The Counters-Based Modified (CBM) traffic conditioner was presented in a previous work as a feasible election for the Assured Service implementation with DiffServ. In this work, we evaluate the end-to-end performance of TCP Reno sources with the CBM traffic conditioner in topologies with one and three network nodes under miscellaneous characteristics, i. e. variable contracted target rates and round trip times. In addition and for the same scenarios, the robustness of the couple CBM-RIO is tested when Assured Service and best-effort sources coexist and compete for network resources. Strong assurance of achieving target bandwidths and even allocation of spare bandwidth across different flows can be provided as shown in simulation results.