Wireless networks are more and more popular, and more specifically as the access technology for all wireless devices generally used (laptops, smartphones, tablets, sensors, ...). It is then frequent to encounter at least one wireless network segment on a communication path. Because of the complexity and limits of the hertzian air medium, the end-to-end communication is impacted by the quality of such wireless networks which are not offering the same amount of resources or the same determinism in the quality of Service (QoS) level. Because of the complexity of the physical transmission mechanisms, and of the MAC layer, traffic observed at the network level can have unexpected characteristics and the network exhibits unexpected performances and QoS. At the opposite of wired network for which monitoring packets at network level is enough, monitoring wireless networks requires to look at physical, MAC and network layers all together and to analyze their correlation levels: this is called cross-layered monitoring in the related literature. This paper then proposes an overview of the monitoring of the quite unknown physical layers of wireless networks, and exhibits how the studies of the 3 layers are necessary for analyzing the wireless network behavior, and more generally of the end-to-end connections. As an example, this paper illustrates how the SNR impacts the delays and jitters in an unexpected way in wireless networks, thus impacting end-to-end delays and jitters.