Tight end-to-end per-flow delay bounds in FIFO multiplexing sink-tree networks

Aggregate scheduling has been proposed as a solution for achieving scalability in large-size networks. However, in order to enable the provisioning of real-time services, such as video delivery or voice conversations, in aggregate scheduling networks, end-to-end delay bounds for single flows are required. In this paper, we derive per-flow end-to-end delay bounds in aggregate scheduling networks in which per-egress (or sink-tree) aggregation is in place, and flows traffic is aggregated according to a FIFO policy. The derivation process is based on Network Calculus, which is suitably extended to this purpose. We show that the bound is tight by deriving the scenario in which it is attained. A tight delay bound can be employed for a variety of purposes: for example, devising optimal aggregation criteria and rate provisioning policies based on pre-specified flow delay bounds.     

Numerical analysis of worst-case end-to-end delay bounds in FIFO tandem networks

This paper addresses the problem of computing end-to-end delay bounds for a traffic flow traversing a tandem of FIFO multiplexing network nodes using Network Calculus. Numerical solution methods are required, as closed-form delay bound expressions are unknown except for few specific cases. For the methodology called the Least Upper Delay Bound, the most accurate among those based on Network Calculus, exact and approximate solution algorithms are presented, and their accuracy and computation cost are discussed. The algorithms are inherently exponential, yet affordable for tandems of up to few tens of nodes, and amenable to online execution in cases of practical significance. This complexity is, however, required to compute accurate bounds. As the LUDB may actually be larger than the worst-case delay, we assess how close the former is to the latter by computing lower bounds on the worst-case delay and measuring the gap between the lower and upper bound.     

Average end-to-end delay computation in IEEE 802.11 ad hoc networks

In this study, we present a new analytic model for evaluating average end-to-end delay in IEEE 802.11 multihop wireless networks. Our model gives closed expressions for the end-to-end delay in function of arrivals and service time patterns. Each node is modelled as a G/G/1/K queue from which we can derive expressions for service time via queueing theory. By combining this delay evaluation with different admission controls, we design a protocol called DEAN (Delay Estimation in Ad hoc Networks). DEAN is able to provide delay guarantees for quality of service applications in function of the application level requirements. Through extensive simulations, we compare the performance evaluation of DEAN with other approaches.     

Adaptive end-to-end QoS for multimedia over heterogeneous wireless networks

There has been a surge of interest for multimedia applications over wireless networks in recent years. A colossal number of ways have been proposed to decrease delay, delay jitter and loss in wireless networks and good user-perceived quality in video over internet. This paper studies the multimedia over heterogeneous wireless networks, requirements and problems, and proposes a new scheme to overcome the obstacles. The proposed scheme, takes into account the effects of Application-Level Wireless Multilevel ECN marking (AWMECN), thus helps us overcome the congestion/loss mistake problems. For handoff, handover and lossy link problems, it is considered that a freezing mechanism is in use in application layer and assumed that the upper layers can be aware of disconnection periods to make the rate adaptation decisions. Also a new scheme has been added to receiver to gracefully degrade the quality when no other action is available to combat the long delays without data which is caused by handoffs and wireless temporary disconnections. The transport layer mechanism is chosen to be UDP for avoiding TCP regarding problems. We believe that obtaining a good quality of video depends on good performance of all layers and tried to use the best mechanism in each layer.     

Multi-level cross-layer protocol for end-to-end delay provisioning in wireless multimedia sensor networks

Frontiers of Information Technology & Electronic Engineering - Rapid developments in information and communication technology in recent years have posed a significant challenge in wireless...     

