Reading about networks leads to self-tutoring: the tutor mentions some ideas about Layer 2 vs Layer 3 in computer networks.
As I understand, Layer 2, aka the link layer, is associated with data transmission in the context of frames. A simplified point of view about it imagines physically connected devices communicating. In broadcast mode, every member forwards all its output to every other member. However, output can be sent to only a specific member. Connected members have no nodes between them; each member is directly connected to any other. The Layer 2 network is self-contained.
Layer 3 uses packets, rather than frames, to organize data. It’s populated by routers. In Layer 3, a given data packet has one intended recipient; the others on the network will not see it. The router conducts each packet to its appropriate destination. Layer 3 is needed when there are intervening nodes between ones that want to communicate – hence, the need for routing the packets of information to their specific destinations. Layer 3 is the context for communication to happen between different networks.
Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.