How many different types of physical media can you think of? 10
Wires – Twisted Pair Two insulated copper wires, twisted in helical (DNA) form. Twisting reduces interference: canceling out electromagnetic interference from external sources Distance up to <5km, repeaters can extend this distance cable with four twisted pairs 11
Properties and Types of Twisted Pair Bandwidth depends on distance, wire quality/ density Cat 3 - 2 wires, 4 pairs in sheath, 16MHz Cat 5 - 2 wires, 4 pair in sheath, more twists = less interference, higher quality over longer distance, 100 MHz Cat 8 – 2000 MHz 12 Don’t worry about this unit for now, just higher value is better!
Coaxial Cable (Co-ax) Copper core with insulation, mesh, and sheath Better shielding than twisted pair = higher speeds over greater distances Bandwidth approaches 1GHz Still widely used for cable TV/Internet 13
Fibre Optics Fibre has enormous bandwidth (THz) and tiny signal loss Data transmission over a fibre of glass Common for high rates and long distances e.g. backbone links between ISP facilities, Fibre- to-the-Home (FTTH) 14
Transmission of Light Through Fibre 3 components: light source, transmission medium, detector Semantics: light = 1, no light = 0 (basic binary system) Signalling using LED’s or semiconductor lasers A detector generates electrical pulse when light hits it Refraction between air/silica boundary is compensated for by design - total internal reflection Light source (LED, laser) Photodetector Light trapped by total internal reflection 15
Fibre Optic Cables Single-mode Narrow core (10um), light can’t even bounce around Used with lasers for long distances, e.g., 100km Multi-mode 50um core, light can bounce Used with LEDs for cheaper, shorter distance links 16
Fibre Optic Connections Connectors and Fibre Sockets (10-20% loss) Mechanical Splice (10% loss) Fusion (<1% loss) 17 Examples: mechanical splice
Fibre Optic Networks Fibre optic cable is a scalable network media - LAN, WAN, long distances Fibre optic cable networks can be organised either as a ring or as a bus network (series of point to point connections) Fibre Optic Ring 18
Comparison of the properties of wires and fibre: Comparison: Wires and Fibre Property Wires Fibre Distance Short (100s of m) Long (tens of km) Bandwidth Moderate Very High Security Easy to tap Hard to tap Cost Inexpensive More Expensive Convenience Easy to use Harder to use 19
Wireless Transmission Mobile users requires a mobility enabled network - contrast with the wired networks Wireless networks can provide advantages even in fixed location environments Wireless data transmission networks have a common basis - electromegnatic wave propagation Unlike previous media, wireless signals are broadcasted over a region Potential signal collisions – Need regulations 20
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- Three '18
- fibre optic networks, fibre optics, Claude Shannon Father