We study the problem of scheduling activities of several types under the constraint that at most a fixed number of activities can be scheduled in any single time-slot. Any given activity type is associated with a service cost and an operating cost that increases linearly with the number of time-slots since the last service of this type. The problem is to find an optimal schedule that minimizes the long-run average cost per time-slot. Applications of such a model are the scheduling of maintenance service to machines, multiitem replenishment of stock, and minimizing the mean response time in Broadcast Disks. Broadcast Disks gained a lot of attention recently since they are used to model backbone communications in wireless systems, Teletext systems, and web caching in satellite systems. The first contribution of this paper is the definition of a general model that combines into one several important previous models. We prove that an optimal cyclic schedule for the general problem exists a...

This paper describes how Dynamic WindowConstrained Scheduling (DWCS) can guarantee real-time service to packets from multiple streams with different performance objectives. We show that: (1) DWCS can guarantee that no more than x packets miss their deadlines for every y consecutive packets requiring service, as long as the minimum aggregate bandwidth requirement of all real-time packet streams does not exceed the available bandwidth, (2) using DWCS, the delay of service to realtime packet streams is bounded even when the scheduler is overloaded, (3) DWCS can ensure that the delay bound of any given stream is independent of other streams, and (4) a fast response time for best-effort packet streams, in the presence of real-time packet streams, is possible. Furthermore, if a feasible schedule exists, each stream is guaranteed a minimum fraction of available bandwidth over a finite window of time. 1. Introduction Many real-time, distributed applications, such as telemedicine, virtual env...

The data broadcast problem is to nd a schedule for broadcasting a given set of messages over multiple channels. The goal is to minimize the cost of the broadcast plus the expected response time to clients who periodically and probabilistically tune in to wait for particular messages. The problem models disseminating data to clients in asymmetric communication environments, where there is a much larger capacity from the information source to the clients than in the reverse direction. Examples include satellites, cable TV, internet broadcast, and mobile phones. Such environments favor the \push-based" model where the server broadcasts (pushes) its information on the communication medium and multiple clients simultaneously retrieve the speci c information of individual interest. This sort of environment motivates the study of \broadcast disks" in Information Systems [1; 7]. In this paper we present the rst polynomial-time approximation scheme for the data broadcast problem for the cas...

Abstract. The Data Broadcast Problem consists of finding an infinite schedule to broadcast a given set of messages so as to minimize a linear combination of the average service time to clients requesting messages, and of the cost of the broadcast. This problem also models the Maintenance Scheduling Problem and the Multi-Item Replenishment Problem. Previous work concentrated on a discrete-time restriction where all messages have transmission time equal to 1. Here, we study a generalization of the model to a setting of continuous time and messages of non-uniform transmission times. We prove that the Data Broadcast Problem is strongly NP-hard, even if the broadcast costs are all zero, and give 3-approximation algorithms. Key Words. broadcasting.

The design of programs for broadcast disks which incorporate real-time and fault-tolerance requirements is considered. A generalized model for real-time fault-tolerant broadcast disks is defined. It is shown that designing programs for broadcast disks specified in this model is closely related to the scheduling of pinwheel task systems. Some new results in pinwheel scheduling theory are derived, which facilitate the efficient generation of realtime fault-tolerant broadcast disk programs.

This paper describes an algorithm for scheduling packets in real-time multimedia data streams. Common to these classes of data streams are service constraints in terms of bandwidth and delay. However, it is typical for realtime multimedia streams to tolerate bounded delay variations and, in some cases, finite losses of packets. We have therefore developed a scheduling algorithm that assumes streams have window-constraints on groups of consecutive packet deadlines. A window-constraint defines the number of packet deadlines that can be missed in a window of deadlines for consecutive packets in a stream.

Emerging broadband switches must accommodate the diverse traffic parameters and quality-of-service requirements of voice, data, and video applications. End-toend performance guarantees depend on connections complying with traffic contracts as their cells travel through the network. This paper presents a leaky-bucket shaper architecture that scales to a large number of connections with diverse burstiness and bandwidth parameters. In contrast to existing designs, the proposed architecture arbitrates fairly between connections with conforming cells by carefully integrating leaky-bucket traffic shaping with ratebased scheduling algorithms. Through a careful combination of per-connection queueing and approximate sorting, the shaper performs a small, bounded number of operations in response to each arrival and departure, independent of the number of connections and cells. When the shaper must handle a wide range of rate parameters, a hierarchical arbitration scheme can reduce the implementa...

There has been an increasing need of timely and predictable communication services for embedded real-time systems in automated factories and industrial process controls. Work has been done on real-time communication with deadline guarantees in point-to-point, token bus/token ring/FDDI, and DQDB (Distributed Queue Dual Bus) networks. However, due to the random access nature of the CSMA/CD type multiaccess networks, they are not suitable for applications with stringent timing constraints. In this paper, we consider real-time communication services with absolute deadline guarantees in multiaccess local area networks equipped with a centralized scheduler, such as the SP50 FieldBus [1], an industrial standard protocol for process control and manufacturing applications. Similar to most token-passing networks, in a centralizedscheduling multiaccess network, the access to the bus is controlled by a token. Only the station currently holding the token has the exclusive right to use the multiacce...

Packet switching in connection-oriented networks that may have multiple parallel links between pairs of switches is considered. An e cient packet-scheduling algorithm that guarantees a deterministic quality of service toconnections with real-time constraints is proposed { this algorithm is a generalization of some recent multiprocessor scheduling algorithms, and o ers realtime performance guarantees similar to those o ered by earlier fair-scheduling strategies such as Weighted Fair Queueing and proportional-share schemes.

We study the problem of scheduling files over a broadcast channel in an asymmetric environment. The goal is to minimize the mean response time for clients who access the broadcast channel. Asymmetric channels gained a lot of attention since they are used to model wireless communication, Teletext systems, and web caching in satellite systems. This paper addresses the 2-files case. We design a simple algorithm that defines the optimal schedule given the demand probability for each file. Our solution is extended to include other important factors, such as dependencies between files, variable-length files, and different priorities for the clients. Adding dependencies is important in the web caching environment since clients may wish to access more than one file in the broadcast channel. For all the above extensions, we prove the surprising result that there exists a simple optimal schedule. Such a schedule is composed of a repeated pattern of AA \Delta \Delta \Delta AB where A is the more ...