One of the metrics used to ensure an efficient management of network services is the packet delay. However, packet delay is highly variable due to queuing mechanism in many network devices, including the host systems. In this paper, the protocol stack packet delay on Linux system is presented. Also, a new RTT probe model based on packet train is proposed in order to achieve a stable RTT measurement without making any modification, optimization and tuning to the current Linux kernel. Experiment results show that using packet train the minimum peak RTT could be determined from the “tail” packets and that its variation is within few microseconds.