問71
頻出度★★★
WANに関する記述として，最も適切なものはどれか。
平成25年度 秋期 ITパスポート試験 問71
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 71
Incorrectア
A line that uses a wide frequency band for high-speed communication, such as ADSL or optical fiber, is a description of a broadband (wide-band) line. That is merely one example of the line technology used when building a WAN; it is not the definition of a WAN. A WAN is not determined by the speed or bandwidth of the line, but is defined by its range — the fact that it links sites that are far apart. Even if a slow line is used, it is a WAN as long as it connects separate sites.
Incorrectイ
The statement that all kinds of information terminals and devices are connected by diverse wired and wireless networks so that services can be used anytime and anywhere is a description of a ubiquitous network society (in recent usage, a vision of society that also includes IoT). It describes the form of society that networks bring about, and is a different concept from the technical definition of a WAN, which is about connecting separate sites.
Incorrectウ
Building a network by using radio waves instead of cables is a description of a wireless LAN (Wi-Fi). This is a classification based on the difference in transmission medium — wired versus wireless — and moreover its scope is basically a LAN within one site. Whether something is a WAN is determined by the range it connects, not by the transmission medium, so this statement is not a description of a WAN.
- エ
正解 The correct answer is エ. A WAN (Wide Area Network) is a network that uses the lines and network services provided by telecommunications carriers to connect LANs located far apart geographically, such as a head office and a branch office. In contrast to a LAN (local area network), which you build with your own equipment inside your own site or building, a WAN crosses public roads and public spaces, so you cannot lay your own lines; you must rent carrier services (leased lines, wide-area Ethernet, IP-VPN, Internet VPN, and so on) to build it, and that is its decisive feature. Choice エ states exactly the two essential points — that it uses a telecommunications carrier's network services, and that it connects geographically distant LANs — without adding or omitting anything, so it is the most appropriate description.
ここがポイント
- Definition of a WAN (wide area network): a network that uses a telecommunications carrier's network services to connect geographically distant LANs, such as those between a head office and a branch office. Grasp it as a contrast — a LAN is built inside one site with your own equipment, while a WAN rents carrier lines to link separate sites.
- Tell the confusable neighboring terms apart: broadband (high-speed lines with a wide frequency band, such as ADSL and optical fiber) refers to a property of the line, wireless LAN is a classification by transmission medium (radio waves), and a ubiquitous network is a vision of a society connected anytime and anywhere. None of them shares the axis of classification used for LAN and WAN, which are defined by the range a network covers.
用語