In order to provide seamless handoff for QoS connections in 802.16-2004/WLAN environment, a cross layer design approach is proposed to manage the bandwidth requirement of mobile node during movement. The main concept of the dynamic bandwidth management proposed in this paper is to treat the layer 2 connection of 802.16 as a pipe that aggregates multiple layer 3 RSVP connections with the same class of service. As the layer 3 connections are integrated into a pipe, bandwidth can be managed in a more statistical way. The control procedure of RSVP connection is designed in accordance with the signaling procedure of 802.16. In order to manage the bandwidth effectively, the Admitted Bandwidth Utilization Portion (ABUP) is defined as a threshold of the layer 2 pipe to determine whether the reserved bandwidth is enough or not. This threshold also plays an important role for the acceptance of handoff connection and new connection. The performance of the proposed scheme is examined through exhaustive simulations. Our results show that our scheme demonstrates a quite good performance in managing resources for RSVP connections in 802.16/WLAN environment.