In the world of video conferencing, one of the most annoying aspects of networks are firewalls. When setting up calls, a lot of ports are needed. RTP requires a port for media in each direction, plus their RTCP port (usually RTP port + 1). Double that number again for the audio channels and just for luck, add an extra port for BFCP/H.239 content.
For a company that relies on video conferencing, multiplying this many ports by the number of external calls they expect to have concurrently, and this poses a problem.