The guaranty of the Quality of Service (QoS) in the Mobile Ad hoc NETwork (MANET) is a need to generalize their deployment [1]. Indeed, the performances of wireless network are related to many parameters: the load of the network, the number of nodes, the state of the radio link, etc. It is very difficult to quantify exactly all these parameters. So, we propose to use the Round-Trip Time (RTT) as an estimator of the network exchange capacity and its available bandwidth. A fine analysis of this estimator based on the theory of EWMA filters is proposed: the Adaptive Zone filter. The purpose of the presented work is to improve the performance of existing algorithms by using a more progressive behaviour than the traditional Flip-Flop filter. The performances of the Adaptive Zone filter are analysed through simulation under OPNET®. The prospects of the RTT estimator utilization are finally clarified.