COE 341: Data & Computer Communications Dr. Marwan Abu-Amara Chapter 4: Transmission Media

COE 341 – Dr. Marwan Abu-Amara Agenda Overview Guided Transmission Media Twisted Pair Coaxial Cable Optical Fiber Wireless Transmission Antennas Terrestrial Microwave Satellite Microwave Broadcast Radio Infrared COE 341 – Dr. Marwan Abu-Amara

COE 341 – Dr. Marwan Abu-Amara Overview Media Guided - wire Unguided - wireless Transmission characteristics and quality determined by: Medium Signal For guided, the medium is more important For unguided, the bandwidth produced by the antenna is more important Key concerns are data rate and distance COE 341 – Dr. Marwan Abu-Amara

COE 341 – Dr. Marwan Abu-Amara Design Issues Key communication objectives are: High data rate Low error rate Long distance Bandwidth: Tradeoff - Larger for higher data rates - But smaller for economy Transmission impairments Attenuation: Twisted Pair > Cable > Fiber (best) Interference: Worse with unguided… (medium is shared!) Number of receivers In multi-point links of guided media: More connected receivers introduce more attenuation COE 341 – Dr. Marwan Abu-Amara

Electromagnetic Spectrum COE 341 – Dr. Marwan Abu-Amara

Study of Transmission Media Physical description Main applications Main transmission characteristics COE 341 – Dr. Marwan Abu-Amara

Guided Transmission Media Twisted Pair Coaxial cable Optical fiber COE 341 – Dr. Marwan Abu-Amara

Transmission Characteristics of Guided Media     Frequency Range Typical Attenuation Typical Delay Repeater Spacing Twisted pair (with loading) 0 to 3.5 kHz 0.2 dB/km @ 1 kHz 50 µs/km 2 km Twisted pairs (multi-pair cables) 0 to 1 MHz 0.7 dB/km @ 1 kHz 5 µs/km Coaxial cable 0 to 500 MHz 7 dB/km @ 10 MHz 4 µs/km 1 to 9 km Optical fiber 186 to 370 THz 0.2 to 0.5 dB/km 40 km COE 341 – Dr. Marwan Abu-Amara

COE 341 – Dr. Marwan Abu-Amara Twisted Pair COE 341 – Dr. Marwan Abu-Amara

COE 341 – Dr. Marwan Abu-Amara UTP Cables COE 341 – Dr. Marwan Abu-Amara

COE 341 – Dr. Marwan Abu-Amara UTP Connectors COE 341 – Dr. Marwan Abu-Amara

COE 341 – Dr. Marwan Abu-Amara Note: Pairs of Wires It is important to note that these wires work in pairs (a transmission line) Hence, for a bidirectional link One pair is used for TX One pair is used for RX COE 341 – Dr. Marwan Abu-Amara

Twisted Pair - Applications Most commonly used guided medium Telephone network (Analog Signaling) Between house and local exchange (subscriber loop) Within buildings (Digital Signaling) To private branch exchange (PBX) For local area networks (LAN) 10Mbps or 100Mbps Range: 100m COE 341 – Dr. Marwan Abu-Amara

Twisted Pair - Pros and Cons Cheap Easy to work with Cons: Limited bandwidth Low data rate Short range Susceptible to interference and noise COE 341 – Dr. Marwan Abu-Amara

Twisted Pair - Transmission Characteristics Analog Transmission Amplifiers every 5km to 6km Digital Transmission Use either analog or digital signals Repeater every 2km or 3km Limited distance Limited bandwidth (1MHz) Limited data rate (100Mbps) Susceptible to interference and noise COE 341 – Dr. Marwan Abu-Amara

Attenuation in Guided Media COE 341 – Dr. Marwan Abu-Amara

Ways to reduce EM interference Shielding the TP with a metallic braid or sheathing Twisting reduces low frequency interference Different twisting lengths for adjacent pairs help reduce crosstalk COE 341 – Dr. Marwan Abu-Amara

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) COE 341 – Dr. Marwan Abu-Amara

