anything else As wave moves from one medium to another, its speed changes Direction bending of wave at boundary Towards more dense medium Index of refraction sin(angle of incidence)/sin(angle of refraction) Vary with wavelength Also called refractive index

Wireless – Refraction May cause sudden change of direction at transition between media May cause gradual bending if medium density is varying Density of atmosphere decreases with height Result in bending towards earth of radio waves

Wireless – Impairment Free space loss Signal disperses with distance Greater for higher frequencies But consider antenna gain that can compensate, higher frequencies are better Atmospheric absorption Water vapour and oxygen absorb radio signals Water greatest at 22 GHz, less below 15 GHz Oxygen greatest at 60 GHz, less below 30 GHz Rain and fog scatter radio waves

Wireless – Impairment Multipath Better to get line of sight if possible Signal can be reflected causing multiple copies to be received May be no direct signal at all May reinforce or cancel direct signal Refraction May result in partial or total loss of signal at receiver

Wireless Free space loss

Wireless – Multipath Interference

Transmission Media – Conclusion Guided Unguided Understanding the properties