Cisco Unified Communications Manager is the call processing entity of the Unified Communications infrastructure and is responsible for call setup and teardown.  In addition to this base level of processes it is also responsible for many feature related services such as basic presence, conferencing, music on hold, and single number reach.

Call setup and teardown refers to the process of one IP phone calling another and the phone checking with the Unified Communications Manager (UCM) to ensure that the other party exists and is available.  Once these basic things have happened the next part of the process is for the first phone to figure out how to reach the other phone.  This is handled by basic routing and switching  but also now coupled with the UCM and its dial plan.  Once the two phones have determined that they are aware and reachable they begin to communicate independently of the UCM and have a point to point IP stream between the two respective endpoints.  This can be seen to be quite efficient with respect to bandwidth utilization.   Other systems that require an IP stream between the IP PBX and the respective endpoints at all times but this is not as efficient from a bandwidth perspective.

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