sec 153(1): assessment order u/s 143 or 144 should be passed within 21 months from the end of assessment year in which the income was was first assessable.
sec 143(2): time limit : no notice shall be served after the expiry of 6months from the end of the relevant FY in which the return is filed.
what is this assessment order under section 143 or 144?how can it be issued when the notice cannot be given after 6months?how is this assessment order u/s 143 or 144 different from notice under section 143.