The Data Link Layer is only responsible for transferring a datagram from one host over a single physical link to another host. Most if not all of the Data Link Layer functionality resides in the AirDrop's MAC engine. The AirDrop MAC engine accepts data and wraps it into an 802.11b frame that can be received and "unwrapped" by the station the data was addressed to. The AirDrop MAC engine also automatically generates the preamble and CRC when an 802.11b frame is transmitted. In addition, the AirDrop's MAC engine also makes sure the RF medium is clear before attempting to send a message and automatically retries failed send operations. The AirDrop MAC engine is also responsible for checking the incoming frame's hardware address to determine if the incoming frame belongs to it or another station on the network.