The traffic-flow analysis (TFA) [1] is a novel method for the performance estimation of communication systems. TFA is a combination of simulation and numerical methods. In the first step, TFA distributes the traffic in units of properly chosen size using the actual routing algorithm of the network. In the second step, TFA adjusts the time distribution of the traffic according to the finite capacities of the network. The convergence of the algorithm used in the second step of TFA is proven in this paper. The speed of convergence is also examined.