Abstract: Issues related to fair sharing of bandwidth in assured forwarding based differentiated services networks have been discussed in many research papers. Some of the factors that can bias fair sharing of bandwidth are round trip time （RTT）, packet size, the number of flows in aggregate and target rate etc. The assured services architecture relies on packet marking mechanism at the edge router, and on queue management mechanism at the core router. The purpose of DTBM is to achieve proportional fair sharing of bandwidth among heterogeneous TCP flows. By measuring local throughput to adjust the threshold, DTBM can change the marking probability to achieve fairness. The major benefits of DTBM are its simplicity, least sensitivity to parameters, and transparency to the end hosts. The simulation results indicate that compared to TSW2CM, CATC, TokenBucket, and srTCM for different network scenarios, DTBM performs better in providing fairness among heterogeneous TCP flows.