Issue
What are the bCX and b3 COV subscription limits?
Product Line
Andover Continuum
Environment
- CyberStation
- bCX4040
- bCX4920
- b3 devices
Cause
Confusion on the limits for COV subscription in the Continuum BACnet devices.
Resolution
The b3 controllers are restricted to 32 devices, which means they can
simultaneously establish COV CLIENTsubscriptions with up to 32
different devices (Andover Continuum or third-party).
The bCX1 and the b4920 permit COV CLIENT relationships with up to 255 devices.
These limits are device limits and NOT point limits, so if a bCX has established COV subscriptions with 500 points on device X, it can still set up multiple COV subscriptions with up to 254 other BACnet devices.
IMPORTANT- See Limit of how many devices a Bacnet controller can know about (Known devices).
This limit does not apply to the number of other controllers which a COV exporter can deliver COV data to as a COV SERVER. For instance if a particular controller had a global point like OAT that 50 other controllers wanted and subscribed to this particular controller for that COV, this is allowed because each COV subscription has within it the target controller's address information and does not use the known device limit. There are two cautions that must be stated regarding this example however.
- Refer to What are the differences between Standard Continuum Import/Export and Continuum BACnet COV?.
- Each COV subscription in an exporting controller takes away user memory. Each subscription uses approximately 56 Bytes of user memory. So the limit of how many other devices can subscribe COV's in an individual controller is limited by free memory in the exporting controller.
