1Standards and Concepts

• 1.1Network components and basic concepts

  Covers the correspondence between the layered TCP/IP model and the OSI reference model, encapsulation that wraps upper-layer data in lower-layer headers, the difference between a frame (L2) and a packet (L3), and the two kinds of addressing—MAC address and IP address—as the foundation for telling which layer a symptom belongs to.

• 1.2Bandwidth and throughput

  Covers the difference between bandwidth (a link's theoretical maximum capacity) and throughput (the actual effective amount that flows), latency as a measure of delay, and the difference between a speed test (against a server) and iperf (between two points)—framed as the judgment of using numbers to isolate a "it is slow" complaint.

• 1.3Network types and topologies

  Covers "network types" classified by scale—LAN/WAN/MAN/CAN/PAN/WLAN—and the difference between physical topology (how devices are actually cabled) and logical topology (how data flows), as the foundation for telling "what scale a situation is about" and "whether a diagram shows wiring or flow."

• 1.4Cloud and on-premises

  Covers the difference between on-premises (devices in your own facility) and cloud (using a provider's infrastructure), the cloud service models SaaS/PaaS/IaaS, the deployment models public/private/hybrid cloud, and the spread of remote work and hybrid work, as basic judgment about "which model fits a requirement."

• 1.5Common applications and protocols

  Covers choosing between reliable connection-oriented TCP and low-latency connectionless UDP, plus common protocols and port numbers—HTTP/HTTPS, DNS, DHCP, FTP/SFTP/TFTP, NTP, and ICMP—as the foundation for identifying "which port, and TCP or UDP" a given communication uses.