I figured it would be helpful to add this info from Google support:
Hangouts are adaptive in the ways they attempt to establish a network
connection between a participant on your network and the Google
The connection methods are attempted in this preferenced order: A
UDP connection from the participant to Google on ports 19302 through 19309
A TCP connection from the participant to Google on ports 19305
A TCP connection from the participant to Google on port 80
A TCP connection from the participant to Google on port 443
The ideal connection for a user to make to a hangout is through UDP.
To allow this connection attempt to succeed, you must allow routes
from your network to UDP ports 19302 through 19309.
At a minimum, your corporate network must allow access to the Internet
on TCP ports 80 and 443 in order for hangouts to work.
In addition, we recommend opening these additional ports on TCP for
the following clients:
5222, 5223, 5224 XMPP clients
5228 and 5229 Android phones
5269 XMPP federation
Consult the documentation from your firewall vendor if you need
information about opening UDP and TCP ports.
All traffic back to the client from our conference servers will originate >from the same port that the client is sending to, and be directed back to the >port that the client is sending from.
The UDP traffic consists of STUN, RTP, and RTCP packets, with SRTP encrypted >data payloads.
We are unable to provide any specific IP addresses for our conference servers.