We consider variable bit rate video connections in the B-ISDN where the quality of service in terms of data loss and network delay must be guaranteed using appropriate congestion control mechanisms. We follow a preventive traffic control strategy based on the notion of traffic contract and connection accecptance control. We suggest that video connections be characterized by a set of burstiness constraints that define the traffic contract. We show how video coders can ensure that their output conforms to the traffic contract thus avoiding data loss at the user-network interface. Based on these burstiness constraints, we propose simple and easily implementable ressource allocation schemes that allow the QoS parameters to be guaranteed.