Latency Rate Research Articles

Enhanced PF Scheduling Algorithm for LTE Networks

Scheduling Algorithm is a key Radio ResourceManagement (RRM) mechanism to achieve Quality of Service(QoS) requirements and to optimize system performance of LongTerm Evolution (LTE) network. The LTE standard does notspecify a scheduling algorithm and some schedules have beenproposed in the literature. Most of them consider the channelstate or some QoS metric, however, they do not consider thePF characteristics and the delay required by the user. Then, anenhanced scheduling algorithm was proposed based on Latency-Rate (LR) server theory and system characteristics specifiedby the LTE standard. Properties of this proposal have beeninvestigated theoretically and through simulations. A simulationis presented with video traffic and also performance comparisonswith Proportional Fairness (PF) and Modified Largest WeightedDelay First (MLWDF) schedulers. The results show that theproposed schedule has a better performance compared with theabove schedulers.

Certifying execution time in multicores

This article presents a semantics-based program verification framework for critical embedded real-time systems using the worst-case execution time (WCET) as the safety parameter. The verification algorithm is designed to run on devices with limited computational resources where efficient resource usage is a requirement. For this purpose, the framework of abstract-carrying code (ACC) is extended with an additional verification mechanism for linear programming (LP) by applying the certifying properties of duality theory to check the optimality of WCET estimates. Further, the WCET verification approach preserves feasibility and scalability when applied to multicore architectural models.The certifying WCET algorithm is targeted to architectural models based on the ARM instruction set and is presented as a particular instantiation of a compositional data-flow framework supported on the theoretic foundations of denotational semantics and abstract interpretation. The data-flow framework has algebraic properties that provide algorithmic transformations to increase verification efficiency, mainly in terms of verification time. The WCET analysis/verification on multicore architectures applies the formalism of latency-rate (LR) servers, and proves its correctness in the context of abstract interpretation, in order to ease WCET estimation of programs sharing resources.

Packet Scheduling in High-speed Networks Using Improved Weighted Round Robin

A variety of applications with different QoS requirements are supported simultaneously in the high-speed packet-switched networks, packet scheduling algorithms play a critical role in guaranteeing the performance of routing and switching devices. This study presents a simple, fair, efficient and easily implementary scheduling algorithm, called Successive Minimal-weight Round Robin (SMRR). In each round, SMRR provides the same service opportunity, which is equivalent to the minimal weight of the current round, for all active data flows. On the basis of the concept of Latency-Rate (LR) servers, we obtain the upper bound on the latency of SMRR and WRR (Weighted Round Robin) respectively and the results indicate that SMRR makes a significant improvement on the latency bound in comparison to WRR. We also discuss the fairness and implementation complexity of SMRR and the theoretical analysis shows that SMRR preserves the good implementation complexity of O (1) with respect to the number of flows and has better fairness than WRR.

An Efficient Approach of Scheduling with Call Admission Control to Fixed WiMAX Networks

The major challenge for the second decade of this century is the implementation of access to high-speed internet, known as broadband internet. Thus, the IEEE (Institute of Electrical and Electronics Engineers) has developed a new standard for wireless access, called IEEE 802.16. Also known as WiMAX (Worldwide Interoperability for Microwave Access), it is an emerging technology for next generation wireless networks which supports a large number of users, both mobile and nomadic (fixed), distributed across a wide geographic area. Based on these assumptions, and considering that the standard does not specify a scheduling algorithm, a new scheduler with call admission control was proposed based on Latency-Rate (LR) server theory and with system characteristics as specified by the system standard using the WirelessMAN-OFDM (Orthogonal Frequency Division Multiplexing) air interface. The proposed scheduler calculates the time frame (TF) in order to maximize the number of stations allocated in the system while managing the delay required for each user. Properties of this proposal have been investigated theoretically and through simulations. The results of simulations show that an upper bound on the delay can be achieved for a large range of network loads, with bandwidth optimization.

Service Interval Optimization with Delay Bound Guarantee for HCCA in IEEE 802.11e WLANs

IEEE 802.11e Medium Access Control (MAC) is a supplement to the IEEE 802.11 Wireless Network (WLAN) standard to support Quality of Service (QoS). The 802.11e MAC defines a new coordination function, namely Hybrid Coordination Function (HCF), which takes the QoS requirements of flows into account and allocates Transmission Opportunity (TXOP) to stations. On the basis of mean sending rate, delay of Variable Bit Rate (VBR) traffic cannot be bounded with the reference HCF scheduling algorithm proposed in this supplement. In this paper, we propose a new Connection Admission Control (CAC) and a scheduling algorithm that utilize the token bucket and a modified Latency-Rate (LR) scheduling algorithm to guarantee a bounded delay for HCF Controlled Channel Access (HCCA). The new Service Interval (SI) is calculated to optimize the number of stations accommodated and takes into account delay bound and token bucket parameters. We show that it is possible to obtain worst-case performance guarantees on delay. First, we analyze the behavior of the new scheduler with a loss free wireless channel model and after this, with a burst loss model and we explain how it is possible to extend this scheduler for a multi-rate scheme. Properties of the proposal are investigated both theoretically and using ns-2 simulations. We present a set of simulations with both Constant Bit Rate (CBR) and VBR flows and performance comparisons with HCF scheduling algorithm. The results show that the delay upper bound can be achieved for a large range of networks load with bandwidth optimization.

