— This paper presents a new end-to-end available bandwidth measurement tool called IGMPS (Improved Gap Model using Packet Size parameter). IGMPS is a lightweight tool based on a new deterministic model of packet delays derived from the Probe Gap Model which uses packet pair technique for actively assessing bottleneck link characteristics. In a previous work that presented a detailed analysis of the capabilities and limitations of packet dispersion techniques, it is showed that probing packet size parameter has a considerable effect on the measurement accuracy. Based on this insight, the model implemented in IGMPS takes into account this parameter and introduce it in available bandwidth estimation formula. Through measurements on several network testbed configurations, we evaluated IGMPS in terms of accuracy, convergence time and intrusiveness and found that IGMPS provides available bandwidth estimates with high accuracy. We investigated the effect of several deciding factors on IGMP...