問70
頻出度★★★
インターネット上でデータを送るときに, データを幾つかの塊に分割し, 宛先, 分割した順序, 誤り検出符号などを記したヘッダを付けて送っている。このデータの塊を何と呼ぶか。
平成26年度 秋期 ITパスポート試験 問70
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 70
Incorrectア
A domain is an identifying name that expresses a computer or network on the Internet in a form that is easy for people to read (for example example.co.jp, a name that expresses an organization and its hierarchy), and DNS maps it to an IP address. It is a name used to call a destination, not the chunk of data that is actually sent, so it is wrong.
- イ
正解 The correct answer is イ, Packet. On the Internet (TCP/IP), the data you want to send is not pushed through as one whole piece; it is first split into chunks of a manageable size and then sent. Each split chunk is given a header that records the destination address, the source address, a sequence number showing which chunk it is, an error-detection code (checksum), and so on, and the result is a packet. The receiving side looks at the sequence numbers in the headers to reassemble the chunks into their original order, and uses the error-detection code to check whether anything was corrupted on the way. The description given in the question, namely split chunks of data plus a header carrying control information, matches exactly the definition of a packet. A communication method that exchanges data in units of packets like this is called packet communication; because it does not occupy a line exclusively, many communications can share the line efficiently.
Incorrectウ
A port is a number used to distinguish the multiple communications (applications) running on a single computer (a port number; for example, HTTP is 80 and HTTPS is 443). It is the number of the window that shows which service the data is addressed to, not a term for a split chunk of data, so it is wrong.
Incorrectエ
A router is a communication device that interconnects multiple networks and selects the route to forward to next by looking at the destination written in a packet header (a device that performs route control). It is the equipment that carries packets, not the chunk of data being carried, so it is wrong.
ここがポイント
- A packet = the result of splitting the data to be sent into chunks of a certain size and attaching a header with the destination, a sequence number, an error-detection code, and so on. Exchanging data in these units is packet communication, which lets a line be shared efficiently.
- Distinguish the roles of the network terms: domain = identification by name, port = a number that distinguishes applications, router = a device that selects a route and forwards packets, packet = the chunk of data that is actually sent.
用語