Physical Layer Terms and Definitions

Physical Layer

The lowest layer in the OSI model responsible for transmitting raw bits over a physical medium.

Guided Transmission Media

Transmission media that uses a physical path like wires or fiber optics to transmit data.

Unguided Transmission Media

Transmission that uses wireless methods like radio waves, microwaves, or infrared.

Persistent Storage

Storage devices used to transport data physically (e.g., hard drives, tapes).

Twisted Pair

A pair of copper wires twisted together to reduce electromagnetic interference.

UTP (Unshielded Twisted Pair)

Twisted pair cable without additional shielding, commonly used in LANs.

STP (Shielded Twisted Pair)

Twisted pair cable with shielding to reduce interference.

Cat 5

A category of UTP cable used for Fast Ethernet (100 Mbps).

Cat 5e

Enhanced Cat 5, used for Gigabit Ethernet (1 Gbps).

Cat 6

UTP cable used for 10-Gigabit Ethernet over short distances.

Cat 6A

Higher-quality Cat 6 cable supporting better performance.

Cat 7

Shielded Ethernet cable, rarely used in standard installations.

Cat 8

High-performance cable for data centers, supports very high speeds.

RJ11

Connector with 4 wires, used for telephone lines.

RJ45

Connector with 8 wires, used in Ethernet cables.

Simplex Link

A one-way communication link; data flows in only one direction.

Half-Duplex Link

Data flows in both directions, but not at the same time.

Full-Duplex Link

Data can flow in both directions simultaneously.

Coaxial Cable

A type of cable with better shielding and bandwidth than twisted pair.

Power Lines

Household electrical wiring that can be used for data transmission, though not ideal.

Fiber Optics

Transmission medium using light through glass fibers for high-speed, long-distance data transmission.

Single-Mode Fiber

Fiber optic cable with a narrow core, used for long-distance, high-speed communication with lasers.

Multi-Mode Fiber

Fiber optic cable with a wider core, used for shorter distances with LED light sources.

TAT-14

A transatlantic fiber optic cable system for communication across oceans.

Electromagnetic Spectrum

Range of all frequencies of electromagnetic radiation used for communication.

FHSS (Frequency Hopping Spread Spectrum)

A method of transmitting radio signals by rapidly switching frequencies.

DSSS (Direct Sequence Spread Spectrum)

A technique that spreads signals across a wider bandwidth using a pseudorandom code.

UWC (Ultra-Wideband Communication)

A wireless technology that transmits data over a wide frequency spectrum at low power.

Radio Transmission

Wireless transmission using radio waves; good building penetration and range.

Microwave Transmission

Line-of-sight wireless communication using high-frequency microwaves.

Infrared Transmission

Short-range wireless transmission using infrared light; requires line-of-sight.

Light Transmission

Communication using lasers or LEDs for high-speed, secure transmission.

Modulation

The process of varying a signal to encode data.

Multiplexing

Combining multiple signals for transmission over a single communication channel.

FDM (Frequency Division Multiplexing)

Multiplexing technique using different frequency bands for each signal.

TDM (Time Division Multiplexing)

Multiplexing that shares channel time between multiple signals.

CDMA (Code Division Multiple Access)

A multiplexing method where each signal is encoded with a unique code.

WDM (Wavelength Division Multiplexing)

Multiplexing technique used in fiber optics where different wavelengths carry different signals.

PSTN (Public Switched Telephone Network)

The traditional circuit-switched telephone network for voice communication.

Local Loop

The connection from a subscriber’s premises to the telephone company's central office.

ADSL (Asymmetric Digital Subscriber Line)

A type of DSL where download speed is greater than upload speed.

FttH (Fiber to the Home)

A broadband network architecture that delivers optical fiber directly to residences.

POP (Point of Presence)

A physical location where different networks or communication devices interconnect.

LEC (Local Exchange Carrier)

A company that provides local telephone service.

IXC (Interexchange Carrier)

A company that provides long-distance communication services.

POTS (Plain Old Telephone Service)

Traditional analog telephone service.

DSL (Digital Subscriber Line)

A family of technologies that provide internet access via telephone lines.

OFDM (Orthogonal Frequency Division Multiplexing)

A digital modulation method using multiple carrier frequencies.

PCM (Pulse Code Modulation)

A method of converting analog signals to digital form using sampling.

SONET (Synchronous Optical Network)

A standardized protocol that transfers multiple digital bit streams over optical fiber.

SDH (Synchronous Digital Hierarchy)

The international equivalent of SONET for optical data transport.

STS (Synchronous Transport Signal)

The basic building block of SONET used to carry data.

Circuit Switching

A communication method where a dedicated circuit is established for the entire duration of a transmission.

Packet Switching

A method of data transmission where data is broken into packets and sent independently over the network.

1G

First-generation mobile networks using analog voice (e.g., AMPS).

AMPS (Advanced Mobile Phone System)

An early analog mobile phone system in North America.

2G

Second-generation networks using digital voice and basic data.

GSM (Global System for Mobile Communications)

A standard for 2G digital cellular networks.

3G

Third-generation networks offering faster data and improved voice quality (e.g., UMTS).

UMTS (Universal Mobile Telecommunications System)

A 3G mobile cellular system using CDMA.

HSPDA (High-Speed Downlink Packet Access)

A 3G enhancement providing faster download speeds.

4G

Fourth-generation mobile networks offering high-speed data (e.g., LTE).

LTE (Long Term Evolution)

A standard for 4G mobile communication with high data rates.

IPv6

Internet Protocol version 6, designed to replace IPv4 with more address space.

OFDMA (Orthogonal Frequency Division Multiple Access)

A method of encoding digital data on multiple carrier frequencies.

MIMO (Multiple Input Multiple Output)

Wireless technology that uses multiple antennas to improve performance.

5G

Fifth-generation mobile networks with ultra-fast speeds and low latency.

DOCSIS (Data Over Cable Service Interface Specification)

A telecommunications standard for internet over cable TV systems.

ISP (Internet Service Provider)

A company that provides internet access to users.

HFC (Hybrid Fiber-Coax)

A broadband network combining optical fiber and coaxial cable.

GEO (Geostationary Earth Orbit)

Satellites that remain in a fixed position relative to the Earth's surface.

LEO (Low Earth Orbit)

Satellites that orbit closer to Earth and offer lower latency.

MEO (Medium Earth Orbit)

Satellites with altitudes between LEO and GEO.

VSAT (Very Small Aperture Terminal)

A satellite communication system for remote internet access.

Starlink

A satellite internet constellation project developed by SpaceX for global coverage.