基于区分服务的IP QoS控制技术

为了提供服务质量保证和支持实时应用,传统IP网络的服务模型已经被扩展,区分服务模型是其中重要的一种。这里首先概述了基于区分服务的IPQoS的控制技术,介绍了一种使用QoS管理器和反馈功能控制QoS的体系结构。该结构的标记器和整形器/策略器的参数受来自计量器的反馈的影响,并且QoS管理器能够使管理员动态地调整控制参数。     

基于块对角算法的MIMO系统资源调度策略

提出一种基于块对角算法的多输入多输出系统空时二维资源调度策略．通过空域注水算法对功率进行分配，并通过时域各用户功率和比特的动态调整，把资源分配从空间维扩展到空时二维，在一定的时间周期内。各用户的数据速率满足服务质量需要。同时不再受块对角算法用户数必须小于基站天线数的限制，仿真表明．改进的块对角算法能够大大提高多用户多输入多输出系统的功率效率，并且保证用户问的公平性。     

Scheduling Real-Time Traffic With Deadlines over a Wireless Channel

Recently, there has been widespread interest in the extension of data networks to the wireless domain. However, scheduling results from the wireline domain do not carry over to wireless systems because wireless channels have unique characteristics not found in wireline channels, namely, limited bandwidth, bursty channel errors and location-dependent channel errors.In this paper, we study the problem of scheduling multiple real-time streams with deadlines, over a shared channel. We show that, in general, unlike the wireline case, the earliest due date (EDD) or shortest time to extinction (STE) policy is not always the optimal policy, even if the channel state is perfectly known and EDD is implemented only over channels in a Good state. Here, optimality is measured with respect to the number of packets lost due to deadline expiry. However, for most values of the channel parameters that are of practical interest, we show through analytical and numerical results that the EDD policy over Good channels is nearly optimal. Finally, through simulations, we also show that by combining this policy with fair scheduling mechanisms would result in scheduling algorithms that provide some degree of isolation between the sources as well as provide a natural way of compensating channels that see prolonged error bursts.     

安全保障：无线Mesh网络中支持QoS的DSR路由协议的改进与实现

随着无线Mesh网络传输多媒体业务需求的增加,要求网络支持服务质量（QoS）,本文基于DSR协议设计了一个支持QoS的路由协议算法QDSR（QoS-DSR）。该算法保证了数据流的带宽、时延的QoS需求,根据路径跳数和节点拥塞情况定义路由代价函数,选择最优路径。仿真结果表明,与DSR相比,QDSR提高了网络吞吐量,降低了平均端到端延时,提高了网络利用率,更好地满足业务的QoS需求,并且具有更强的适用性和可扩展性。     

A Medium Access Control Protocol for Real Time Video over High Latency Satellite Channels

We report the results of extensive simulation work on a new satellite medium access control (MAC) protocol for medium quality interactive video. This MAC protocol uses combined random access/demand assigned multiple access (RA/DAMA). The underlying multiple access physical layer is time division multiple access (TDMA). The RA/DAMA MAC seeks to adaptively minimize the delay of each network layer (nl) packet that arrives to the output queue by transmitting packets on either a collision free demand assigned channel or on a collision possible random access channel. Combined with this dual channel transmission method is a new technique for acquiring demand assigned bandwidth, called a packet flow rate metric (PFRM). This metric seeks to track the slow time behavior of video traffic, leading to a significant reduction in the amount of DAMA signaling. All simulations were conducted using SMACS, the Satellite Medium Access Control Simulator [4], a simulation tool built into ns-2.0 (network simulator version 2) [10]. This simulation tool allowed us to evaluate our MAC protocol using an actual 2 hour long video trace rather than a parametric video traffic generator. Our results show that if light packet loss is tolerable (less than 3%), then significantly lower delays and higher link utilization can be achieved.     

Extended Performance Evaluation of PRADOS: A Scheduling Algorithm for Traffic Integration in a Wireless ATM Network

The MAC protocol, known as MASCARA (Mobile Access Scheme based on Contention And Reservation for ATM), is an infrastructure-based, adaptive TDMA scheme, which combines reservation- and contention-based access methods to provide multiple access efficiency and Quality-of-Service (QoS) guarantees to wireless ATM terminal connections that share a common radio channel. Radio channel sharing is performed by the PRADOS (Prioritized Regulated Allocation Delay Oriented Scheduling) algorithm. In this paper we assess the capability of PRADOS to guarantee to voice and data traffic types the QoS they need. The analysis leads to the conclusion that PRADOS cannot avoid the interference between the various types of traffic. A criterion to alleviate this drawback is also outlined at the end of the paper.     

面向数控系统的三级调度模型研究

针对硬实时系统中多种类型任务并存的特点,提出一种三级实时调度模型--TLRtS(three-level real-time scheduling).该模型将整个系统空间划分为硬实时、软实时和非实时空间,分别用来处理硬实时、软实时和非实时任务.TLRtS模型不仅可以动态加载多种实时调度算法,还可以集成相应的资源访问控制协议,解决了任务之间存在资源竞争的问题.实验结果表明,此方法既保证了所有硬实时任务严格按照其时间约束在截止期前完成,又尽可能地提高了软实时和非实时任务的服务质量.     

“Pay bursts only once” does not hold for non-FIFO guaranteed rate nodes

We consider end-to-end delay bounds in a network of guaranteed rate (GR) nodes. We demonstrate that, contrary to what is generally believed, the existing end-to-end delay bounds apply only to GR nodes that are FIFO per flow. We show this by exhibiting a counter example. Then, we show that the proof of the existing bounds has a subtle, but important, dependency on the FIFO assumption, which was never noticed before. Finally, we give a tight delay bound that is valid in the non-FIFO case; it is noticeably higher that the existing one. In particular, the phenomenon known as “pay bursts only once” does not apply to non-FIFO nodes. These findings are important in the context of differentiated services. Indeed the existing bounds have been applied to cases where a flow (in the sense of the GR definition) is an aggregate of end-user microflows, and it is not generally true that a router is FIFO per aggregate; thus, the GR node model of a differentiated services router cannot always be assumed to be FIFO per flow.     

协作中继网络中节点传输时间和位置优化算法

在协作中继网络中提出一种基于(Quality-of-Service,QoS)驱动的协作节点传输时间和协作节点位置优化算法。基于当前用户的QoS时延需求,从理论上可推导出解码转发中继模式下系统容量表达式。以最大化系统容量为目标,可获得最优的协作节点传输时间和最优的协作节点位置。仿真结果表明,该优化算法能够自适应地确定最优节点的位置和传输时间,从而获得最大化系统容量,进一步有效提升整个系统的性能。     

Queueing Delay Analysis for the Joint Scheduling Exploiting Multiuser Diversity over a Fading Channel

In this paper, we consider a joint packet scheduling algorithm for wireless networks and investigate its characteristics. The joint scheduling algorithm is a combination of the Knopp and Humblet (KH) scheduling, which fully exploits multiuser diversity, and the probabilistic weighted round-robin (WRR) scheduling, which does not use multiuser diversity at all. Under the assumption that the wireless channel process for each user is described by the Nakagami-m model, we develop a formula to estimate the tail distribution of the packet delay for an arbitrary user under the joint scheduling. Numerical results exhibit that under the joint scheduling, the ratio of the number of slots assigned for the WRR scheduling to that for the KH scheduling dominates the characteristics of the delay performance.