In TR-069, the 4 Value Change event code is used when a parameter set for notification is changed by any mechanism other than the ACS. These conditions are set using the SetParameterAttributes RPC.
There are three different notification states. None, Passive, and Active. As arguments in the SetParameterAttributes RPC, these are noted as 0, 1, and 2, respectively.
Setting a parameter for “None” or “No” notification removes any previous notification settings. This may be rejected or ignored for parameters that are considered “Forced Active”. More on that in a moment.
Setting a parameter for “Passive” notification means that, should the value of the parameter change, the CPE must include the 4 VALUE CHANGE event, and the changed parameter value, in its next Inform RPC to the ACS. It doesn’t initiate a connection right away, but delivers the notification at the next most convenient time - for example, during a Periodic Inform, or after a Connection Request.
Setting Passive notification can never be rejected on any parameter, however, it may be ignored for parameters that are set for Forced Inform or Forced Active notification.
Lastly, setting a parameter for “Active” notification means that, should the value of the parameter change, the CPE must immediately initiate a CWMP session to inform the ACS of the change, including the 4 VALUE CHANGE event code and the parameter value in the Inform RPC. The setting of active notification can be rejected for parameters that are transitory or change frequently, at the CPE’s discretion - for example, setting Active Notification on the “Uptime” parameter would cause endless CWMP sessions!
There are some parameters that either cannot be changed or have default behavior. Defined in the data model, these include “Forced Inform”, “Forced Active”, and “Default Active” notification. Forced Inform parameters are those parameters that must be included in every Inform RPC. Forced Active notification parameters MUST always be set to active notification, and should ignore requests to do otherwise. Default Active notification parameters begin with Active Notification set in their attributes upon a factory reset.
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