COE 341 Data Computer Communications Dr Marwan AbuAmara

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

Agenda n n Overview Guided Transmission Media q q q n Twisted Pair Coaxial Cable Optical Fiber Wireless Transmission q q q Antennas Terrestrial Microwave Satellite Microwave Broadcast Radio Infrared COE 341 – Dr. Marwan Abu-Amara 2

Overview n Media q q n Transmission characteristics and quality determined by: q q n n n Guided - wire Unguided - wireless 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 3

Design Issues n Key communication objectives are: q q n Transmission impairments q q n High data rate Low error rate Long distance Bandwidth: Tradeoff - Larger for higher data rates - But smaller for economy Attenuation: Twisted Pair > Cable > Fiber (best) Interference: Worse with unguided… (medium is shared!) Number of receivers q In multi-point links of guided media: More connected receivers introduce more attenuation COE 341 – Dr. Marwan Abu-Amara 4

Electromagnetic Spectrum COE 341 – Dr. Marwan Abu-Amara 5

Study of Transmission Media n n n Physical description Main applications Main transmission characteristics COE 341 – Dr. Marwan Abu-Amara 6

Guided Transmission Media n n n Twisted Pair Coaxial cable Optical fiber COE 341 – Dr. Marwan Abu-Amara 7

Transmission Characteristics of Guided Media Frequency Range Typical Attenuation Typical Delay Repeater Spacing Twisted pair (with loading) 0 to 3. 5 k. Hz 0. 2 d. B/km @ 1 k. Hz 50 µs/km 2 km Twisted pairs (multi-pair cables) Coaxial cable 0 to 1 MHz 0. 7 d. B/km @ 1 k. Hz 5 µs/km 2 km 0 to 500 MHz 7 d. B/km @ 10 MHz 4 µs/km 1 to 9 km Optical fiber 186 to 370 THz 0. 2 to 0. 5 d. B/km 5 µs/km 40 km COE 341 – Dr. Marwan Abu-Amara 8

Twisted Pair COE 341 – Dr. Marwan Abu-Amara 9

UTP Cables COE 341 – Dr. Marwan Abu-Amara 10

UTP Connectors COE 341 – Dr. Marwan Abu-Amara 11

Note: Pairs of Wires n n It is important to note that these wires work in pairs (a transmission line) Hence, for a bidirectional link q q One pair is used for TX One pair is used for RX COE 341 – Dr. Marwan Abu-Amara 12

Twisted Pair - Applications n n Most commonly used guided medium Telephone network (Analog Signaling) q n Within buildings (Digital Signaling) q n Between house and local exchange (subscriber loop) To private branch exchange (PBX) For local area networks (LAN) q q 10 Mbps or 100 Mbps Range: 100 m COE 341 – Dr. Marwan Abu-Amara 13

Twisted Pair - Pros and Cons n Pros: q q n Cheap Easy to work with Cons: q q Limited bandwidth Low data rate Short range Susceptible to interference and noise COE 341 – Dr. Marwan Abu-Amara 14

Twisted Pair - Transmission Characteristics n Analog Transmission q n Digital Transmission q q n n Amplifiers every 5 km to 6 km Use either analog or digital signals Repeater every 2 km or 3 km Limited distance Limited bandwidth (1 MHz) Limited data rate (100 Mbps) Susceptible to interference and noise COE 341 – Dr. Marwan Abu-Amara 15

Attenuation in Guided Media COE 341 – Dr. Marwan Abu-Amara 16

Ways to reduce EM interference n n n 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 17

Unshielded and Shielded TP n Unshielded Twisted Pair (UTP) q q n Ordinary telephone wire Cheapest Easiest to install Suffers from external EM interference Shielded Twisted Pair (STP) q q q Metal braid or sheathing that reduces interference More expensive Harder to handle (thick, heavy) COE 341 – Dr. Marwan Abu-Amara 18

STP: Metal Shield COE 341 – Dr. Marwan Abu-Amara 19

UTP Categories n Cat 3 q q q n Cat 4 q n q q n n up to 20 MHz Cat 5 q n up to 16 MHz Voice grade found in most offices Twist length of 7. 5 cm to 10 cm up to 100 MHz Commonly pre-installed in new office buildings Twist length 0. 6 cm to 0. 85 cm Cat 5 E (Enhanced) –see tables Cat 6 Cat 7 COE 341 – Dr. Marwan Abu-Amara 20

Near End Crosstalk (NEXT) n n n 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 Transmitted Power, P 1 Disturbing pair Coupled Received Disturbed pair Power, P 2 “NEXT” Attenuation = 10 log P 1/P 2 d. Bs 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 21

