CS461 Transmission Media PDF

CS461 Transmission Media Design Factors Guided Media Wireless Transmission Media Transmission Wireless Media CS461: Computer Networks HiLCoE School of Computer Science and Technology  CS461...

CS461 Transmission Media Design Factors Guided Media Wireless Transmission Media Transmission Wireless Media CS461: Computer Networks HiLCoE School of Computer Science and Technology  CS461 Contents Transmission Media Design Factors Guided Media Design Factors Wireless Transmission Wireless Media Guided Media Wireless Transmission Wireless Media  CS461 Design Factors Transmission Media I Key concerns are data rate and distance: maximise both Design Factors I Design factors: Guided Media I Bandwidth Wireless Transmission I Transmission impairments Wireless Media I Interference I Number of receivers  CS461 Electromagnetic Spectrum for Transmission Media Telecommunications Design Factors Guided Media Wireless Transmission Wireless Media  CS461 Contents Transmission Media Design Factors Guided Media Design Factors Wireless Transmission Wireless Media Guided Media Wireless Transmission Wireless Media  CS461 Electrical Cables Transmission Media I Transmit electrical signals on a conductor, e.g. copper Design Factors I Cable carrying electrical current radiates energy, and Guided Media can pick-up energy from other sources Wireless Transmission I Can cause interference on other cables Wireless Media I Other sources can cause interference on the cable I Interference results in poor quality signals being received I To minimise interference: I Keep the cable lengths short I Keep the cables away from other sources I Design the cables to minimise radiation and pick-up I Use materials to shield from interference I Organise multiple wires so they dont interfere with each other  CS461 Twisted Pair Transmission Media I Two insulated copper wires arranged in spiral pattern Design Factors I Most commonly used and least expensive medium Guided Media I Used in telephone networks and in-building Wireless Transmission communications Wireless Media I Telephone networks designed for analog signalling (but supporting digital data) I Also used for digital signalling I Two varieties of twisted pair: shielded (STP) and unshielded (UTP); also multiple categories (CAT5)  CS461 Coaxial Cable Transmission Media I Two conductors, one inside the other Design Factors I Provide much more shielding from interference than Guided Media twisted pair: Higher data rates; More devices on a Wireless Transmission shared line; Longer distances Wireless Media I Widely used for cable TV, as well as other audio/video cabling I Used in long-distance telecommunications, although optical fibre is more relevant now  CS461 Optical Fibre Transmission Media I Light (optical rays) is guided within glass or plastic Design Factors fibres Guided Media I Used in long-distance telecommunications, as well as Wireless Transmission telephone systems, LANs, and city-wide networks Wireless Media I Advantages of optical fibre over electrical cables: 1. Lower loss: can transfer larger distances 2. Higher bandwidth: a single fibre is equivalent to 10’s or 100’s of electrical cables 3. Small size, light weight: lowers cost of installation 4. Electromagnetic isolation  CS461 Comparison of Guided Media Transmission Media Design Factors Electrical Cables Guided Media I Moderate data rates: 1Gb/s Wireless Transmission I Maximum distance: 2km (twisted pair); 10km (coaxial) Wireless Media I Cheapest for low data rates I UTP: easy to install, susceptible to interference I STP, Coaxial Cable: rigid, protection against interference Optical Cables I Very high data rates: 100Gb/s+ I Maximum distance: 40km I Expensive equipment, but cost effective for high data rates I Difficult to install  CS461 Contents Transmission Media Design Factors Guided Media Design Factors Wireless Transmission Wireless Media Guided Media Wireless Transmission Wireless Media  CS461 Wireless Transmission Model Transmission Media Common wireless systems for communications include: Design Factors I Terrestrial microwave, e.g. television transmission Guided Media Wireless I Satellite microwave, e.g. IPstar Transmission I Broadcast radio, e.g. IEEE 802.11 WiFi (wireless LAN) Wireless Media I Infrared, e.g. in-home communications Transmit Receive Antenna Antenna Signal