In the Segmented Metasys BACnet/IP network architecture, the IT network is used as the backhaul for the BAS access switches, as well as for the network engine s when the network engine s are physically connected to the IT network. The BAS access switches are always directly connected to the IT network, always reside in an IT VLAN, and are assigned an IP address from the IT network’s address space.
If the network engine s need to communicate with other BACnet devices in the IT network or will be connected directly to the IT network, they also reside in an IT VLAN and are assigned an IP address from the IT network's address space such that network engine s are visible from the IT network.
If there are no BACnet devices in the IT network, or if there are but the Metasys devices do not need to communicate with them, the network engine s can reside in the BAS network’s private address space. If the network engine s are placed in the private address space, then the Metasys server must reside in the IT VLAN allocated to the BAS network for the network engines and IP controllers to be visible from the IT network by way of the Metasys server .
The Metasys IP controllers are always assigned to the BAS network's VLANs and are assigned IP addresses from the BAS network's private address space such that they are not directly visible from the IT network. The controllers are still indirectly visible from the IT network through the Metasys server and/or network engine s.
The network engine s and the BAS access switches can be connected to the IT network using a single IT VLAN or by using multiple IT VLANs. In either case, the network engine s and BAS access switches can be connected to IT access layer switches by way of either trunks or access ports on the IT switches. There are pros and cons to both methods, which are discussed in more detail in the following sections.