Exchange Server 2013 : Exchange Clients - Design Considerations (part 2) - Client Performance

3. Client Performance

Design teams are typically concerned with two aspects of client performance. First, they are concerned with the performance of the client itself from the end-user perspective. This makes up a huge part of the user experience, and it should not be overlooked. Microsoft was very cognizant of this fact during the development of Windows 7 and Office 2010, and these design principles were carried forward to Windows 8 and Office 2013. If the client performance is perceived to be slow by the end user, it doesn't matter what you did with the Exchange service—the perception is simply that “Exchange is slow.”

Second, the client choice has a performance impact on Exchange Server. Some clients, such as MAPI or POP3, are extremely light when it comes to using Exchange system resources, while others are much heavier, such as Outlook Web App or IMAP4. Table 1 was derived from a fantastic white paper released by Microsoft for Exchange Server 2010. It compares client types and their resource usage in Exchange Server 2010. This data is not yet available for Exchange Server 2013, but it is included here for comparison purposes between the client types and to highlight the differences that client choice can have on server resource usage.

TABLE 1: CPU usage for Exchange 2010 Client Access role

http://technet.microsoft.com/en-us/library/ff803560(v=EXCHG.141).aspx

Outlook provides some useful information that helps you determine the source of performance problems. The Outlook Connection Status dialog, as shown in Figure 1, can be viewed either by starting Outlook using the/rpcdiag switch or by Ctrl+right-clicking the Outlook icon in the taskbar. This dialog reveals details about each logical connection to your Exchange Server, including RPC response latency information.

FIGURE 1 Outlook Connection Status dialog

There are three columns of interest here: Avg Resp, Avg Proc, and Version. Avg Resp is the average response time from the server, including network latency. Avg Proc is the time that Exchange spent processing the requests. Version is the version of the Exchange server that processed the request.

Figure 1 shows an example from my mailbox, which is connected to Exchange 2013 in Office 365. I am located in England, and my mailbox is hosted in North America. You begin by finding the line with the highest Req/Fail value and then pick the values for Avg Resp (167 ms) and Avg Proc (11 ms). These values tell you that Exchange has dealt with my requests on average in 11 ms. If you subtract this value from the Avg Resp value of 167 ms (167 ms - 11 ms = 156 ms), you can see that the network latency between Exchange and me is 156 ms on average. This is extremely useful when you are trying to determine if a poor user experience is caused by Exchange Server or by the network connection. If Avg Proc is less than 50, Avg Resp is less than 200, and the client is still experiencing poor performance, then the most likely cause is the client device itself.