A. All text and Session Initiation Protocol (SIP) communications are routed via the OCS, but this is just text (and it's compressed by default). For voice and video communications that involve two parties, the traffic is sent point to point and isn't communicated via the OCS server. Say I have two people in the U.S. and an OCS server in the UK. If the two people were having a voice or video conversation, the traffic wouldn't be sent via the UK.
If there are more than two people communicating, however, all traffic is sent via the conferencing services. All the traffic in my example would route via the UK, even though all the people communicating are in the US.
Related Reading:
Check out hundreds more useful Q&As like this in John Savill's FAQ for Windows. Also, watch instructional videos made by John at ITTV.net.