Layer 1 Review and Network Fundamentals

Vocabulary review covering OSI Layer 1 (Physical layer) concepts, transmission media, signaling characteristics, hardware, and foundational Layer 2 distinctions.

Physical layer

OSI Layer 1; the layer that sends and receives raw bits as signals over a medium.

Bit

A binary value of 0 or 1.

Signal

A changing electrical, optical, or radio quantity used to represent information.

Medium

The physical path that carries a signal, such as copper, fiber, or air.

Amplitude

The strength or size of a signal wave.

Frequency

How many cycles of a repeating wave occur each second, measured in hertz (Hz).

Wavelength

The physical distance covered by one complete wave cycle.

Modulation

Changing a carrier signal’s properties so it can represent data.

Attenuation

Signal loss as it travels through a medium or over distance.

Interference

Unwanted energy that disrupts a signal.

Electromagnetic interference (EMI)

Interference from electrical or electromagnetic sources, such as motors or power cables.

Crosstalk

Unwanted signal energy from one wire pair leaking into another pair.

Signal-to-noise ratio (SNR)

The strength of the wanted signal compared with background noise.

Twisted-pair cable

Copper Ethernet cable with insulated wire pairs twisted together to reduce interference.

UTP

Unshielded twisted pair; twisted-pair cable without added conductive shielding.

STP

Shielded twisted pair; twisted-pair cable with shielding to help limit interference.

Fiber-optic cable

A cable that carries information as pulses of light through glass or plastic fiber.

RJ45 (8P8C) connector

The familiar modular connector commonly used on Ethernet patch cables.

Bandwidth / link capacity

The rated or theoretical maximum data rate a link can carry; the word also has a frequency-range meaning in signal theory.

Throughput

The data rate actually achieved over a link under real conditions.

Duplex

The direction pattern for communication: half-duplex takes turns; full-duplex sends both ways at once.

Repeater

A physical-layer device that regenerates or retransmits a signal to extend a link.

Hub

A multiport repeater that repeats incoming bits to its other ports.

Transceiver

A device or module that both transmits and receives signals.

Media converter

A device that changes a signal from one media type to another, such as copper Ethernet to fiber.

Power over Ethernet (PoE)

A method for delivering electrical power and data over Ethernet cabling.

Frame

A Layer 2 unit of data that organizes bits and includes link-level information such as MAC addresses.

MAC address

A link-layer address used to identify a network interface on a local network.

Encapsulation

Adding protocol information as data moves down network layers; at Layer 2, data is placed into a frame before Layer 1 transmits its bits.

WPA2 / WPA3

Wi-Fi security protocols at the data-link layer; they protect wireless communication, while Layer 1 carries the radio signal.