問69
頻出度★★★
ADSL において, 加入者宅と電話局間で利用する通信媒体はどれか。
平成24年度 秋期 ITパスポート試験 問69
テクノロジ系ネットワーク › ネットワーク応用
This question's explanation and your answers so far.
解説
問 69
- ア
正解 The correct answer is ア “Analog telephone line (metal)”. ADSL (Asymmetric Digital Subscriber Line) is a technology that reuses the metal telephone line (copper twisted pair) already installed between the subscriber's home and the telephone exchange (local office) directly for high-speed data communication. Voice calls use frequencies only up to about 4 kHz, so ADSL places the data signal on the higher, unused frequency bands above that. As a result, a single analog telephone line can carry “telephone” and “Internet access” at the same time. A splitter and an ADSL modem are placed at the subscriber's home, and a splitter and a DSLAM at the telephone exchange, separating voice and data by frequency. No construction to lay a new dedicated line is required, and the existing telephone network can be used as it is — this is the greatest advantage of ADSL and the core point this question asks about. Note that “Asymmetric” means that the downstream speed (exchange → home) is allocated higher than the upstream speed (home → exchange).
Incorrectイ
Bringing a coaxial cable into the subscriber's home is the cable Internet method that uses a CATV (cable television) network. It carries data on the unused frequency bands of the coaxial cable used for television, which is a different technology from ADSL. ADSL uses the metal telephone line running from the telephone exchange, so coaxial cable does not apply.
Incorrectウ
Laying optical fiber all the way to the subscriber's home is FTTH (Fiber To The Home), which is what fiber-optic line services are. A feature of ADSL is exactly that it can use the existing telephone line as it is, without construction work to lay optical fiber, so optical fiber is wrong. Optical fiber may indeed be used in the backbone network beyond the telephone exchange, but what this question asks about is the medium between the subscriber's home and the telephone exchange.
Incorrectエ
Wireless (radio waves) is used by wireless access methods such as wireless LAN, mobile phone networks (LTE and so on), and FWA (Fixed Wireless Access). ADSL is wired: the subscriber's home and the telephone exchange are connected by a physical metal line. The DSL (Digital Subscriber Line) in the name ADSL itself indicates that it uses the subscriber line, that is, the telephone line.
ここがポイント
- ADSL is a technology that reuses the existing analog telephone line (metal) and places data on the high frequency bands that voice does not use. Its greatest advantage is that no new cabling work is required.
- Distinguish access lines by their medium: ADSL = metal telephone line, FTTH = optical fiber, cable Internet = coaxial cable of CATV, wireless LAN and LTE = radio waves.
用語