This diagram illustrates the Data Link layer (Layer 2) of the OSI model. When obtaining data from the Physical layer, the Data Link layer checks for physical transmission errors and packages bits into frames. The Data Link layer also manages physical addressing schemes such as MAC addresses for Ethernet networks, controlling access of any various network devices to the physical medium. Because the Data Link layer is the single most complex layer in the OSI model, it is often divided into two parts, the Media Access Control sublayer and the Logical Link Control sublayer.
Related References -
OSI Model Tutorial, MAC Address Tutorial
OSI Model Network layer