A new service class, called VBR
$^+$
(Reininger, Ramamurthy and Raychaudhuri, in: ATM Forum Contribution 94‐0353, 1994), has been proposed for multimedia applications on ATM networks. VBR
$^+$
extends the functionality of the traditional VBR service with the added capability of dynamic resource renegotiation. It makes the specification and modification of the usage parameter controls flexible, and potentially can increase the network resource utilization through statistical multiplexing. These advantages come at the expense of a more complex connection admission controller which should be designed to handle bandwidth renegotiation efficiently. In this paper a connection admission controller for VBR
$^+$
service class is proposed. We identify the desirable features of a VBR
$^+$
connection admission controller, and present a novel one that can achieve them through (1) dynamic resource partitioning, and (2) dynamic resource redistribution among active connections. Simulation results showing the performance of the controller using a number of actual video traces are presented. The results show that the controller is robust in admitting a variety of video sources with widely different traffic burstiness. By partitioning the resource pool dynamically, and distributing resources among contending connections fairly, it can maintain very good quality, and can achieve high utilization. Comparison with traditional VBR service reveals that the CAC is able to provide comparable quality with higher network utilization.
