High Level Architecture(HLA) is a specification for interoperation among heterogeneous simulators which are executed in a distributed environment. HLA originally allows a number of federates to join in a federation using a single RTI(Run-Time Infrastructure). To interoperate federations without modifying RTI, agent federate, which represents behavior of a federation, can be used. Agent federate can use MOM(Management Object Model) service or agent-user protocol to acquire information of a federation. This paper performs various experiments to measure performance of two architectures. MOM service shows a loss of performance but can be applied without modifying user federates. Experiment results can be used to determine appropriate architecture for interoperation of federations.