Reverse Ajax

Reverse Ajax refers to an Ajax design pattern that uses long-lived HTTP connections to enable low-latency communication between a web server and a browser. Basically it is a way of sending data from client to server and a mechanism for pushing server data back to the browser.

This server–client communication takes one of two forms:

• Client polling, the client repetitively queries (polls) the server and waits for an answer.
• Server pushing, a connection between a server and client is kept open, the server sends data when available.

Reverse Ajax describes the implementation of any of these models, including a combination of both. The design pattern is also known as Ajax Push, Full Duplex Ajax and Streaming Ajax.

Examples

The following is a simple example. Imagine we have 2 clients and 1 server, client1 to sends the message "hello" to every other client.

With traditional Ajax (polling):

• client1 sends the message "hello"
• server receives the message "hello"
• client2 polls the server
• client2 receives the message "hello"
• client1 polls the server
• client1 receives the message "hello"

With reverse Ajax (pushing):

• client1 sends the message "hello"
• server receives the message "hello"
• server sends the message "hello" to all clients

Note that with reverse Ajax less traffic is generated and the message has been transferred with less delay (low-latency).

See also

• Ajax
• BOSH
• Comet
• Icefaces
• Push technology
• Pull technology

External links

• The Slow Load Technique/Reverse AJAX - Simulating Server Push in a Standard Web Browser
• Exploring Reverse Ajax
• Reverse Ajax with DWR (an Java Ajax framework)
• Changing the Web Paradigm - Moving from traditional Web applications to Streaming-AJAX