: Transmission media (fiber, copper, wireless), digital modulation, and how bits actually move across a wire. The Data Link Layer
: High-level protocols like DNS, HTTP, SMTP, and the architecture of the World Wide Web. Network Security Computer Networks Tanenbaum Slides
Andrew S. Tanenbaum’s Computer Networks remains a foundational resource for understanding network architecture through its "bottom-up" approach, beginning with hardware and progressing to software applications. : Transmission media (fiber
While many professors post their custom versions, you can find the official or highly-regarded versions here: Official Publisher Site (Pearson/Prentice Hall) Computer Networks Tanenbaum Slides