Non-asymptotic end-to-end performance bounds for networks with long range dependent fBm cross traffic

Fractional Brownian motion (fBm) emerged as a useful model for self-similar and long-range dependent aggregate Internet traffic. Asymptotic, respectively, approximate performance measures are known for single queueing systems with fBm through traffic. In this paper end-to-end performance bounds for a through flow in a network of tandem queues under open-loop fBm cross traffic are derived. To this end, a rigorous sample path envelope for fBm is proven that complements previous approximate results. The sample path envelope and the concept of leftover service curves are employed to model the remaining service after scheduling fBm cross traffic at a queuing system. Using composition results for tandem systems from the stochastic network calculus end-to-end statistical performance bounds for individual flows in networks under fBm cross traffic are derived. The discovery is that these bounds grow in O(n(logn)^1/(2-2H)) for n systems in series where H is the Hurst parameter of the cross traffic. Explicit results on the impact of the variability and the burstiness of through and cross traffic on network performance are shown. Our analysis has direct implications on fundamental questions in network planning and service management.     

Towards an end-to-end delay analysis of LEO satellite networks for seamless ubiquitous access

LEO satellite networks, with moderate propagation delay and low terminal power requirement, are considered as a promising solution to providing global seamless access services for ubiquitous computing. In order to satisfy the requirement of accessing computing resource for users, end-to-end delays should be bounded for a continual and reliable connectivity. But given dynamic topology and non-uniform distribution of terrestrial users, end-to-end delays within LEO satellite networks are liable to fluctuate. Hence, to examine the delay constraint, an analytical model based on a tandem queue is established under a hot-spot traffic pattern, which is unfavorable for bounded delays. The departure interval moments of a target flow are calculated and fitted for the next link as input parameters, from which queuing delays under cross flows are iteratively obtained. The analytical results show that this model is able to depict the influence by the traffic pattern with satisfying accuracy, which is valuable for the design of routing schemes in satellite networks.     

Rate control of multi class priority flows with end-to-end delay and rate constraints for QoS networks

To address end-to-end quality of service (QoS) requirements, we derive a novel distributed combined rate and end-to-end delay control in a network serving multi-class flows with priority packet scheduling. We show that the control is globally asymptotically stable without information time lags. The stable flows attain the end-to-end delay requirements and have no packet loss. We also show that by enhancing the network with bandwidth reservation and admission control, minimum rate is also guaranteed. The stability with very long time lags of a discrete time version control with non-greedy flows and random packet arrivals is studied numerically by an NS2 packet-based simulation of the Australian Academic and Research Network.     

Determining update latency bounds in Galactica Net

The paper looks at the problem of ensuring the performance of real-time applications hosted on Galactica Net, a mesh-based distributed cache coherent shared memory multiprocessing system. A method for determining strict upper bounds on worst case latencies in wormhole routed networks of known or unknown communication patterns is presented. From this, a tool for determining upper bounds for shared memory update latencies is developed, and it is shown that the update latency of Galactica Net is deterministic. The analytical bounds are then compared with maximum latencies observed in simulations of GNet, with which they compare favorably. Finally, it is shown that the tool for determining update latency bounds is useful for comparing differing GNet system configurations in order to minimize update latency bounds.     

主动端到端离散式时延分布估计方法研究

对于网络质量评估链路性能推测无疑是至关重要的,然而现有的估计方法通常只能推测层次数有限的简单网络,无法应用于大规模网络。提出了一种基于不完整数据极大似然估计算法,估计网络内部链路时延分布,该方法通过不同的发包策略将树状网络拓扑划分成不同的两层三链子树,针对每个子树估计每条＂链＂的时延,随后通过移植算法将路径时延划分到各链路中,逐一对每个子树使用该方法计算从而得到整个网络链路时延情况。利用NS2仿真实验验证了该算法的可行性和准确性。     

一种基于支持向量回归的互联网端到端延迟预测算法

互联网端到端延迟是指IP分组沿着互联网中一条确定路径进行传输的延迟,端到端延迟的精确预测是大量网络活动的基础,从网络协议设计到网络监测,再从确保端到端QoS性能到各种实时业务性能提升。提出一种新的端到端延迟的预测方法,主要贡献有:a)将互联网端到端延迟预测的问题转换为多元回归的预测问题,提出了基于多元回归的端到端延迟预测框架;b)采用支持向量回归SVR方法来求解端到端延迟的多元回归问题,提出了基于SVR的互联网端到端延迟预测算法。最后使用互联网采集的RTT数据来验证提出的算法,实验结果表明,提出的预测算法具有快速和精确特点,是一种适合实际应用的预测算法。     

