The document discusses various functions and protocols of the data link layer, including: 1. Framing of data, error detection using checksums, and flow control to prevent faster senders from overwhelming slower receivers. 2. Common data link layer protocols like stop-and-wait and sliding window protocols using go-back-N and selective repeat to allow multiple frames to be transmitted. 3. Error detection techniques like parity bits, checksums, and cyclic redundancy checks to detect errors in transmitted frames.