Protocols and Addressing

Network protocols are agreed rules that let devices exchange data without knowing each other's internal design. Addressing schemes give every device and service a reachable identity. Together, they solve the fundamental problem of networking: getting data from here to there, intact, across systems built by different people.

This course covers the protocol stack from physical framing through transport delivery, and the addressing at each layer that makes forwarding decisions possible.

Layered architecture

Network communication is organized in layers. Each layer has one job and relies on the layer below it for delivery.

The TCP/IP model uses four layers:

• Link layer. Moves frames between directly connected devices on a single network segment. Handles physical addressing (MAC), media access, and error detection for one hop.
• Internet layer. Moves packets across network boundaries using logical addressing (IP). Makes routing decisions to reach distant destinations.
• Transport layer. Provides end-to-end communication between applications. Adds port numbers, and optionally reliability and flow control.
• Application layer. Implements the actual service: HTTP, DNS, SMTP, SSH, and everything else a user or program interacts with.

The OSI seven-layer model provides finer distinctions (splitting the link layer into physical and data-link, and adding session and presentation layers), but TCP/IP is how the internet actually works. Use OSI vocabulary when it clarifies a specific boundary; use TCP/IP layers for operational thinking.

Encapsulation