Transmission Properties for Shielded & Unshielded TP Desirable Attenuation- Larger is better! Undesirable Attenuation- Smaller is better Signal Attenuation (d. B per 100 m) Frequency (MHz) Category 3 UTP Category 5 UTP 1 2. 6 2. 0 4 5. 6 16 13. 1 150 -ohm STP Near-end Crosstalk Attenuation (d. B) Category 3 UTP Category 5 UTP 150 -ohm STP 1. 1 41 62 68? 4. 1 2. 2 32 53 58 8. 2 4. 4 23 44 50. 4 25 — 10. 4 6. 2 — 41 47. 5 100 — 22. 0 12. 3 — 32 38. 5 300 — 21. 4 — — COE 341 – Dr. Marwan Abu-Amara — 31. 3 22

Twisted Pair Categories and Classes Category 3 Class C Category 5 Class D Bandwidth 16 MHz 100 MHz Cable Type UTP Link Cost (Cat 5 =1) 0. 7 Category 5 E Category 6 Class E Category 7 Class F 100 MHz 200 MHz 600 MHz UTP/FTP SSTP 1 1. 2 1. 5 2. 2 COE 341 – Dr. Marwan Abu-Amara 23

Coaxial Cable Physical Description: COE 341 – Dr. Marwan Abu-Amara 24

Physical Description COE 341 – Dr. Marwan Abu-Amara 25

Coaxial Cable Applications n n Most versatile medium Television distribution q n Long distance telephone transmission q q n n Cable TV 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 26

Coaxial Cable - Transmission Characteristics n Analog q q q n Amplifiers every few km Closer if higher frequency Up to 500 MHz Digital q q Repeater every 1 km Closer for higher data rates COE 341 – Dr. Marwan Abu-Amara 27

Attenuation in Guided Media COE 341 – Dr. Marwan Abu-Amara 28

Optical Fibers n An optical fiber is a very thin strand of silica glass q n Two critical factors stand out: q q n 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 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 q The core n q Narrow cylindrical strand of glass with refractive index n 1 The cladding n Tubular jacket surrounding the core with refractive index n 2 n The core must have a higher refractive index than the cladding for the propagation to happen COE 341 – Dr. Marwan Abu-Amara 29

Optical Fibers (Contd. ) q Protective outer jacket n Protects against moisture, abrasion, and crushing Individual Fibers: (Each having core & Cladding) Single Fiber Cable Multiple Fiber Cable COE 341 – Dr. Marwan Abu-Amara 30

Reflection and Refraction n At a boundary between a denser (n 1) and a rarer (n 2) medium, n 1 > n 2 (e. g. water-air, optical fiber corecladding) a ray of light will be refracted or reflected depending on the incidence angle Increasing Incidence angle, 1 2 rarer n 2 v 2 = c/n 2 denser n 1 > n 2 1 1 Refraction v 1 = c/n 1 2 critical Critical angle refraction COE 341 – Dr. Marwan Abu-Amara Total internal reflection 31

Optical Fiber Refraction at boundary for i < critical. Escaping light is absorbed in jacket Rarer Denser Rarer n 2 n 1 n 1 > n 2 COE 341 – Dr. Marwan Abu-Amara i Total Internal Reflection at boundary for i > critical 32

Attenuation in Guided Media COE 341 – Dr. Marwan Abu-Amara 33

Optical Fiber - Benefits n Greater capacity q n n Smaller size & weight Lower attenuation q q n An order of magnitude lower Relatively constant over a larger frequency interval Electromagnetic isolation q q n Data rates of hundreds of Gbps Not affected by external EM fields: n No interference, impulse noise, crosstalk Does not radiate: n Not a source of interference n Difficult to tap (data security) Greater repeater spacing q 10 s of km at least COE 341 – Dr. Marwan Abu-Amara 34

Optical Fiber - Applications n n n Long-haul trunks Metropolitan trunks Rural exchange trunks Subscriber loops LANs COE 341 – Dr. Marwan Abu-Amara 35

Optical Fiber - Transmission Characteristics n Act as wave guide for light (1014 to 1015 Hz) q n Light Emitting Diode (LED) q q q n Covers portions of infrared and visible spectrum Cheaper Wider operating temp range Last longer Injection Laser Diode (ILD) q q More efficient Greater data rate COE 341 – Dr. Marwan Abu-Amara 36

n 1 n 2 Dispersion: Optical Fiber Transmission Modes Spread in arrival Refraction i < critical Shallow reflection time Large Cladding 2 ways: n 1 n 2 Core Deep reflection Smaller • v = c/n • n 1 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 37

