We've seen a lot of N2 installations where the Metasys supervisory controllers were installed at a central location with N2 bus risers to each floor. Our recommendation is to eliminate those long runs whenever possible. The longer the N2 bus is the more suseptable it is to EMF and other formas of interference.
If, there is Ethernet connectivity throughout the building install the S4 Open Appliance (OPC-N2 Router or BACnet-N2 Router) as close to the first N2 device as you can. At that point connect to the Ethernet backbone where there will be high speed capabilitiesnd error detection and correction provided as part of the network.