The communication link is a vital component of distribution automation (DA). This chapter highlights DA communications and their basic concepts. DA rarely rely on a "greenfield" situation because an existing infrastructure may be present for both communications and control, where media and protocols have already been established. The physical link provides the communication medium between the feeder equipment transmitting and receiving units. The communication protocol may specify the address of the device the message is being sent, the address of the device that sent the message, information about the type of data in the message, the data itself, and error detection or other information. Different advantages and drawbacks are encountered among the different communication options available, and the appropriate selection of a communication technology depends on many factors. Distribution line carrier (DLC) uses the distribution power line as the conductor for the signal, thus can be cost-effective particularly in urban areas where most substations are underground and served by cable.