— In this paper we describe a time-based admission control scheme for Multimedia over IP services in wireless LANs based on the IEEE 802.11e standard. We build on an existing work where it was defined a parameter, called Network Utilization Characteristic (NUC), to measure the temporal occupancy of the wireless channel of an IEEE 802.11 network. The work we present is twofold. At first, we extend this parameter to 802.11e systems. A simple Markov chain is used for this purpose. Then we build an admission control scheme based on the so-extended NUC and verify its effectiveness in a practical case: a network with mixed voice and video traffic. Simulations, also with different link qualities, are used to validate the effectiveness of our scheme. Keywords – Admission Control, IEEE 802.11e, Network Utilization Characteristic (NUC), Voice over WLAN (VoWLAN).