The Do Not Disturb or function on most PBX or PABX systems prevents calls from ringing on an extension for which DND is activated. Some Do Not Disturb (DND) attributes include directing the call to a preassigned extension (like a secretary or assistant), busy signal, DND signal, or recorded message generated by the telephone switch. Some switches allow the call to go through to the extension but restrict the response to a visual indication. Some PBX systems allow the assignment of DND circumvention codes to supervisors.