Which two functions are performed at the MAC sublayer of the OSI data link layer?

The MAC (Media Access Control) sublayer of the OSI data link layer is primarily responsible for managing how data packets are placed on the network medium and controlled. One key function is to control the Network Interface Card (NIC), which includes handling the transmission protocols and access to the physical medium.

Additionally, the MAC sublayer implements a trailer to detect errors through mechanisms like Frame Check Sequence (FCS). This ensures that when data is transmitted, it can be checked for integrity upon receipt. If any errors are detected, the MAC layer can signal for retransmission. This focus on error detection and hardware control is why the identified choice aligns well with the roles of the MAC sublayer.

In contrast, the other functions in the choices relate to different layers of the OSI model or different networking functionalities that fall outside the direct responsibilities of the MAC sublayer. For example, encryption and decryption are generally handled at the higher layers for security, packet routing is a function of the network layer, and connecting multiple networks typically involves higher-level operations beyond what the MAC sublayer manages.