SAM Agent Network Traffic Diagram

I know I've seen this before.  But, now I can't seem to find it.  What I'm looking is a diagram for communications between the new Agent an the primary SAM poller/server.  I know the communications are over port 17777 but I would like to know if the communications is one way or bi-directional.  I would assume that if you were to deploy the agent from the Primary server then communications would initiate from the primary server.  Is that the only time communications are initiated from the primary SAM server?  After agent installation on the target node does communications always initiate from the agent node?

Thanks