BACnet devices on one network do not need to know the LAN technology of other BACnet networks with which they wish to communicate. BACnet/IP devices are no different. When a message is sent from a BACnet/IP device to a non-BACnet/IP device, the NPCI contains the DNET, DLEN, and DADR fields of the destination device and the message is directed to a router to that network, the same as always. Likewise, the router fills in the SNET and SADR fields using the B/IP network's network number and the B/IP address of the originating device.
In this example, a message is being sent from the non-BACnet/IP device to the BACnet/IP device. The non-BACnet/IP device has no idea that it is communicating with an IP device, and the address size happens to be exactly the same size as an Ethernet address, so all current BACnet devices can interoperate in a BACnet/IP internetwork without any modification.
Remote and global broadcasts are just as straightforward...