HTML and CSS Reference
a NOte ON the terMINOLOGY
there are a number of different terms that have been used to describe the http-based realtime web solutions.
most of these are umbrella terms that encompass the various methods developers use to achieve a server to
client communication over http.
these terms include Comet, http server push, and aJaX push, among a slew of others. the problem is that
although some of these terms have very specific definitions and techniques—especially Comet—they tend to
hold different meanings for different people.
the position held in this topic is that Comet is a term used to define a paradigm within an application structure:
namely that of simulating bidirectional communication between the server and the client using two http connections.
Figure 1-4. The Comet paradigm means two-way communication between client and server 11
Comet applications can deliver data to the client at any time, not only in response to user input. The data
is delivered over a single, previously-opened connection.
there have even been arguments that newer technologies such as html5 Websockets are part of the Comet
paradigm and not a replacement for it. however, alex russell (who coined the term) has now confirmed that
we should consider Comet as an umbrella term for old http-based hacks and look to the future with a new
technology called Websockets. 12
11 Diagram and quote source: http://infrequently.org/2006/03/comet-low-latency-data-for-the-browser/