SessionID in ASP.NET MVC

session Id every 2-3 request will be changes shouldn't it remain the same because : ASP.NET keeps assigning new session ids until you place something into the Session variable

Session.SessionID

so you can't use it for make it use Session Start and save a variable on Session. Like this :

void Session_Start(object sender, EventArgs e) {
  session["SessionID"] = Guid.NewGuid().ToString();
}