Explicit Endpoint Admission Control with Service Vector (EEAC-SV) is a solution that allows a multi-hop connection in a Diffserv network to utilize different service classes in different routers along the path, thus enabling the network to provide QoS with fine granularity and improved network utilization. EEAC-SV relies on the QoS information in the pre-marked probing packet to select the optimal service vector. However, owing to the overhead constraint, the QoS information in the probing packet can only be conveyed in a quantized manner. The mathematical model indicates that with the same amount of overhead, the performance of EEAC-SV can be optimized with the proper packet marking strategy. In this paper, we propose the Smart Packet Marking strategy to improve the EEAC-SV performance in terms of reducing the false routing probability. Smart Packet Marking is a stochastic solution which, based on the knowledge of the history of network QoS performances and user behaviors, defines the boundaries of each quantization level in such a way to improve the routing accuracy. Through extensive simulations, we demonstrate that Smart Packet Marking outperforms the packet marking strategy that does not take stochastic information into consideration.