Differentiated services network (DiffServ) aims to provide the same service to a group of connections that have similar Quality of Service requirements. One of the essential function to realize DiffServ is the traffic conditioning mechanisms to support the required services. The paper proposes the enhanced traffic conditioning mechanism which alleviates a bias against reserved bandwidth size. The simulation results show that the new mechanism is rather insensitive of size of reserved bandwidth, and performs better both in terms of throughput assurance and fair distribution of excess bandwidth in case of well-provisioned and over-provisioned network environment.