Hi WWW,
"Director" is the callsign of an Approach Radar Control Unit primarily concerned with the vectoring of inbound aircraft to an airport. The function may be split into an Intermediate Director who issues initial instructions to aircraft entering or approaching the stacks, and a Final Director who is resposible for vectoring aircraft to the final approach aid and providing the correct vortex wake spacing. Int. Directors will give initial descent clearance,impose speed control, and usually determine the best landing order to achieve maximum runway utilisation. When the aircraft are established on suitable headings the Int. Director will hand them over to the Fin. Director for the final turn onto approach for the landing runway. Further descent is given as necessary,and speeds adjusted as required before transfer to the Tower Controller.
"Radar" is the callsign of an Approach Radar Control Unit which will work inbound, outbound and overflying traffic as necessary, providing Radar Control, RIS and RAS appropriate to the type of airspace and local instructions.
"Approach" is the callsign of a Unit which will provide at least an Approach Procedural Service to participating aircraft. A pilot will usually make his initial call to "Approach".
Hope this is useful.