Who can initiate an optional referendum at the national level?

The Interim National Constitution of the Republic of Sudan (from 2005) http://www.mpil.de/shared/data/pdf/inc_official_electronic_version.pdf

ReferendumArt. 217 (1) The President of the Republic or the National Assembly, by resolution passed by more than half of the members, may refer to referendum any matter of national or public interest.(2) The National Elections Commission shall conduct the referendum for all the electorate; the subject submitted to referendum would achieve the confidence of the people by obtaining more than half of the number of votes cast.(3) Any resolution which has achieved the consent of the people by referendum shall have authority above any other legislation. It shall not be annulled save by another referendum.