Data Link Layer

The Data Link Layer is layer two of the OSI model.

The Data Link Layer resides above the Physical Layer and below the Network Layer.

The Data Link Layer is responsible for communications between adjacent network nodes. Hubs and switches operate at the Data Link Layer.

The Data Link Layer is logically divided into two sub-layers, The Media Access Control (MAC) Sub-layer and the Logical Link Control (LLC) Sub-layer.

Media Access Control Sub-layer

The MAC Sub-layer is responsible for addressing on the Local Area Network.

The MAC Sub-layer is also responsible for determining when nodes on a Local Area Network are allowed to transmit. In Ethernet, this is accomplished using the CSMA/CD protocol.

Logical Link Sub-layer

The LLC Sub-layer is responsible for synchronizing frames, error checking, and flow control.

Data Link Layer Standards

Standards which operate at the Data Link Layer include: Ethernet, Wi-Fi, Frame Relay, ATM, and PPP.