철도통합무선통신망(LTE-R)에서 EMS(Element Management System), EMS-R (E…

철도통합무선통신망(LTE-R)에서 EMS(Element Management System), EMS-R (Element Management System-Radio), EMS-C(Element Management System-Core), EPC(Evolved Packet Core)의 용어를 설명하시오.