With the rapid growth of wireless communication networks, we are facing the challenge of integration of diverse wireless networks such as WLAN and WWAN. Therefore, it becomes important to think at vertical handoff solution where the user can move seamlessly among various type of networks, to provide the best QoS to the higher layers applications. In this paper, we propose a method to estimate the channel occupancy rate metric of an IEEE 802.11 network from the physical layer. This method can be applied for any network that use the CSMA/CA protocol. Our theorical results are validated using experimental measurements captured by RAMMUS RF Plateform.