Elements of the Physical Layer

Communications Model

Source and destination are data terminating equipment (DTE).

Transmitter and receiver are data circuit terminating equipment (DCE).

<aside> 💡

</aside>

The communication process is as follows:

• The source is where the data is generated. Serves as an input to the transmitter.
• The transmitter transforms the data from the source (eg. 1s and 0s) into electromagnetic signals (energy).
• The transmission system (or transmission medium) is where the information, encoded as electromagnetic signals, travels to reach the destination.
• The receiver takes the signal from the transmission system and tries to transform it back into the source data form (eg. 1s and 0s). Serves as the input to the destination.
• The destination takes the incoming data from the receiver.

Signals

Transmission Terminology

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

</aside>

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.

Signal Types

Analog Signals

Also known as continuous signals.

The signal intensity varies in a smooth fashion over time.