The up-coming Gbps high-speed networks are expected to support a wide range of communication-intensive, real-time multimedia applications. The requirement for timely delivery of digitized audio-visual information raises new challenges for the next generation integrated-service broadband networks. One of the key issues is the Quality-of-Service (QoS) routing. It selects network routes with sufficient resources for the requested QoS parameters. The goal of routing solutions is two-fold: (1) satisfying the QoS requirements for every admitted connection and (2) achieving the global efficiency in resource utilization. Many unicast/multicast QoS routing algorithms were published recently, and they work with a variety of QoS requirements and resource constraints. Overall, they can be partitioned into three broad classes: (1) source routing, (2) distributed routing and (3) hierarchical routing algorithms. In this paper we give an overview of the QoS routing problem as well as the existing solutions. We present the strengths and the weaknesses of different routing strategies and outline the challenges. We also discuss the basic algorithms in each class, classify and compare them, and point out possible future directions in the QoS routing area.

This memo describes extensions to the OSPF protocol to support QoS routes. The focus of the document is on the algorithms used to compute QoS routes and on the necessary modifications to OSPF to support this function, e.g., the information needed, its format, how it is distributed, and how it is used by the QoS path selection process. Aspects related to how QoS routes are established and managed are also briefly discussed, but the development of detailed specifications is left for further study. The goal of this document is to identify a framework and possible approaches to allow deployment of QoS routing capabilities with the minimum possible impact to the existing routing infrastructure. Guerin,Orda,Williams Expires 10 May 1997 [Page i] Internet Draft QoS Routing Mechanisms 5 November 1996 Contents Status of This Memo i Abstract i 1. Introduction 1 1.1. Overall Framework . . . . . . . . . . . . . . . . . . . . 1 1.2. Simplifying Assumptions . . . . . . . . . . . . . . . . . 2 2. Pa...

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.

The goal of Quality-of-Service (QoS) routing is to find a network path which has sufficient resources to satisfy certain constraints on delay, bandwidth and/or other metrics. The network state information maintained at every node is often imprecise in a dynamic environment because of nonnegligible propagation delay of state messages, periodic updates due to overhead concern, and hierarchical state aggregation [6]. The information imprecision makes QoS routing difficult. The traditional shortest-path routing algorithm does not provide satisfactory performance with imprecise state information. We propose a distributed routing scheme, called ticketbased probing, which searches multiple paths in parallel for a satisfactory one. The scheme is designed to work with imprecise state information. It allows the dynamic tradeoff between the routing performance and the overhead. The state information of intermediate nodes is collectively used to guide the routing messages along the most appropria...

We investigate the problem of optimal resource allocation for end-to-end QoS requirements on unicast paths and multicast trees. Specifically, we consider a framework in which resource allocation is based on local QoS requirements at each network link, and associated with each link is a cost function that increases with the severity of the QoS requirement. Accordingly, the problem that we address is how to partition an end-to-end QoS requirement into local requirements, such that the overall cost is minimized. We establish efficient (polynomial) solutions for both unicast and multicast connections. These results provide the required foundations for the corresponding QoS routing schemes, which identify either paths or trees that lead to minimal overall cost. In addition, we show that our framework provides better tools for coping with other fundamental multicast problems, such as dynamic tree maintenance. Keywords --- QoS, QoS-dependent costs, Multicast, Routing, Broadband ne...

In this short paper we give a very simple fully polynomial approximation scheme for the restricted shortest path problem. The complexity of this ffl-approximation scheme is O(jEjn(loglog n + 1=ffl)), which improves Hassin's original result [Has92] by a factor of n. Furthermore, this complexity bound is valid for any graph, regardless of the cost values. This generalizes Hassin's results which apply only to acyclic graphs. Our algorithm is based on Hassin's original result [Has92] with two improvements. First we modify Hassin's result and achieve time complexity of O(jEjn(log log(UB=LB) + 1=ffl)), where UB and LB are upper and lower bounds for the problem. This modified version can be applied to general graphs with any cost values. Then we combine it with our second contribution, which shows how to find an upper and a lower bound such that UB=LB n, to obtain the claimed result. 1

