About Comet and HTTP Streaming

Push technology

Comet is a form of Push technology allowing a web server to continually stream data to a browser. This is opposed to the traditional model of the browser requesting documents synchronously. There are several different underlying techniques used to implement Comet including Hidden iFrame, XMLHttpRequest/Script Long Polling, and embedded plugins such as Flash. The introduction of HTML 5 WebSockets in to future browsers will provide an alternative mechanism for HTTP Streaming. StreamHub uses a "best-fit" approach utilizing the most performant and reliable technique for each browser.

Uses of Comet

Comet is used primarily in pages which require asynchronous messages or events to be sent to the browser. It is often used as a message transport in enterprise middleware. Many spread-betting websites, financial portals, and trading applications make use of Comet to update prices in real-time. It is likely you have already used Comet, it is used for event notifications and chat in many everday websites such as Facebook, Google Mail, and Meebo.

Why a Comet server?

Traditional web servers such as Apache and Microsoft IIS were built to handle lots of short-lived HTTP requests, whereas Comet requires lots of long-lived connections and logic to handle the asynchronous sending of messages. Plugins and modules are available but fail to scale to the demands of Comet. Since the server needs to maintain a connection for every client the normal thread-per-connection model does not work. Streamhub is purpose built to be a highly-scalable Comet server. It has an event-driven architecture which removes the need for a thread-per-connection, allowing it to scale to thousands of concurrent users.

What is Bayeux/Reverse Ajax/HTTP Push?

There are many different terms, some with subtle differences, used to describe the 'umbrella' concept of pushing data from a server to a client. StreamHub doesn't require you to understand these underlying details, it wraps up all the technical workings in a simple API. However, if you wish to explore these various terms and how they relate to StreamHub, continue browsing below:

• Reverse Ajax
• Ajax Push
• Bayeux
• Push Engine