The S4 Group, Inc.

The JCI design of the N2 bus is fixed at 9600 Bd. We have to live with that. It can’t be changed.

So, the problem becomes how do we accommodate BACnet IP transactions coming in at Ethernet speeds?

One of the things that we did was set the BACnet APDU and APDU Segment Timeout parameters the much higher default levels in the BACnet-N2 Router than you would normally expect for a BACnet IP device. This tells the BACnet client talking to us to be much more tolerant with timeouts, etc.

We also made it possible for you to update those parameters through our management console so that you can make adjustments before the BACnet client tries to do a BACnet discovery. Here’s a screenshot.

Another thing that we did was build performance and error rate statistics into the system so that you have the ability to easily monitor how hard you are driving the N2 bus. We do everything we can to keep it from getting saturated but sometimes this means that you have to slow down the scan rate in the BACnet client.

From a planning point of view, if you find that you have very large N2 buses it is sometimes advisable to split those legacy busses into multiple segments. That doesn’t allow us to make it run any faster than 9600 Bd, but it does spread the load across multiple interfaces typically improving both performance and reliability.