Office Communications Server 2007 R2 Workload Architecture Poster

You will have a global view of Office Communications Server 2007 R2 traffic flow between component like : IM and Presence, Conferencing, Application Sharing, and Enterprise Voice.
You can see the different server roles, the needs in term of server certificate, and also the firewall and DNS configuration requirements.

Ref :

http://www.microsoft.com/downloads/details.aspx?FamilyID=AF2C17CB-207C-4C52-8811-0ACA6DFADC94&displaylang=en