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Policy execution can be synchronous or asynchronous. In synchronous policy execution, the component requesting a policy decision requests a policy decision and waits for the result. The PDP-X uses and PDP-A use synchronous policy execution. In asynchronous policy execution, the component that requests a policy decision does not wait for the decision. Indeed, the decision may be passed to another component. The PDP-D uses and PDP-A use asynchronous policy execution.
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