The author states that a difference between Realie and Etherpad is that he users Web Sockets for client/server comm. I'm fairly certain that Etherpad uses Web Sockets too. Am I mistaken?
Etherpad had 3 modes of transport between client and server: short-polling, long-polling, and streaming, each with varying support for different browser/OS/proxy settings. The client starts the connection with the most widely supported method (short-polling), and then attempts to "upgrade" the connection by testing out faster connection types.
I think the messages from client to server always had to do an HTTP post, so we did incur the overhead of all the HTTP headers with each post from client to server, which happened at most twice per second.
You can view the client-side JS code for handling these 3 connection types here:
I didn't write this, but that's my understanding of how it works.
You can also get around the overhead of HTTP headers by using a Flash shim, but we never got that to work well through weird proxy configurations and misbehaving ISPs.
