DATAMAN Lab, Rutgers University

QoS Provisioning in Wireless Data Networks

Given a standard cellular infrastructure, in order to support data calls, a call admission discipline should be imposed in order to provide a bounded quality of service. The main difference between voice calls and data calls is that while voice calls may be dropped at handoff, data calls may just be degraded. This relaxation on one hand provides a guarantee that a call will never be dropped, and the degradation will be dealt with at the higher transport layer, and on the other hand makes it more difficult to provide guarantees for the ongoing calls.

Finding the right policy for accepting new calls must of course take into account the traffic patterns and the present state of the network. A "perfect" admission decision could be taken if the future calls and their traffic and QoS requirements would be known. The challenge is to find an admission policy that achieves a high utilization, and provides as close as possible a performance to the "perfect" case. One must accept that it is not possible to provide hard guarantees in a cellular network, unless utilization is sacrificed: it is always possible for all mobiles accepted in the network to crowd one single cell. We are looking for a policy that works across all traffic patterns and load conditions. Hierarchy may provide advantages from both cell based and region based admissions, while offsetting their drawbacks. Ideally, regions would be dynamic, that is their shape will change with the changing traffic conditions.

QoS and protection in optical networks

We consider off-line versions of path provisioning and path protection problems for general circuit switched networks. Both problems deal with a given network topology and a list of integral demand flows. The objective is to route the flows and to allocate the bandwidth in a way that minimizes the total amount of bandwidth used for working and protection paths. We consider path-based protection where, in case of a single link failure, all the flows utilizing the failed link can be rerouted to a precomputed set of paths. We demonstrate that flow splitting can bring significant advantages for both provisioning and protection problems. Since the problem is NP-complete, we propose and analyze two simple heuristics. We show that one of these heuristics performs almost as well as the optimal solution. Dragos Niculescu