13.3 Call Flow Between Cisco Unified Communications Manager and Cisco VCS

This topic describes the call flow between Cisco Unified Communications Manager and Cisco TelePresence Video Communication Server (VCS).

The call flow for a call that is placed from a Cisco Unified Communications Manager endpoint is as follows:

  1. An endpoint that is registered with Cisco Unified Communications Manager dials 4001.
  2. The route pattern 4XXX is matched and refers to a SIP trunk that points to Cisco VCS.
    Note

    If the endpoint dialed a URI, then a SIP route pattern that matches the host portion of the called URI must be matched. The SIP route pattern then refers to the SIP trunk that points to Cisco VCS.

    Route patterns and SIP route patterns can refer directly to a specific SIP trunk or they can use a route list and route group construct to refer to one or more SIP trunks.

  3. The SIP trunk that points to Cisco VCS sends the call setup message (SIP INVITE) to Cisco VCS.
  4. Cisco VCS receives the call through a neighbor zone. The presentation of the calling number isnumber@ip_of_cucm (for example, 2001@10.1.5.15). The presentation of the called number isnumber@ip_of_vcs (for example, 4001@10.1.6.19).
  5. To return the call from the Cisco VCS endpoint, a transform in Cisco VCS translates the calling number to a pattern with a domain (2001@hq.cisco.com). The transform is also used for the called pattern. The called pattern must be transformed to the URI address (4001@hq.cisco.com) that is registered with Cisco VCS.
  6. The call is forwarded to the called endpoint (4001@hq.cisco.com).

The call flow for a call that is placed from a Cisco VCS endpoint is as follows:

  1. An endpoint that is registered with Cisco VCS makes a call to +1201201200.
  2. The called number matches a transform that translates this number to the format number@domain(+12012012001@hq.cisco.com).
  3. Because the translated pattern is not found on a locally registered endpoint, Cisco VCS tries to find a search rule. A search rule is matched and it points to a neighbor zone.
  4. The neighbor zone points to Cisco Unified Communications Manager and a SIP INVITE message is sent to Cisco Unified Communications Manager.
  5. Cisco Unified Communications Manager receives the call over the SIP trunk that points to Cisco VCS. Cisco Unified Communications Manager tries to find the called number on a registered endpoint.
  6. The call is forwarded to the called endpoint.
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