1. Internet
The internet is a global network of interconnected computers and devices.
It enables sharing of information, resources, and communication worldwide.
Uses protocols like TCP/IP to transmit data.
2. WAN (Wide Area Network)
Covers a large geographical area, such as cities, countries, or continents.
Connects multiple LANs and MANs.
Example: The internet itself is the largest WAN.
3. MAN (Metropolitan Area Network)
Covers a medium-sized area, like a city or campus.
Larger than a LAN but smaller than a WAN.
Example: A city’s public Wi-Fi network or a university campus network.
4. LAN (Local Area Network)
Covers a small area, like a single building, office, or home.
Usually used for internal communication and resource sharing.
Example: Wi-Fi in an office or home.
5. PAN (Personal Area Network)
Covers a very small area, typically around a single person.
Used for personal devices like smartphones, laptops, or wearables.
Example: Bluetooth connections between a phone and headphones.
OSI MODEL -
The OSI (Open Systems Interconnection) model is a conceptual framework that standardizes how data is transmitted over a network. It has seven layers, each with specific responsibilities:
1. Physical Layer
Purpose: Handles the physical connection between devices.
Key Functions:
Transmitting raw bits (0s and 1s) over a physical medium like cables or wireless signals.
Ensures proper voltage, signal timing, and data rates.
Examples: Ethernet cables, Wi-Fi, Bluetooth.
2. Data Link Layer
Purpose: Ensures error-free data transfer between two directly connected nodes.
Key Functions:
Frame creation and error detection.
MAC (Media Access Control) addressing.
Examples: Switches, MAC addresses, Ethernet.
3. Network Layer
Purpose: Handles data routing, forwarding, and addressing across networks.
Key Functions:
Determines the best path for data packets.
Uses logical addressing (IP addresses).
Examples: Routers, IP addresses, IPv4/IPv6.
4. Transport Layer
Purpose: Ensures reliable data transfer between systems.
Key Functions:
Error checking, data segmentation, and flow control.
Protocols like TCP (reliable) and UDP (unreliable).
Examples: TCP, UDP, ports (e.g., 80 for HTTP).
5. Session Layer
Purpose: Manages sessions (dialogues) between applications.
Key Functions:
Establishes, maintains, and terminates connections.
Synchronizes data exchange.
Examples: APIs, session management protocols.
6. Presentation Layer
Purpose: Ensures data is in a readable format for applications.
Key Functions:
Data encryption, compression, and translation.
Converts data formats (e.g., JPEG, MP3).
Examples: SSL/TLS encryption, data format translation.
7. Application Layer
Purpose: Provides services and interfaces for user applications.
Key Functions:
Interacts directly with software applications.
Handles high-level protocols like HTTP, FTP, SMTP.
Examples: Web browsers, email clients, FTP tools.
TCP/IP Models -
The TCP/IP model (Transmission Control Protocol/Internet Protocol model) is a simplified version of the OSI model. It is widely used in network communication and has four layers:
1. Application Layer
Purpose: Provides services and interfaces for end-user applications.
Combines the functions of the OSI model's Application, Presentation, and Session layers.
Key Protocols:
HTTP/HTTPS: Web browsing.
SMTP/IMAP/POP3: Email communication.
FTP: File transfer.
DNS: Domain name resolution.
Examples: Web browsers, email clients, file transfer tools.
2. Transport Layer
Purpose: Ensures reliable or fast delivery of data between devices.
Responsible for error checking, data segmentation, and flow control.
Key Protocols:
TCP (Transmission Control Protocol): Reliable, ordered, and connection-oriented.
UDP (User Datagram Protocol): Fast, connectionless, and best-effort.
Examples: Video streaming (UDP), web browsing (TCP).
3. Internet Layer
Purpose: Handles addressing, routing, and packet forwarding across networks.
Equivalent to the OSI model's Network Layer.
Key Protocols:
IP (Internet Protocol): Provides logical addressing (IPv4, IPv6).
ICMP (Internet Control Message Protocol): Used for diagnostics (e.g., ping).
ARP (Address Resolution Protocol): Maps IP addresses to MAC addresses.
Examples: Routers, IP addresses, network gateways.
4. Network Access Layer (or Link Layer)
Purpose: Manages data transfer between devices on the same network.
Combines the functions of the OSI model's Physical and Data Link layers.
Key Protocols:
Ethernet: Wired communication.
Wi-Fi: Wireless communication.
PPP (Point-to-Point Protocol): For direct communication between two nodes.
Examples: Ethernet cables, switches, Wi-Fi access points.
HTTP AND HTTPS PORT -
HTTP (HyperText Transfer Protocol)
Port: 80 (default).
Purpose: Used for transmitting unencrypted data between a web browser and a web server.
Security: Not secure; data is sent as plain text, vulnerable to interception.
HTTPS (HyperText Transfer Protocol Secure)
Port: 443 (default).
Purpose: Used for transmitting encrypted data using SSL/TLS for secure communication.
Security: Provides encryption, authentication, and data integrity.
Routers & Switches -
1. Routers
Purpose: Connects multiple networks and directs data packets between them.
Functionality:
Routes data based on IP addresses.
Connects local networks (LANs) to larger networks (e.g., the internet).
Can provide network address translation (NAT) and assign IP addresses using DHCP.
Example Use: Connecting a home network to the internet.
Key Feature: Operates at the Network Layer (Layer 3 of the OSI model).
2. Switches
Purpose: Connects multiple devices within the same network (LAN).
Functionality:
Directs data based on MAC addresses.
Creates a network where devices can communicate directly.
Reduces network congestion by sending data only to the intended recipient.
Example Use: Connecting computers, printers, and servers in an office.
Key Feature: Operates at the Data Link Layer (Layer 2 of the OSI model).