Editing High-Level Data Link Control (section)

====Error Recovery====
; Frame reject (FRMR) response
: The FRMR response contains a description of the unacceptable frame, in a standardized format. The first 1 or 2 bytes are a copy of the rejected control field, the next 1 or 2 contain the secondary's current send and receive sequence numbers (and a flag indicating that the frame was a response, applicable only in balanced mode), and the following 4 or 5 bits are error flags indicating the reason for the rejection.  The secondary repeats the same FRMR response to every poll until the error is cleared by a mode set command or RSET.  The error flags are:
:* W: the frame type (control field) is not understood or not implemented.
:* X: the frame type is not understood with a non-empty information field, but one was present.
:* Y: the frame included an information field that is larger than the secondary can accept.
:* Z: the frame included an invalid receive sequence number N(R), one which is not between the previously received value and the highest sequence number transmitted.  (This error cannot be cleared by receiving RSET, but can be cleared by ''sending'' RSET.)
:* V: the frame included an invalid send sequence number N(S), greater than the last number acknowledged plus the transmit window size.  This error is only possible if a transmit window size smaller than the maximum has been negotiated.
:* The error flags are normally padded with 0 bits to an 8-bit boundary, but HDLC permits frames which are not a multiple of a byte long.
; Reset (RSET) command
: The RSET command causes a secondary to reset its receive sequence number so the next expected frame is sequence number 0.  This is a possible alternative to sending a new mode set command, which resets both sequence numbers.  It is acknowledged with UA, like a mode set command.