The Level of the event conveys to the user the importance of the event. There are 6 default severities, and explained in [MSDN-PLA-LevelType]. In addition, providers have the ability to define their own severities as well. ETW allows for the definition of 255 different severities. The event tracing subsystem will automatically check the Level value of the event being logged by the trace provider against the Level that was specified when the controller enabled the provider to that session, and if the severity of the event is greater than or equal to that of the session, the event will be logged to the proper session. For example, a network trace provider might utilize two pre-defined levels, "Critical" and "Informational". The network provider logs "Critical" events when it encounters an error either sending or receiving a packet, while all other events which convey state information about the packet have an "Informational" severity.