Header Definition

The portion of a data block, cell, frame, or packet that precedes the text field or payload and provides information such as the source address and destination address. The header often includes synchronization bits that serve to synchronize the operations of the transmit and receive devices across the link. Certain data protocols also use fields in the header to identify the length of the text field and the type of data, to indicate the level of tolerance for delay or loss during network transit, and any optional headers that might follow. For example, an Internet Protocol (IP) header might indicate that a Transmission Control Protocol (TCP) header follows. See also block, cell, data format (illustration), frame, packet, payload, text field, and trailer.