平成26年度 秋期 ITパスポート試験 問66

正解 The correct answer is イ, “Gateway”. A gateway is a device that interprets all layers of the OSI basic reference model, including those above the transport layer up to the topmost application layer, and bridges different protocol systems. In the case described in the question — making mobile phone email receivable on a PC as internet email — the mail format and protocol on the mobile phone network side must be interpreted and converted into internet-side protocols such as SMTP and POP. What is required here is not simple signal relaying or forwarding based on the destination, but the function of translating the protocol itself, so only a gateway can play this role. The phrase “enabling communication between networks that cannot communicate with each other directly” also points to the very definition of a gateway: connecting networks that cannot be linked directly because their protocols differ.