Delays are the major factor in the performance analysis of the control network. Topologies most in use and data
characteristics of the network control system are considered, and corresponding delay models under different scheduling policies are derived based on stochastic network calculus. Then the distribution of delays and stochastic upper bound on delays of real-time data in the control network are calculated. The results are compared with the guaranteed upper bound on delays derived by deterministic network calculus, and the pessimism of the latter bound is evaluated.