Because the preprocessing and postprocessing times are
typically constant compared with the waiting time and the
transmission time, and are a limitation of computer processing
parameters rather than network physical and protocol
parameters, we will ignore them in the following discussion.
The queueing time, Tqueue, is the time a message waits in the
buffer at the source node while previous messages in the queue
are sent. It depends on the blocking time of previous messages
in queue, the periodicity of messages, and the processing load.
In some control applications, old messages are discarded,
effectively setting queue T to zero; however, this strategy may
require a nonstandard network protocol. In the following
discussions, the blocking time, frame time, and propagation
time for each of the three candidate control networks should be
introduced first.