OSI Model and Networking Fundamentals

A vocabulary-style set of flashcards covering OSI model concepts, layers, data units, signaling types, error checking, addressing, and foundational networking organizations.

OSI Model

Open Systems Interconnection reference model; a universal standard for networking that standardizes communications across LANs, MANs, WANs, and defines seven layers from Physical to Application.

Stack

A group of OSI layers treated as a unit; each layer provides services to the layer above and uses services from the layer below.

Physical Layer (Layer 1)

Bottom OSI layer responsible for transmitting raw bit streams over physical media; defines voltage levels, signaling, and physical connections.

Data Link Layer (Layer 2)

Second OSI layer that ensures error-free data transfer over the physical layer; includes framing, addressing, error detection; contains LLC and MAC sublayers.

Network Layer (Layer 3)

Third OSI layer that regulates movement of packets along network routes; handles physical and logical routes; acts as traffic director.

Transport Layer (Layer 4)

Fourth OSI layer that provides end-to-end delivery of data and ensures reliable transmission; may segment data into smaller units.

Session Layer (Layer 5)

Fifth OSI layer that establishes, maintains, and terminates communication sessions; coordinates data exchange and recovery from errors; supports TWA and TWS modes.

Presentation Layer (Layer 6)

Sixth OSI layer that formats, translates, and encrypts data for the application; handles encoding standards like ASCII and EBCDIC.

Application Layer (Layer 7)

Top OSI layer providing user applications access to network services; supports email, file transfer, remote access, and interaction with software.

Frame

Unit of data at the Data Link Layer; a structured data packet used for transmission over a network.

Packet

Discrete unit of data at the Network Layer; PDU that moves across networks and contains routing information.

Bit

The basic unit of data in digital communications; a 0 or 1.

CRC (Cyclic Redundancy Check)

An error-detection method used to verify data integrity in frames and packets.

LLC (Logical Link Control)

Data Link Layer sublayer responsible for flow control, error control, frame synchronization, and avoiding network congestion.

MAC (Media Access Control)

Data Link Layer sublayer that handles physical addressing and access control to the network medium.

MAC Address

A unique 48-bit hardware address assigned to a network interface; often shown as hexadecimal like 00:04:AC:84:28:DE.

OUI (Organizationally Unique Identifier)

The first half of a MAC address identifying the vendor/manufacturer; the second half is the interface-specific identifier.

ASCII

An 8-bit character coding method that supports 128 characters; commonly used with UNIX/Linux, Windows, and Mac OS X.

EBCDIC

Extended Binary Coded Decimal Interchange Code; an 8-bit character encoding used by IBM and some older systems.

Digital Signal

A signal that uses discrete voltage levels to represent binary data (0s and 1s); preferred for LANs and high-speed WANs.

Analog Signal

A continuous signal with varying voltage or wavelength; examples include natural voice, light, radio signals.

EMI (Electromagnetic Interference)

Interference caused by magnetic fields from electrical devices that disrupt signal transmission.

RFI (Radio Frequency Interference)

Interference from devices emitting radio waves (e.g., radios, TVs) that disrupt signals.

TWA (Two-Way Alternate / Half-Duplex)

Half-duplex communication where only one direction at a time is allowed (e.g., walkie-talkie).

TWS (Two-Way Simultaneous / Full-Duplex)

Full-duplex communication where sending and receiving occur simultaneously.

Discovery (Network Layer)

Process of gathering location information about networks/nodes to determine efficient routes using metrics.

Encapsulation (OSI concept)

Process of moving data from a higher layer to a lower layer, with each layer adding its own header/trailer for transmission.

Logical vs Physical Routes

Physical routes are actual cables/wireless paths; logical routes are software-based routing paths.

Gateway

A device or software that connects different networks and enables inter-network communication.

IEEE

Institute of Electrical and Electronics Engineers; international organization focused on advancing technology.

ANSI

American National Standards Institute; private, non-profit that monitors standards for US enterprises, government, and international groups.

ITU

International Telecommunication Union; United Nations agency dedicated to safety and quality of ICT products and services.

ISO

International Organization for Standardization; non-governmental federation of national standards bodies; develops and publishes standards.

Network Topology (Physical Layer context)

The physical layout of network connections; a concept managed at the Physical Layer.

Layer-to-Hardware Mapping (OSI)

Corresponding hardware/software shown for each OSI layer (e.g., NICs, MAC/LLC, routers, switches, gateways).