A method to extend BACnet network systems for building automation systems to scale up to large topologies, wherein a BACnet network system comprises a network of BACnet devices (300 - 304, 311, 312), wherein the network of BACnet devices (300 - 304, 311, 312) is organized as a virtual hub-and-spoke network, wherein one of the BACnet devices (300 - 304, 311, 312) is implemented as a directed hub-device to which all other BACnet devices are connected as node-devices (301 - 304, 311, 312) by using WebSocket connections, wherein the method comprises providing node-devices which have a system scope of a building to view and modify the entire building automation system; providing node-devices which have a building scope of a building to realize central functions for the entire building automation system or do the supervisory demand control of floors and supply by primary plants; wherein the node-devices of the system scope and/or the node-devices of the building scope are assigned to supervisory scope BACnet devices (311, 312); providing node-devices (301 - 303) which provide a floor scope of a building to realize room control functions and/or floor level control functions; providing node-devices which provide a plant scope of a building to realize the central supply and equipment control of primary plants and supply; wherein the node-devices (301 - 303) with floor scope and/or the node-devices of the plant scope are assigned to directed scope BACnet devices (301 - 304); wherein the directed hub-device is hosting two WebSocket listeners, wherein the first WebSocket listener is accepting uplink-connections for supervisory scope node-devices (311, 312), wherein broadcast distribution of messages from an uplink-connection among all uplink-connections and all downlink-connections is performed according to the BACnet/SC standard; wherein the second WebSocket listener is accepting downlink-connections from directed scope node-devices (301 - 304); wherein the directed hub-device limits the broadcast distribution of broadcast messages from a downlink-connection to each uplink-connection, and not to any other downlink-connection, wherein the directed hub-device is forwarding or blocking unicast messages from one downlink-connection to another downlink-connection. providing node-devices which have a system scope of a building to view and modify the entire building automation system; providing node-devices which have a building scope of a building to realize central functions for the entire building automation system or do the supervisory demand control of floors and supply by primary plants; wherein the node-devices of the system scope and/or the node-devices of the building scope are assigned to supervisory scope BACnet devices (311, 312); providing node-devices (301 - 303) which provide a floor scope of a building to realize room control functions and/or floor level control functions; providing node-devices which provide a plant scope of a building to realize the central supply and equipment control of primary plants and supply; wherein the node-devices (301 - 303) with floor scope and/or the node-devices of the plant scope are assigned to directed scope BACnet devices (301 - 304); wherein the directed hub-device is hosting two WebSocket listeners, wherein the first WebSocket listener is accepting uplink-connections for supervisory scope node-devices (311, 312), wherein broadcast distribution of messages from an uplink-connection among all uplink-connections and all downlink-connections is performed according to the BACnet/SC standard; wherein the second WebSocket listener is accepting downlink-connections from directed scope node-devices (301 - 304); wherein the directed hub-device limits the broadcast distribution of broadcast messages from a downlink-connection to each uplink-connection, and not to any other downlink-connection, wherein the directed hub-device is forwarding or blocking unicast messages from one downlink-connection to another downlink-connection.