In data transmission or processing, a sequence of bits used to delimit, i.e. Mark, the beginning and end of a frame. Note 1: An 8-bit sequence is usually used as the flag sequence; for example, the 8-bit flag sequence 01111110. Note 2: Flag sequences are used in bit-oriented protocols, such as Advanced Data Communication Control Procedures (ADCCP,) Synchronous Data Link Control (SDLC,) and High-Level Data Link Control (HDLC. )