command reject (HDLC) (CMDR)

Command Reject (CMDR) is a message in the LAP protocol(Link Access Procedure) used to indicate an error condition by a station.

The CMDR message is functionally equivalent to the Block Reject( FRMR) in the LAP-B protocol. An error indicated by CMDR cannot be corrected by repeated frame transmission. Typically, a CMDR occurs when, for example, an I-frame, an S-frame, or a U-frame have invalid data field sizes. The CMDR frame has a data field to indicate the rejection. When a CMDR occurs, a reset occurs at the link layer and all timers and counters are reset. Frames may be lost as a result of the reset.