1. Deparment of Telecommunications, Faculty of Electronic Engineering , Univeersity of Niš , A. Medvedeva 14, 18000 Niš , Serbia
2. Technical Faculty in Bor , University of Belgrade , Vojske Jugoslavije 12, 19210 Bor , Serbia
3. IRITEL AD Beograd , Batajnički put 23, 11080 Belgrade