What do we need to make it work?

Firewall

Your organization probably utilizes a firewall to protect your internal systems from outside intrusion. Firewalls therefore limit access, presenting a problem for those who want to videoconference. While it is possible to merely open ports in the firewall to allow for video conferencing, this is not recommended as it presents a security risk. One viable option is to choose a firewall that allows ports to be opened and closed dynamically, allowing for video conferencing (the Cisco PIX firewall, for example).

Learn more about Firewall Recommendations