Cisco Unified CM Sync
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Cisco Unified CM supports two types of sync:

* Regular API sync - utilizing the regular use of LIST and GET API
  calls to retrieve data; like any other device sync.
* Change Notification Sync - utilizes a service on the Cisco Unified CM side
  to pull information about records that have changed in a given period.
  Note: Model Instance Filters cannot be used in conjunction with a Change Notification Sync.

  The Change Notification Sync type is generally the most efficient sync type to use,
  as it minimizes the amount of data that needs to be retrieved from the Cisco Unified CM
  (especially for updates).

  The Change Notification Sync process works as follows:

  VOSS Automate retrieves the change records from the Cisco Unified CM on a regular interval (configurable).
  For example, this could be every 10 minutes. At the time of a scheduled sync is setup, VOSS Automate 
  processes the change records collected (for example, nightly). VOSS Automate then processes the records accordingly:

  * Add - will do a GET API call to retrieve the full record and add it to VOSS Automate.
  * Update - will do a GET API call to retrieve the full record and update the record in VOSS Automate.
  * Del - will remove the record from VOSS Automate.

  So the efficiency on update syncs is because we do not need to do a GET API call for every single
  record in the system - only those that changed.  In large UC application installations, this can
  make a big difference in Update sync times.