"Clients that use persistent connections SHOULD limit the number of
   simultaneous connections that they maintain to a given server. A
   single-user client SHOULD NOT maintain more than 2 connections with
   any server or proxy. A proxy SHOULD use up to 2*N connections to
   another server or proxy, where N is the number of simultaneously
   active users. These guidelines are intended to improve HTTP response
   times and avoid congestion."

You have the same behavior when trying to download more than 2 files from one web server (domain) with the same browser instance. If you open a new browser (i.e. process iexplore.exe) you will have again 2 connections. This is the reason why you have a maximum of 2 AJAX calls at the same time to one domain.

See RFC 2616 (http://www.faqs.org/rfcs/rfc2616.html).

For IE you can change this, but it is then a non-standard browser:
http://support.microsoft.com/kb/183110

Discuss with others at Google Ajax.NET Professional Group!

2 Comments

• Simone Chiaretta said Thursday, October 20, 2005 8:20:00 PM

  I've a lot of these errors using fiddler...
  the IIS says that there are too many connections...

• Michael Schwarz said Thursday, October 20, 2005 8:37:00 PM

  You have to activate the option "re-use connections" in the Fiddler options.
  
  CIAO
  Michael