問82
頻出度★★★
無線LANの規格はどれか。
平成23年度 特別試験 ITパスポート試験 問82
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 82
Incorrectア
CDMA (Code Division Multiple Access) is a multiple-access (multiplexing) method used in mobile communications such as mobile phones. Each user's signal is multiplied by a different code (a spreading code) and spread over a wide frequency band, so that many terminals can share the same frequency and the same time slot at once. It became widespread as a core technology of third-generation (3G) mobile phones. Although it is a radio technology, its target is the mobile phone network, that is, a wide-area mobile communication network, not a wireless LAN installed within a site. In addition, CDMA is not a standard defined by the IEEE 802 committee but the name of a modulation and multiplexing method, so it does not match what the question asks either.
- イ
正解 The correct answer is イ. IEEE 802.11n is one of the IEEE 802.11 series, the family of wireless LAN standards developed by the 802 committee of the Institute of Electrical and Electronics Engineers (IEEE). IEEE 802 is the committee responsible for standardizing LANs and MANs, and the technology covered differs by the number after the dot: 802.3 covers wired LANs (Ethernet), 802.11 covers wireless LANs, and 802.15 covers short-range wireless such as Bluetooth. So you can tell whether a standard is for wireless LAN simply by checking whether it starts with 802.11. The IEEE 802.11 series includes 802.11b (2.4GHz band, up to 11Mbps), 802.11a (5GHz band, up to 54Mbps), and 802.11g (2.4GHz band, up to 54Mbps). As their successor, 802.11n supports both the 2.4GHz and 5GHz bands and adopts MIMO (Multiple Input Multiple Output), which sends and receives with several antennas at the same time, plus channel bonding, which combines two adjacent channels to widen the bandwidth, achieving transmission speeds on the order of 600Mbps. Also keep in mind that Wi-Fi is the brand name given to products that conform to these standards and pass interoperability certification testing, while the name of the standard itself is the IEEE 802.11 series. Therefore, the wireless LAN standard is イ.
Incorrectウ
IEEE 802.3 is the standard for wired LANs using the CSMA/CD method, that is, Ethernet. It is easy to confuse because it belongs to the same IEEE 802 series, but the numbering clearly separates the subjects: 3 is for wired LANs and 11 is for wireless LANs. IEEE 802.3 assumes that devices are connected by physical cables such as twisted-pair cable or optical fiber, and it specifies transmission methods such as 10BASE-T, 100BASE-TX, and 1000BASE-T. Because it does not use radio waves, it is not a wireless LAN standard; it is a typical distractor that tests the contrast with 802.11.
Incorrectエ
ISDN (Integrated Services Digital Network) is a public communication service that digitized the conventional analog telephone network so that voice and data could be handled together on the same line. In Japan it was offered as services such as INS Net 64 (two 64kbps B channels). It uses wired equipment, namely telephone lines, and is a wide-area communication service, not a technology for building a LAN with radio waves inside a site. Its transmission speed is also orders of magnitude lower than that of wireless LAN, and it is classified not as a LAN standard but as a WAN-side service provided by a telecommunications carrier, so it is incorrect.
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- The numbering of the IEEE 802 series and the technology each covers — IEEE 802 is the committee in charge of standardizing LANs and MANs. 802.3 specifies wired LANs (Ethernet), 802.11 specifies wireless LANs, and 802.15 specifies short-range wireless such as Bluetooth. Since the number in the standard name tells you whether it is wired or wireless, memorize the contrast between 802.3 and 802.11 as it is.
- The generations of wireless LAN standards and their relationship with Wi-Fi — The IEEE 802.11 series evolved through b (2.4GHz / 11Mbps), a (5GHz / 54Mbps), g (2.4GHz / 54Mbps), and n (supporting both 2.4GHz and 5GHz, made faster with MIMO and channel bonding). Wi-Fi is the brand name given to products that conform to these standards and are certified for interoperability; it is not the name of the standard itself. Note also that CDMA is a multiple-access method for mobile phones and ISDN is a public wired service that digitized the telephone network, so neither is a LAN standard.
用語