This paper proposes a control-theoretic modeling approach for service differentiation in multi-hop ad-hoc networks, in which a new priority scheme is applied by considering variable control gains and so-called Transmission Opportunity (TXOP) limits. The model is studied and evaluated based on an IEEE 802.11 DCF WLAN system using the well-known 20-sim dynamic system simulator. The use of the control-theoretical framework, as opposed to an ns-2 simulation, has as advantage that results are obtained much more quickly, and that the model remains much more structured and formalized. By means of the implemented model, the average queue length, queuing delay and network throughput can be evaluated. Simulation results show that our approach is able to satisfy QoS requirements of high-priority stations in both single-hop and multi-hop ad-hoc networks.