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When using Outlook clients in MAPI mode, clients' actions in Outlook translate to remote procedure calls (RPCs) between the clients and the server. If the client is running in online mode, these RPC calls occur synchronously. Any delay by the server in fulfilling these synchronous requests directly affects user experience and the responsiveness of Outlook. Conversely, if the client is running in cached mode, the majority of these requests will be handled asynchronously. Asynchronous processing means that the performance of the RPC mechanism does not affect the overall user experience. The XchgRpcTest monitors the performance of RPC mechanisms between the clients and the Exchange server.

Measurement	Description	Measurement Unit	Interpretation
Rpc_operations	Indicates the rate of RPC operations handled by the Exchange information store during the last measurement period	Operations/sec	Generally, spikes in RPC requests that do not increase RPC operations/sec indicate that there are bottlenecks preventing the store from fulfilling the requests in a timely manner. It is relatively simple to identify where the bottlenecks are occurring with regards to RPC requests and RPC operations/sec. If the client experiences delays, but the RPC requests are zero and the RPC operations/sec are low, the performance problem is happening before Exchange processes the requests (that is, before the Microsoft Exchange Information Store service actually gets the incoming requests). All other combinations point to a problem either while Exchange processes the requests or after Exchange processes those requests.
Current_rpc_requests	Indicates the number of MAPI RPC requests presently being serviced by the Microsoft Exchange Information Store service.	Number	The Exchange server is configured with a pre-set maximum number of RPC requests that can be handled simultaneously (default is 100). If this value is exceeded, client requests to the server will be rejected. This measure should be below 30 most of the time.
Rpc_traffic	Indicates the number of MAPI RPC packets being handled by the Exchange Information Store during the last measurement period. .	Packets/Sec
Rpc_avg_latency	Indicates the number of MAPI RPC packets being handled by the Exchange Information Store during the last measurement period. .	Secs	This value should be below 50ms at all times. A slowdown in RPC packet processing can adversely impact the user experience.