I mentioned I'd do some explaining how the new R2 features work in a prior post.
When you install an R2 SE server or EE pool FE you get the choice of installing a number of new capabilities, specifically:
Each of these have a corresponding service and all run within a new Application Server we shipped with R2 to host Microsoft applications built on top of OCS. You might see this referred to as UCAS or Unified Communications Application Server. There's a service that corresponds to UCAS (RTCAPPSRV) and also ones that correspond to each of these applications - I've indicated the service names next to each one above.
The first two are the plumbing behind the R2 dial-in conferencing capability for audio conferencing. CAA is what answers/authenticates dial-in participants and transfers them into the appropriate meeting. CAS provides entry/exit and mute tones for dial-in participants. ACD or Response Group is used for routing calls to Agents for example in a service desk scenario and finally CCS or Outside Voice Control is used primarily to enable call back scenarios when using single number reach in Communicator Mobile (COMO).
For a good overview check out the R2 Planning Workbook we wrote for TAP customers and partners - the second section gives a comprehensive overview of all R2 roles, capabilities and topologies.