問71
頻出度★★★
隣の部屋に他社が引っ越してきた頃から, 自社の無線LANの通信速度が低下した。原因を調査して, 自社の無線LANの設定を変更することで, 元の通信速度に戻った。このときに変更した内容として, 適切なものはどれか。ここで, 自社のESSIDは, その引っ越してきた他社のものとは異なる文字列である。
平成27年度 春期 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
Changing the encryption key string (passphrase) is only an authentication and confidentiality setting that changes who can connect to that wireless LAN; it has no effect at all on the interference of the radio waves themselves. Since the cause of the speed drop is the other company's radio waves, changing the key will not bring the speed back.
Incorrectイ
Changing from WEP to WPA2 is a security measure that strengthens the encryption method. It improves resistance to eavesdropping and unauthorized connection, but it has no effect in avoiding interference. It does not address the radio interference that is the likely cause in this question, and it also fails to explain why the timing matches the external event of another company moving in.
Incorrectウ
The stealth function (a setting that stops announcing the ESSID in beacons) is a concealment measure that keeps your own wireless LAN from appearing in the list of networks. The radio waves are still transmitted on the same channel as before, so the interference is not resolved. In addition, the question explicitly states that your company's ESSID and the other company's ESSID are different character strings, which shows that a duplicate ESSID or a mistaken connection is not the cause.
- エ
正解 A wireless LAN (IEEE 802.11) divides the radio waves in the 2.4GHz and 5GHz bands into multiple channels. If another nearby wireless LAN uses the same channel, or a channel whose frequency range overlaps, the radio waves interfere with each other, retransmissions increase, and the effective communication speed drops sharply. This question states that the speed dropped “around the time when another company moved into the adjacent room”, which shows that the cause is the radio waves of the newly appeared access point of that other company. Therefore, if you change the wireless channel of your own access point to a free channel that the other company is not using, the interference disappears and the communication speed returns to its original level. Hence エ, “Changed the wireless channel.”, is appropriate.
ここがポイント
- The typical cause of a wireless LAN speed drop is radio interference caused by using the same or an adjacent channel as a nearby access point, and the countermeasure is to change the wireless channel to a free one.
- Changing the encryption key, changing from WEP to WPA2, and making the ESSID stealthy are all security measures, not solutions for a speed drop caused by radio interference.
用語