most firewalls only let you go out via a proxy using port 443. Also port 80 can be used but then you have to wrap your chat protocol in HTTP which is not fun. Most firewalls do not let anything come in, so the software on the appliance/computer inside the corporate LAN has to initiate a connection and go outwards.
This implies that there cannot be a peer-to-peer setup since both peers-to-be can only go out and never connect to the other. And hence there is a server in between the two chat partners.
This implies that there cannot be a peer-to-peer setup since both peers-to-be can only go out and never connect to the other. And hence there is a server in between the two chat partners.