protocol abnormality

In ISDN, a protocol event (a protocol error or other event) that indicates that a potential trouble condition exists on the ISDN interface. Note: Examples of events that are not protocol errors that may indicate potential trouble conditions are (a) the transmission of a DM (disconnect mode) in response to a SABME (set asynchronous balanced mode extended) command, and (b) transmission of a STATUS message. [After T1.218-1991]