問68
頻出度★★☆
インターネット上のコンピュータでは, Web や電子メールなど様々なアプリケーションプログラムが動作し, それぞれに対応したアプリケーション層の通信プロトコルが使われている。これらの通信プロトコルの下位にあり, 基本的な通信機能を実現するものとして共通に使われる通信プロトコルはどれか。
令和5年度 ITパスポート試験 問68
テクノロジ系ネットワーク › 通信プロトコル
This question's explanation and your answers so far.
解説
問 68
Incorrectア
FTP (File Transfer Protocol) is an application-layer protocol for transferring files; it is an upper-layer protocol tied to a specific purpose. It is not the lower-layer protocol that commonly provides the basic communication functions, so it is wrong.
Incorrectイ
POP (Post Office Protocol) is an application-layer protocol for receiving email from a mail server. It is an upper-layer protocol tied to the specific purpose of email, so it is wrong as the common lower-layer protocol.
Incorrectウ
SMTP (Simple Mail Transfer Protocol) is an application-layer protocol for sending and relaying email. It too is an upper-layer protocol tied to a specific application, not the lower-layer protocol that handles the basic communication functions, so it is wrong.
- エ
正解 The correct answer is TCP/IP（エ）. FTP, POP, and SMTP are all “application-layer” protocols tied to specific applications (file transfer, receiving mail, sending mail). The question asks for the protocol that sits below them, is used in common by any application, and handles the basic communication functions (the transmission function that reliably delivers data to the other party, and specifying the destination). That is TCP/IP (the protocol suite centered on TCP and IP), which forms the foundation of the Internet; both the Web and email communicate by using TCP/IP on top of it. Therefore “エ” is appropriate.
ここがポイント
- TCP/IP is the protocol suite that forms the foundation of the Internet; it is used in common regardless of the application and is the lower-layer communication protocol that provides the basic communication functions such as data transmission and destination addressing.
- FTP, POP, SMTP, HTTP, and the like are “application-layer” protocols tied to their respective purposes; they stack on top of the TCP/IP that runs beneath them, and communication is established through this layered structure.
用語