I am always on the lookout for increased performance in WebGIS applications, especially with 9.2.  Part of this search is an understanding of the basic components that I need to use to develop these applications.  I shared part of this at the last ESRI UC.

At the last ESRI User Conference, I gave a presentation on Developing Web Applications with ArcGIS Server .NET.  At the session, I had a few slides that discussed Best Practices one of which was to Understand the network.  More specifically, at most, browser uses 2 simultaneous connections per domain. 

Well, recently, we found more specifics on this in the form of a MS Article ID: 183110 published January 23, 2006.  In summary:

WinInet limits the number of simultaneous connections that it makes to a single HTTP server. If you exceed this limit, the requests block until one of the current connections has completed. This is by design and is in agreement with the HTTP specification and industry standards.

IE uses Wininet.  The HTTP 1.0 spec mandates 4 simultaneous connections while the HTTP 1.1 spec (RFC2616) mandates the two connection limit.

However, in this article it also documents how to override these default settings.  We (Rex Hansen and I) have recently tried this and found that by increasing the default connections to 5, we observed a noticeable performance increase, especially on load. 

NOTE: I do believe that there is a point of diminishing returns and I have not gone to that level of detail yet. Also, the MS Article warns not to do this in your everyday web surfing.

So, for all you WebGIS developers out there, try this out with 9.2 and let me know your findings.  As we do more, I will report it soon.