无线ATM通信网多址访问协议与信道动态分配算法研究

本文为无线ATM通信网提出了可支持话音、数据和图像业务的多址访问控制协议(MAC)和信道动态分配(DCA)算法.所提出的正交码预约多址访问协议(ORMA)可避免各终端在预约竞争时发生碰撞,提高信道利用率.同时,还提出了一种突发业务信道动态分配算法(DCA-BT),ORMA与DCA-BT相结合能有效地提高系统内多媒体业务的质量和信道利用率,增大系统容量,支持多种业务在无线ATM通信网中的应用.     

无线ATM通信网多址访问协议与信道动态分配算法研究

本文为无线ATM通信网提出了可支持话音、数据和图像业务的多址访问控制协议(MAC)和信道动态分配(DCA)算法.所提出的正交码预约多址访问协议(ORMA)可避免各终端在预约竞争时发生碰撞,提高信道利用率.同时,还提出了一种突发业务信道动态分配算法(DCA-BT),ORMA与DCA-BT相结合能有效地提高系统内多媒体业务的质量和信道利用率,增大系统容量,支持多种业务在无线ATM通信网中的应用.     

Ad Hoc网络中具有QoS保障的同步MAC协议

介绍了Ad Hoc网络中保障实时业务QoS要求的时间同步多址接入协议。该类协议以时分多址为基础,通过资源预留为实时业务预约固定的时隙,赋予实时业务接入信道的优先权,保证了实时业务的接入延时,延时抖动以及吞吐量等QoS指标,为Ad Hoc网络支持多媒体业务的接入奠定了基础。     

基于AOS协议信道复用机制的研究

虚拟信道复用机制影响了AOS协议实现效率,提出了一种新的动态自适应虚拟信道复用方法。该方法将包信道复用与虚拟信道复用综合考虑,对不同传输质量要求的虚拟信道采用不同的调度策略。在OPNET仿真平台上对整个协议和该算法进行了建模,在吞吐量、buffer使用深度、传输帧延时三个方面对仿真结果做了分析,并与时间片周期轮询和固定优先级调度算法做了比较,结果证明动态自适应调度算法能在保证平台网数据延时的前提下,最大化空间载荷数据的吞吐量,在延时方面能起到良好的均衡作用,满足不同类型数据的传输要求。     

OBS网络中QoS优先级保证方案研究

文章把信道分组和PPJET(Preemptive Prioritized Just Enough Time)协议以及光纤延时线三者结合使用,提出了一种新的QoS调度方案D-PPJET(Developed-PPJET)协议.在该协议下,高优先级数据包可以被动态地调度到任何可用的信道上去,而低优先级数据包只能在规定的部分信道上调度,并利用光纤延时线(FDL)缓存机制为未成功调度的突发包提供二次调度的机会,这样高优先级业务包调度成功的机会就大大增加,为高优先级业务提供了保证,同时还使得低优先级突发分组丢失率下降.结果表明它能够大大地改善整个网络突发包的丢失率、信道吞吐量及信道利用率.     

基于可靠UDP的卫星IP网关设计

TCP是面向连接的可靠点到点协议,但是由于卫星网络中典型的长延时、高误码率以及非对称带宽的特点,导致TCP通过宽带卫星网络时,信道利用率非常低。可靠UDP协议基于标准UDP协议并在应用中增加窗口、应答和重传算法来实现。网关采用该协议将TCP连接分段,在应用中明显地改善了TCP在宽带卫星信道上传输的性能,增加TCP的信道利用率。     

无线Mesh网络中支持QoS的802.11e协议优化

在无线Mesh网络中,支持QoS的IEEE 802.11eEDCA协议,其固定的队列接入机制,使得在网络负载较重的时高优先业务的QoS得不到应有的保障,同时在网络负载较轻时信道利用率也不高.文中提出了一种动态调整业务接入队列的算法.节点可以根据感知到的网络负载状况自适应调整队列接入方式,在保障高优先级业务QoS要求的同时,尽可能提高信道的利用率.仿真结果表明,在不同网络负载的场景下,该算法相对于IEEE802.11e在QoS保障和利用率方面都有较好的表现.     

支持实时音频业务的以太网MAC协议

提出了一个被称为CSMA/PRI的改进MAC协议用于通过以太网技术向用户提供具有服务品质保证的实时音频业务.依靠减少同时竞争信道资源的工作站数目,所提出的方案改善了网络的传输效率,并缩减了平均的信道分配延时.通过分等级地进行网络资源预约和对不同类型的流量使用不同的碰撞解决算法,对比于现有的CSMA/CD和CSMA/RI协议,建议的改进方案能够向实时音频业务提供更加好的服务.     

OBS网络分组调度LAUC-αSV算法

传统的数据信道分组调度算法如LAUC算法仅仅考虑怎样使信道的浪费最少,而没有考虑到对光纤延时线资源(FDLs)的合理利用.文章中的LAUC-αSV算法同时将信道利用率和光纤延时线利用率两点作为OBS网络性能的指标;两者的资源重要性不同,引入权值α进行衡量,并对算法进行了仿真.     

