I am looking to get a good explanation of all the communication that takes place between federated partners, a diagram would be nice. I would like to focus on all communication that would need to pass the firewall, where it originates and where it is going to. I need a complete listing of what needs to be allowed on the firewall. The minimum firewall configuration required to use Lync with a federated partner. One reason I am trying to understand this communication is we are having an issue. I am able to see my federated partner and send a chat message but they cannot respond. I think we need to configure the firewall. I need to know what servers on their side need access through our firewall and do they just need access to our edge servers? Thanks!