Generalized rate-monotonic scheduling theory: a framework fordeveloping real-time systems

Real-time computing systems are used to control telecommunication systems, defense systems, avionics, and modern factories. Generalized rate-monotonic scheduling theory, is a recent development that has had large impact on the development of real-time systems and open standards. In this paper we provide an up-to-date and self-contained review of generalized rate-monotonic scheduling theory. We show how this theory can be applied in practical system development, where special attention must be given to facilitate concurrent development by geographically distributed programming teams and the reuse of existing hardware and software components     

Virtual time reference system: a unifying scheduling framework forscalable support of guaranteed services

We propose and develop a novel virtual time reference system as a unifying scheduling framework to provide scalable support for guaranteed services. This virtual time reference system is designed as a conceptual framework upon which guaranteed services can be implemented in a scalable manner using the DiffServ paradigm. The key construct in the proposed virtual time reference system is the notion of packet virtual time stamps, whose computation is core stateless, i.e., no per-flow states are required for its computation. We lay the theoretical foundation for the definition and construction of packet virtual time stamps. We describe how per-hop behavior of a core router (or rather its scheduling mechanism) can be characterized via packet virtual time stamps, and based on this characterization establish end-to-end per-flow delay bounds. Consequently, we demonstrate that, in terms of its ability to support guaranteed services, the proposed virtual time reference system has the same expressive power and generality as the IntServ model. Furthermore, we show that the notion of packet virtual time stamps leads to the design of new core stateless scheduling algorithms, especially work-conserving ones. In addition, our framework does not exclude the use of existing scheduling algorithms such as stateful fair queuing algorithms to support guaranteed services     

Coordinated multihop scheduling: a framework for end-to-end services

In multihop networks, packet schedulers at downstream nodes have an opportunity to make up for excessive latencies due to congestion at upstream nodes. Similarly, when packets incur low delays at upstream nodes, downstream nodes can reduce priority and schedule other packets first. The goal of this paper is to define a framework for design and analysis of coordinated multihop scheduling (CMS) which exploits such internode coordination. We first provide a general CMS definition which enables us to classify a number of schedulers from the literature, including G-EDF, FIFO+, CEDF, and work-conserving CJVC as examples of CMS schedulers. We then develop a distributed theory of traffic envelopes which enables us to derive end-to-end statistical admission control conditions for CMS schedulers. We show that CMS schedulers are able to limit traffic distortion to within a narrow range resulting in improved end-to-end performance and more efficient resource utilization. Consequently, our technique exploits statistical resource sharing among flows, classes, and nodes, and our results provide the first statistical multinode multiclass admission control algorithm for networks of work conserving servers.     

Call scheduling algorithms in a multicast switch

Multicast switching is emerging as a new switching technology that can provide efficient transport in a broadband network for video and other multipoint communication services. The authors develop and analyze call scheduling algorithms for a multicast switch. In particular, they examine two general classes of scheduling algorithms: call packing algorithms and call splitting algorithms. The performance improvement by the call packing algorithms examined is shown to be negligible. In contrast, the call splitting algorithms can provide significantly lower blocking by reducing the level of output port contention. However, excessive call splitting could degrade performance because of the additional load introduced to the input ports. The authors present a simple call splitting algorithm called greedy splitting which achieves near-optimal performance     

Parallelizable Bayesian tomography algorithms with rapid,guaranteed convergence

Bayesian tomographic reconstruction algorithms generally require the efficient optimization of a functional of many variables. In this setting, as well as in many other optimization tasks, functional substitution (FS) has been widely applied to simplify each step of the iterative process. The function to be minimized is replaced locally by an approximation having a more easily manipulated form, e.g., quadratic, but which maintains sufficient similarity to descend the true functional while computing only the substitute. We provide two new applications of FS methods in iterative coordinate descent for Bayesian tomography. The first is a modification of our coordinate descent algorithm with one-dimensional (1-D) Newton-Raphson approximations to an alternative quadratic which allows convergence to be proven easily. In simulations, we find essentially no difference in convergence speed between the two techniques. We also present a new algorithm which exploits the FS method to allow parallel updates of arbitrary sets of pixels using computations similar to iterative coordinate descent. The theoretical potential speed up of parallel implementations is nearly linear with the number of processors if communication costs are neglected.     

Production scheduling algorithms for a semiconductor test facility

The authors develop production scheduling algorithms for semiconductor test operations. The operations in the facility under study are characterized by a broad product mix, variable lot sizes and yields, long and variable setup times, and limited test equipment capacity. The approach presented starts by dividing the facility or job shop into a number of work centers. The method then proceeds to sequence one work center at a time. A disjunctive graph representation of the entire facility is used to capture interactions between work centers. The introduction of different management objectives leads to different work center problems and different production scheduling algorithms. The authors present algorithms for two different work center problems. Direction for future research are discussed     

Generalized threshold chase algorithms

 Three generalized threshold Chase algorithms called GTC Ⅰ,GTC Ⅱ and STC are proposed in this paper.They are the combination of the generalized minimum distance(GMD)decoding algorithm with the Chase algorithm.Although the decoding error probabilities of these algorithms are very close to that of the Chase algorithm,the decoding speeds are faster,especially at higher signal-to-noise ratio(SNR),hence they are of greater practical value.The results of computer simulations are given,showing the advantages of these algorithms.     

