The class of queuing systems for the flow of requests, arriving randomly, is considered. The features of systems of this class are determined as a non-stationary flow of requests and hierarchical ...

For example, a customer withdrawal transaction in a banking system can be represented by a DFD, showing that a customer initiates a withdrawal transaction, which is sent to the bank as a data flow.

Queuing theory examines every component of waiting in line, including the arrival process and the number of customers among others, which might be people, data packets, cars, or anything else.