COE 341 – Dr. Marwan Abu-Amara STP: Metal Shield COE 341 – Dr. Marwan Abu-Amara

COE 341 – Dr. Marwan Abu-Amara UTP Categories Cat 3 up to 16MHz Voice grade found in most offices Twist length of 7.5 cm to 10 cm Cat 4 up to 20 MHz Cat 5 up to 100MHz Commonly pre-installed in new office buildings Twist length 0.6 cm to 0.85 cm Cat 5E (Enhanced) –see tables Cat 6 Cat 7 COE 341 – Dr. Marwan Abu-Amara

Near End Crosstalk (NEXT) Coupling of signal from one wire pair to another Coupling takes place when a transmitted signal entering a pair couples back to an adjacent receiving pair at the same end i.e. near transmitted signal is picked up by near receiving pair Disturbing pair Disturbed pair Transmitted Power, P1 Coupled Received Power, P2 “NEXT” Attenuation = 10 log P1/P2 dBs The larger … the smaller the crosstalk (i.e. the better the performance) NEXT attenuation is a desirable attenuation - The larger the better! COE 341 – Dr. Marwan Abu-Amara

Transmission Properties for Shielded & Unshielded TP Undesirable Attenuation- Smaller is better Desirable Attenuation- Larger is better! Signal Attenuation (dB per 100 m) Near-end Crosstalk Attenuation (dB) Frequency (MHz) Category 3 UTP Category 5 UTP 150-ohm STP 1 2.6 2.0 1.1 41 62 68? 4 5.6 4.1 2.2 32 53 58 16 13.1 8.2 4.4 23 44 50.4 25 — 10.4 6.2 47.5 100 22.0 12.3 38.5 300 21.4 31.3 COE 341 – Dr. Marwan Abu-Amara

Twisted Pair Categories and Classes   Category 3 Class C Category 5 Class D Category 5E Category 6 Class E Category 7 Class F Bandwidth 16 MHz 100 MHz 200 MHz 600 MHz Cable Type UTP UTP/FTP SSTP Link Cost (Cat 5 =1) 0.7 1 1.2 1.5 2.2 COE 341 – Dr. Marwan Abu-Amara

COE 341 – Dr. Marwan Abu-Amara Coaxial Cable Physical Description: COE 341 – Dr. Marwan Abu-Amara

COE 341 – Dr. Marwan Abu-Amara Physical Description COE 341 – Dr. Marwan Abu-Amara

Coaxial Cable Applications Most versatile medium Television distribution Cable TV Long distance telephone transmission Can carry 10,000 voice calls simultaneously (though FDM multiplexing) Being replaced by fiber optic Short distance computer systems links Local area networks (thickwire Ethernet cable) COE 341 – Dr. Marwan Abu-Amara

Coaxial Cable - Transmission Characteristics Analog Amplifiers every few km Closer if higher frequency Up to 500MHz Digital Repeater every 1km Closer for higher data rates COE 341 – Dr. Marwan Abu-Amara

Attenuation in Guided Media COE 341 – Dr. Marwan Abu-Amara

COE 341 – Dr. Marwan Abu-Amara Optical Fibers An optical fiber is a very thin strand of silica glass It is a very narrow, very long glass cylinder with special characteristics. When light enters one end of the fiber it travels (confined within the fiber) until it leaves the fiber at the other end Two critical factors stand out: Very little light is lost in its journey along the fiber Fiber can bend around corners and the light will stay within it and be guided around the corners An optical fiber consists of three parts The core Narrow cylindrical strand of glass with refractive index n1 The cladding Tubular jacket surrounding the core with refractive index n2 The core must have a higher refractive index than the cladding for the propagation to happen COE 341 – Dr. Marwan Abu-Amara

Optical Fibers (Contd.) Protective outer jacket Protects against moisture, abrasion, and crushing Individual Fibers: (Each having core & Cladding) Single Fiber Cable Multiple Fiber Cable COE 341 – Dr. Marwan Abu-Amara

