OSI Model Review

unit 4 test #1

OSI Model

A 7‑layer framework used to standardize networking functions and improve compatibility and troubleshooting.

Encapsulation

The process of wrapping data with headers and trailers as it moves down the OSI layers.

PDU (Protocol Data Unit)

The name for data at each OSI layer as it changes form during encapsulation.

Layer 7 Application

Provides network services to end users such as web browsing, email, and streaming; PDU = Data.

Layer 6 Presentation

Converts data between human and machine formats; handles encryption, compression, and file formats; PDU = Data.

Layer 5 Session

Establishes, maintains, and terminates communication sessions between applications; PDU = Data.

Layer 4 Transport

Chooses reliable (TCP) or unreliable (UDP) delivery; handles segmentation and error recovery; PDU = Segments.

TCP (Transmission Control Protocol)

Reliable, connection‑oriented transport protocol that ensures ordered, error‑checked delivery.

UDP (User Datagram Protocol)

Unreliable, connectionless transport protocol used for speed‑critical applications like streaming and gaming.

Layer 3 Network

Handles logical addressing and routing using IP; determines best path for packets; PDU = Packets.

IP Addressing

Logical addressing used to route packets across networks and the internet.

Layer 2 Data Link

Provides MAC addressing and LAN communication; handles framing and error detection; PDU = Frames.

MAC Address

A unique hardware address used for communication on the local network.

Layer 1 Physical

Defines electrical, optical, and radio signaling; cables, connectors, and bit transmission; PDU = Bits.

TCP/IP Model

A 4‑layer practical networking model used in real networks and the internet.

TCP/IP Application Layer

Combines OSI Layers 5–7; supports protocols like HTTP, FTP, DNS, and SMTP.

TCP/IP Transport Layer

Provides TCP and UDP services for end‑to‑end communication.

TCP/IP Internet Layer

Handles IP addressing and routing; includes IP and ICMP.

TCP/IP Network Access Layer

Covers physical and data link functions such as Ethernet, Wi‑Fi, and framing.

OSI vs TCP/IP

OSI has 7 layers for teaching; TCP/IP has 4 layers used in real‑world networking.

Routing

The process of selecting a path for traffic to travel across networks.

LAN (Local Area Network)

A network covering a small geographic area such as a home, school, or office.

WAN (Wide Area Network)

A network spanning large geographic areas, often connecting multiple LANs.