A delimiter is a flag or other character used to separate individual pieces of data. Probably the most common use of delimiters is for frames in connectionless service, where a Starting Delimiter( SD) signals the beginning of a unit of data and an Ending Delimiter( ED) signals the end.
Similarly, in Token Ring and Token Bus, the destination address, source address, payload data, and checksum are enclosed by Starting Delimiter and Ending Delimiter. Occasionally, the ending delimiter is followed by a byte belonging to the data unit, e.g. the frame status (Token Ring), or the starting delimiter is preceded by synchronization pulses in the form of alternating binary zeros and ones, the preamble( Ethernet).
Delimiters are also electronic circuits for amplitude limiting. In this case, levels that exceed a certain level value are limited. Main applications of such limiter circuits are the protection of device inputs against too high voltages or the limitation of FM signals to avoid AM components.