>>Seems to me that if you opt for cookieless sessions i.e:

<sessionState cookieless="true">

then when you open a new tab on the browser it will create a new session per tab. Don't know if this can work for you tho.....
>
>I cannot drop the cookie support. Also, with the number of simultaneous users at the same time, we do not want to store session state on the server side.

Using 'cookieless=true' doesn't prevent you from using cookies - just means that the sessionId is in the URL not in a cookie. So if, for example, you wanted to store the user name per session you could use a cookie with the SessionId as the key and 'UserName' as a sub-key. Something like this:

Protected Sub Page_Load(sender As Object, e As EventArgs)
	Dim sessionId As String = Session.SessionID
	Dim thisUserName As String
	Dim thisAge As String

	Response.Write(sessionId)

	Dim cookies = Request.Cookies

	If cookies(sessionId) IsNot Nothing Then
		thisUserName = cookies(sessionId).Values("UserName")
		thisAge = cookies(sessionId).Values("UserAge")
	Else
		thisUserName = UserProvider.GetName()
		'Get UserName from somewhere
		thisAge = UserProvider.GetAge()
		' etc.
		Dim cookie As New HttpCookie(sessionId)
		cookie.Values.Add("UserName", thisUserName)
		cookie.Values.Add("UserAge", thisAge)
		Response.Cookies.Add(cookie)
	End If
	Response.Write(" Name: " & thisUserName)
	Response.Write(" Age: " & thisAge)
End Sub