I'm only sure because I saw a bunch of RTMP and Flex messages going to the central servers (they all have similar IP addresses) and a lot of UDP traffic going to a pretty much random IP address that changed with every person I talked to.

Also, Fogbugz copilot does something similar. It's described at a high level here: https://www.copilot.com/tech/ which links to http://nutss.gforge.cis.cornell.edu/stunt.php