🌐 Network Models

Understanding network models is crucial to grasp how data moves across devices and networks. The most commonly used model is the OSI (Open Systems Interconnection) model, which organizes network functions into layered architecture.

🧱 The OSI Model (7 Layers)

The OSI model breaks down network communication into 7 layers:

🧍 Application Layer (Layer 7)
Interfaces directly with the user. Protocols: HTTP, FTP, DNS
🪄 Presentation Layer (Layer 6)
Formats data — encryption, compression, encoding.
🎭 Session Layer (Layer 5)
Manages sessions and connections between systems.
🚛 Transport Layer (Layer 4)
Ensures end-to-end delivery. Protocols: TCP, UDP
🏷️ Network Layer (Layer 3)
Handles IP addressing and routing. Protocols: IP, ICMP
📦 Data Link Layer (Layer 2)
Manages MAC addressing and frame delivery.
🧾 Physical Layer (Layer 1)
Deals with raw bits — cables, signals, and transmission mediums.

🧠 Tip: Think of it as a package delivery system — from preparing the item to shipping and finally handing it to the recipient.

🧱 What Are Frames?

A frame is a data packet at Layer 2 (Data Link). It includes:

Destination & source MAC addresses
Payload (actual data)
Error checking info (like CRC)

Frames are used in LAN (Local Area Network) environments for delivering data across the same network.

🆔 What is a MAC Address?

A MAC address (Media Access Control) is a unique hardware identifier assigned to a network interface card (NIC).
Format: 00:1A:2B:3C:4D:5E (48-bit address)

It operates at the Data Link Layer
Used for local communication
Cannot be routed across different networks

🔐 Think of MAC as your device’s permanent "name tag" on a local network.

🔌 Ports and Services

Ports are like virtual doors on your device, allowing it to handle multiple services and applications simultaneously. Each service communicates using a specific port number and protocol (TCP or UDP).

Here are some common ports and the services they represent:

HTTP (Port 80, TCP):
Used for unencrypted web traffic.
HTTPS (Port 443, TCP):
Secure version of HTTP, used for encrypted web traffic.
FTP (Port 21, TCP):
Used for transferring files between computers.
DNS (Port 53, UDP/TCP):
Resolves domain names to IP addresses.
SSH (Port 22, TCP):
Provides secure remote access to devices.

🎯 Ports are handled by the Transport Layer (Layer 4) and can use either TCP (connection-oriented) or UDP (connectionless) depending on the service.

🌍 IP Address Types

There are two main IP versions: IPv4 and IPv6.

IPv4

Format: 192.168.1.1
32-bit address
~4.3 billion possible addresses

IPv6

Format: 2001:0db8:85a3::8a2e:0370:7334
128-bit address
Designed to solve IPv4 exhaustion

IP Address Categories:

Public IP – Routable on the internet
Private IP – Used within LAN (e.g., 192.168.x.x)
Static IP – Manually assigned
Dynamic IP – Assigned via DHCP

✅ Summary

By understanding these core networking concepts, you're building the foundation for:

Diagnosing network issues
Configuring network devices
Preparing for deeper networking topics

📁 Next Up: Cables, Connectors & Topologies ➡️