This thesis describes the algorithms developed to improve the overload performance of frame relay networks. These algorithms were developed by incorporating a number of congestion control techniques in the existing LAPD protocol (as defined in recommendation CCITT Q.920-Q.921). In addition, the performance analysis of the model is given. Simulation models were developed to evaluate the performance of these networks. A network simulation tool, OPNET, was used for this purpose. The performance of the enhanced model was compared with the existing protocol. A significant improvement was observed in the throughput and delay performance of frame relay networks. The results were obtained by executing extensive simulations and collecting data over a number of simulation runs. The effectiveness of the congestion control techniques was tested by analysing the dynamic performance of the model. These techniques, if implemented in the existing protocol, will ensure the good userperceived network performance at all loads.