Transmission Terminology

<aside> 💡 Medium, when used to describe a “channel of communication”, has plurar form media. 1 medium, multiple media.

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Context: data transmission occurs between transmitter and receiver over some transmission medium. Communication is in the form of electromagnetic waves.

• Guided media — waves are guided along a physical path (eg. twisted pair, coaxial cable, optical fiber)
• Unguided media (wireless) — waves are not guided (eg. propagation through air, vacuum, and seawater)
• Direct link — a transmission path along which signals propagate from transmitter to receiver with no intermediate devices, other than devices for increasing signal strength (eg. ampilifiers, receivers). Applies to guided and unguided media.
• Point to point — a guided transmission medium which (1) provides a direct link between two devices and (2) only those two devices share the transmission medium.
• Multipoint — more than two devices share the same medium.

A transmission may be simplex, half duplex, or full duplex.

• Simplex — signals are transmitted in only one direction; one station is transmitter, the other is receiver.
• Half-duplex — both stations may transmit, but only one at a time.
• Full duplex — both stations may transmit simultaneously; signals are being carried in both directions at the same time.

Guided Transmission Media

Twisted Pair

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• The least expensive and most widely used guided transmission medium
• Attenuation is very strong with frequency
• Low noise immunity
  • Crosstalk is a problem
  • Poor channel characteristics
• Easy to install, repair, etc.
• Low cost

Coaxial Cable

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• Attenuation linear with frequency
• Better noise immunity
• Error rate:
  • baseband: $10^{-7}$
  • broadband: $10^{-9}$
• 1km baseband cable → 2Gbps
• 100km broadband cable → 300-450MHz
• Moderate cost