Prompted by the advent of QoS routing in the Internet, we investigate the properties that path weight functions must have so that hop-by-hop routing is possible and optimal paths can be computed with a generalized Dijsktra's algorithm. For this purpose we define an algebra of weights which contains a binary operation, for the composition of link weights into path weights, and an order relation. Isotonicity is the key property of the algebra. It states that the order relation between the weights of any two paths is preserved if both of them are either prefixed or appended by a common, third, path. We show that isotonicity is both necessary and sufficient for a generalized Dijkstra's algorithm to yield optimal paths. Likewise, isotonicity is also both necessary and sufficient for hop-by-hop routing. However, without strict isotonicity, hop-by-hop routing based on optimal paths may produce routing loops. They are prevented if every node computes what we call lexicographic-optimal paths. These paths can be computed with an enhanced Dijkstra's algorithm that has the same complexity as the standard one. Our findings are extended to multipath routing as well. As special cases of the general approach, we conclude that shortestwidest paths can neither be computed with a generalized Dijkstra's algorithm nor can packets be routed hop-by-hop over those paths. In addition, loop-free hop-by-hop routing over widest and widest-shortest paths requires that each node computes lexicographic-optimal paths, in general.

Multicast services have been increasingly used in large scale continuous media applications. The quality-of-service (QoS) requirements of these continuous media applications prompt the necessity for QoS-driven, constraint-based multicast routing. This article provides a comprehensive overview of existing multicast routing algorithms, protocols, and their QoS extension. In particular, we classify multicast routing problems according to their optimization functions and performance constraints, present basic routing algorithms in each problem class, and discuss their strengths and weakness. We also categorize existing multicast routing protocols, outline the issues and challenges in providing QoS in multicast routing, and point out possible future research directions.

This paper investigates the problem of routing flows with Quality-of-Service (QoS) requirements through one or more networks, when the information available for making such routing decisions is inaccurate. Inaccuracy in the information used in computing QoS routes, e.g., network state such as link and node metrics, arises naturally in a number of different environments that are reviewed in the paper. Our goal is to determine the impact of such inaccuracy on the ability of the path selection process to successfully identify paths with adequate available resources. In particular, we focus on devising algorithms capable of selecting path(s) that are most likely to successfully accommodate the desired QoS, in the presence of uncertain network state information. For the purpose of our analysis, we assume that this uncertainty is expressed through probabilistic models, and we briefly discuss sample cases that can give rise to such models. We establish that the impact of uncertainty is minima...

In this paper a practically efficient QoS routing method is presented, which provides a solution to the delay constrained least cost routing problem. The algorithm uses the concept of aggregated costs and provides an efficient method to find the optimal multiplier based on Lagrange relaxation. This method is proven to be polynomial and it is also efficient in practice. The benefit of this method is that it also gives a lower bound on the theoretical optimal solution along with the result. The difference between the lower bound and the cost of the found path is very small proving the good quality of the result. Moreover, by further relaxing the optimality of paths, an easy way is provided to control the trade-off between the running time of the algorithm and the quality of the found paths. We present a comprehensive numerical evaluation of the algorithm, by comparing it to a wide range of QoS routing algorithms proposed in the literature. It is shown that the performance of the proposed polynomial time algorithm is close to the optimal solution computed by an exponential algorithm. Keywords---QoS routing, delay, optimization, Lagrange relaxation I.

Constraint-based routing gradually becomes an essential enabling mechanism for a variety of emerging network services such as virtual private networking and QoS support. A number of recent works have recognized its significance and investigated many aspects of the operation of constraint based routing and in particular its variant that is concerned with determining paths for requests with specific QoS requirements, known as QoS routing. In this work we build on previous results on the cost of QoS routing and investigate the performance/cost trade-offs involved in the operation of a representative QoS routing architecture, elaborate on the constituents of this cost, and identify the main methods for containing the cost that QoS routing incurs on routers. Our results show that the cost of QoS routing is not excessive and that there indeed exist operational configurations, that can achieve reasonable performance gains with only a minimal increase in processing cost when compared...

