Detection: Techniques like parity checks, checksums, and Cyclic Redundancy Checks (CRC) add redundant information to the data. The receiver uses this information to determine if errors occurred during transmission.
Recovery (Correction): More advanced techniques, such as Forward Error Correction (FEC) codes or Automatic Repeat Request (ARQ), allow the receiver to either correct minor errors or request retransmission of corrupted data.

Multiplexing:

A technique that allows multiple data streams to share a single physical communication channel simultaneously, optimizing bandwidth usage.

FDM (Frequency Division Multiplexing): Divides the total bandwidth of a medium into multiple, non-overlapping frequency bands. Each data stream is assigned a different frequency band. Example: Radio broadcasting, where different stations transmit on different frequencies.
TDM (Time Division Multiplexing): Divides the access to a single channel into time slots. Each data stream is allocated a specific, recurring time slot to transmit its data. Example: Older digital telephone systems.
WDM (Wavelength Division Multiplexing): A form of FDM used in fiber optic communication, where multiple data streams are transmitted simultaneously using different wavelengths (colors) of light over a single optical fiber.
CDM (Code Division Multiplexing): Each data stream is given a unique "spreading code." All data streams transmit simultaneously over the same frequency band, but their unique codes allow the receiver to separate them. Example: CDMA cellular networks.

Spreading (Spread Spectrum):

A technique where a signal's bandwidth is intentionally spread over a much wider frequency band than the minimum required. This makes the signal more resistant to noise, interference, and jamming, and also allows for secure communication as it's harder to detect or intercept. CDMA is a type of spread spectrum technology.

Modulation:

The process of varying one or more properties (amplitude, frequency, or phase) of a periodic waveform (the carrier signal) with the information-carrying signal. This allows data to be transmitted efficiently over various media and facilitates multiplexing.

AM (Amplitude Modulation): Varies the amplitude (strength) of the carrier wave according to the data signal.
FM (Frequency Modulation): Varies the frequency of the carrier wave according to the data signal.
PM (Phase Modulation): Varies the phase of the carrier wave according to the data signal.
QAM (Quadrature Amplitude Modulation): Combines AM and PM to transmit more bits per symbol.

1.3 Network Topologies

Network topology refers to the geometric arrangement of devices and communication channels in a network. It can be physical (how cables are laid out) or logical (how data flows).

Bus Topology:
All devices are connected to a single central cable, called the backbone or bus. Data transmitted by one device travels along the bus and is seen by all other devices. Only one device can transmit at a time. Simple and inexpensive for small networks, but a break in the backbone cable brings down the entire network.