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Modern control networks such as EtherNet/IP™, Modbus/TCP and BACnet/IP® use Ethernet for communications due to its high speed, lowering cost and in some instances, the necessity to operate over structured wiring. Although the study of Ethernet does not require an understanding of application protocols, knowledge of application protocols has become increasingly important as modern networks are deployed. The latest protocols are all based upon Object Modeling which can be quite confusing to someone who has not been exposed to this abstract concept. Object Modeling a Physical BACnet Device introduced object modeling, object properties, and services as they pertain to a physical BACnet/IP device. Achieving BACnet Compliance continues the discussion by addressing the requirements for achieving BACnet compliance.

BACnet Interoperable Building Blocks (BIBBs)

A primary goal of the BACnet standard is interoperability among vendors of BACnet equipment. Users also need to make sense of the vast family of BACnet products that range from simple sensors to workstations and building controllers. Not all devices need to provide the same services, so how do we classify devices? The BIBB concept was introduced later in the standards development process as a way of classifying the numerous available services into more manageable processes as would be needed in a building automation application. The resulting 67 BIBBs can be found in Annex K and are classified into five groups:

  • Data Sharing (16)
  • Alarm and Event Management (13)
  • Scheduling (3)
  • Trending (5)
  • Device and Network Management (30)

At first glance it would appear that things are getting more complicated than less. How could we get 67 BIBBs from only 38 possible services? One answer is to understand who the requesting device is and who the executing device is. In the jargon of BIBBs, an A device is one that uses the data (client) while the B device is the one that provides the data (server). Study Tables 1 and 2 which show two Data Sharing BIBBs.

Table 1 — ReadProperty-A (DS-RP-A)

Table 2 — ReadProperty-B (DS-RP-B)

Notice that both BIBBs use the same ReadProperty, but in one operation Client A is initiating the request while in the second operation Server B is executing the operation. Devices are not required to both initiate and execute services, but some do.

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