問64
頻出度★★★
二つの拠点を専用回線で接続した WAN でパケットを送受信する場合, 可用性を高める例として, 適切なものはどれか。
平成31年度 春期 ITパスポート試験 問64
テクノロジ系システム構成要素 › システムの評価指標
This question's explanation and your answers so far.
解説
問 64
- ア
正解 Availability is the degree to which a system can keep being used without going down, expressed by how high its availability rate is. A typical way to raise availability is redundancy: preparing multiple pieces of equipment that play the same role, so that if one fails the others can keep handling the work. Choice ア adds, on top of the existing leased line, another line provided by a different telecommunications carrier, and sends and receives packets over the two lines. Even if one line or one carrier's side fails, communication can continue over the other line, so the availability (availability rate) of the whole WAN improves. Choosing a different carrier also lowers the risk that a wide-area failure at a single carrier brings both lines down at the same time, which is part of the aim. Therefore ア is appropriate.
Incorrectイ
Detecting and correcting packet errors on the receiving side is a measure of reliability (error control) that keeps communication data accurate. It does not rescue a situation where the line itself has failed and communication is impossible, so it is not an example of improving availability (the degree to which a system can keep being used).
Incorrectウ
Performing virus scanning on the sending side and sending only safe packets is a security measure that prevents malware from getting in. It is not a mechanism that keeps communication going when a line fails, so it is not an example of improving availability.
Incorrectエ
Encrypting packets before sending them is a confidentiality (security) measure that keeps the content from being read even if it is eavesdropped. It has nothing to do with continuity when a line becomes unusable, so it is not an example of improving availability.
ここがポイント
- Availability = the degree to which a system can keep being used without going down, expressed by its availability rate. The basic way to raise it is redundancy (preparing multiple pieces of equipment so that if one breaks, operation continues).
- The three elements of information security are confidentiality, integrity, and availability. Error correction is error control in communication (a measure for transmission reliability), encryption serves confidentiality, and virus scanning is a malware countermeasure; none of them is a measure for improving availability.
用語