technology behind html based chat systems like facebook and google talk

Question

Can anyone give me a brief rundown of how Facebook and Google Talk work, are there persistent connections involved similar to the classic Java based chat systems whereby a server manages the connections and directs messages to the necessary destination or are they stateless? I'd like to create something similar to these but I'm not sure where to start and if I need to have custom services running on a server I may have to rethink my approach.

I'm not after a full-blown explanation but I am interested to know if there's a stateless approach that doesn't require services running on a server. If Html5 is required that's ok.

Answer 1

Both use the Jabber protocol: http://www.jabber.org/