Active intra-ONU scheduling with proportional guaranteed bandwidth in long-reach EPONs

The unused slot remainder (USR) problem in Ethernet Passive Optical Networks and long-reach Passive Optical Networks (LR-PONs) results in both a lower bandwidth utilization and a greater packet delay. In a previous study by the current group, an Active intra-ONU Scheduling with predictive queue report scheme was proposed for resolving the USR problem by predicting the granted bandwidth in advance based on the arrival traffic estimates of the optical network units (ONUs). However, it was found that the higher bandwidth prediction error in the proposed scheme prevents the network performance from being improved. Accordingly, the present study proposes a non-predictive-based ONU scheduling method designated as Active intra-ONU Scheduling with proportional guaranteed bandwidth (ASPGB) to improve the performance of LR-PONs. In the proposed method, the maximum guaranteed bandwidth of each ONU is adapted dynamically in accordance with the ratio of the ONU traffic load to the overall system load. Importantly, the proposed dynamic bandwidth allocation approach reduces the dependence of the network performance on the granted bandwidth prediction since the maximum guaranteed bandwidth determined by the Optical Line Terminal more closely approaches the actual bandwidth demand of each ONU. To solve the idle time problem arising in the event of an excess bandwidth reallocation, ASPGB is integrated with an improved early allocation (IEA) algorithm (a kind of Just-In-Time scheduling). The simulation results show that the IEA-ASPGB scheme outperforms previously published methods in terms of bandwidth utilization and average packet delay under both balanced and unbalanced traffic load conditions.     

Adaptive downlink scheduling and rate selection: a cross-layer design

In this paper, we discuss a cross-layer design for joint user scheduling and adaptive rate control for downlink wireless transmission. We take a stochastic learning-based approach to achieve this. The scheduling is performed at the medium access control (MAC) layer, whereas the rate selection takes place at the physical/link (PHY/LINK) layer. These two components residing in the two layers exchange information to ensure that user defined rate requests are satisfied by the right combination of transmission schedules and rate selections. The method is highly efficient for low mobility applications with mobile speeds in the order of a few kilometers per hour. While simple to implement, this technique requires no explicit channel estimation phase. The only feedback used are the single bit ACK/NACK signal indicating the correct reception/failure of the packet. As shown in the convergence theorems, the algorithm achieves optimal performance in "stationary" channels. With slowly varying channels, the rate selection algorithm sees a "quasi-stationary" channel and adaptively converges to an optimal solution. Simulations performed using a third-generation wireless system, namely, high-speed downlink packet access (HSDPA) validate the theoretical results.     

无线网络中的分组调度算法

探讨了将有线网络的分组调度算法引入无线网络需要改进的事项,分析了公平排队算法,建立了一个基本的无线分组调度模型,并综述了一些目前存在的无线分组调度算法。     

Neural scheduling algorithms for time-multiplex switches

In an N×N time-multiplex switch, transmission conflict arises when two or more input adaptors transmit packets to the same output adaptor simultaneously. To resolve transmission conflict, we propose two neural-based scheduling algorithms which use a large number of simple processing elements to perform scheduling in parallel. The first algorithm uses N² hysteresis McCulloch-Pitts (1943) neurons to determine conflict-free transmission schedules with maximum throughput. The second algorithm resolves transmission conflict among the first M packets in each input queue. It determines suboptimal transmission schedules using only NM neurons (M2=250000 to NM=5000     

Implementing scheduling algorithms in high-speed networks

The fluid generalized processor sharing (GPS) algorithm has desirable properties for integrated services networks and many packet fair queueing (PFQ) algorithms have been proposed to approximate GPS. However, there have been few high-speed implementations of PFQ algorithms that can support a large number of sessions with diverse rate requirements and at the same time maintain all the important properties of GPS. The implementation cost of a PFQ algorithm is determined by: (1) computation of the system virtual time function; (2) maintenance of the relative ordering of the packets via their timestamps (scheduling); and (3) regulation of packets based on eligibility time, in some algorithms. While most of the recently proposed PFQ algorithms reduce the complexity of computing the system virtual time function, the complexity of scheduling and traffic regulation is still a function of the number of active sessions. In addition, while reducing the algorithmic or asymptotic complexity has been the focus of most analysis, it is also important to reduce the complexity of basic operations in order for the algorithm to run at high speed. We develop techniques to reduce both types of complexities for networks of both fixed and variable size packets. Regulation and scheduling are implemented in an integrated architecture that can be viewed as logically performing sorting in two dimensions simultaneously. By using a novel grouping architecture, we are able to perform this with an algorithmic complexity independent of the number of sessions in the system at the cost of a small controllable amount of relative error. To reduce the cost of basic operations, we propose a hardware-implementation framework and several novel techniques that reduce the on-chip memory size, off-chip memory bandwidth, and off-chip access latency. The proposed implementation techniques have been incorporated into commercial ATM switch and IP router products     

