VPAllocator VPN

Figure 5 shows the functional design of a VP admission controller and a VPG controlleraccording to our implementation. In this design, the VP admission controller includes twoobjects: a VC capacity allocator and a coordinator. The allocator receives requests from a VCconnection manager in the customer domain. The coordinator changes the capacity of the VPupon request from the VPG controller. It changes the capacity of the VP only when the bandwidth requirements of the active calls in the VP do not exceed the new capacity. The VPG controller includes four objects. The trigger object periodically initiates the VP capacity allocatorto run the VP allocation algorithm. The coordinator sends the new VP capacities to the coordinators of the associated VP admission controllers, using a synchronization protocol. Finally, anestimator object collects statistics from the VP admission controllers. This data is used by thecapacity allocator.Obviously, there exist many ways of realizing the above design, with respect to control algorithms, mechanisms for trigger realization, synchronization protocols, and centralized or distributed implementation of the controllers. For example, the control system may include oneVP admission controller per VP or one centralized controller for the whole VPN. The sameapplies for VPG control. Also, VP admission controllers can send bandwidth requests to VPGcontrollers, triggered by a pressure function, or a VPG controller can periodically recomputethe VP capacities and distribute them to VP admission controllers. Similarly, the synchronization protocols between the VP admission controller and the VPG controller can be realized indifferent ways. One possibility is that the VP admission controller, upon receiving a request tochange the VP size, checks whether the current utilization is above or below the new size. Ifthe utilization is below, the VP size is changed and a confirmation is sent to the coordinator ofthe VPG controller. If it is not below, the VP size remains the same and a failure reply is sentinstead. In another possible implementation, when the attempt for changing the VP size is notsuccessful, the VP admission controller waits and blocks further calls from being admitted.Then, the utilization of the VP can only be decreased, as calls can leave but no new calls areadmitted. When the utilization drops below the new size, the VP size is updated and the replysent to the VPG controller. A customer's choice for a specific design of the control system isbased upon its control objectives and requirements for the control system, which relate to system size, expected traffic and signalling load, efficiency of resource control and robustness of VC state VC CapAllocatorVP capCoordinatorchangeVC Request    VP Admission ControllerconfirmTrigger EstimatorVPG,VP    VP StatisticstopologyVPAllocator    VPG, VPVPG Controller   capacityCoordinator CapFigure 5  Functional model of a VP admission controller interacting with a VPG controller   capthe control system. In order to enable the realization of a large class of control objectives andcontrol schemes, we have designed a generic controller as one of the building blocks of a customer control system. This generic controller enables many interaction patterns among controllers and is constructed in a modular way.Figure 6 shows a functional model of the generic control