In this paper a simple model for uniform traffic with periodic input patterns is suggested. Periodic input patterns (PI-Patterns) represent a further development of the family of patterns (S-Patterns) proposed in our previous investigations. Our simulation studies use the Generalized Nets (GN) model of the known PIM-algorithm. The simulation results of a GN-model using PI-Patterns are presented and compared with results obtained for S-Patterns. It is shown that the upper bound for the throughput of PIM-algorithm for the S-Patterns is the value of throughput for uniform traffic with PI-Patterns.