ITS323 Transmission Media Design Factors Guided Media Wireless Transmission Wireless Media Transmission Media ITS323: Introduction to Data Communications Sirindhorn International Institute of Technology Thammasat University Prepared by Steven Gordon on 23 May 2012 ITS323Y12S1L04, Steve/Courses/2012/s1/its323/lectures/media.tex, r2334
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ITS323
TransmissionMedia
Design Factors
Guided Media
WirelessTransmission
Wireless Media
Transmission Media
ITS323: Introduction to Data Communications
Sirindhorn International Institute of TechnologyThammasat University
Prepared by Steven Gordon on 23 May 2012ITS323Y12S1L04, Steve/Courses/2012/s1/its323/lectures/media.tex, r2334
ITS323
TransmissionMedia
Design Factors
Guided Media
WirelessTransmission
Wireless Media
Contents
Design Factors
Guided Media
Wireless Transmission
Wireless Media
ITS323
TransmissionMedia
Design Factors
Guided Media
WirelessTransmission
Wireless Media
Design Factors
I Key concerns are data rate and distance: maximise bothI Design factors:
I BandwidthI Transmission impairmentsI InterferenceI Number of receivers
ITS323
TransmissionMedia
Design Factors
Guided Media
WirelessTransmission
Wireless Media
Electromagnetic Spectrum forTelecommunications
ITS323
TransmissionMedia
Design Factors
Guided Media
WirelessTransmission
Wireless Media
Contents
Design Factors
Guided Media
Wireless Transmission
Wireless Media
ITS323
TransmissionMedia
Design Factors
Guided Media
WirelessTransmission
Wireless Media
Electrical Cables
I Transmit electrical signals on a conductor, e.g. copperI Cable carrying electrical current radiates energy, and
can pick-up energy from other sourcesI Can cause interference on other cablesI Other sources can cause interference on the cableI Interference results in poor quality signals being received
I To minimise interference:I Keep the cable lengths shortI Keep the cables away from other sourcesI Design the cables to minimise radiation and pick-up
I Use materials to shield from interferenceI Organise multiple wires so they dont interfere with
each other
ITS323
TransmissionMedia
Design Factors
Guided Media
WirelessTransmission
Wireless Media
Twisted Pair
I Two insulated copper wires arranged in spiral patternI Most commonly used and least expensive medium
I Used in telephone networks and in-buildingcommunications
I Telephone networks designed for analog signalling (butsupporting digital data)
I Also used for digital signalling
I Two varieties of twisted pair: shielded (STP) andunshielded (UTP); also multiple categories (CAT5)
ITS323
TransmissionMedia
Design Factors
Guided Media
WirelessTransmission
Wireless Media
Coaxial Cable
I Two conductors, one inside the otherI Provide much more shielding from interference than
twisted pair: Higher data rates; More devices on ashared line; Longer distances
I Widely used for cable TV, as well as other audio/videocabling
I Used in long-distance telecommunications, althoughoptical fibre is more relevant now
ITS323
TransmissionMedia
Design Factors
Guided Media
WirelessTransmission
Wireless Media
Optical Fibre
I Light (optical rays) is guided within glass or plasticfibres
I Used in long-distance telecommunications, as well astelephone systems, LANs, and city-wide networks
I Advantages of optical fibre over electrical cables:1. Lower loss: can transfer larger distances2. Higher bandwidth: a single fibre is equivalent to 10’s or
100’s of electrical cables3. Small size, light weight: lowers cost of installation4. Electromagnetic isolation
ITS323
TransmissionMedia
Design Factors
Guided Media
WirelessTransmission
Wireless Media
Comparison of Guided Media
Electrical Cables
I Moderate data rates: 1Gb/s
I Maximum distance: 2km (twisted pair); 10km (coaxial)
I Cheapest for low data rates
I UTP: easy to install, susceptible to interference
I STP, Coaxial Cable: rigid, protection againstinterference
Optical Cables
I Very high data rates: 100Gb/s+
I Maximum distance: 40km
I Expensive equipment, but cost effective for high datarates
I Difficult to install
ITS323
TransmissionMedia
Design Factors
Guided Media
WirelessTransmission
Wireless Media
Point-to-Point Transmission Characteristics ofGuided Media
ITS323
TransmissionMedia
Design Factors
Guided Media
WirelessTransmission
Wireless Media
Attenuation of Typical Guided Media
ITS323
TransmissionMedia
Design Factors
Guided Media
WirelessTransmission
Wireless Media
Contents
Design Factors
Guided Media
Wireless Transmission
Wireless Media
ITS323
TransmissionMedia
Design Factors
Guided Media
WirelessTransmission
Wireless Media
Wireless Transmission Model
Common wireless systems for communications include:
I Terrestrial microwave, e.g. television transmission
I Satellite microwave, e.g. IPstar
I Broadcast radio, e.g. IEEE 802.11 WiFi (wireless LAN)
I Infrared, e.g. in-home communications
Transmitter Receiver
Antenna AntennaReceiveTransmit
Signal
ITS323
TransmissionMedia
Design Factors
Guided Media
WirelessTransmission
Wireless Media
Antennas
I Antenna converts between electrical current andelectromagnetic waves
I Waves are within the Radio Frequency (RF) band of 3kHz to 300 GHz
I Antenna characteristics are same whether sending orreceiving
I Direction and propagation of a wave depends onantenna shape
I Isotropic antenna: power propagates in all directionsequally (spherical pattern, ideal)
I Omni-directional antenna: power propagates in alldirections on one plane (donut)
I Directional antenna: power concentrated in particulardirection
I Power output in particular direction compared to powerproduced by isotropic antenna is antenna gain [dBi]