Notice under Section 148

Hi all

Received a notice from Income tax department under Section 148 of Income tax act,1961. Again received under Section 154 of the income tax act, 1961. Are they two different assessments, or Section 154 is continuation of notice under Section 148. Please clarify. They are for same assessment year. Is it possible that they do assessment under Section 154 for a notice under Section 148.

Thanks