Originally, the host computer would handle all of the functions now divided among other devices in the system. Essentially, the host computer is being moved further away from the communications control functions. Hardware and software have been developed and are being developed for peripheral devices to handle communication duties. The COMMUNICATIONS CONTROL UNIT is an interface between the communications line and the computer. The communication control unit is basically a peripheral device that purifies data transmission signals and relieves the computer of unnecessary monitoring duties. It is also called the ROUTER.

The CONCETRATOR is normally located on the terminal side of the data communication system. The concentrator takes data from a large number of low- and medium-speed lines and combines them for retransmission over one or more high-speed lines. Factors that can affect TRANSMISSION RATE include: type of modem, line discipline, type of communication channel and transmission medium. Analog transmission is the most readily available and can be used on switched or leased telephone lines.

PROTOCOLS are groups of rules and procedures that initiate and maintain communication. They give the messages the right priority. Well known protocols are TCP/IP- Transfer and Communication Protocol/Internet Protocol used by the Internet, and PPP- Point to Point Protocol.