Learn in the textbookThe OSI Reference Model and Its 7 Layers
DefinitionThe data link layer (データリンク層) is Layer 2; it reliably passes data between devices that are directly connected, such as by a cable.
ExplanationA device connected to a network is called a node (ノード), and this layer groups bits into units called frames (フレーム) and sends them between neighboring nodes. It identifies the destination by the MAC address (MACアドレス) assigned to each device, and it also detects errors that occur during transmission. A switch (switching hub, スイッチングハブ), which reads the destination MAC address of a frame to pick the port to send it out of, is a device at this layer.
AnalogyIt is like a clerk in one building who checks the room number and hands papers to the room next door.
Memory hookA link is one ring in a chain. Picture it covering just one ring: the stretch between two neighbors.