一种网络延迟精确控制的调度算法

在网络数据传输调度中，基于最早时限优先（EDF）的算法具有单点最优的延迟界限控制能力。现有的各种EDF改进算法，主要着眼于提供延迟上界的保证能力，而当采用机顶盒之类的缓冲能力较弱的设备作为客户终端时，还需要网络提供精确的延迟下界控制能力。在原有EDF改进算法的基础上提出了精确延迟界控制的最早时限优先算法。该算法不但能同时保证延迟上界和下界，还使得节点可以独立地决定为数据流分配的缓冲区大小，并增加了节点允许抖动量的取值范围，从而提高了节点数据的转发效率。     

WSN中单数据流端到端延迟上界研究

在WSN中采用独立分析（SFA）法求得的单数据流端到端延迟上界有时比整体分析（TFA）法求得的总数据流端到端延迟上界要大, 这不符合物理意义。针对这一问题, 分析了现有TFA法与SFA法在数据流服务分配机制上的差别, 并指出这两种方法求得的延迟上界不具有可比性。随后在修正流经节点数据流输出上界的基础上, 推导出与TFA法数据流服务分配机制相匹配的单数据流端到端延迟上界表达式。公式推导与数值分析结果均表明, 本方法求得的单数据流端到端延迟上界能够被TFA法总数据流端到端延迟上界所包络, 符合物理意义且更精确。     

Stochastic backlog and delay bounds of generic rate-based AIMD congestion control scheme in cognitive radio sensor networks

Performance guarantees for congestion control schemes in cognitive radio sensor networks (CRSNs) can be helpful in order to satisfy the quality of service (QoS) in different applications. Because of the high dynamicity of available bandwidth and network resources in CRSNs, it is more effective to use the stochastic guarantees. In this paper, the stochastic backlog and delay bounds of generic rate-based additive increase and multiplicative decrease (AIMD) congestion control scheme are modeled based on stochastic network calculus (SNC). Particularly, the probabilistic bounds are modeled through moment generating function (MGF)-based SNC with regard to the sending rate distribution of CR source sensors. The proposed stochastic bounds are verified through NS2-based simulations.     

Deterministic end-to-end delay guarantees with rate controlled EDF scheduling

Quality of Service (QoS) in terms of end-to-end delay guarantees to real-time applications is an important issue in emerging broadband packet networks. Earliest Deadline First (EDF) scheduling, in conjunction with per-hop traffic shaping (jointly called Rate Controlled EDF or RC-EDF) has been recognised as an effective means of end-to-end deterministic delay provisioning. This paper addresses the issue of identifying RC-EDF shaping parameters that realize maximal network utilizations. We first prove that finding “optimal” shapers is in general infeasible, and then propose a heuristic choice derived from the flow’s hop-length. Our choice varies gracefully between known optimal settings for the limiting values of the hop-length, and outperforms shaper selections proposed previously in the literature.     

Worst-case end-to-end delays evaluation for SpaceWire networks

SpaceWire is a standard for on-board satellite networks chosen by the ESA as the basis for multiplexing payload and control traffic on future data-handling architectures. However, network designers need tools to ensure that the network is able to deliver critical messages on time. Current research fails to address this needs for SpaceWire networks. On one hand, many papers only seek to determine probabilistic results for end-to-end delays on Wormhole networks like SpaceWire. This does not provide sufficient guarantee for critical traffic. On the other hand, a few papers give methods to determine maximum latencies on wormhole networks that, unlike SpaceWire, have dedicated real-time mechanisms built-in. Thus, in this paper, we propose an appropriate method to compute an upper-bound on the worst-case end-to-end delay of a packet in a SpaceWire network.     

