ce to subscribe to COV



ce to subscribe to COV notifications.

Convert Polarsoft BACnet data to the protocol adapt

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                                      The server must accept the subscription.

 
Monitor
COV Server device monitors the property values of subscribed objects and the COV change criteria.
Notify
When a change has occurred that meets the COV change criteria the server sends notifications to the subscribers or for those objects with a COV Period defined, notifications are sent based on the period if there has been no change.


 
Process Notification
The data client must process the notification and update the display, log ….
Unsubscribe / Renew Subscription
If the data client no longer needs the subscription it unsubscribe. If it needs the subscription maintained then the client should periodically re-subscribe.

The system is a little more complex than this. For example, subscriptions have durations and there is more than one way the notification can be sent,



18.5.   Key Elements of the COV Technology



COV Server : 

A BACnet device that supports COV, accepts subscriptions and sends COV notifications messages to a COV Client.

COV Client : 

A BACnet device, typically a SCADA or Logging application, which can subscribe for COV notification and which can process the notification messages.

Subscription :  

Establishes a relationship between a COV Server and a COV Client. 
Subscriptions have the following attributes ;
"       Subscription to an Object or to a Property
BACnet provides two services for subscription. One subscribes to an object and the other to a property of an object. 
"       Identification of the Subscriber
The server needs to know where to send the notifications.
"       Object Identifier
Eg. Analog Input 1
If subscribing to a property then the property must be identified too.
"       Lifetime
Is indefinite or a specific number of seconds.  Values can be large.
"       Notification Type
Notification can be sent with/without requiring confirmation from the data client. 
"       COV Increment
This parameter is only used in subscriptions to object