Data-Link layer is responsible for transporting data within a network. This layer uses a Media Access Controller (MAC) to generate the frames that will be transmitted .The Data-link layer packages the higher-layer data into frames. This packaging process is referred to as framing or encapsulation.

The Data-Link layer consists of two sub layers:

• Logical Link Control (LLC) sub layer
• Media Access Control (MAC) sub layer

Logical Link Control (LLC) sub layer

• It provides flow control.
• The packet received from Network layer is further divided into frames depending on the frame size of Network Interface Card.
• The LLC sub layer serves as the intermediary between the physical link and all higher layer protocols. It ensures that protocols like IP can function regardless of what type of physical technology is being used.

Media Access Control (MAC) sub layer

• The MAC controls the physical transmission media. The wireless transmission media used for Wi-Fi® or 802.11 has different requirements from the wired transmission media used for Ethernet or 802.3, and therefore needs a different MAC and PHY. The upper layer software is not aware of or affected by the physical interface.
• When transmitting data, this layer adds a header containing the source and destination MAC addresses to the packet received from the Network layer (layer 3). The frame it creates will then be forwarded to the Physical layer.
• When receiving data, this layer is used to determine if the frame received by the host contains the host’s MAC address. If it does, the data is forwarded up to the Network layer.