Resource constrained scheduling of uniform algorithms

A method for optimizing the schedule and allocation of uniform algorithms onto processor arrays is derived. The main results described in the following paper are: (1) single (integer) linear programs are given for the optimal schedule of regular algorithms with and without resource constraints, (2) the class of algorithms is extended by allowing certain non-convex index domains, (3) efficient branch and bound techniques are used such that problems of relevant size can be solved. Moreover, additional constraints such as cache memory, bus bandwidths and access conflicts can be considered also. The results are applied to an example of relevant size.     

Efficient algorithms for scheduling data broadcast

With the increasing acceptance of wireless technology, mechanisms to efficiently transmit information to wireless clients are of interest. The environment under consideration is asymmetric in that the information server has much more bandwidth available, as compared to the clients. It has been proposed that in such systems the server should broadcast the information periodically. A broadcast schedule determines what is broadcast by the server and when. This paper makes the simple, yet useful, observation that the problem of broadcast scheduling is related to the problem of fair queueing. Based on this observation, we present a log‐time algorithm for scheduling broadcast, derived from an existing fair queueing algorithm. This algorithm significantly improves the time‐complexity over previously proposed broadcast scheduling algorithms. Modification of this algorithm for transmissions that are subject to errors is considered. Also, for environments where different users may be listening to different number of broadcast channels, we present an algorithm to coordinate broadcasts over different channels. Simulation results are presented for proposed algorithms.     

Stochastic bound on delay for guaranteed rate nodes

We find that the probabilistic bound on delay in the article by Goyal et al. (see Springer Multimedia Syst., vol.5, p.157-63, 1997) is incorrect. The problem originates from: 1) the difference between stationary and Palm probabilities and 2) treating the arrival counting process over some random time intervals as if the time interval would be fixed. The error is propagated to some later work, e.g., recently by Bensaou et al.(see IEEE/ACM. Trans. Networking, vol.9, p.591-603, Oct. 2001), which derived some probabilistic delay bounds based on Goyal et al. in 1997. We give fixes to the above problem     

IEEE 802.16网络中保障QoS的多用户业务调度算法

基于IEEE 802.16协议,研究了宽带无线接入网中保障Qos的上行多用户多业务资源分配和调度问题.首先,对该问题建立跨层分析模型,即基于TDM-OFDMA物理层的多址接入队列调度模型.随后提出了基于凸优化方法的最小剩余聚合工作负载算法.可以证明,只要到达业务的QOS参数值在该算法的稳定域内,那么它就能渐进地保证业务的QoS要求,同时还能最小化调度系统的剩余聚合工作负载.仿真实验的数值结果进一步证明了本算法的确能够在可接受的复杂度范围内保证4类服务的Qos要求.     

一种支持QoS的OBS网络数据信道调度协议

综合考虑了突发包所经历跳数和突发包的长度等因素,文章给出了一种新型的支持服务质量(QoS)的光突发交换(OBS)数据信道调度协议--考虑跳数的改进型JET模式下的优先级抢占(H-PPJET)协议.文章在OBS网络环境中对H-PPJET协议进行了仿真,并与JET模式下的优先级抢占(PPJET)协议进行了对比,仿真结果表明,H-PPJET协议改善了网络的吞吐量和丢包率性能.     

A statistical framework for EDF scheduling

Earliest deadline first (EDF) has become one of the most promising scheduling schemes for providing quality-of-service differentiation over high speed networks. In this letter, we study the deadline violation (loss) probability at an EDF scheduling switch. An analytical framework has been developed for estimating the loss probabilities for the aggregated traffic and the individual flows. This enables us to determine whether a given flow can meet its deadline with the required loss probability. As illustrated from the simulation results using real network traffic, the asymptotic approximations presented are accurate enough to predict the real metrics.     

The rate region of a cooperative scheduling system

A wireless communication system where a common base station is scheduled to transmit information to multiple mobile users on a time division (TD) basis is considered. The capacity region of this system is found for the two user case and the optimal scheduling scheme is proposed which achieves the boundary of the capacity region. Furthermore, the optimal scheduling scheme is found for the case when the remote mobile users can perform downlink cooperation and the achievable rate region of the downlink cooperative system is characterized. Finally, a simple iterative algorithm is proposed for finding the resource allocation parameters and the scheduling scheme for the cooperative system.