This document discusses different techniques for data link layer flow control and error control in computer networks. It begins by defining flow control and error control, then describes stop-and-wait automatic repeat request (ARQ) and how it operates but is inefficient. Sliding window flow control is introduced as a more efficient approach that allows multiple frames to be transmitted before waiting for acknowledgments. Two types of sliding window protocols are covered: go-back-N ARQ, which retransmits multiple frames upon an error, and selective repeat ARQ, which selectively retransmits only the frame in error.