This paper proplses a model of routing control and accesstraffic control to solve the dynamic assignment of the capacity for communications network.Firstly

equation of system status（ estimating busy-circuitnumber of trunks）are derived

and at the same time

the control strategy os assessed.Secondly.the optimal model for the dynamic assignment of the capacity is designed.and for the "fairness"

quadratic programming model isgiven. Finally

the paper discusses the realization mechanism of the realization mechanism of the above methodology and illustrates the pracgti-cability by instances.