How are real time updates in Facebook, Twitter and Google Plus performed

When I try to implement a real time update system on my 开发者_如何学Pythonsite, I usually make an ajax call, say every 5 secs to a processing file, say getUpdates.php (not sure if it's the right way to do). Get the updates from there and display it. Doing that, when I look at firebug or the developer tools in Chrome and Safari, I can see the file being called ever 5 secs in the XHR section of the tool; after which the updates are displayed.

In case of Google plus, twitter and Facebook, I don't see such a regular call although updates are appearing right in front of me.

How is it that they are doing or is it me not noticing such a regular call??

They use "Long polling" I think. Sounds like a fine excuse to dabble with node js if you ask me. :)