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Module 1: Physical Layer & Data Communication

20257m

How is data transmitted using guided and unguided media? Explain simplex, half-duplex and full-duplex communication.

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Data transmission over media

Guided media

Signals travel along a physical path (conductor), as electrical signals or light.

  • Twisted pair: electrical signals on copper pairs (LANs, telephone)
  • Coaxial cable: electrical signals, better shielding (cable TV)
  • Optical fiber: data sent as light pulses by total internal reflection; very high bandwidth, immune to EMI

Unguided media

Signals travel through free space as electromagnetic waves, with no physical conductor.

  • Radio waves: omnidirectional (radio, TV, Wi-Fi)
  • Microwaves: line-of-sight, unidirectional (cellular, satellite)
  • Infrared: short range (remote controls)
Guided Unguided
Path Physical cable Air / free space
Security Higher Lower (can be intercepted)
Mobility Fixed High
Interference Low Higher

Transmission modes

SVGVector Architecture Diagram (SVG)
AB AB AB Simplex Half-duplex Full-duplex one direction only both ways, one at a time both ways at the same time
Mode Description Example
Simplex Communication in one direction only; the receiver cannot reply Keyboard to computer, TV broadcast, radio
Half-duplex Both directions, but not simultaneously; the link is shared by turns Walkie-talkie, old Ethernet hub
Full-duplex Both directions at the same time (separate paths or frequencies) Telephone, switched Ethernet

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