Control (1-2 bytes) (LAPD)

Protocol: LAPD LAPD PCI

Field: control

Length: 1-2 bytes

Contents: frame format / sequence number.

LAPD, HDLC, and LLC share the same control field codes. There are three frame types: Information, Supervisory, Unnumbered.

N(r) = receive sequence number

N(s) = send sequence number

Control (1 byte) (LAPB)

Control (1-2 bytes) (LLC)