This article presents N-MAC (for Network-MAC), a cross layer design framework that enables the implementation of scheduling policies by resolving some problems related to the wireless environment. N-MAC is based on CSMA/CA protocol and offers a low complexity which makes it suitable for Wireless Sensor Networks. The idea of N-MAC is that a router collects data from its children and other routers before starting their transmission. This way offers the possibility to schedule arrived packets, perform data aggregation and congestion control more easily.