One of the truths often overlooked by those who wish to rush into the cloud is that the characteristics of their network will change dramatically. Some of the traffic that is currently processed internally will have to be channeled out across the Internet to the selected cloud provider. For example, all of the client traffic from applications such as Outlook or OWA will now travel via HTTPS to the cloud provider instead of being directed to an internal Exchange server. And if we believe the marketing positioning, everyone will have massive increases in mailbox quotas with the resulting increase on OST size… and that data has to be synchronized!
The niggling questions that therefore occur is how much bandwidth is likely to be needed, where that bandwidth should be provided to best service large user communities, and what kind of latency needs to exist to ensure that users experience roughly the same kind of performance across the cloud that they get when Exchange is provided internally.
Of course, one of the great benefits of running Outlook in cached Exchange mode is that it hides many of the network glitches that can occur when you depend on the Internet to get from client to server. Background drizzle-mode synchronization keeps the replica folders updated on the client so that most network interruptions pass unnoticed. But while new messages are received in the background, Outlook uses a special thread to send new messages. Connecting to Exchange Online in Office 365 to send a new message, especially one with a reasonably large attachment (say 1MB) is when I sometimes see performance suffer a tad when compared to connecting to an internal Exchange server.
I’m perfectly willing to accept that part of the problem is due to the characteristics of the Internet connection that goes into my house. I also accept that many other hops exist to make the connection from the local telephone exchange to the datacenter of my ISP to Microsoft. In fact, the complexity of the connection is frightening at times! On the other hand, you can argue that the flexibility of Internet connectivity is a huge strength.
In any case, if you’re in the process of figuring out how to move your company to the cloud, you might find that this blog post by Microsoft’s Neil Johnson contains much valuable and interesting information about how network link latency affects Outlook 2010. It’s certainly worth reading if only to throw additional light on to the tolerance Outlook has for different latencies.