Transmitter Receiver  CS461 Antennas Transmission Media I Antenna converts between electrical current and Design Factors electromagnetic waves Guided Media I Waves are within the Radio Frequency (RF) band of 3 Wireless Transmission kHz to 300 GHz Wireless Media I Antenna characteristics are same whether sending or receiving I Direction and propagation of a wave depends on antenna shape I Isotropic antenna: power propagates in all directions equally (spherical pattern, ideal) I Omni-directional antenna: power propagates in all directions on one plane (donut) I Directional antenna: power concentrated in particular direction I Power output in particular direction compared to power produced by isotropic antenna is antenna gain [dBi]  CS461 Wireless Propagation Transmission Media I Ground Wave Propagation (below 2 MHz): signal Design Factors follows contour of Earth, e.g. AM radio Guided Media I Sky Wave Propagation (2–30 MHz: signal reflected Wireless Transmission between ionosphere and Earth, e.g. amateur radio, Wireless Media international radio stations I Line-of-Sight Propagation (above 30 MHz): signal not reflected; antennas must be in effective line-of-sight; used for most communications  CS461 Different Propagation Characteristics Transmission Media Design Factors Guided Media Wireless Transmission Wireless Media  CS461 Wireless Transmission Impairments Transmission Media Free Space Loss: Signal disperses with distance; therefore Design Factors signal attenuates over distance Guided Media Atmospheric Absorption: Water vapour and oxygen in Wireless Transmission atmosphere may attenuate signals; only Wireless Media significant for specific frequencies (e.g. 22GHz, > 30 GHz) Multipath: Signals reflect off obstacles; multiple copies of signal arrive at receiver with varying delays causing reinforcement or cancellation Refraction: Signals are refracted through atmosphere; only part of wave received  CS461 Examples of Multipath Interference Transmission Media Design Factors Guided Media Wireless Transmission Wireless Media  CS461 Contents Transmission Media Design Factors Guided Media Design Factors Wireless Transmission Wireless Media Guided Media Wireless Transmission Wireless Media  CS461 Terrestrial Microwave Transmission Media I Parabolic antenna (usually 1-3 m) used to transmit Design Factors point-to-point to another antenna Guided Media I Line-of-sight communications; often antennas are Wireless Transmission placed high (towers, buildings) to avoid obstacles Wireless Media I Long-distance telecommunications (alternative to optical fibre, coaxial cable), e.g. voice and TV transmission I Short communications between buildings (e.g. office buildings in city) I Mobile telephone systems (GSM, CDMA, 3G)  CS461 Satellite Microwave Transmission Media I Communications satellite acts as microwave relay Design Factors station Guided Media I Links two or more ground/earth stations Wireless Transmission I Receives signal on one frequency (uplink), repeats or Wireless Media amplifies, and transmits on another frequency (downlink) I Point-to-point or broadcast configuration I Geostationary Orbit (GEO): satellite appears stationary from Earth; cover about 13 Earth surface; 36,000 km above Earth I Low Earth Orbit (LEO): 100’s of km above Earth; orbit Earth every 1–2 hours; footprint with radius of 3000–4000 km  CS461 Satellite Communication Configurations: Transmission Media Point-to-point link Design Factors Guided Media Wireless Transmission Wireless Media  CS461 Transmission Satellite Communication Configurations: Media Design Factors Broadcast link Guided Media Wireless Transmission Wireless Media  CS461 Applications for Satellites Transmission Media I TV distribution Design Factors I Long-distance telephone transmission Guided Media Wireless I Private business networks Transmission I Very Small Aperture Terminals (VSATs) allow for low Wireless Media cost Earth stations I Global positioning, e.g. GPS  CS461 Typical VSAT Configuration Transmission Media Design Factors Guided Media Wireless Transmission Wireless Media  CS461 Broadcast Radio Transmission Media I Microwave uses directional antennas; broadcast radio Design Factors can use omni-directional Guided Media I Frequencies from 30 MHz to 1 GHz Wireless Transmission I FM radio Wireless Media I UHF and VHF television I Wireless networking