Engineering and commissioning BACnet/SC projects

Projects set up with BACnet/SC ports instead of BACnet/IP ports must have a working hub. The hub needs to be able to reach any of its BACnet/SC nodes. If a hub fails or stops working, the nodes cannot be reached unless a failover hub is configured and running, so it can take over the communication.

When engineering and commissioning BACnet/SC projects, consider the following principles.

• ABT Site is just another BACnet/SC node, so any ABT Site instance mandatorily needs valid certificates to connect to BACnet/SC devices.
  Note: While ABT Site can also engineer devices via BACnet/IP to bootstrap /SC devices, it is not recommended, as it complicates the engineering and commissioning and will only work as long as the BACnet/IP datalink on the devices are not yet locked down.
• Provide a failover hub as redundancy for both, engineering and runtime. If there is no failover hub , downtime of a hub will lead to downtime of node-to-node communication.
• Engineer and commission in the following order:

1. Primary hub
2. Failover hub
3. Nodes

• Test the end-to-end communication between the BACnet/SC nodes to ensure the proper function of the primary hub.
• Unplug the primary hub and retest the end-to-end communication between the BACnet/SC nodes to check the proper operation of the failover hub.
• Reconnect the primary hub and test the end-to-end communication between BACnet/SC nodes and BACnet/IP (and/or BACnet MS/TP) devices (=to ensure the routing function of the hub is working).
• To maintain communication with non-BACnet/SC capable devices, at least one controller must be designated as BACnet/IP to BACnet/SC router. ABT Site configures hubs with this designation by default. Failover hubs do not take over routing functions to BACnet/IP, they are only responsible for maintaining BACnet/SC communication.
• While designing BACnet/SC topologies, keep in mind that all separate BACnet/SC networks must have unique network numbers. If the current configuration has both, BACnet/SC and BACnet/IP, enabled, avoid communication loops. Different UDP ports and network numbers are required for the hub and the nodes. ABT site supports this in the default configuration.
• The ‘number of accepted hub connections’ property can be modified in ABT site. All devices have been tested with the default value and it is highly recommended to use the default values. The value can be exceeded but there is no guarantee for the stability and quality of the hub/node communication.

In multi-vendor projects, it may be difficult to provide all required certificates for all BACnet/SC devices at the beginning of the engineering and commissioning phase. In that case, start the engineering by setting up the BACnet/SC networks as BACnet/IP networks, but load the certificates into devices wherever possible. Once all BACnet/SC devices are successfully equipped with their respective certificates, the respective temporary BACnet/IP networks can be switched over to BACnet/SC.

The same order for engineering and commissioning applies:

1. Primary hub
2. Failover hub
3. Nodes

This order is due to the fact that a node cannot be reached unless its hub is operational, so that activating a node without activating its hub results in a non-reachable device.