Strategies for Dynamic Capacity Management

We study networks based on virtual paths, i.e. rearrangable end-to-end transport network. Virtual paths networks are readily implemented in any network using the synchronous digital hierarchy and/or the asynchronous transfer mode. The concept and its advantages, for example cost savings, network operation simpli cation and enhanced network management capabilities, are discussed. Algorithms for virtual path designs are reviewed and a new algorithm is presented which is found to compare favourably with the algorithm providing the most similar features. Applying it to a real network, we turn to operational aspects of recon gurable networks such as methods and parameters for tra c estimation and network updating. The validity of the results is demonstrated by means of simulations of a number of networks subject to variable tra cs. 1 Virtual Path Networks A virtual path (VP) is formed by reserving a certain amount of transmission capacity on a series of links and cross connecting the reserved channels through possible, intermediate transit nodes. Interconnecting all origin-destination pairs (OD-pairs) by means of VPs, a virtual path network is obtained, gure 1. Such a network forms a higher layer which is logically independent of the underlying physical network. The process of creating and/or rearranging a (logical) network of VPs between a number of end nodes is called capacity management [8], bandwidth management [16], bandwidth switching [1] or bandwidth control [25], and is performed at a network management centre (NMC). VPs are engineered for each OD-pair respectively so that current tra c demands can be carried with an acceptable grade of service. However, it is not always possible to accomodate all demands to their full extent. Hence capacity allocation must be made in such a way that some performance metric, e.g. network pro t from carried tra c minus carrying costs, is maximised. Since the optimality of a certain VP con guration depends on link capacities and currently o ered tra cs, VP assignments must be re-evaluated in response to changes. We refer to this process as dynamic capacity management (DCM). DCM can be performed either in advance or on demand. The former means that assignments are prede ned and changed in an independent manner while individual call attempts control rearranging in the latter. We focus on the former, as this is the one most favoured by low transmissionto-processing costs [8, 9]. Some of the motives behind VP networks and DCM [2, 7, 8, 9, 24, 25] are Reduced network costs resulting from simpli ed transit exchanges. Simpli ed multiplexing due to service-dedicated end-to-end VPs. Faster call handling by excluding intermediate node processing at set-up time. The work reported herein was partly carried out at the Teletra c Research Centre, The University of Adelaide, G.P.O. Box 498, Adelaide, South Australia 5001, Australia.