問62
頻出度★★★
ブロードバンド回線の特徴のうち, 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62
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 62
Incorrectア
This confuses the type of modem with the transmission medium it works on. An ADSL modem is a device that sends data over telephone lines (metal lines) using the high frequency band not used by voice, and it cannot be connected to a CATV network. To use broadband Internet over a CATV network, you need a “cable modem”, which uses a free channel on the coaxial cable.
- イ
正解 The correct answer is “イ”. A broadband line is a general term for a line that has a far wider bandwidth than traditional dial-up over telephone lines (narrowband, around tens of kbps) and can therefore carry high-speed, large-volume communication. ADSL, CATV Internet, and FTTH (optical fiber) are typical examples, all offering transmission speeds on the order of several Mbps to several Gbps. Uses that push a large amount of data per unit of time, such as video streaming, online meetings, and downloading large files, are exactly where this wide bandwidth pays off. Therefore, “It is a line suited for communication of large-volume data such as video” is an appropriate characteristic of a broadband line.
Incorrectウ
The conclusion is the opposite of reality. Most broadband services are built on the premise of an always-on connection at a flat monthly rate, so broadband is in fact well suited for always-on connection. It is true that in some CATV and FTTH schemes multiple users share the bandwidth and the effective speed drops during congestion, but that is a cause of lower speed, not a reason why it would be “not suited for always-on connection”.
Incorrectエ
The restriction “only in optical fiber networks” is wrong. A broadband router is placed between the line termination equipment on the WAN side (an ONU, ADSL modem, cable modem, and so on) and the multiple terminals on the LAN side, letting them share the line through NAT/NAPT and DHCP. It is used with ADSL, CATV, and mobile lines as well, so it is not exclusive to optical fiber networks.
ここがポイント
- Broadband line = a general term for wide-bandwidth, high-speed lines (ADSL / CATV / FTTH, etc.). In contrast with narrowband (dial-up), remember that it is suited for large-volume data communication and always-on connection.
- Matching line types with connection devices: telephone line → ADSL modem, CATV coaxial cable → cable modem, optical fiber → ONU (line termination equipment). A broadband router, on the other hand, is used regardless of line type, to share the line on the LAN side.
用語