Hussein F. Salama

A distributed algorithm for delay-constrained unicast routing

We study the NP-hard delay-constrained least-cost path problem, and propose a simple, distributed heuristic solution: the delay-constrained unicast routing (DCUR) algorithm. The DCUR requires limited network state information to be kept at each node: a cost vector and a delay vector. We prove the DCURs correctness by showing that it is always capable of constructing a loop-free delay-constrained path within finite time, if such a path exists. The worst case message complexity of the DCUR is O(|V|/sup 3/) messages, where |V| is the number of nodes. However simulation results show that, on average, the DCUR requires much fewer messages. Therefore, the DCUR scales well to large networks. We also use simulation to compare the DCUR to the optimal algorithm, and to the least-delay path algorithm. Our results show that the DCURs path costs are within 10% from those of the optimal solution.

The delay-constrained minimum spanning tree problem

We formulate the problem of constructing broadcast trees for real-time traffic with delay constraints in networks with asymmetric link loads as a delay-constrained minimum spanning tree (DCMST) problem in directed networks. Then, we prove that this problem is NP-complete, and we propose an efficient heuristic to solve the problem based on Prims algorithm for the unconstrained minimum spanning tree problem. Simulation results under realistic networking conditions show that our heuristic performance is close to optimal. Delay-constrained minimum Steiner tree heuristics can be used to solve the DCMST problem. Simulation results indicate that the fastest delay-constrained minimum Steiner tree heuristic, DMCT is not as efficient as the heuristic we propose, while the most efficient delay-constrained minimum Steiner tree heuristic, BSMA, is much slower than our proposed heuristic and does not construct delay-constrained broadcast trees of lower cost.

Evaluation of multicast routing algorithms for real-time communication on high-speed networks

Multicast (MC) routing algorithms capable of satisfying the QoS requirements of real-time applications will be essential for future high-speed networks. We compare the performance of all of the important MC routing algorithms when applied to networks with asymmetric link loads. Each algorithm is judged based on the quality of the MC tree it generates and its efficiency in managing the network resources. Simulation results over random networks show that unconstrained algorithms are not capable of fulfilling the QoS requirements of real-time applications in wide-area networks. One algorithm, reverse path multicasting, is not suitable for asymmetric networks irrespective of the requirements of the application. The three constrained Steiner tree (CST) heuristics reported to date are also studied. Simulations show that all three heuristics behave similarly and that they can manage the network efficiently and construct low cost MC trees that satisfy the QoS requirements of real-time traffic. The execution times of the CST heuristics depend on the MC group size, but they are always larger than those of the unconstrained algorithms.

Reservation mechanisms for efficient resource management in internetworks

Distributed multimedia applications with quality of service requirements that must be guaranteed by the underlying network are evolving at a fast pace. Resource reservation protocols are therefore essential to enable efficient resource management in internetworks. We survey existing resource reservation protocols and the reservation styles they support. Current protocols do not permit different reservation styles to be combined within the same session. We show, using simulation of realistic scenarios, that allowing different reservation styles to coexist within the same session yields more efficient resource management and provides more satisfactory service to the applications. We then propose a complete mechanism for implementing the shared dynamic reservation style, along with three techniques to enhance its effectiveness in managing the network resources. The effectiveness of these three techniques is evaluated using simulation.