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Module 2: Network Models

To understand how networks function, we use reference models that break down communication into layers. The two most important models are OSI and TCP/IP.
OSI Model vs TCP/IP Model

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2.1 The OSI Model

The Open Systems Interconnection (OSI) model has 7 layers.
  1. Physical Layer: Bits, cables, signals.
  2. Data Link Layer: Frames, MAC addresses, switching.
  3. Network Layer: Packets, IP addresses, routing.
  4. Transport Layer: Segments, TCP/UDP, reliability.
  5. Session Layer: Session management.
  6. Presentation Layer: Data formatting, encryption.
  7. Application Layer: User applications (HTTP, SMTP).

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2.2 The TCP/IP Model

The TCP/IP model is the practical implementation used in the Internet today. It condenses the OSI layers into 4 (or 5) layers.
  1. Network Interface (Physical + Data Link)
  2. Internet (Network)
  3. Transport (Transport)
  4. Application (Session + Presentation + Application)

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2.3 Encapsulation

Data is wrapped with headers (and trailers) as it moves down the layers.
  • Application: Data
  • Transport: Segment (Data + TCP Header)
  • Internet: Packet (Segment + IP Header)
  • Link: Frame (Packet + Frame Header + Trailer)
Packet Encapsulation

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Next Module

Module 3: Physical & Data Link

Explore the bottom layers of the stack.