I have been working on a multi-part article for Technet magazine that explains how Communicator works with OCS and other components to provide various voice, conferencing and presence features. The first of these series of articles was published in February edition that explained how presence works. The next one in the July edition explains how voice works. These articles also shed light on the important role that client endpoints play in the OCS system and provide an end to end perspective. This particular article highlights the role client endpoints play in setting up voice calls, what happens when numbers are dialed and how they are processed in the system, how calls are forked, what inbound and outbound routing functions are etc. The article also provides a map of the events that take place from the point that a call is initiated to the point that the call is answered and then terminated.