分布式测控系统中的多址协议研究

为保证各类业务的QoS要求及信道的利用率，本文提出在分布式测控系统中采用Polled-CSMA协议，该协议以Polling方式处理实时性要求高的流式业务，以CSMA方式处理实时性要求不高的突发性业务，分析结果表明，该协议可以满足分布式测控系统中数据传输的QoS要求。     

LHFS-支持公平服务的CICQ混合调度策略

 针对现有联合输入交叉点排队交换结构(CICQ,Combined Input and Cross-point Queuing)调度策略无法提供基于"流"的服务质量保障,探讨了在CICQ交换结构实施基于流调度的可能性,提出一种能够为到达流提供公平服务的分层混合公平服务调度策略—LHFS(Layered and Hybrid Fair Scheduling).LHFS对每个输入、输出端口可独立地进行变长分组交换,其算法复杂度为O(1),具有良好可扩展特性.理论分析结果表明,LHFS能够为业务流提供时延上限和公平性保障.最后,基于SPES(Switching Performance Evaluation System)仿真系统对LHFS的性能进行了评估.     

面向航天器有线无线混合场景的流调度机制研究

随着各国深空探测任务的开展,空间站的建设需求日益增加,而航天器内部大量的数据通信总线在一定程度上影响了航天器的有效载荷。因此,该文将无线通信方式引入到航天器通信系统设计中,但传统无线通信难以保障时敏数据的端到端传输时延,该文提出了一种有线无线融合的时间敏感网络(TSN)流调度方案。设计了一种上下行时隙分离的TDMA时隙分配机制,通过对航天器内部业务类型与有线无线融合传输链路的时延关系进行建模分析,构建了以时敏业务平均端到端时延最小的目标函数,采用粒子群算法对时隙分配方案进行快速求解。最后在Pycharm平台对所提算法进行对比测试,并在EXata网络仿真平台搭建航天传感器采集网络进行验证。实验结果表明,该文所提出的有线无线融合流调度方案能为时敏业务提供稳定、有界的时延保障。     

一种改进的多播路由算法

低代价最短路径树是一种广泛使用的多播树,它能够在保证传送时延最小的同时尽量降低带宽消耗。DDSP(Destination-Driven Shortest Path)算法是一个性能较好,计算效率较高的低代价最短路径树算法,在该算法基础上,通过改进结点的搜索过程,提出一种改进的快速低代价最短路径树算法。由算法分析和实验比较得出,改进算法的计算效率高于DDSP算法,且算法构造的最短路径树的性能也优于DDSP算法构造的树．     

准静止状态下的高空平台实时业务信道分配

受平台准静止状态的影响,高空平台（ HAPS)通信网络内存在大量的切换呼叫,且业务量动态变化。 HAPS网络可传输多种业务,其中实时业务在切换过程中具有较高的时延要求。通过为切换呼叫预留信道可降低平台不稳定对服务质量（ QoS)造成的影响。在基于服务优先级的多业务信道分配算法基础上,重点对实时业务的信道分配算法进行改进,提出了一种基于概率的预留信道借用策略。该算法可根据网络内业务量的实时统计数据控制新呼叫业务的准入。仿真结果表明：与固定预留信道算法和门限预留信道算法相比,该算法能够适应网络内业务量的动态变化,在保证切换呼叫掉线率满足期望值的条件下提升系统的整体性能,降低平台不稳定造成的性能损失。     

Minimizing Cost and Delay in Shared Multicast Trees

Existing tree construction mechanisms are classified into source‐based trees and center‐based trees. The source‐based trees produce a source‐rooted tree with a low delay. However, for the applications with multiple senders, the management overheads for routing tables and resource reservations are too high. The center‐based trees are easy to implement and manage, but a priori configuration of candidate center nodes is required, and the optimization nature such as tree cost and delay is not considered. In this paper, we propose a new multicast tree building algorithm. The proposed algorithm basically builds a non‐center based shared tree. In particular, any center node is not pre‐configured. In the proposed algorithm, a multicast node among current tree nodes is suitably assigned to each incoming user. Such a node is selected in a fashion that tree cost and the maximum end‐to‐end delay on the tree are jointly minimized. The existing and proposed algorithms are compared by experiments. In the simulation results, it is shown that the proposed algorithm approximately provides the cost saving of 30 % and the delay saving of 10 %, compared to the existing approaches. In conclusion, we see that the cost and delay aspects for multicast trees can be improved at the cost of additional computations.     

The New Routing Algorithm for the ARPANET

The new ARPANET routing algorithm is an improvement over the old procedure in that it uses fewer network resources, operates on more realistic estimates of network conditions, reacts faster to important network changes, and does not suffer from long-term loops or oscillations. In the new procedure, each node in the network maintains a database describing the complete network topology and the delays on all lines, and uses the database describing the network to generate a tree representing the minimum delay paths from a given root node to every other network node. Because the traffic in the network can be quite variable, each node periodically measures the delays along its outgoing lines and forwards this information to all other nodes. The delay information propagates quickly through the network so that all nodes can update their databases and continue to route traffic in a consistent and efficient manner. An extensive series of tests were conducted on the ARPANET, showing that line overhead and CPU overhead are both less than two percent, most nodes learn of an update within 100 ms, and the algorithm detects congestion and routes packets around congested areas.     

