Who can initiate an optional referendum at the national level?

Constitution (1996)http://www.info.gov.za/documents/constitution/1996/index.htm

84. Powers and functions of President 2. The President is responsible for[?] g. calling a national referendum in terms of an Act of Parliament [?]

Electoral Commission Act (Act 51 of 1998)http://www.elections.org.za/content/WorkArea/DownloadAsset.aspx?id=987

Section 2 Application of Act(2) Notwithstanding anything to the contrary in any other law contained, the President may, after consultation with the Commission, by proclamation in the Gazette?(a) declare that a referendum shall be held in order to ascertain the views of voters on a matter specified in the proclamation;(b) determine that the referendum shall be held in the Republic, or in a part of the Republic specified in theproclamation, on a day or consecutive days and, subject to this Act, during the hours so specified;(c) determine who shall be entitled, in accordance with this Act, to vote at the referendum; and(d) determine what question or questions to ascertain the views of voters, must appear on the ballot paper.