▁air ▁traffic ▁management , ▁ ▁and ▁ensure ▁that ▁air ▁traffic ▁is ▁safe ▁and ▁efficient . ▁ ▁Function s ▁The ▁C NS ▁has ▁the ▁following ▁three ▁main ▁functions . ▁ ▁Communic ation ▁Communic ation , ▁i . e . ▁av iation ▁communication , ▁refers ▁to ▁radio ▁communication ▁between ▁two ▁or ▁more ▁aircraft , ▁or ▁the ▁exchange ▁of ▁data ▁or ▁ver bal ▁information ▁between ▁aircraft ▁and ▁air ▁traffic ▁control . ▁For ▁contin ental ▁air space , ▁V H F ▁( c ivil ) ▁and ▁U H F ▁( mil it ary ) ▁systems ▁are ▁used ▁whereas ▁for ▁ocean ic ▁areas , ▁high ▁frequency ▁systems ▁and ▁S AT COM s ▁are ▁used . ▁ ▁Navigation ▁Navigation , ▁i . e . ▁air ▁navigation , ▁refers ▁to ▁the ▁process ▁of ▁planning , ▁recording , ▁and ▁cont rolling ▁the ▁movement ▁of ▁an ▁aircraft ▁from ▁one ▁place ▁to ▁another ▁by ▁providing ▁accurate , ▁reliable ▁and ▁se am less ▁position ▁determ ination ▁cap ability . ▁ ▁Sur ve ill ance ▁Sur ve ill ance ▁systems ▁are ▁used ▁by ▁air ▁traffic ▁control ▁to ▁determine ▁the ▁position ▁of ▁aircraft . ▁There ▁are ▁two ▁types ▁of ▁surve ill ance ▁systems : ▁ ▁Cooper ative ▁systems ▁Cooper ative ▁systems ▁( a . k . a . ▁dependent ▁surve ill ance ): ▁Under ▁this ▁form ▁of ▁surve ill ance , ▁systems ▁on ▁the ▁ground ▁( such ▁as ▁SS R ) ▁communicate ▁with ▁equipment ▁( such ▁as ▁trans pond ers ) ▁on ▁board ▁the ▁aircraft ▁to ▁determine ▁the ▁position ▁and ▁other ▁details ▁of ▁the ▁aircraft .