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.

We present Start-time Fair Queuing (SFQ) algorithm that is computationally efficient, achieves fairness regardless of variation in a server capacity, and has the smallest fairness measure among all known fair scheduling algorithms. We analyze its throughput, single server delay, and end-to-end delay guarantee for variable rate Fluctuation Constrained (FC) and Exponentially Bounded Fluctuation (EBF) servers. We show that SFQ is better suited than Weighted Fair Queuing for integrated services networks and it is strictly better than Self Clocked Fair Queuing. To support heterogeneous services and multiple protocol families in integrated services networks, we present a hierarchical SFQ scheduler and derive its performance bounds. Our analysis demonstrates that SFQ is suitable for integrated services networks since it: (1) achieves low average as well as maximum delay for low-throughput applications (e.g., interactive audio, telnet, etc.); (2) provides fairness which is desirable for VBR video; (3) provides fairness, regardless of variation in server capacity, for throughput-intensive, flow-controlled data applications; (4) enables hierarchical link sharing which is desirable for managing heterogeneity; and (5) is computationally efficient.

To support the requirements for the transmission of continuous media, such as audio and video, multiservice packet switching networks must provide service guarantees to connections, including guarantees on throughput, network delays, and network delay variations. For the most demanding applications, the network must offer a service which can provide deterministic guarantees for the maximum delay ofpackets from all connections, referred to as bounded delay service. The admission control functions in a network with a bounded delay service must have available schedulability conditions that detect violations of delay guarantees in a network switch. In this study, exact schedulability conditions are presented for packet switches which transmit packets based on an Earliest-Deadline-First (EDF) or a Static-Priority (SP) algorithm. The schedulability conditions are given in terms of a general traffic model, making the conditions applicable to a large class of traffic specifications. A comparison of the new schedulability conditions with existing, less accurate, conditions show the e ciency gain obtained by using exact conditions. Examples are presented that show how the selection of a particular traffic specification and a schedulability condition impact the efficiency of a bounded delay service.

Next-generation distributed systems will support corLtLzLzLous medLa (digztal audio and video) in the same framework as other data. Many applications that use continuous media need guaran-teed end-to-end performance (bounds on throughput and delay). To reliably support these requirements, system components such as CPU schedulers, networks, and file systems must offer performance guarantees. A rnetasclzedtder coordinates these components, negotiating end-to-end guarantees on behalf of clients. The CM-resource model, described in this paper, provides a basis for such a metascheduler. It defines a workload parameterizatlon, an abstract interface to resources, and an algorithm for reserving multiple resources. The model uses an economic approach to dividing end-to-end delay, and it allows system components to “work ahead,” improving the performance of nonreal-time workload.

This paper presents stride scheduling, a deterministic scheduling technique that efficiently supports the same flexible resource management abstractions introduced by lottery scheduling. Compared to lottery scheduling, stride scheduling achieves significantly improved accuracy over relative throughput rates, with significantly lower response time variability. Stride scheduling implements proportional-share control over processor time and other resources by cross-applying elements of rate-based flow control algorithms designed for networks. We introduce new techniques to support dynamic changes and higher-level resource management abstractions. We also introduce a novel hierarchical stride scheduling algorithm that achieves better throughput accuracy and lower response time variability than prior schemes. Stride scheduling is evaluated using both simulations and prototypes implemented for the Linux kernel.

In this paper, we develop a general model, called Latency-Rate servers (LR-servers), for the analysis of traffic scheduling algorithms in broadband packet networks. The behavior of an LR scheduler is determined by two parameters --- the latency and the allocated rate. We show that several well-known scheduling algorithms, such as Weighted Fair Queueing, VirtualClock, Self-Clocked Fair Queueing, Weighted Round Robin, and Deficit Round Robin, belong to the class of LR-servers. We derive tight upper bounds on the end-to-end delay, internal burstiness, and buffer requirements of individual sessions in an arbitrary network of LR- servers in terms of the latencies of the individual schedulers in the network, when the session traffic is shaped by a leaky bucket. Thus, the theory of LR-servers enables computation of tight upper-bounds on end-to-end delay and buffer requirements in a heterogeneous network, where individual servers may support different scheduling architectures, and under diff...

We propose a class of non-work-conserving service disciplines, called the Rate-Controlled Service Disciplines. When coupled with suitable admission control algorithms, Rate-Controlled Service Disciplines can provide end-to-end deterministic and statistical performance guarantees on a per-connection basis in an arbitrary topology packet-switching network. The key feature of a rate-controlled service discipline is the separation of the server into two components: a rate-controller and a scheduler. This separation makes it possible to obtain end-to-end performance characteristics by applying single node analysis at each switch. It also has several other distinct advantages: it decouples the allocation of bandwidths and delay bounds, uniformly distributes the allocation of buffer space inside the network to prevent packet loss, and allows arbitrary combinations of rate-control policies and packet scheduling policies. Rate-controlled service disciplines provide a general framework w...

This thesis presents flexible abstractions for specifying resource management policies, together with efficient mechanisms for implementing those abstractions. Several novel scheduling techniques are introduced, including both randomized and deterministic algorithms that provide proportional-share control over resource consumption rates. Such control is beyond the capabilities of conventional schedulers, and is desirable across a broad spectrum of systems that service clients of varying importance. Proportional-share scheduling is examined for several diverse resources, including processor time, memory, access to locks, and disk bandwidth. Resource rights are encapsulated by abstract, first-class objects called tickets. An active client consumes resources at a rate proportional to the number of tickets that it holds. Tickets can be issued in different amounts and may be transferred between clients. A modular currency abstraction is also introduced to flexibly name, share, and protect ...

This paper focuses on the problem of providing run-time support to real-time applications and non-real-time applications in an open system environment. It extends the two-level hierarchical scheduling scheme in [12] for scheduling independently developed applications. The extended scheme removes the following two restrictive requirements of the scheme in [12]: (1) real-time applications that are scheduled preemptively must consist solely of periodic tasks, and (2) applications must not share global resources (i.e., resources used by more than one applications). Consequently, the extended scheme allows us to deal with a much broader range of real-time applications. 1 Introduction Recent advances in real-time systems technology have given us many good schemes for scheduling hard real-time applications. Examples are [1, 2, 5, 8]. A weakness shared by most existing schemes is that schedulability analysis must be done globally (i.e., by analyzing all applications in the system together) in...

Can the introduction of traffic classes improve upon the performance of ATM networks? We investigate this issue within the framework provided by a class of networks that guarantees quality of service. To provide a meaningful comparison we define the concept of schedulable region, a region in the space of loads for which the quality of service is guaranteed. We show the dependence of the schedulable region on the scheduling algorithm employed, the quality of service parameters and the traffic statistics. An efficient real-time scheduling algorithm is introduced that substantially increases the schedulable region without incurring prohibitive complexity costs. The schedulable region associated with this algorithm is compared with the ones generated by the static priority scheduling algorithm and a variant of the minimum laxity threshold algorithm. The size and shape of the schedulable region is explored by means of simulations.