In this paper, we investigate the problem of topology aggregation (TA) for scalable, QoS-based routing in ATM networks. TA is the process of summarizing the topological information of a subset of network elements. This summary is flooded throughout the network, and is used by various nodes to determine appropriate routes for connection requests. A key issue in the design of a TA scheme is the appropriate balance between compaction and the corresponding routing performance. The contributions of this paper are twofold. First, we introduce a source-oriented approach to TA, which provides better performance than existing approaches. The intuition behind this approach is that the advertised topologystate information is used by source nodes to determine tentative routes for connection requests. Accordingly, only relevant information to source nodes needs to be advertised. We integrate the source-oriented approach into three new TA schemes that provide different tradeoffs between compaction a...

One of the key issues in providing end-to-end quality-of-service (QoS) guarantees in packet networks is how to determine a feasible route that satisfies a set of constraints. In general, finding a path subject to multiple additive constraints (e.g., delay, delay-jitter) is an NP-complete problem that cannot be exactly solved in polynomial time. Accordingly, several heuristics and approximation algorithms have been proposed for this problem. Many of these algorithms suffer from either excessive computational cost or low performance. In this paper, we provide an efficient approximation algorithm for finding a path subject to two additive constraints. The worst-case computational complexity of this algorithm is within a logarithmic number of calls to Dijkstra's shortest path algorithm. Its average complexity is even much lower than that, as demonstrated by simulation experiments. The performance of the proposed algorithm is justified via theoretical bounds that are provided for ...

A major algorithmic challenge posed by QoS routing is the need to promptly identify a suitable path upon a connection request, while at the same time ensure that the selected path is satisfactory, both in terms of the connection's QoS requirements, as well as in terms of the global utilization of network resources. In many practical cases, a precomputation scheme offers a suitable solution to the problem: a background process prepares a data base, which enables to identify a suitable path upon each connection request, through a simple, fast, procedure. While much work has been done in terms of path selection algorithms, the precomputation perspective got little attention. Simplistic adaptations of standard algorithms turn to be inefficient. Accordingly, we consider the precomputation perspective, focusing on two major settings of QoS routing. The first is the (practically important) special case where the QoS constraint is of the "bottleneck" type, e.g. a bandwidth requirement, and network optimization is sought through hop minimization. For this setting, the standard Bellman-Ford algorithm offers a straightforward precomputation scheme. However, we show that, by exploiting the typical hierarchical structure of large-scale networks, one can achieve a substantial improvement in terms of computational complexity. Then, we turn to consider the more general setting of "additive" QoS constraints (e.g., delay) and general link costs. As the routing problem becomes NP-hard, we focus on "-optimal approximations, and derive a precomputation scheme that offers a major improvement over the standard approach.

Abstract—We present a new algorithm, A*Prune, to list (in order of increasing length) the first K Multiple-Constrained-Shortest-Path (KMCSP) between a given pair of nodes in a digraph in which each arc is associated with multiple Quality-of-Service (QoS) metrics. The algorithm constructs paths starting at the source and going towards the destination. But, at each iteration, the algorithm gets rid of all paths that are guaranteed to violate the constraints, thereby keeping only those partial paths that have the potential to be turned into feasible paths, from which the optimal paths are drawn. The choice of which path to be extended first and which path can be pruned depend upon a projected path cost function, which is obtained by adding the cost already incurred to get to an intermediate node to an admissible cost to go the remaining distance to the destination. The Dijkstra’s shortest path algorithm is a good choice to give a good admissible cost. Experimental results show that A*Prune is comparable to the current best known-approximate algorithms for most of randomly generated graphs. BA*Prune, which combines the A*Prune with any known polynomial time-approximate algorithms to give either optimal or-approximate solutions to the KMCSP problem, is also presented. Keywords—shortest paths, constraint based routing, QoS routing, multiple constrained path selection, Dijkstra algorithm, NP complete. I.