Optical Fiber – Transmission modes n Spread of received light pulse in time (dispersion) is bad: q q n n Caused by propagation through multiple reflections at different angles of incidence Dispersion increases with: q q n Causes inter-symbol interference bit errors Limits usable data rate and usable distance Larger distance traveled Thicker fibers with step index Can be reduced by: q q q 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 38

Optical Fiber – Wavelength Division Multiplexing (WDM) n A form of FDM (channels sharing the medium by occupying different frequency bands) n Multiple light beams at different frequencies (wavelengths) transmitted on the same fiber n Each beam forms a separate communication channel n Example: 256 channels @ 40 Gbps each 10 Tbps total data rate COE 341 – Dr. Marwan Abu-Amara 39

Optical Fiber – Four Transmission bands (windows) in the Infrared (IR) region n Selection based on: q q q 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 40

Attenuation in Guided Media COE 341 – Dr. Marwan Abu-Amara 41

Wireless Transmission n 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 q q Radio & TV broadcast Cellular Communications Microwave Links Wireless Networks COE 341 – Dr. Marwan Abu-Amara 42

Wireless Transmission Frequencies n Radio: 30 MHz to 1 GHz q q n Microwave: 2 GHz to 40 GHz q q n Omni-directional Broadcast radio Microwave Highly directional Point to point Satellite Infrared Light: 3 x 1011 to 2 x 1014 q Localized communications COE 341 – Dr. Marwan Abu-Amara 43

Antennas n n Electrical conductor (or system of. . ) used to radiate/collect electromagnetic energy Transmission q q q n Reception q q q n Radio frequency electrical energy from transmitter Converted to electromagnetic energy by antenna Radiated into surrounding environment 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 44

Radiation Pattern n Power radiated in all directions Not same performance in all directions Radiation Patterns Isotropic antenna is (theoretical) point in space q q q n Radiates in all directions equally Gives spherical radiation pattern Used as a reference for other antennae Directional Antenna q Concentrates radiation in a given desired direction n q Isotropic Used for point-to-point, line of sight communications Gives “gain” in that direction relative to isotropic COE 341 – Dr. Marwan Abu-Amara Directional 45

Parabolic Reflective Antenna n n Used for terrestrial and satellite microwave Source placed at focus will produce waves reflected from parabola parallel to axis q q n n 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 46

Parabolic Reflective Antenna Axis COE 341 – Dr. Marwan Abu-Amara 47

Antenna Gain, G n n n Measure of directionality of antenna Power output in particular direction compared with that produced by isotropic antenna Measured in decibels (d. B) 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 q Determines antenna gain COE 341 – Dr. Marwan Abu-Amara 48

Antenna Gain, G: Effective Areas n An isotropic antenna has a gain G = 1 (0 d. Bi) i. e. n A parabolic antenna has: n A = Actual Area = p r 2 n Substituting we get: n Gain in d. Bi = 10 log G Important: Gains apply to both TX and RX antennas n COE 341 – Dr. Marwan Abu-Amara 49

Terrestrial Microwave n n n Parabolic dish Focused beam Line of sight q n n 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 50

Terrestrial Microwave: Propagation Attenuation n As signal propagates in space, its power drops with distance according to the inverse square law d’ = distance in l’s While with a guided medium, signal drops exponentially with distance… giving larger attenuation and lower repeater spacing i. e. loss in signal power over distance traveled, d • Show that L increases by 6 d. Bs for every doubling of distance d. • For guided medium, corresponding attenuation = a d d. Bs, a = d. Bs/km COE 341 – Dr. Marwan Abu-Amara 51

Satellite Microwave n n n Satellite is relay station Satellite receives on one frequency (uplink), amplifies or repeats signal and transmits on another frequency (downlink) Requires geo-stationary orbit q n Height of 35, 784 km Applications q q q Television Long distance telephone Private business networks COE 341 – Dr. Marwan Abu-Amara 52

Satellite Point to Point Link Relay Downlink Uplink COE 341 – Dr. Marwan Abu-Amara 53

Satellite Broadcast Link COE 341 – Dr. Marwan Abu-Amara 54

Broadcast Radio n Omni-directional No dishes q No line of sight requirement q No antenna alignment q n Applications q q n FM radio UHF and VHF television Suffers from multipath interference q Reflections (e. g. TV ghost images) COE 341 – Dr. Marwan Abu-Amara 55

Infrared n n n Modulate non-coherent infrared light Line of sight (or reflection) Blocked by walls No licensing required for frequency allocation Applications q q TV remote control IRD port COE 341 – Dr. Marwan Abu-Amara 56