問68
頻出度★★★
室内で複数のコンピュータを接続する LAN を構築したい。必要なものはどれか。
平成23年度 秋期 ITパスポート試験 問68
テクノロジ系ネットワーク › ネットワーク方式
This question's explanation and your answers so far.
解説
問 68
Incorrectア
The Internet is a wide-area network (the WAN side) formed by interconnecting networks all over the world, and it lies outside the LAN. What this question asks for is interconnecting several computers within the limited area of a room, and there is no need to communicate with the outside. In fact, a LAN in which the PCs in a room share files and share printers works perfectly well even with no Internet connection at all. In other words, the Internet is not an essential element for building a LAN; it is merely something you connect to as needed after the LAN is in place, so this choice is wrong.
Incorrectイ
A splitter is a device used on an ADSL line to separate and combine the low-frequency signals for voice calls and the high-frequency signals for data communication that share a single telephone line. Its job is to make it possible to use a telephone and an ADSL modem at the same time over the same line, and it is installed near the point where the telephone line enters the premises. It is ultimately a device for making use of an external line (the WAN side), and it has no function for interconnecting the computers inside a room, so this choice is wrong.
- ウ
正解 The correct answer is ウ. A LAN (Local Area Network) is a network that interconnects devices such as computers and printers within a limited area, for example a single building, room, or floor. This question asks about the most basic case of that: building a wired LAN that connects several computers inside one room. With only two computers you could connect them directly with a single cable, but as soon as you want to link three or more devices to each other, you inevitably need a device that gathers the LAN cables coming from each machine in one place and relays and distributes the signals. That concentrating device is the hub. A hub has multiple LAN ports, and it passes data received on one port out to the other ports, so that every connected device joins the same network. The arrangement in which devices radiate out by cable from a hub at the center is called a star topology, and it is the standard configuration of wired LANs today. Note that early repeater hubs simply sent the data they received out to every port, whereas the switching hubs (Layer 2 switches) that are widespread today learn the MAC addresses of the connected devices and send data only to the destination port, so needless traffic is reduced and efficiency is better. Either way, they share the same role of being a concentrating device that brings multiple computers together into one LAN, so what is needed to build a LAN in a room is ウ, the hub.
Incorrectエ
A modem (MODEM, modulator-demodulator) is a device that converts (modulates) the digital signals handled by a computer into signals that can be sent over an analog line such as a telephone line, and on reception converts them back (demodulates) into the original digital signals. In other words, it is a WAN-side device used when connecting a LAN to an external communication line, that is, when connecting to the Internet, and it plays no part in linking together the several computers inside a room. It is unnecessary in a room LAN that makes no external connection, so this choice is wrong.
ここがポイント
- The role of a LAN and a hub — A LAN (Local Area Network) is a network that interconnects devices within a limited area such as a building or a room. To connect three or more computers with cables, you need a concentrating device that gathers the cables in one place and relays the signals, namely a hub; the configuration in which devices radiate out from a hub at the center is called a star topology. The switching hubs that are mainstream today learn MAC addresses and forward data only to the destination port.
- Telling LAN-side devices from WAN-side devices — Hubs, switches, LAN cables, and wireless LAN access points are the devices that make up the inside of a LAN. Modems, splitters, ONUs, and the WAN side of a router, on the other hand, are devices for connecting to an external line, and they are unnecessary in a room LAN that does not connect to the Internet.
用語