The S4 Group, Inc. participated in BACnet International’s Plug Fest for the first time. Each year, the BACnet Testing Laboratories Working Group invites manufacturers of BACnet products to come together to test interoperability. Also known as the Interoperability Workshop, approximately 50 companies attended Plug Fest this past November in Atlanta, Georgia. Participants are paired with each other for 1 to 2 hour sessions for intense interoperability testing. The S4 Group focused on verifying protocol compliance of the S4 Open: BACnet-N2 Router with several companies that manufacture BACnet-based building control systems. Our primary interest was to make sure that BACnet discovery support worked consistently with all BACnet clients. We were quite satisfied with the results from all of the systems that we had the opportunity to work with.