3Endpoints and Media Types

• 3.1Cables and connectors

  Covers the difference between copper twisted pair (Cat5e/6/6a, up to about 100 m, subject to EMI) and optical fiber (single-mode (SMF) for long distance with a laser vs. multimode (MMF) for medium distance with an LED), plus the common connectors coax, RJ-45, RJ-11, and fiber connectors, framed as the judgment of "which cable for this distance and environment."

• 3.2Wi-Fi, cellular, and wired differences

  Organizes the license-free 2.4/5/6 GHz bands used by Wi-Fi (802.11), the non-overlapping channels 1/6/11 on the congestion-prone 2.4 GHz, interference sources like microwave ovens and Bluetooth, and the difference from licensed cellular—framed as the judgment of choosing "wireless or wired" and "which band" by situation.

• 3.3Endpoint devices

  Covers the roles and identification of endpoints at the edge of the network—PCs, mobile devices, IP phones, network printers, servers, and IoT devices—through the lens of "what does this device provide, and what to check when it will not connect."

• 3.4Establishing and verifying connections per OS

  Covers the network utilities on Windows/Linux/macOS/Android/iOS, how to run troubleshooting commands like ping and ipconfig (Windows) / ifconfig and ip (Linux), and the wireless-client settings (SSID, authentication, WPA mode), framed as the procedure of "how to verify and connect on each OS."