Reflection and Refraction At a boundary between a denser (n1) and a rarer (n2) medium, n1 > n2 (e.g. water-air, optical fiber core-cladding) a ray of light will be refracted or reflected depending on the incidence angle Increasing Incidence angle, 1 rarer 2 v2 = c/n2 n2 denser 1 2 n1 critical n1 > n2 1 v1 = c/n1 Refraction Critical angle refraction Total internal reflection COE 341 – Dr. Marwan Abu-Amara

COE 341 – Dr. Marwan Abu-Amara Optical Fiber Refraction at boundary for . Escaping light is absorbed in jacket i < critical Rarer n2 Denser Denser n1 n1 Rarer i Total Internal Reflection at boundary for i > critical n1 > n2 COE 341 – Dr. Marwan Abu-Amara

Attenuation in Guided Media COE 341 – Dr. Marwan Abu-Amara

Optical Fiber - Benefits Greater capacity Data rates of hundreds of Gbps Smaller size & weight Lower attenuation An order of magnitude lower Relatively constant over a larger frequency interval Electromagnetic isolation Not affected by external EM fields: No interference, impulse noise, crosstalk Does not radiate: Not a source of interference Difficult to tap (data security) Greater repeater spacing 10s of km at least COE 341 – Dr. Marwan Abu-Amara

Optical Fiber - Applications Long-haul trunks Metropolitan trunks Rural exchange trunks Subscriber loops LANs COE 341 – Dr. Marwan Abu-Amara

Optical Fiber - Transmission Characteristics Act as wave guide for light (1014 to 1015 Hz) Covers portions of infrared and visible spectrum Light Emitting Diode (LED) Cheaper Wider operating temp range Last longer Injection Laser Diode (ILD) More efficient Greater data rate COE 341 – Dr. Marwan Abu-Amara

Optical Fiber Transmission Modes Dispersion: Spread in arrival time Refraction Deep reflection Shallow reflection n2 i < critical n1 Large Core Cladding 2 ways: n1 n2 Smaller v = c/n n1 lower away from center…this speeds up deeper rays and compensates for their larger distances, arrive together with shallower rays Smallest COE 341 – Dr. Marwan Abu-Amara

Optical Fiber – Transmission modes Spread of received light pulse in time (dispersion) is bad: Causes inter-symbol interference  bit errors Limits usable data rate and usable distance Caused by propagation through multiple reflections at different angles of incidence Dispersion increases with: Larger distance traveled Thicker fibers with step index Can be reduced by: Limiting the distance Thinner fibers and a highly focused light source  Single mode: High data rates, very long distances Graded-index thicker fibers: The half-way solution COE 341 – Dr. Marwan Abu-Amara

Optical Fiber – Wavelength Division Multiplexing (WDM) A form of FDM (channels sharing the medium by occupying different frequency bands) Multiple light beams at different frequencies (wavelengths) transmitted on the same fiber Each beam forms a separate communication channel Example: 256 channels @ 40 Gbps each  10 Tbps total data rate COE 341 – Dr. Marwan Abu-Amara

COE 341 – Dr. Marwan Abu-Amara Optical Fiber – Four Transmission bands (windows) in the Infrared (IR) region Selection based on: Attenuation of the fiber Properties of the light sources Properties of the light receivers S C L Bandwidth, THz 33 12 4 7 Note: l in fiber = v/f = (c/n)/f = (c/f)/n = l in vacuum/n i.e. l in fiber < l in vacuum COE 341 – Dr. Marwan Abu-Amara

Attenuation in Guided Media COE 341 – Dr. Marwan Abu-Amara

Wireless Transmission Free-space is the transmission medium Need efficient radiators, called antenna, to take signal from transmission line (wireline) and radiate it into free-space (wireless) Famous applications Radio & TV broadcast Cellular Communications Microwave Links Wireless Networks COE 341 – Dr. Marwan Abu-Amara

Wireless Transmission Frequencies Radio: 30MHz to 1GHz Omni-directional Broadcast radio Microwave: 2GHz to 40GHz Microwave Highly directional Point to point Satellite Infrared Light: 3 x 1011 to 2 x 1014 Localized communications COE 341 – Dr. Marwan Abu-Amara

