1.3Network types and topologies

Networks are named by scale, and the name is a signpost for "how far, and under whose responsibility" something is handled. Whether the matter is inside one room (a LAN) or spans cities and countries (a WAN) changes both who to contact and how to respond. This section covers network types classified by scale and the difference between how devices are connected (physical topology) and how data flows (logical topology), as the basis for correctly reading diagrams and situations.

1.3.1Network types by scale

• A LAN (Local Area Network) covers a limited area such as one building or floor—an office or home under a switch. A WAN (Wide Area Network) spans cities, countries, or continents, linking sites over carrier circuits; the internet is a vast collection of WANs.
• A MAN (Metropolitan Area Network) is city-scale (between LAN and WAN), linking multiple sites within a city. A CAN (Campus Area Network) spans multiple buildings across a campus of a university or company. The scale ordering LAN < CAN < MAN < WAN helps keep them straight.
• A PAN (Personal Area Network) is a tiny network within a few meters around a person (a personal range like Bluetooth earbuds or phone tethering). A WLAN (Wireless LAN) is a LAN made wireless with Wi-Fi—the same area as a LAN, but connecting via radio rather than cable.

1.3.2Physical vs. logical topology

• Physical topology is the visible shape of how devices and cables are actually arranged and wired. Typical examples: star (all devices connect to a central switch), bus (all along one trunk), ring (connected in a loop), and mesh (richly interconnected). Rack and cabling diagrams mainly show this.
• Logical topology is the logical shape of how data actually flows, which may not match the physical wiring. For instance, even when the physical shape is a star (all devices gathered on a switch), within one segment a broadcast reaches everyone, so the flow (logical) must be considered separately from the wiring diagram.

On the help desk you are juggling several tickets. The first: "cannot print to the printer on the same floor." This is within one building—the LAN scope—so what to check is the nearby switch and the PC's LAN settings, not to call an outside carrier. The second: "the leased line to a branch in another prefecture is down." This spans sites—the WAN scope—so checking beyond the demarcation point, with the carrier, comes into view. Determining "which type (scale) the matter is" first naturally settles who to ask and what to check. Next, suppose you look at a network diagram from a branch and think, "it is a star where everything gathers on the switch, so if one device breaks the others are unaffected." Here lies the pitfall of confusing physical and logical. Even if the wiring shape (physical topology) is a star, if those devices are in the same segment (one logical island), a broadcast storm or loop affects the whole island—in terms of data flow (logical topology), they are all "one connected land." When you read a diagram, always be conscious of whether it depicts the shape of the wiring or the flow of data—this small effort prevents mistaken root-cause isolation. At the introductory stage, having an accurate measuring stick of classification—"type (scale)" and "physical/logical"—matters more than complex calculation and becomes the foundation for every later chapter.

1.3.3Section summary

• Networks classify by scale: PAN (meters) < LAN/WLAN (a building) < CAN (campus) < MAN (city) < WAN (wide area)
• Physical topology is the wiring shape (star, etc.); logical topology is how data flows—the two may not match
• Determining "which type (scale)" a matter is first settles who to check with (internal or a WAN carrier) and the direction of the response