In this paper we introduce and investigate a #new" path optimization problem which we denote as the All Hops Optimal Path #AHOP# problem. The problem involves identifying, for all hop counts, the optimal, i.e., minimum weight, path between a given source and destination. Our interest in such a problem originated in the context of Quality-of-Service #QoS# routing in networks. A goal of QoS routing is to improve a network's ability to satisfy user requirements by selecting paths for individual requests, which are based on both the network state and the request requirements, e.g., minimum bandwidth or maximum end-to-end delay constraints. In addition, in order to ensure e#cient network operation, it is desirable that the paths also use the minimum possible amount of network resources, e.g., minimize the number of links #hops# used. As a results of these additional constraints, the path selection computation increases in complexity, and it becomes important to amortize this incre...

In this paper we describe an efficient algorithm for the constrained shortest path problem which is defined as follows. Given a directed graph with two weights on each link e, a cost l e and a delay t e , find the cheapest path from a source to all destinations such that the delay of each path is no more than a given threshold. The constrained shortest path problem arises in Quality-of-Service-sensitive routing in data networks and is of particular importance in realtime services. The problem formulation and the algorithmic framework presented are quite general; they apply to IP, ATM, and optical networks. Unlike previous algorithms, our algorithm generates paths from one source to all destinations. Our algorithm is strongly polynomial, and is asymptotically faster than earlier algorithms. We corroborate our analysis by a simulation study. I. INTRODUCTION The basic problem in QoS-sensitive routing for emerging services such as VoIP (Voice over IP), video, interactive multimedia etc....

The core-stateless service architecture alleviates the scalability problems of the integrated service framework while maintaining its guaranteed service semantics. The admission control methods proposed to support core-stateless guaranteed services have significant drawbacks. We propose a scalable and robust distributed admission control architecture to support corestateless guaranteed services. Our architecture maintains high network utilization while ensuring that resources are not overallocated. In our architecture, admission control is performed at the ingress edge routers of a request on an edge-to-edge path basis. A token-passing mechanism is used as the resource management framework. The token helps in dynamic and fair division of bandwidth and allows completely distributed resource allocation on a link unless it is close to saturation. The edge routers co-operate to provide fault tolerance effectively acting as a resilient overlay network. Our admission control framework can support statistical guarantees and diffserv architecture's premium service as well. The resource management part of our architecture is well-suited to aid QoS routing algorithms. Analytical and simulation results are presented to show the effectiveness of our architecture.

Label switched networks have become increasingly attractive to both network providers and customers. By creating aggregate, bandwidth-reserved flows, these networks offer routing flexibility, predictable bandwidth usage, and quality-of-service (QoS) provisioning. This flexibility in routing enables fault-persistent QoS reservations, where connectivity and allotted bandwidth remains available, even if some links or network nodes fail. The automatic switch-over from a now-defunct path to a new, working path is known as restoration. Restoring bandwidth-guaranteed paths requires allocation of resources on backup paths that will be used in the event of faults. In this paper, we investigate distributed algorithms for routing with backup restoration. Specifically, we propose a new concept of Backup Load Distribution Matrix that captures partial network state, greatly reducing the amount of routing information maintained and transmitted while achieving efficient bandwidth usage. We present and simulate two new distributed routing algorithms, which provide significant improvements in rejection rates and provide substantial savings in bandwidth used and call setup time compared to existing algorithms.

In order to provide various services with different quality requirements, the current Internet is expected to turn into a QoS based Internet under the Differentiated Service (DiffServ) architecture. A variety of works have been done in the field of constraint based routing to provide QoS guaranteed or assured services by developing novel routing protocols and algorithms. However, most of these efforts focus on intra-domain routing rather than inter-domain routing. In this paper, we discuss issues of finding routes with QoS requirements among multiple domains, called inter-domain QoS routing. We first investigate the needs and problems faced when introducing inter-domain QoS routing into the Internet. Then, we present a model for interdomain QoS routing and describe its building blocks. Finally, we present five mechanisms for operating inter-domain QoS routing in DiffServ networks.