Quantum-Based Earliest Deadline First Scheduling for Multiservices

Latency-rate (LR) schedulers have shown their ability in providing fair and weighted sharing of bandwidth with an upper bound on delivery latency of packets while earliest departure first (EDF) schedulers have shown their ability in providing LR-decoupled service whereby the delivery latency of packets is not bounded by the reserved rate. However, EDF schedulers require traffic shapers to ensure flow protection. We propose quantum-based earliest deadline first scheduling (QEDF), a quantum-based scheduler that provides flow protection, throughput guarantee and delay bound guarantee for flows that require LR-coupled and LR-decoupled types of reservations. It classifies flows into time-critical (TC), jitter-sensitive (JS), and rate-based (RB) classes and uses a quality-of-service forwarding rule to determine the next packet to be serviced by the scheduler. It provides nonpreemptive priority service to TC queues. This allows LR-decoupled reservation for flows that have a low rate and intolerable delay. Packets from JS queues can be delayed by other packets if forwarding the latter will not result in the former missing its deadline. As a quantum-based scheduler, the QEDF scheduler provides throughput guarantees for RB queues. We present both analytical and simulation results of QEDF, whereby we evaluated QEDF in its deployment as a single-class as well as a multiservice scheduler

Deterministic Edge-to-Edge Delay Bounds for a Flow under Latency Rate Scheduling in a DiffServ Network

SUMMARY With the occurrence of new applications such as Voice over IP (VoIP) and multimedia conference, there is an ongoing discussion about realizing QoS in the Internet today. Because of its potential scalability in support of QoS guarantees, the Differentiated Service (DiffServ) architecture with aggregate packet scheduling has recently attracted much attention in the networking community as a feasible solution for providing Internet QoS. Thus, it is important to understand delay bound of an individual flow in the DiffServ architecture in order to provide delay-sensitive applications. In this paper, we study, via both analysis and simulation, the deterministic bound on edge-to-edge delay of a flow in a DiffServ network domain with FIFO aggregation and a class-based Latency Rate (LR) server that provides guaranteed performance with rate reservation for a traffic class. We derive edge-to-edge delay bound for a single flow as a function of allocated service rate for a traffic class, token bucket parameters adopted for flows at the network ingress, and information about joining and leaving flows. We compare the obtained delay bound with previous works using analytic results, and then conduct simulation to confirm the results. The derived bound is less than that of previous studies in all cases.

On fundamental tradeoffs between delay bounds and computational complexity in packet scheduling algorithms

We clarify, extend, and solve a long-standing open problem concerning the computational complexity for packet scheduling algorithms to achieve tight end-to-end delay bounds. We first focus on the difference between the time a packet finishes service in a scheduling algorithm and its virtual finish time under a GPS (General Processor Sharing) scheduler, called GPS-relative delay. We prove that, under a slightly restrictive but reasonable computational model, the lower bound computational complexity of any scheduling algorithm that guarantees O(1) GPS-relative delay bound is /spl Omega/(logn). We also discover that, surprisingly, the complexity lower bound remains the same even if the delay bound is relaxed to O(n/sup a/) for 0<a<1. This implies that the delay-complexity tradeoff curve is flat in the interval [O(1),O(n)). We later conditionally extend both complexity results (for O(1) or O(n/sup a/) delay) to a much stronger computational model, the linear decision tree. Finally, we show that the same complexity lower bounds are conditionally applicable to guaranteeing tight end-to-end delay bounds, if the delay bounds are provided through the Latency Rate (LR) framework.

Relationship between guaranteed rate server and latency rate server

To analyze scheduling algorithms in computer networks, two models have been proposed and widely used in the literature, namely the Guaranteed Rate (GR) server model and the Latency Rate (LR) server model. While a lot scheduling algorithms have been proved to belong to GR or LR or both, it is not clear what is the relationship between them. The purpose of this paper is to investigate this relationship. We prove that if a scheduling algorithm belongs to GR, it also belongs to LR and vice versa. In addition, we review several other models that are also used for analysis of scheduling algorithms and discuss their relationship with LR model and GR model.

On the relationship between absolute and relative fairness bounds

The fairness of scheduling disciplines used in communication networks has frequently been evaluated using one of two fairness measures: the absolute fairness bound (AFB) and the relative fairness bound (RFB). We present a tight bounded relationship between these measures of fairness. The bounds established are exactly reached in the case of many real scheduling disciplines, thus leading to an easy conversion between these two measures. In the case of latency-rate (LR) servers, this also leads to an easy determination of the upper bound on the latency of a flow from the more tractable relative fairness bound of the scheduler. Our results also indicate that in many real contexts, the two measures of fairness approach each other as the number of flows increases, confirming the RFB as an adequate measure of fairness.