In this thesis, we propose a dynamic traffic adjustment scheme for end-to-end proportional differentiated services (EEPDS) on MPLS networks. When the Egress LSR (Label Switch Router) first observes that the proportional ratio of multiple flows could not be maintained, it will locate the performance bottlenecks by sending control messages to all the traversed LSR. In the proposed scheme, the identified bottleneck routers may have to drop the packets of traffic flows that do not require any QoS assurance (for example, the best-effort flows). Moreover, if dropping packets of the best-effort flows could not meet the goals of maintaining proportional ratios, the Ingress LSR would have to shape the traffic rates of sending flows proportionally based on the throughput values observed by the Egress LSR. Once a bottleneck router regains its sufficient bandwidth released by other traffic flows, it will send out control packets to notify the Ingress LSR to recover the original sending rates. Eventually, the proposed EEPDS mechanism can meet the goals of maintaining the proportional ratios by dynamically tuning the traffic flows. For the purpose of demonstration, we implement the EEPDS scheme by using MNS simulator. According to the experimental results, the EEPDS scheme has shown that it can meet the proportional ratios of multiple traffic flows even under severe network congestions, where multiple performance bottlenecks may occur. Finally, we observe that the processing overhead of the proposed EEPDS scheme is very small, since it is triggered only when the Egress LSR detects the situation of unsatisfied proportional ratios.