you client just listens on any port you pick. then it calls the webserver to
register its ipaddress and port number. the webserver can call back in the
future. this will require the client to open their firewall to the new port
number. if they are using nat translation, then they will need to setup a
static ipaddress map in the router, and give the nat'd ipaddress to the
webserver.

-- bruce (sqlwork.com)