general format identifier (X.25) (GFI)

The General Format Identifier (GFI) is a data field in the header of the X.25 protocol.

The General Format Identifier is a four-bit data field consisting of the Q bit, the D bit, and the XY bits. The GFI information defines the basic format for the rest of the packet. This includes the identification of control and payload data as well as the connection establishment and acknowledgment( ACK) by the receiver.