Is it ensure, insure, or assure?
Layer two, the second lowest layer in the OSI seven layer model. The data link layer splits data into frames (see fragmentation) for sending on the physical layer and receives acknowledgement frames. It performs error checking and re-transmits frames not received correctly. It provides an error-free virtual channel to the network layer. The data link layer is split into an upper sublayer, Logical Link Control (LLC), and a lower sublayer, Media Access Control (MAC).
Example protocols at this layer are ABP, Go Back N, SRP.