Network Basics & Models

Foundation Module - Learn how networks are structured and organized

What You'll Learn

1. Understand network types and topologies
2. Master the OSI 7-layer model
3. Compare OSI with TCP/IP model
4. Know common protocols at each layer

1. Introduction to Networks

What is a Computer Network? A network is a collection of interconnected devices (nodes) that can share resources and communicate.

Network Types by Size

Network Topologies

Bus Topology:          Star Topology:
                              Hub
[PC1]--[PC2]--[PC3]      PC1   |   PC3
       |                    \  |  /
      Bus                     Hub
                              |
                            PC2

Ring Topology:         Mesh Topology:
    [PC1]                  PC1----PC2
   /     \                  | \  / |
[PC4]    [PC2]              |  \/  |
   \     /                  | /\  |
    [PC3]                  PC3----PC4

2. OSI Model (7 Layers)

Open Systems Interconnection - Standard reference model for network communication.

Layer 7: Application    - User interface (HTTP, FTP, SMTP)
Layer 6: Presentation   - Data format, encryption (SSL, JPEG)
Layer 5: Session        - Session management (NetBIOS)
Layer 4: Transport      - End-to-end delivery (TCP, UDP)
Layer 3: Network        - Routing, IP addressing (IP, ICMP)
Layer 2: Data Link      - MAC addressing, framing (Ethernet)
Layer 1: Physical       - Bits on wire (Cables, Hubs)

Memory Trick: "All People Seem To Need Data Processing" (Application → Physical, top to bottom)

OSI Layers Detailed

PDU = Protocol Data Unit (what data is called at each layer)

3. TCP/IP Model (4 Layers)

The practical model used by the Internet.

TCP/IP Model          OSI Model
                    
Application    ←→   Application, Presentation, Session
Transport      ←→   Transport
Internet       ←→   Network
Network Access ←→   Data Link, Physical

TCP/IP Layers

4. OSI vs TCP/IP Comparison

5. Common Protocols Summary

Application Layer

• HTTP/HTTPS: Web browsing (port 80/443)
• FTP: File transfer (port 21)
• SMTP: Sending email (port 25)
• POP3/IMAP: Receiving email (port 110/143)
• DNS: Domain name resolution (port 53)
• Telnet/SSH: Remote access (port 23/22)

Transport Layer

• TCP: Reliable, connection-oriented
• UDP: Fast, connectionless

Network Layer

• IP: Logical addressing
• ICMP: Error reporting (ping)
• ARP: IP to MAC resolution

Key Takeaways

Remember:

• Data flows DOWN at sender, UP at receiver
• Each layer adds its header (encapsulation)
• Router works at Layer 3, Switch at Layer 2