BACnet/IP protocol allows communication between the components of a building automation and control system (for example, HVAC, lighting control, security systems and related equipment).

The BACnet/IP protocol defines a number of services that are used to communicate between devices and the objects that are acted upon by those services.

Term Definition
APDU Application protocol data unit, that data portion of a BACnet message.
Confirmed message A message for which the device expects an answer.
COV, COV increment Change of value, sets the amount by which a value has to change in order for the meter to send a subscription notification.
Device A BACnet device is a unit that is designed to understand and use BACnet protocol (for example, a BACnet-enabled meter or software program). It contains information about the device and device data in objects and object properties. Your meter is a BACnet device.
Object Represents the device and device data. Each object has a type (for example, analog input or binary input) and has a number of properties.
Present value The current value of an object.
Property The smallest piece of information in BACnet communications, it consists of a name, data type and value.
Service Messages from one BACnet device to another.
Subscription A relationship between a BACnet client and the meter, so that when the present value property of an object changes on the meter, a notification is sent to the client.
Subscription notification The message the meter sends to indicate a COV event has occurred.
Unconfirmed message A message for which the device does not expect an answer.
BACnet Broadcast Management Device (BBMD) A BACnet/IP device (or software application) residing on a BACnet/IP subnet that forwards BACnet broadcast messages from devices on its subnet to peer BBMDs and registered foreign devices on other subnets.
Foreign device A BACnet/IP device (or software application) that resides on a remote IP subnet and registers with a BBMD to facilitate the sending and receiving of broadcast messages to/from devices accessible by the BBMD.

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