OSI Data Link Layer

The data link layer of the OSI reference model is responsible for transferring data between nodes that are on the same logical segment.

The segment is where all nodes can send data to each other using hardware addresses, regardless of the physical topology of the network or whether they share access to the same transmission media. In fact, a Layer 2 segment might include multiple physical segments, such as NICs, switches, and wireless access points (WAPs).

Oftentimes, local networks don't use a mesh node layout or directly connect nodes with one another to avoid cabling costs. They usually use the star node layout, in which each node in the network is connected to a central node that is responsible for forwarding data to the correct end system. To do this, each node must have a Data Link layer address.

The Data Link layer address also performs an encapsulating function, organizing the stream of bits received from the Physical layer into frames, each frame containing a Network layer packet, control info in the form of header bits, and a basic error check for data corruption.