Mission-critical business applications need immediate and guaranteed data delivery. Attempts have been made (like Comet) to adapt AJAX techniques to support such applications These attempts have been based on using unreliable push techniques or resource-greedy polling techniques. However, Ajax On-Demand is an adaptation of AJAX for such applications that doesn't suffer from these disadvantages. The concept of upside-down AJAX (a.k.a. Reverse Ajax, Comet, or AJAX Push) has been talked up quite a bit lately, so let's see what all of this interest is about. The business proposition is actually pretty clear. There are types of applications that require notification to a user about changes on the server as soon as possible. As a rule, such applications belong to the class of mission-critical business applications, which need immediate and guaranteed data delivery. Examples of this class of application are broker's software, security monitoring, and load balancing. In a pre-AJAX era, there was no doubt that the whole-page refreshing of a Web application was not suitable for these purposes. When AJAX came on the scene, people started to look for a way to adapt it for use in this area where the thick client was still king.
