The SessionStateModule.Start event is raised at the beginning of a request when a new session is started. A new session is started if a request is made that does not contain a session identifier, the session identifier is invalid, or the session associated with a session identifier has expired.
The Session_OnStart event is used to perform any initialization work for a session such as setting up default values for session variables.
You can specify a handler for the SessionStateModule.Start event by adding a public subroutine named Session_OnStart to the Global.asax file.
For more information about the Global.asax file, see Global.asax Syntax.