分组交换网络调度算法——SFQ+的研究

分组调度是实现计算机网络QoS保证的核心问题。该文描述了SFQ+分组调度算法，在SFQ算法的基础上引入了DWCS的动态窗函数约束机制，并与传统的SFQ和DWCS算法作了比较，给出了算法的性能评价，对算法的扩展进行了展望。     

On processor sharing and its applications to cellular data network provisioning

To develop simple traffic engineering rules for the downlink of a cellular system using Proportional Fairness (PF) scheduling, we study the “strict” and “approximate” insensitivity of a Processor Sharing (PS) system, specifically for the Egalitarian (EPS) and Discriminatory (DPS) variants of PS. Assuming homogeneous channel conditions, all concurrent flows are allocated an equal share of downlink transmission slots regardless of flow types and locations. The cell system is modeled as an EPS queue. We prove the performance insensitivity of EPS in a relevant new case that has not been studied in the literature. Considering heterogenous channel conditions, the system is modeled as the DPS queue in which each traffic type is divided into subclasses with different assigned weights. Asymmetric weights among the subclasses model the unequal channel sharing that occurs with PF scheduling. Our results show that the first-order performance of the DPS is largely insensitive to the input traffic characteristics, as long as the weights among subclasses are not highly skewed. Our findings, confirmed by the simulation of a cellular system, imply reduced complexity for traffic provisioning procedures. However, our study also shows that the first-order performance is sensitive to the traffic details when there is discrimination among different traffic types. This observation implies that the introduction of differentiated services may pose a great challenge to network provisioning in future cellular systems.     

MANET中基于速率的流量控制算法研究

由于MANET中网络的动态变化特征,TCP隐含式AIMD流量控制不适应于该领域。本文介绍了基于速率的显式流量控制策略（EXACT）,并分析了它对网络中再路由和带宽变化的反应。在高速动态变化的MANET环境下,通过ns-2系统模拟,本文评价了EXACT在网络传输公平和效率等方面的性能。     

一种基于标准化QoS公平的反馈控制实时调度算法

任务间的QoS公平性是多QoS级别的可调节动态实时调度系统中的一个重要问题.本文引入了标准化QoS公平的概念,在公平性中加入了任务的重要性因素,并构造了具有PID反馈控制环节的实时调度算法NF-QoS来达到标准化QoS公平.利用NF-QoS对系统截止期错失率进行实时采样,定期反馈给PID控制器,根据PID控制器计算的结果对各任务QoS级别进行调整,以保证各任务公平地得到处理器资源.实验结果表明,NF-QoS不仅合理地协调了系统利用率和截止期错失率,并且有效地提高了系统的QoS公平性.     

按需轮循的蓝牙微微网调度算法与性能评估

提出了一种低时延、高信道利用率与公平性好的按需轮循的蓝牙微微网调度算法.首先通过速率估计过程计算出上行链路分组到达率的估计值,然后在主调度过程中分别计算各链路对自上次轮循时刻到当前时刻的分组到达数量的估计值与等待时间,根据提出的动态轮循选择规则选出优先度最高的链路对进行轮循,再根据自适应轮循间隙规则计算出下次轮循应该进行的时间.分别在混合、下行与上行三种传输模型的仿真中进行了与其他经典算法的性能比较.结果表明:算法在前两种传输模型中具有最佳的整体性能,尤其是时延分别降低了24.1%与41.4%以上,在第三种传输模型中也具有较佳的整体性能.该算法效率高、实现复杂度低,可应用于蓝牙与其他无线网络.     

移动环境公平支付协议的设计与分析研究

结合固定网络中的支付协议并充分考虑移动装置和无线网络的特点,提出了一种移动环境公平支付协议。利用模型检验工具对协议进行分析并将该协议与其他支付协议进行比较,分析和比较结果表明,该协议具有公平、保密、高效等特点,适用于移动环境。     

多媒体无线网中QoS降级的公平性研究

对无线，移动多媒体网中多服务类、多优先级的适应多媒体应用QoS降级的公平性问题进行了研究。提出降级因子加权平方和最小的降级原则，不但考虑了类间和类内优先级，而且考虑了用户的QoS降级深度。接着，证明对离散型适应多媒体应用，降级因子加权平方和最小的降级原则满足广义的按比例公平性，而对连续型适应多媒体应用，满足按比例公平性。最后，用量子遗传算法对所给问题进行了求解，结果进一步验证了所提算法的有效性。     

基于最优化的多媒体多播速率控制

传输多媒体流的一种有效方法是采用多速率多播,但多速率多播的速率控制面临许多挑战,如异构性、公平性、实时性及服务质量(QoS)等。提出了一种两阶段优化的策略进行多媒体多播速率控制。把问题公式化为求系统效用最大化的最优化问题,推导出有效的算法。方法综合考虑了服务质量、异构性等,且满足协议间的公平性和多播会晤内各接收者间的公平性。仿真实验表明算法的有效性,与现有的算法相比系统总效用大大提高。     

Temporal fairness guarantee in multi-rate wireless LANs for per-flow protection

Wireless LAN technologies such as IEEE 802.11a and 802.11b support high bandwidth and multi-rate data transmission to match the channel condition (i.e., signal to noise ratio). While some wireless packet fair queuing algorithms to achieve the per-flow throughput fairness have been proposed, they are not appropriate for guaranteeing QoS in multi-rate wireless LAN environments. We propose a wireless packet scheduling algorithm that uses the multi-state (multi-rate) wireless channel model and performs packet scheduling by taking into account the channel usage time of each flow. The proposed algorithm aims at per-flow protection by providing equal channel usage time for each flow. To achieve the per-flow protection, we propose a temporally fair scheduling algorithm called Contention-Aware Temporally fair Scheduling (CATS) which provides equal channel usage time for each flow. Channel usage time is defined as the sum of the packet transmission time and the contention overhead time due to the CSMA/CA mechanism. The CATS algorithm provides per-flow protection in wireless LAN environments where the channel qualities of mobile stations are dynamic over time, and where the packet sizes are application-dependent. We also extend CATS to Decentralized-CATS (D-CATS) to provide per-flow protection in the uplink transmission. Using an NS-2 simulation, we evaluate the fairness property of both CATS and D-CATS in various scenarios. Simulation results show that the throughput of mobile stations with stable link conditions is not degraded by the mobility (or link instability) of other stations or by packet size variations. D-CATS also shows less delay and less delay jitter than FIFO. In addition, since D-CATS can coordinate the number of contending mobile stations, the overall throughput is not degraded as the number of mobile stations increases. This work was supported in part by the Brain Korea 21 project of Ministry of Education and in part by the National Research Laboratory project of Ministry of Science and Technology, 2004, Korea.     

一种自适应的多跳蜂窝网络模型

提出了一种自适应的多跳蜂窝网络模型，通过动态的网络模式切换机制，终端可以根据网络状态在蜂窝和多跳两种网络模式间切换。该模型结合了蜂窝和多跳网络的优点，可以有效地提升无线数据网络的传输性能。仿真结果表明，该模型在增加了网络吞吐量、减少功耗的同时还具有较好的公平性。