Computer network – definition
A collection of connected devices that communicate to exchange data and share resources such as files, printers, or internet connections.
PAN (Personal Area Network)
Smallest network type used for personal devices (e.g., Bluetooth, phone tethering). Covers a few meters.
LAN (Local Area Network)
Connects devices within a limited area such as a building or school. High speed, low latency, privately managed.
WLAN (Wireless LAN)
A LAN that uses wireless communication (Wi‑Fi) instead of cables. Typically uses access points for connectivity.
MAN (Metropolitan Area Network)
Covers a city or campus area; connects multiple LANs. Example: city‑wide fiber network.
WAN (Wide Area Network)
Covers large geographic areas and connects multiple LANs or MANs via routers and leased lines. Example: the Internet.
Router – function
Connects multiple networks together, forwards packets based on IP addresses, and operates at OSI Layer 3 (Network).
Switch – function
Connects devices in the same LAN, forwards frames based on MAC addresses, and operates at OSI Layer 2 (Data Link).
Hub – function
Simple device that broadcasts all incoming data to every port. Operates at OSI Layer 1 (Physical); inefficient due to collisions.
Access point – function
Provides wireless connectivity for client devices and bridges them to the wired LAN. Operates at Layer 2.
Server – function
A computer that provides resources or services (e.g., web, file, email) to clients over a network.
Client – function
A device or program that requests services or resources from a server (e.g., web browser requesting a web page).
TCP (Transmission Control Protocol)
Ensures reliable, ordered, error‑checked delivery of data between devices. Connection‑oriented and used by HTTP, FTP, email.
IP (Internet Protocol)
Defines addressing and routing of packets between networks using IP addresses. Operates at OSI Layer 3.
HTTP (Hypertext Transfer Protocol)
Protocol for transferring web pages. Operates at the application layer and uses TCP port 80.
HTTPS (HTTP Secure)
HTTP encrypted with SSL/TLS for confidentiality, integrity, and authentication. Uses TCP port 443.
FTP (File Transfer Protocol)
Transfers files between client and server. Uses TCP ports 20/21. Reliable but not encrypted by default.
DNS (Domain Name System)
Translates domain names (e.g., example.com) into IP addresses. Uses UDP/TCP port 53.
SMTP (Simple Mail Transfer Protocol)
Sends emails from client to server or between mail servers. Uses TCP port 25.
POP3 (Post Office Protocol v3)
Retrieves emails from a server and downloads them to a client. Uses TCP port 110.
IMAP (Internet Message Access Protocol)
Retrieves and synchronizes emails between client and server. Keeps copies on the server. Uses TCP port 143.
OSI layers
- Physical 2. Data link
- Network 4. Transport
- Session 6. Presentation
- Application
OSI Model – overview
A conceptual model dividing network communication into seven layers. Each layer provides services to the layer above.
Layer 1 – Physical
Transmits raw bits over a medium (cables, radio). Defines voltages, connectors, timing. Devices: hubs, cables.
