The BC might detect that an RT is not responding at all, or that whenever the RT responds it causes corruption of the bus. It is undesirable to retry more than just a few times, as this would stretch the bus list and cause delays in the transmission of other messages. The various RT numbers and sub-addresses that are used are specific to an aircraft. This ICD defines each and every message that the BC should transfer over the bus, and the precise contents of each message. The ICD defines every data field in every message, in which word and bit the data field resides, the nature of data that the data field contains, and other information that is used to convert the data in this field into an engineering-units value.
Data is dynamic, mostly sampled periodically, and is encoded in a variety of formats.
Data elements can be as simple as a single bit, or as complex as floating point numbers. You need to be able to inject scenarios by simulating data to the unit. Once the unit is built and ready for integration with the real system, you need a powerful monitor that will tell you what goes wrong and where. You then need to pass your unit through verification and qualification tests, and finally, the unit requires maintenance, part of which deals with its communications connections.