問64
頻出度★★★
ルータの機能の説明として, 適切なものはどれか。
平成22年度 春期 ITパスポート試験 問64
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 64
Incorrectア
Optically reading photos, pictures, and text documents and converting them into digital data is a description of an image scanner. It is an input device that brings analog information, such as information on paper, into a form a computer can handle, and it has no function for transferring data over a network.
Incorrectイ
Performing mutual conversion between digital signals and analog signals is a description of a modem (a modulator-demodulator). It modulates the digital signals of a computer into a form that can be sent over an analog line such as a telephone line, and demodulates them back to the original form on the receiving side; it does not carry out the processing of looking at a destination and choosing a route.
- ウ
正解 The correct answer is ウ. A router is a relay device that connects multiple networks, and it operates at the network layer (Layer 3) of the OSI reference model. It looks at the destination IP address of a packet it receives, compares that address against the routing table it holds, decides which line or which device it should send the packet to next in order to deliver it to its destination, and then forwards it. This work of choosing a path is called routing (route control), and it is what makes it possible to interconnect separate networks such as an in-house LAN and the Internet. Choice ウ, “It controls the communication route of data and relays between networks,” states exactly these two essential points — route control and relaying between different networks — so it is an appropriate description of the function of a router.
Incorrectエ
Using a network to store Web page data and provide it in response to viewing requests is a description of a Web server. A Web server is the side that keeps content and responds to requests, providing an application-layer service, so its role differs from that of a router, which is a device that relays packets.
ここがポイント
- Router = a relay device at the network layer (Layer 3). It selects the best forwarding destination from the destination IP address and the routing table — this is route control (routing) — and thereby interconnects different networks.
- Do not mix up the roles of network devices and peripheral devices. Memorize them as a matched set: scanner = image input; modem = mutual conversion between digital and analog signals; Web server = storing and providing Web content; router = route control and relaying between networks.
用語