I am developing a 3-tired ASP.NET C# web application and was wondering where should the sessions be managed. I have a SessionManager class as follows:

public sealed class SessionManager
        {
            private const string USER = "User";
            private SessionManager()
            {
            }

            public static SessionManager Instance
            {
                get { return _instance; }
            }


            public User User
            {
                get { return HttpContext.Current.Session[USER] as User; }
                set { HttpContext.Current.Session[USER] = value; }
            }
    }

Now should the session information be managed in the Business Logic Layer or should it be managed in the Presentation Layer?