The ISDN_Monitor does not terminate if you are monitoring a D channel and the trunk is disabled. You must stop the ISDN_Monitor yourself by using Ctrl+C. No tracing information is shown on the screen when you re-enable the trunk until the previous instance of ISDN_Monitor is stopped, and a new instance of ISDN_Monitor is started. This is because the ISDN Layer 2 process is terminated after the trunk is disabled, and a new ISDN Layer 2 process is started when the trunk is re-enabled.