One of the activities of the ACTS project EXPERT is to perform trials demonstrating the use of advanced Resource Management and Routing (RM&R) algorithms in ATM networks. The RM&R model chosen for these trials is based on the Virtual Trunk (VT) concept. In ATM networks, a VT is a virtual path connection setup by the network for reducing connection awareness at the transit nodes. A virtual trunk is considered as a connection by the network supporting it (the VP network) and as a logical trunk by the connections supported. In this context, VTs are considered to be VBR connections. In order to adapt the VT level to the changes in traffic, we use dynamic virtual trunks. In this paper, we compare the VBR-over-VBR approach to a more traditional VBR-over-CBR approach. The comparison is based on the simulations performed in the EXPERT project by WP3.2. In addition, a dynamic VP bandwidth allocation method is demonstrated by simulations.