Learn in the textbookThe OSI Reference Model and Its 7 Layers
DefinitionThe network layer (ネットワーク層) is Layer 3; it sends data across multiple networks by choosing a route that reaches a distant destination.
ExplanationChoosing the path to the destination is called routing (ルーティング), and data travels in units called packets (パケット). The destination is identified by an IP address (IPアドレス). A router, which links networks together, is the device that decides where to forward each packet at this layer.
AnalogyIt is like a sorting center that reads the address and decides which relay stations a parcel must pass through.
Memory hookThis is the layer that connects networks to one another. The "route" in routing means the path to follow.