Wireless networks today often rely on an underlying infrastructure, such as cellular-like networks where there are specific access points which allow wireless users to connect to a fixed (wired) infrastructure. On the other hand, it is possible also to operate with a stand-alone wireless network, also called MANET (Mobile Ad hoc NETwork), where each mobile device can act as a router for its neighbors. In both cases, Quality of Service is difficult to be guaranteed, because of the varying bandwidth and the possibility of disconnection, added to the limited memory size and power constraints of mobile devices.