Data communications refers to the transmission of digital data between two or more computers and a computer network or data network that allows computers to exchange data. The physical connection between networked computing devices is established using either cable media or wireless media. The International Standards Organization (ISO) developed the Open Systems Interconnection (OSI) model. At OSI Model, Layer 2, data packets are encoded and decoded into bits. It furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization. In this paper we discuss the design issues of Data link layer framing ,addressing, flow control and error control how it was happened and how it was handled by data link layer will be discussed