We present heuristics for multicast tree construction for communication that depends on: i) bounded end-to-end delay along the paths from source to each destination, and ii) minimum cost of the multicast tree, where edge cost and edge delay can be independent metrics. This problem of computing such a constrained multicast tree is NP-complete. We show that the heuristics demonstrate good average case behavior in terms of cost, as determined through simulations on a large number of graphs.

Recent studies provide evidence that Quality of Service (QoS) routing can provide increased network utilization compared to routing that is not sensitive to QoS requirements of traffic. However, there are still strong concerns about the increased cost of &OS routing, both in terms of more complex and frequent computations and increased routing protocol over-head. The main goals of this paper are to study these two cost components, and propose solutions that achieve good routing performance with reduced processing cost. First, we identify the parameters that determine the protocol traffic overhead, namely (a) policy for triggering updates, (b) sen-sitivity of this policy, and (c) clamp down timers that limit the rate of updates. Using simulation, we study the relative significance of these factors and investigate the relationship between routing performance and the amount of update traf-fic. In addition, we explore a range of design options to reduce the processing cost of QoS routing algorithms, and study their effect on routing performance. Based on the con-clusions of these studies, we develop extensions to the basic QoS routing, that can achieve good routing performance with limited update generation rates. The paper also ad-dresses the impact on the results of a number of secondary factors such as topology, high level admission control, and characteristics of network traffic.

Abstract—We discuss an implementation of QoS routing extensions to the OSPF routing protocol and evaluate its performance over a wide range of operating conditions. Our evaluations are aimed at assessing the cost and feasibility of QoS routing in IP networks. The results provide insight into the respective weights of the two major components of QoS routing costs, processing cost and protocol overhead and establish strong empirical evidence that the cost of QoS routing is well within the limits of modern technology and can be justified by the performance improvements. I.

Establishing a multicast tree in a point-to-point network of switch nodes, such as a wide-area ATM network, can be modeled as the NP-complete Steiner problem in networks. In this paper, we introduce and evaluate two distributed algorithms for finding multicast trees in point-to-point data networks. These algorithms are based on the centralized Steiner heuristics, the shortest path heuristic (SPH) and the Kruskalbased shortest path heuristic (K-SPH), and have the advantage that only the multicast members and nodes in the neighborhood of the multicast tree need to participate in the execution of the algorithm. We compare our algorithms by simulation against a baseline algorithm, the pruned minimum spanning-tree heuristic, which is the basis of many previously published algorithms for finding multicast trees. Our results show that the competitiveness (the ratio of the sum of the heuristic tree's edge weights to that of the best solution found) of both of our algorithms was on the average ...

this paper, we concentrate on improving this trade-off by devising methods that increase the performance of QoS routing, when cost constraints, i.e., limitations on link state update traffic, affect the accuracy of the information on which it operates. In particular, we study the performance of "safety-based" routing, which incorporates knowledge of the underlying inaccuracy in computing a "safety" measure for links, and uses it when computing paths. Using detailed simulations, we evaluate the effectiveness of safetybased routing and investigate the dependence of its performance on the assumptions made when computing link safety. Our findings show that for many operating conditions, safety-based routing is successful in improving routing performance while maintaining low update traffic volumes.

In multicasting routing, the main objective is to send data from one or more source to multiple destinations, while at the same time minimizing the usage of resources. Examples of resources which can be minimized include bandwidth, time and connection costs. In this paper we survey applications of combinatorial optimization to multicast routing. We discuss the most important problems considered in this area, as well as their models. Algorithms for each of the main problems are also presented.

We propose a new distributed delay-constrained unicast routing algorithm which can always find a delay-constrained path with small message complexity if such a path exists. At each network node, limited information about the network state is needed and only a small amount of computation is required. Simulation results show that the proposed algorithm has much better cost performance than the least delay path algorithm.

Quality of Service (QoS) routing algorithms have become the focus of recent research due to their potential for increasing the utilization of an Integrated Services Packet Network (ISPN) that handles requests with QoS requirements. While heuristics for determining paths for such requests have been formulated for a variety of QoS models, little attention has been given to the overall processing complexity of the QoS routing architecture. Although ondemand path computation is very attractive due to its simplicity, many believe that its processing cost will be prohibitive in environments with high request rates. In this work, we first characterize the processing cost of QoS routing algorithms that use the constrained widest-shortest path heuristic to compute QoS paths in a link state based routing environment. By simulating a variety of realistic traffic conditions we investigate the effectiveness of path precomputation in reducing the amount of routing protocol computation. We mainly wan...

With the proliferation of multimedia group applications, the construction of multicast trees satisfying Quality of Service (QoS) requirements is becoming a problem of prime importance. Many of the multicast applications (such as video broadcasts and teleconferencing) require the network to support dynamic multicast sessions wherein the membership of the multicast group changes with time. In this paper, we propose and evaluate an algorithm called CRCDM (Controlled Rearrangement for Constrained Dynamic Multicasting) for on-line update of multicast trees to adjust to changes in group membership. The CRCDM algorithm is based on a concept called Quality Factor (QF) that represents the usefulness of a portion of the multicast tree to the overall multicast session. When the usefulness of a particular region of the tree drops below a threshold, a rearrangement technique is used to suitably modify the tree. Our algorithm aims to satisfy the delay-constraints of all current group members, at the same time minimizing the cost of the constructed tree. We compare the performance of our algorithm, by simulation, with that of an off-line Steiner heuristic; with ARIES [2], a recently published algorithm for on-line update of unconstrained trees; and with the algorithm proposed in [10] for on-line update of delay-constrained trees. The simulation results indicate that our algorithm provides excellent cost-competitiveness that is better than that provided by the algorithm described in [10], minimizes changes in the multicast tree after each update, and performs favorably even when compared with the unconstrained ARIES heuristic. Keywords: Multicast routing, On-line Steiner problem, Dynamic multicast groups, Rearrangement algorithm, QoS, Group communication This work was...

Quality of Service (QoS) routing algorithms have become the focus of recent research due to their potential for increasing the utilization of an Integrated Services Packet Network (ISPN) serving requests with QoS requirements. While heuristics for determining paths for such requests have been formulated for a variety of QoS models, little attention has been given to the overall processing complexity of the QoS routing protocol. Although on-demand path computation is very attractive due to its simplicity, many believe that its processing cost will be prohibitive in environments with high request rates. In this work, we study alternatives to on-demand path computation that can reduce this processing overhead. In addition to the well known solution of path pre-computation we introduce and study path caching, an incremental modification of on-demand path computation. Our simulation results show that caching is an effective alternative to path pre-computation and that both path caching and ...