The scarcity of energetic resources in mobile computers is a very limiting factor. In this paper we propose a solution that tries to balance energy consumption and QoS requirements. Our solution follows an application-independent approach and, therefore, it can be used concurrently, and without modifications, by any network application. Furthermore, our solution is independent from the sub-network technology. We implemented this solution and we extensively tested it. Experimental results have shown that a relevant energy saving (about 70% on average) can be achieved with respect to the legacy approach based on the TCP/IP protocol stack. Furthermore, these savings are obtained without a significant degradation in the QoS perceived by the user. We also compared our application-independent approach with an application-dependent one (i.e., a solution tailored to Web browsing) which performs (slightly) better. However, the application-independent solution still guarantees significant savings, and fits better a general-purpose mobile environment.