Minimizing Internal Speedup for Performance Guaranteed Switches With Optical Fabrics

We consider traffic scheduling in an N times N packet switch with an optical switch fabric, where the fabric requires a reconfiguration overhead to change its switch configurations. To provide 100% throughput with bounded packet delay, a speedup in the switch fabric is necessary to compensate for both the reconfiguration overhead and the inefficiency of the scheduling algorithm. In order to reduce the implementation cost of the switch, we aim at minimizing the required speedup for a given packet delay bound. Conventional Birkhoff-von Neumann traffic matrix decomposition requires N2 - 2N + 2 configurations in the schedule, which lead to a very large packet delay bound. The existing DOUBLE algorithm requires a fixed number of only 2N configurations, but it cannot adjust its schedule according to different switch parameters. In this paper, we first design a generic approach to decompose a traffic matrix into an arbitrary number of Ns (N² - 2N + 2 > N_S > N) configurations. Then, by taking the reconfiguration overhead into account, we formulate a speedup function. Minimizing the speedup function results in an efficient scheduling algorithm ADAPT. We further observe that the algorithmic efficiency of ADAPT can be improved by better utilizing the switch bandwidth. This leads to a more efficient algorithm SRF (scheduling residue first). ADAPT and SRF can automatically adjust the number of configurations in a schedule according to different switch parameters. We show that both algorithms outperform the existing DOUBLE algorithm.     

Dynamic core provisioning for quantitative differentiated services

Efficient network provisioning mechanisms that support service differentiation are essential to the realization of the Differentiated Services (DiffServ) Internet. Building on our prior work on edge provisioning, we propose a set of efficient dynamic node and core provisioning algorithms for interior nodes and core networks, respectively. The node provisioning algorithm prevents transient violations of service level agreements (SLA) by predicting the onset of service level violations based on a multiclass virtual queue measurement technique, and by automatically adjusting the service weights of weighted fair queueing schedulers at core routers. Persistent service level violations are reported to the core provisioning algorithm, which dimensions traffic aggregates at the network ingress edge. The core provisioning algorithm is designed to address the difficult problem of provisioning DiffServ traffic aggregates (i.e., rate-control can only be exerted at the root of any traffic distribution tree) by taking into account fairness issues not only across different traffic aggregates but also within the same aggregate whose packets take different routes through a core IP network. We demonstrate through analysis and simulation that the proposed dynamic provisioning model is superior to static provisioning for DiffServ in providing quantitative delay bounds with differentiated loss across per-aggregate service classes under persistent congestion and device failure conditions when observed in core networks.     

Analysis of average burst-assembly delay and applications in proportional service differentiation

In Optical Burst-Switched (OBS) networks, the limitation of optical buffering devices make it impractical to deploy conventional delay-based differentiation algorithms such as Active Queue Management, Weighted Fair Queuing, etc. Furthermore, only the delay that appears due to the burst-assembly process constitutes a variable quantity (all the other sources of delay are mostly fixed), it is then reasonable to make use of the burst-assembly algorithm to provide class-based delay differentiation. The aim of the following study is twofold: first it defines an average assembly delay metric, which represents the assembly delay experienced by a random arrival at the burst assembler of an edge OBS node; and second, this metric is used to define and configure a two-class burst-assembly policy, which gives preference to high-priority traffic over low-priority packet arrivals. The results show that, (1) tuning the parameters of the two-class assembly algorithm, the two classes of traffic exhibit different burst-assembly delay; and, (2) such parameters can be adjusted to provide a given differentiation ratio in the light of the proportional QoS differentiation approach proposed in the literature. A detailed analysis of the two-class assembly algorithm is given, along with an exhaustive set of experiments and numerical examples that validate the equations derived.     

Multicast-based inference of network-internal delay distributions

Packet delay greatly influences the overall performance of network applications. It is therefore important to identify causes and locations of delay performance degradation within a network. Existing techniques, largely based on end-to-end delay measurements of unicast traffic, are well suited to monitor and characterize the behavior of particular end-to-end paths. Within these approaches, however, it is not clear how to apportion the variable component of end-to-end delay as queueing delay at each link along a path. Moreover, there are issues of scalability for large networks. In this paper, we show how end-to-end measurements of multicast traffic can be used to infer the packet delay distribution and utilization on each link of a logical multicast tree. The idea, recently introduced in Caceres et al. (1999), is to exploit the inherent correlation between multicast observations to infer performance of paths between branch points in a tree spanning a multicast source and its receivers. The method does not depend on cooperation from intervening network elements; because of the bandwidth efficiency of multicast traffic, it is suitable for large-scale measurements of both end-to-end and internal network dynamics. We establish desirable statistical properties of the estimator, namely consistency and asymptotic normality. We evaluate the estimator through simulation and observe that it is robust with respect to moderate violations of the underlying model.