Transfer Mode: The header includes information about the contents of the payload and about the method of transmission. The header contains only 5 octets. It was shortened as much as possible, containing the minimum address and control functions for a working system. The sections in the header are a series of bits which are recognized and processed by the ATM layer. Sections included in the header are Generic Flow Control (GFC), Cell Loss Priority (CLP), Payload Type, Header Error Control, the Virtual Path Identifier and the Virtual Channel Identifier. The Header is the information field that contains the revenue bearing payload. A GFC is a 4-bit field intended to support simple implementations of multiplexing. The GFC is intended to support flow control. The CLP bit is a 1-bit field that indicates the loss priority of an individual cell. Cells are assigned a binary code to indicate either high or low priority. A cell loss priority value of zero indicates that the cell contents are of high priority. High priority cells are least likely to be discarded during periods of congestion. Those cells with a high priority will only be discarded after all low priority cells have been discarded. Cell loss is more detrimental to data transmission than it is to voice or video transmission. Cell loss in data transmission results in corrupted files. The Payload Type section is a 3-bit field that discriminates between a cell payload carrying user data or one carrying management information. User data is data of any traffic type that has been packaged into an ATM cell. An example of ...
