I often get the question: how does the Communication flow in OCS, because i have firewall between my internal networks. My answer is normally: it depends on what you are doing.
But now there is a drawing to show together with the list of ports, nice J
This poster of Office Communications Server 2007 R2 describes the traffic flow of protocols and ports used in each workload. Communications Server 2007 R2 supports the following workloads: IM and Presence, Conferencing, Application Sharing, and Enterprise Voice. These filtered views can assist you in architecting your deployment of Communications Server 2007 R2. The different server roles are described along with server certificate requirements. Firewall and DNS configuration requirements are also described.
get it here