Optimizing end-to-end performance of data-intensive computing pipelines in heterogeneous network environments

Supporting high-performance data-intensive computing pipelines in wide-area networks is crucial for enabling large-scale distributed scientific applications that require minimizing end-to-end delay for single-input applications or maximizing frame rate for streaming applications. We formulate and categorize the data-intensive computing pipeline mapping problems into six classes with two optimization objectives, i.e. minimum end-to-end delay and maximum frame rate, and three network constraints, i.e. no, contiguous, and arbitrary node reuse. We design a dynamic programming-based optimal solution to the problem of minimum end-to-end delay with arbitrary node reuse and prove the NP-completeness of the rest five problems, for each of which, a heuristic algorithm based on a similar optimization procedure is proposed. These heuristics are implemented and tested on a large set of simulated pipelines and networks of various scales and their performance superiority is illustrated by extensive simulation results in comparison with existing methods.     

Dynamic end-to-end capacity in IEEE 802.16 wireless mesh networks

The IEEE 802.16 standard defines mesh mode as one of its two operational modes in medium access control (MAC). In the mesh mode, peer-to-peer communication between subscriber stations (SSs) is allowed, and transmissions can be routed via other SSs across multiple hops. In such an IEEE 802.16 mesh network, accurate and reliable determination of dynamic link capacity and end-to-end capacity of a given multi-hop route is crucial for robust network control and management. The dynamic capacities are difficult to determine in a distributed system due to decentralized packet scheduling and interference between communicating nodes caused by the broadcast nature of radio propagation. In this paper, we first propose a method for computing the dynamic link capacity between two mesh nodes, and extend that to determine the dynamic end-to-end capacity bounds of a multi-hop route based on the concept of Bottleneck Zone. The physical deployments of networks are also considered in the capacity estimation. We demonstrate the effectiveness and accuracy of our methods for computing dynamic link capacity and end-to-end capacity bounds through extensive simulations.     

Availability of end-to-end ideal QoS in IP packet networks

Network processor technology has advanced to the point where high-precision time-based store-and-forward logic is readily incorporated into packet switches and routers. With appropriate scheduling, packets from multiple flows can be serviced without contending for link resources. Accordingly, packet flows traversing a network of switching elements can have both path and time determinacy attributes which support ideal end-to-end QoS (zero jitter, zero loss, acceptable end-to-end latency) for real-time UDP packet flows and guaranteed goodput for TCP flows. One approach to packing a network with a relatively large number of such deterministic flows, i.e. achieving high availability of the ideal QoS service in a network, uses precise buffering of packets at each switch, which introduces latency. This paper describes analysis methods for quantifying how much buffering may be necessary to achieve high (99.999%) availability. For typical network topologies the analysis shows that buffering latency requirements are very small compared to transport delays, even when the network is highly utilized with heterogeneous (e.g. voice, video, circuit emulation, and data) traffic. Actual physical implementations have empirically validated the analysis results as well as the scalability of the end-to-end, time-based forwarding approach and the end-to-end availability of ideal QoS services in IP packet networks.     

Optimal capacity allocation for Web systems with end-to-end delay guarantees

Providing quality of service guarantees have become a critical issue during the rapid expansion of the e-Commerce area. We consider the problem of finding the optimal capacity allocation in a clustered Web system environment so as to minimize the cost while providing the end-to-end performance guarantees. In particular, we consider constraints on both the average and the tail distribution of the end-to-end response times. We formulate the problem as a nonlinear program to minimize a convex separable function of the capacity assignment vector. We show that under the mean response time guarantees alone, the solution has a nice geometric interpretation. Various methods to solve the problem are presented in detail. For the problem with tail distribution guarantees, we develop an approximation method to solve the problem. We also derive bounds and show that the solution is asymptotically optimal when the service requirement becomes stringent. Numerical results are presented to further demonstrate the robustness of our solutions under data uncertainty.