CBEC vide Notification no. 5/2017 -Central tax dated 19th June 2017  specifies the persons who are only engaged in making supplies of taxable goods or services or both, the total tax on which is liable to be paid on reverse charge basis by the recipient of such goods or services or both under sub-section (3) of section 9 of the said Act as the category of persons exempted from obtaining registration under GST.