A wireless LAN (無線LAN) is a LAN that links devices using radio waves instead of cables.
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PCs and smartphones usually reach a wired LAN or the internet through an access point (アクセスポイント), a device that sends and receives radio signals and relays devices onto the network. Radio signals weaken with distance and walls, so where the equipment sits affects connection quality. Because the signals also reach outside the building, encrypting traffic and guarding the access point against misuse are essential.
AnalogyIf a wired LAN is a desk phone with a line run to every desk, a wireless LAN is a cordless phone whose handset reaches its base by radio. With no cord you can move around freely, but stray too far from the base and the voice starts to break up.
How to rememberWireless is wire plus less: no wire, so the link is made by radio.
Exam points
ExamWPA2 is one method for encrypting wireless LAN traffic. It fixes the weaknesses of WEP, an older wireless LAN encryption method that can be cracked in a short time.
ExamOf the frequency bands (周波数帯) wireless LANs use, the 2.4 GHz band copes with obstacles better and reaches farther than the 5 GHz band, but it is prone to interference from appliances such as microwave ovens. Interference lowers the transmission speed.
ExamLPWA, used for IoT devices, is a wireless method that is slower than a wireless LAN but covers a wide area on very little power.
Wi-Fi is the brand name carried by IEEE 802.11 wireless LAN products that an industry group has certified as able to connect with other makers' products.
Certification is run by the industry group Wi-Fi Alliance, and its logo signals that products from different makers should connect with each other. Today the word is used almost as a synonym for wireless LAN.
AnalogyIt works like a standards-compliance mark on home appliances. Seeing the mark tells you that products from different makers can be used together.
How to rememberThe name is said to have been coined to echo Hi-Fi, the term for high-fidelity audio.
Exam points
ExamIEEE 802.11 is the family of wireless LAN (無線LAN) standards and includes 802.11n and others. IEEE 802.3 is the standard for wired LAN (有線LAN), that is, Ethernet (イーサネット).
ExamEach wireless LAN standard fixes which frequency band it uses; for example, an 802.11a device, which uses only the 5 GHz band, cannot talk to an 802.11b device, which uses only the 2.4 GHz band.
ExamIn WPA2, the PSK is a shared passphrase (パスフレーズ) used to authenticate connections, and each device's encryption key is derived from it.
Wi-Fi Direct is a standard that connects Wi-Fi devices directly to each other without a dedicated access point device.
Connection via an access point
Wi-Fi Direct
Traffic path
From the device through the access point to the other end
Straight from the device to the other end
Dedicated access point device
Required
Not needed (one device doubles as the access point)
Example use
Joining a home or office network
Sending data between nearby devices
One of the connected devices temporarily doubles as the access point, so devices can talk to each other even where there is no router. For example, a smartphone can send data straight to a printer to print it.
AnalogyIt is like handing a letter directly to the person in front of you instead of sending it through the post office.
Exam points
Mix-upAn ad hoc network (アドホックネットワーク) is a wireless LAN form in which all devices communicate with each other as equals. Wi-Fi Direct differs in that one device doubles as the access point.
Mesh Wi-Fi (メッシュWi-Fi) is a setup that links several wireless LAN devices in a mesh so that together they extend radio coverage.
A main router and several satellite units relay signals among themselves, and each device connects to whichever unit is nearest at the moment. The whole system works as a single network with one network name, so connections tend to hold as you move around the building.
AnalogyIt is like lighting every corner of a room by placing small lamps around it rather than making a single lamp brighter.
How to rememberMesh is the netting of a window screen. Picture points joined to one another by many lines.
Exam points
Mix-upMesh Wi-Fi is a setup for extending radio coverage, so its purpose differs from that of Wi-Fi Direct, which links devices directly without a dedicated access point.
WPS is a feature that completes the settings for joining a device to a wireless LAN through a simple action such as pressing a button or entering a PIN code.
Press the router's WPS button
Choose WPS connection on the device
Settings pass to the device automatically
Connected
With nothing typed in, the device starts an encrypted connection.
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Normally you type the network name and the encryption password into the device by hand, but with WPS the devices exchange them automatically. That saves effort and avoids typos, but the PIN method has a known weakness: a brute-force attack can break it in a short time.
How to rememberWPS stands for Wi-Fi Protected Setup. The last word, Setup, tells you what the feature is for.
Exam points
Mix-upWPS is a feature that simplifies connection setup, and its role differs from that of methods that encrypt traffic, such as WPA2.
An ESSID is the network name of a wireless LAN, and a device picks this name to decide which network to join.
An ESSID is also called an SSID, and the administrator can choose any name up to 32 characters. Several access points can be given the same ESSID so that they are treated as one network. Turning off ESSID broadcasting so the name does not show up in nearby devices' lists is called the stealth feature (ステルス機能, also ステルス化).
AnalogyIt is like the signboards on a row of shops. Even among invisible radio waves, you can read the name on the sign and choose which shop to walk into.
How to rememberESSID stands for Extended Service Set Identifier. The final word, Identifier, shows that it is a name for telling networks apart.
Exam points
ExamAn ESSID does not encrypt anything by itself; encryption comes from methods such as WPA2 and their keys.
ExamThe stealth feature (ステルス機能) only keeps the name off device lists so the network is harder to find; anyone who picks up the radio traffic can still learn the ESSID, so it only lowers the risk of unauthorized connections.
ExamOne access point can carry several ESSIDs, each with its own encryption method and its own limits on what it can reach.
A MAC address (MACアドレス) is a physical address, unique to each device, that is assigned to a network device's communication hardware at manufacture.
Part
Length
Content
First half
24 bits
Number identifying the manufacturer (assigned by IEEE)
Second half
24 bits
Number the manufacturer gives each device
Whole
48 bits
Number that identifies one device
It is written as pairs of hexadecimal digits separated by hyphens, as in 00-1A-2B-3C-4D-5E. Within the same network, this number tells which device is on the other end of the communication.
AnalogyIt is like the serial number stamped on each product. Even with identical models lined up, the number picks out the one unit.
How to rememberMAC stands for Media Access Control and has nothing to do with Mac computers.
Exam points
ExamMAC addresses are allocated so that no two in the world are the same: IEEE hands out the manufacturer number in the first half, and each manufacturer numbers the second half so that none clash.
ExamMAC address filtering (MACアドレスフィルタリング) registers the MAC addresses of permitted devices on the access point in advance and refuses connections from any other device.
Mix-upAn IP address (IPアドレス) is a logical address (論理アドレス) that marks a destination on the network, and routers use it to decide where to forward data.
Wireless LAN signals reach outside the building, so they need encryption with WPA2 or a similar method and protection against misuse of access points.
The IEEE 802.11 family of standards defines how wireless LAN technology works, and Wi-Fi is the name for products certified to interconnect under those standards.
Radio signals weaken with distance and obstacles and slow down when other signals interfere, so equipment placement and the frequency band in use affect connection quality.