IEEE 802.11 networks constitute a suitable infrastructure for accurate indoor positioning. However, existing approaches based on fingerprinting present drawbacks that make them not suitable for most of applications. This paper presents an innovative TOA-based ranging technique over IEEE 802.11 networks intended to be the essential step of an indoors location system. This approach is based on round trip time measurements using standard IEEE 802.11 link layer frames and a statistical post-processing to mitigate the noise of the measurements. A prototype has been implemented in order to assess the validity and evaluate the performance of the proposed technique. First results show ranging accuracies of less than one meter of error in LOS situations.