The protocol operating at the data-link layer of the Open Systems Interconnection (OSI) reference model describes the nature of the network medium and performs the final preparation of outgoing data before it is transmitted. This protocol also receives incoming data, evaluates it, and, if necessary, passes it on to the appropriate network layer protocol. This chapter examines the protocols most commonly found at the data-link layer and how they affect the performance of the network. These protocols are vital to any study of computer networking, as they determine how the network is constructed and how computers actually transmit and receive data.
This chapter requires a basic understanding of the OSI reference model, as described in Chapter 1, "Networking Basics," and familiarity with the hardware components of the network, as examined in Chapter 2, "Network Hardware."