I want to know the technology behind the web base ICQ - go.icq.com. 
It is a Java Applet ICQ that can be used behind firewall.

Here are my guess:
** It uses port 80 to connect to the server becuase it can be used
behind firewall.
** From the source of the page that contains the Java Applet, the
server is at iht-d01.icq.com
** Since the server needs to notify the user when someone sends a
messsage to the user, the server must keep a connection to the user. 
So I guess the Java Applet needs to open a Socket connect to port 80
of the server.

What I don't understand are:
1) Port 80 on the server should already been used as a webserver (go
to iht-d01.icq.com will return a webpage).  How can the server uses
port 80 to listen to the client's socket connection request at the
same time?
2) The number of user uses Webbase ICQ should easily exceed tens or
hundreds of thousands.  Looks like all the users connect to the same
server (iht-d01.icq.com).  How can one server keeps all the live
socket connections?
3)  This question is not as important as the previous two.  It will be
great if you know the answer.  What language is the server application
that talks to the Java applet written in?

Kelvin