hi everybody
i want one of my user to get disconnected automatically if he is idle for some time say 10 min.what i have done is created a user with profile.the syntax is

CREATE PROFILE IDE_PRAS LIMIT
IDLE_TIME 10;


ALTER USER XYZ
PROFILE IDE_PRAS 10;

but my prob is the user is not getting disconnecting automatically.what steps should i take other than this.
any help is really appriciated.
thanks
pras