In this paper, we propose to use the idealized Hierarchical Generalized Processor Sharing (H-GPS) model to simultaneously support guaranteed real-time, rate-adaptive best-effort, and controlled link-sharing services. We design Hierarchical Packet Fair Queueing (H-PFQ) algorithms to approximate H-GPS by using one-level variable-rate PFQ servers as basic building blocks. By computing the system virtual time and per packet virtual start/finish times in unit of bits instead of seconds, most of the PFQ algorithms in the literature can be properly defined as variable-rate servers. We develop techniques to analyze delay and fairness properties of variable-rate and hierarchical PFQ servers. We demonstrate that in order to provide tight delay bounds with an H-PFQ server, it is essential for the one-level PFQ servers to have small Worst-case Fair Indices (WFI). We propose a new PFQ algorithm called WF 2 Q+ that is the first to have all the following three properties: (a) providing the tightest...

This paper argues for the need to design a new processor scheduling algorithm that can handle the mix of applications we see today. We present a scheduling algorithm which we have implemented in the Solaris UNIX operating system [Eykholt et al. 1992], and demonstrate its improved performance over existing schedulers in research and practice on real applications. In particular, we have quantitatively compared against the popular weighted fair queueing and UNIX SVR4 schedulers in supporting multimedia applications in a realistic workstation environment...

In this paper, we study hierarchical resource management models and algorithms that support both link-sharing and guaranteed real-time services with decoupled delay (priority) and bandwidth allocation. We extend the service curve based QoS model, which defines both delay and bandwidth requirements of a class, to include fairness, which is important for the integration of real-time and hierarchical linksharing services. The resulting Fair Service Curve linksharing model formalizes the goals of link-sharing and realtime services and exposes the fundamental tradeoffs between these goals. In particular, with decoupled delay and bandwidth allocation, it is impossible to simultaneously provide guaranteed real-time service and achieve perfect link-sharing. We propose a novel scheduling algorithm called Hierarchical Fair Service Curve (H-FSC) that approximates the model closely and efficiently. The algorithm always guarantees the performance for leaf classes, thus ensures real-time services, while minimizing the discrepancy between the actual services provided to the interior classes and the services defined by the Fair Service Curve link-sharing model. We have implemented the H-FSC scheduler in the NetBSD environment. By performing simulation and measurement experiments, we evaluate the link-sharing and real-time performances of H-FSC, and determine the computation overhead.

In this paper, we review the basic mechanisms used in packet networks to support Quality-of-Service QoS guarantees. We outline the various approaches that have been proposed, and discuss some of the trade-offs they involve. Specifically, the paper starts by introducing the different scheduling and buffer management mechanisms that can be used to provide service differentiation in packet networks. The aim is not to provide an exhaustive review of existing mechanisms, but instead to give the reader a perspective on the range of options available and the associated trade-off between performance, functionality, and complexity. This is then followed by a discussion on the use of such mechanisms to provide specific end-to-end performance guarantees. The emphasis of this second part is on the need for adapting mechanisms to the different environments where they are to be deployed. In particular, fine grain buffer management and scheduling mechanisms may be neither necessary nor cost effective in high speed backbones, where "aggregate" solutions are more appropriate. The paper discusses issues and possible approaches to allow coexistence of different mechanisms in delivering end-to-end guarantees.

Providing packet-level... In this paper, we propose a new scheduling model that addresses this conflict. The main results of this paper are the following: (a) a two-tier service model that provides a minimum "fair" allocation of the channel bandwidth for each packet flow and additionally maximizes spatial reuse of bandwidth, (b) an ideal centralized packet scheduling algorithm that realizes the above service model, and (c) a practical distributed backoff-based channel contention mechanism that approximates the ideal service within the framework of the CSMA/CA protocol.

Proportional share resource management provides a flexible and useful abstraction for multiplexing timeshared resources. However, previous proportional share mechanisms have either weak proportional sharing accuracy or high scheduling overhead. We present VirtualTime Round-Robin (VTRR), a proportional share scheduler that can provide good proportional sharing accuracy with O(1) scheduling overhead. VTRR achieves this by combining the benefits of fair queueing algorithms with a round-robin scheduling mechanism. Unlike many other schedulers, VTRR is simple to implement. We have implemented a VTRR CPU scheduler in Linux in less than 100 lines of code. Our performance results demonstrate that VTRR provides accurate proportional share allocation with constant, sub-microsecond scheduling overhead. The scheduling overhead using VTRR is two orders of magnitude less than the standard Linux scheduler for large numbers of clients.

This report considers the problems of scheduling transmissions in broadcast environments, including, wireless environments. Issues that affect the design of fair scheduling algorithms, and several alternative approaches to implementing fair scheduling in single-hop and multi-hop environments are identified. 3 Abstract ........................................................................................................................................... 2 1 Fair Queuing............................................................................................................................. 4 2 Broadcast Environments ..........................................................................................................7 2.1 Wired Local Area Network............................................................................................... 7 2.2 Wireless Local Area Network........................................................................................... 8 2.3 Multi...

Distributed fair queueing in a multihop, wireless ad-hoc network is challenging for several reasons. First, the wireless channel is shared among multiple contending nodes in a spatial locality. Location-dependent channel contention complicates the fairness notion. Second, the sender of a flow does not have explicit information regarding the contending flows originated from other nodes. Fair queueing over ad-hoc networks is a distributed scheduling problem by nature. Finally, the wireless channel capacity is a scarce resource. Spatial channel reuse, i.e., simultaneous transmissions of flows that do not interfere with each other, should be encouraged whenever possible. In this paper, we re-examine the fairness notion in an ad-hoc network using a graph-theoretic formulation, and extract the fairness requirements that an ad-hoc fair queueing algorithm should possess. To meet these requirements, we propose Maximize-Local-Minimum Fair Queueing (MLM-FQ), a novel distributed packet scheduling algorithm where local schedulers self-coordinate their scheduling decisions and collectively achieve fair bandwidth sharing. We then propose Enhanced MLM-FQ (EMLM-FQ) to further improve the spatial channel reuse and limit the impact of inaccurate scheduling information resulted from collisions. EMLM-FQ achieves statistical short-term throughput and delay bounds over the shared wireless channel. Analysis and extensive simulations confirm the effectiveness and efficiency of our self-coordinating localized design in providing global fair channel access in wireless ad-hoc networks.

and useful abstraction for multiplexing time-shared resources. We present Group Ratio Round-Robin (GR ), the first proportional share scheduler that combines accurate proportional fairness scheduling behavior with O(1) scheduling overhead on both uniprocessor and multiprocessor systems. GR uses a novel client grouping strategy to organize clients into groups of similar processor allocations which can be more easily scheduled. Using this grouping strategy, GR combines the benefits of low overhead round-robin execution with a novel ratio-based scheduling algorithm. GR can provide fairness within a constant factor of the ideal generalized processor sharing model for client weights with a fixed upper bound and preserves its fairness properties on multiprocessor systems.

The widescale deployment of packetized wireless network services currently lacks a mechanism to provide QoS in the framework of existing backbone networks. This paper describes a wireless scheduling algorithm that can provide QoS bounds to ATM traffic. It transforms the standard ATM traffic classes into parameters for a priority, fair queuing algorithm, implemented at the wireless MAC layer. By supporting existing ATM traffic, the scheduler avoids the need to redefine QoS specifically for the packetized wireless channel. Bounds are derived for delay and throughput on the individual CBR and rt-VBR virtual connections. The scheduler