Once you know what the data is, you learn how to move it reliably (TCP) or quickly (UDP). Network Layer:
The "killer app" of the internet is the web. By starting with HTTP and browsers, students immediately see the relevance. No one wakes up excited to learn about "Carrier Sense Multiple Access with Collision Detection" (CSMA/CD). But everyone wants to know why their Zoom call keeps freezing. The top-down approach answers the "Why?" before the "How?" computer networking top-down approach
At this layer, we learn about packets, IP addresses, and routing tables. How does your packet get from your laptop in New York to Google's server in California? We learn about hops, next-hop routing, and the magic of the IP address. Once you know what the data is, you
Now that the application has an IP address and a request, it must send it reliably. The application hands the HTTP data to the Transport Layer. No one wakes up excited to learn about
At the absolute bottom, we finally discuss the voltage levels, fiber optics, and radio frequencies. By the time we reach this point, the student already understands exactly what the physical layer is supposed to accomplish (moving a frame from switch A to switch B), which makes the physics much easier to digest.