In this article we present a framework for the emerging Internet quality of service (QoS). All the important components of this framework --- integrated services, RSVP, differentiated services, multiprotocol label switching (MPLS), and constraintbased routing --- are covered. We describe what integrated services and differentiated services are, how they can be implemented, and the problems they have. We then describe why MPLS and constraint-based routing have been introduced into this framework, how they differ from and relate to each other, and where they fit into the differentiated services architecture. Two likely service architectures are presented, and the end-to-end service deliveries in these two architectures are illustrated. We also compare ATM networks to router networks with differentiated services and MPLS. Putting all these together, we give the readers a grasp of the big picture of the emerging Internet QoS. 12 IEEE Network . March/April 1999 9 and differenti...

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.

In this paper, 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. DCUR requires limited network state information to be kept at each node: a cost vector and a delay vector. We prove DCUR's 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 DCUR is O(|V|³) messages, where |V| is the number of nodes. However, simulation results show that,on the average, DCUR requires much fewer messages. Therefore, DCUR scales well to large networks. We also use simulation to compare DCUR to the optimal algorithm, and to the least-delay path algorithm. Our results show that DCUR's path costs are within 10% from those of the optimal solution.

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.

With the constraints of network topologies and link capacities, achieving the optimal end-to-end throughput in data networks has been known as a fundamental but computationally hard problem. In this paper, we seek efficient solutions to the problem of achieving optimal throughput in data networks, with single or multiple unicast, multicast and broadcast sessions. Although previous approaches lead to solving NP-complete problems, we show the surprising result that, facilitated by the recent advances of network coding, computing the strategies to achieve the optimal end-to-end throughput can be performed in polynomial time. This result holds for one or more communication sessions, as well as in the overlay network model. Supported by empirical studies, we present the surprising observation that in most topologies, applying network coding may not improve the achievable optimal throughput; rather, it facilitates the design of significantly more efficient algorithms to achieve such optimality. Index terms: Graph theory, Information theory, Mathematical programming/optimization, Simulations.

All of the advantages of application-layer overlay networks arise from two fundamental properties: (1) The network nodes in an overlay network, as opposed to lower-layer network elements such as routers and switches, are end systems and have capabilities far beyond basic operations of storing and forwarding; and (2) The overlay topology, residing above a densely connected IP-layer wide-area network, can be constructed and manipulated to suit one's purposes. In this paper, we seek to significantly...

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.

Abstract-- Widespread use of wireless devices presents new challenges for network operators, who need to provide service to ever larger numbers of mobile end users, while ensuring Quality-of-Service guarantees. In this paper we describe a new distributed routing algorithm that performs dynamic load-balancing for wireless access networks. The algorithm constructs a load-balanced backbone tree, which simplifies routing and avoids per-destination state for routing and per-flow state for QoS reservations. We evaluate the performance of the algorithm using several metrics including adaptation to mobility, degree of load-balance, bandwidth blocking rate, and convergence speed. We find that the algorithm achieves better network utilization by lowering bandwidth blocking rates than other methods. I.

Alternate path routing has been well-explored in telecommunication networks as a means of decreasing the call blocking rate and increasing network utility. However, aside from some work applying these concepts to unicast flows, alternate path routing has received little attention in the Internet community. We describe and evaluate an architecture for alternate path routing for multicast flows. For path installation, we design a receiver-oriented alternate path protocol and prove that it reconfigures multicast trees without introducing loops. For path computation, we propose a scalable local search heuristic that allows receivers to find alternate paths using only partial network information. We use a simulation study to demonstrate the ability of local search to find alternate paths approximately as well as a link-state protocol, with much lower overhead. I.

We study a network model in which each network link is associated with a set of delays and costs. These costs are a function of the delays and reflect the prices paid in return for delay guarantees. Such a cost structure can model a setting in which the service provider provides multiple service classes with a different price and delay guarantee for each class. We are given a source node s, a sink node t, and an end-to-end delay constraint D. Our aim is to choose an s-t path and determine a set of per link delay guarantees along this path so as to satisfy the constraint D while minimizing the total cost incurred. In the case where the s-t path is known, we aim to optimally partition the end-to-end delay constraint into link constraints along the path. We present approximation algorithms for both problems, since they are known to be NP-hard. Our algorithms guarantee to produce solutions that are within a factor 1 + " of the optimal, where " is a parameter of our choice. The running ti...