The Averaged RPC latency is the measure of how long it takes to for a packet to be processed. Below is the description on the counter from Microsoft taken from the Exchange Server Analyzer tool.
The RPC Averaged Latency performance counter records the average time, in milliseconds (ms), that it takes for the last 1024 packets to be processed. The latency represents how long it takes from the time the Store.exe process received the packet to the time it returned the packet. The RPC Averaged Latency performance counter does not include any network latency or any latency that is introduced by anything other than the Store.exe process. Although the RPC Averaged Latency performance counter data does not include network transit time, it does provide data about the shortest time period that client computers have waited for a response from the server. If the RPC Averaged Latency performance counter data is lower than 50 ms, the server can process the requests in a reasonable amount of time. If the counter stays greater than 50 ms for more than several seconds, this indicates that the server is having difficulty keeping up with the load. As a result, users may experience delays when accessing their e-mail. If average latency is greater than 100 ms, users will receive the following pop-up window from their Microsoft Office Outlook® client computers: "Retrieving data from Exchange Server."
This is monitored from perfmon as part of the MSExchangeIS object.
MSExchangeIS\RPC Averaged Latency
Brad