COE 341 – Dr. Marwan Abu-Amara Antennas Electrical conductor (or system of..) used to radiate/collect electromagnetic energy Transmission Radio frequency electrical energy from transmitter Converted to electromagnetic energy by antenna Radiated into surrounding environment Reception Electromagnetic energy impinging on antenna Converted to radio frequency electrical energy Fed to receiver Same antenna often used for both TX and RX in 2-way communication systems COE 341 – Dr. Marwan Abu-Amara

COE 341 – Dr. Marwan Abu-Amara Radiation Pattern Power radiated in all directions Not same performance in all directions Isotropic antenna is (theoretical) point in space Radiates in all directions equally Gives spherical radiation pattern Used as a reference for other antennae Directional Antenna Concentrates radiation in a given desired direction Used for point-to-point, line of sight communications Gives “gain” in that direction relative to isotropic Radiation Patterns Isotropic Directional COE 341 – Dr. Marwan Abu-Amara

Parabolic Reflective Antenna Used for terrestrial and satellite microwave Source placed at focus will produce waves reflected from parabola parallel to axis Creates (theoretical) parallel beam of light/sound/radio In practice, some divergence (dispersion) occurs, because source at focus has a finite size (not exactly a point!) On reception, signal is concentrated at focus, where detector is placed The larger the antenna (in wavelengths) the better the directionality COE 341 – Dr. Marwan Abu-Amara

Parabolic Reflective Antenna Axis COE 341 – Dr. Marwan Abu-Amara

COE 341 – Dr. Marwan Abu-Amara Antenna Gain, G Measure of directionality of antenna Power output in particular direction compared with that produced by isotropic antenna Measured in decibels (dB) Increased power radiated in one direction causes less power radiated in another direction (Total power is fixed) Effective area, Ae, relates to size and shape of antenna Determines antenna gain COE 341 – Dr. Marwan Abu-Amara

Antenna Gain, G: Effective Areas An isotropic antenna has a gain G = 1 (0 dBi) i.e. A parabolic antenna has: Substituting we get: Gain in dBi = 10 log G Important: Gains apply to both TX and RX antennas A = Actual Area = p r2 COE 341 – Dr. Marwan Abu-Amara

Terrestrial Microwave Parabolic dish Focused beam Line of sight Curvature of earth limits maximum range  Use relays to increase range (multi-hop link) Long haul telecommunications Higher frequencies give higher data rates but suffers from larger attenuation COE 341 – Dr. Marwan Abu-Amara

Terrestrial Microwave: Propagation Attenuation As signal propagates in space, its power drops with distance according to the inverse square law While with a guided medium, signal drops exponentially with distance… giving larger attenuation and lower repeater spacing d’ = distance in l’s i.e. loss in signal power over distance traveled, d Show that L increases by 6 dBs for every doubling of distance d. For guided medium, corresponding attenuation = a d dBs, a = dBs/km COE 341 – Dr. Marwan Abu-Amara

COE 341 – Dr. Marwan Abu-Amara Satellite Microwave Satellite is relay station Satellite receives on one frequency (uplink), amplifies or repeats signal and transmits on another frequency (downlink) Requires geo-stationary orbit Height of 35,784km Applications Television Long distance telephone Private business networks COE 341 – Dr. Marwan Abu-Amara

Satellite Point to Point Link Relay Downlink Uplink COE 341 – Dr. Marwan Abu-Amara

Satellite Broadcast Link COE 341 – Dr. Marwan Abu-Amara

COE 341 – Dr. Marwan Abu-Amara Broadcast Radio Omni-directional No dishes No line of sight requirement No antenna alignment Applications FM radio UHF and VHF television Suffers from multipath interference Reflections (e.g. TV ghost images) COE 341 – Dr. Marwan Abu-Amara

COE 341 – Dr. Marwan Abu-Amara Infrared Modulate non-coherent infrared light Line of sight (or reflection) Blocked by walls No licensing required for frequency allocation Applications TV remote control IRD port COE 341 – Dr. Marwan Abu-Amara