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

The Logical Link Control (LLC) sublayer of the OSI data link layer performs two main functions:

1. Error and Flow Control: The LLC sublayer is responsible for the control of errors and the flow of data. It ensures that data is sent and received without errors and in the correct sequence. It also controls the rate of data transmission between devices to prevent a fast sender from overwhelming a slow receiver.

2. Multiplexing and De-multiplexing: The LLC sublayer also provides multiplexing mechanisms that allow several upper-layer protocols to share a single physical data link. It distinguishes different network protocols and then routes their data to the correct network layer protocol at the receiving end. This is done by adding a protocol discriminator field to the data frame.