This unit examines how IP datagrams are transmitted between directly connected network devices in each network segment. A variety of networking schemes, including Ethernet, PPP, ATM, X.25, and frame relay are discussed. An overview of services provided by the link layer (including error-detection and error-correction) is given, as well as descriptions of the protocols used to control multiple accesses to a single communication medium, such as a LAN. The unit describes relevant hardware, including hubs, bridges, and switches, and discusses the addressing of network devices.
For network-layer protocols to move datagrams from a source host to a destination host via other hosts or networking devices, datagrams must follow a specified route. This unit examines how the link layer transfers datagrams via a communication channel between two adjacent network devices.