Hybrid optimization for QoS control in IP Virtual Private Networks

A multiservice IP Virtual Private Network is considered, where Quality of Service is maintained by a DiffServ paradigm, in a domain that is supervised by a Bandwidth Broker (BB). The traffic in the network belongs to three basic categories: Expedited Forwarding (EF), Assured Forwarding (AF) and Best Effort (BE). Consistently with the DiffServ environment, the Service Provider’s Core Routers (CRs) only treat aggregate flows; on the other hand, the user’s Edge Routers (ERs) keep per-flow information and convey it to the BB. The latter knows at each time instant the number (and the bandwidth requirements) of flows in progress within the domain for both EF and AF traffic categories. A global strategy for admission control, bandwidth allocation and routing within the domain is introduced and discussed in the paper. The aim is to minimize blocking of the ‘‘guaranteed’’ flows (EF and AF), while at the same time providing some resources also to BE traffic. In order to apply such control actions on-line, a computational structure is sought, which allows a relatively fast implementation of the overall strategy. In particular, a mix of analytical and simulation tools is applied jointly, by alternating ‘‘local’’ decisions, based on analytical models, with flow-level simulation that determine the effect of the decisions on the whole system and provide feedback information. The convergence of the scheme (under a fixed traffic pattern) is investigated and the results of its application under different traffic loads are studied by simulation on three test networks.