Lost Carrier: session is terminated when device dropped DCD(Data Carrier Detect). This can either mean the user or his device closed the laptop, in which case there is no problem, or can mean that the signal was dropped or took a noise hit too severe for the device to recover from, or can mean that the local device dropped DCD for some other reason.
“Reason of termination” of sessions explained
Lost Service: Service can no longer be provided; for example, user’s connection to a host was interrupted. That could be due to users losing wireless connectivity.
No reason: It means that the session ended unexpectedly, for example because of a power outage.