无线网状网中基于TDMA模式的QoS路由策略

为支持无线网状网中具有服务质量（QoS）需求的实时应用,提出基于TDMA模式服务质量路由策略TD-MQR。对网络进行分层,提出新的链路指标值,在考虑链路容量和无线信道间干扰的基础上对网络的流量进行路由和调度。仿真表明,该协议能够对WMN中实时应用提供QoS保证。     

适用于实时应用的网络服务自适应系统

随着网络带宽可用性的提高以及网络延迟的减少,如何在端主机上保证网络传输的服务质量(End-hostQoS)已经逐渐成为一个关键的问题。尤其是针对分布式实时应用的环境:媒体流服务器,视频会议以及VoIP((Voiceover Internet Protocol)是一种以IP电话为主,并推出相应的增值业务的技术应用)。End-hostQoS的实现需要操作系统的支持,比如提供网络层的系统调度和流量控制。笔者在这篇文章中提出的QoS自适应系统可以在最优使用系统资源的基础上提供per-flow或者per-service-class的差别服务。并且通过将EDF调度算法同PID控制理论相结合,保证系统的实时响应、适应网络波动,在服务器瞬间过载的情况下,保证网络服务质量的平稳过渡。     

Admission control by implicit signaling in support of voice over IP over ADSL

Voice over DSL (VoDSL) is a technology that enables the transport of data and multiple voice calls over a single copper-pair. Voice over ATM (VoATM) and Voice over IP (VoIP) are the two main alternatives for carrying voice over DSL. ATM is currently the preferred technology, since it offers the advantage of ATM’s built-in Quality of Service (QoS) mechanisms. IP QoS mechanisms have been maturing only in recent years. However, if VoIP can achieve comparable performance to that of VoATM in the access networks, it would facilitate end-to-end IP telephony and could result in major cost savings. In this paper, we propose a VoIP-based VoDSL architecture that provides QoS guarantees comparable to those offered by ATM in the DSL access network. Our QoS architecture supports Premium and Regular service categories for voice traffic and the Best-Effort service category for data traffic. The Weighted Fair Queuing algorithm is used to schedule voice and data packets for transmission over the bottleneck link. Fragmentation of large data packets reduces the waiting time for voice packets in the link. We also propose a new admission control mechanism called Admission Control by Implicit Signaling. This mechanism takes advantage of application layer signaling by mapping it to the IP header. We evaluate the performance of our QoS architecture by means of a simulation study. Our results show that our VoIP architecture can provide QoS comparable to that provided by the VoATM architecture.     

无线多媒体网络中一种基于测量网络状态的动态呼叫接纳控制算法

提出了一种无线多媒体网络中基于测量网络状态的动态呼叫接纳控制算法.它区分了实时和非实时业务,在网络带宽资源不足时可通过降低非实时业务带宽确保实时业务呼叫连接的可靠性;还可根据当前网络状况调整预留带宽大小,使小区实时业务切换呼叫掉线率低于设定的门限值.大量仿真结果显示该算法具有低实时业务切换呼叫掉线率和与固定预留方案相当的带宽利用率,而只以略高的新呼叫阻塞率为代价,适合各种不同概率发生时实际应用的情况.     

Supporting configurability and real time in RTD channels

Network communication services that can be configured to customize functionality provide significant advantages over monolithic versions, but can be difficult to construct if the services must also provide real‐time guarantees on message delivery. This paper describes how practical issues related to the combination of configurability and real time have been addressed in real‐time dependable (RTD) channels, a communication abstraction that has been prototyped using the Cactus system. The architecture and implementation of RTD channels are described, including facilities for translating an application's quality of service requirements into configuration‐specific resource requirements, and an admission control architecture that uses system‐wide information to determine whether sufficient resources exist to create new channels. In addition, the results of experiments that demonstrate that the desired channel properties—including real‐time guarantees—are provided for various configurations are presented. Finally, practical problems and lessons learned from implementing RTD channels on the general‐purpose MK 7.3 Mach operating system are discussed. Copyright © 2001 John Wiley & Sons, Ltd.     

适合于移动多媒体网络的呼叫接纳控制算法

移动多媒体网络应该能够同时支持传统的数据业务和实时交互式多媒体业务,并能够为用户提供QoS保证.在无线移动网中提供QoS保证,呼叫接纳控制扮演着重要的角色.通过对呼叫接纳算法中资源预留方案进行了分析总结,提出了一种适合于移动多媒体网络的自适应呼叫接纳控制算法.     

Preemption-Aware Instantaneous Request Call Routing for Networks With Book-Ahead Reservation

This paper presents a new preemption-aware quality of service (QoS) routing algorithm for instantaneous request (IR) call connections in a QoS-enabled network where resources are shared between IR and book-ahead (BA) call connections. BA reservation, which confirms the availability of resources in advance, is a highly attractive technique for time sensitive applications that require high amount of bandwidth with guaranteed QoS. One of the major concerns for the implementation of BA reservation is the need for preemption of on-going IR calls to accommodate BA calls when resource scarcity arises. Preemption disrupts service continuity of on-going calls which is considered as severely detrimental from users' perceived QoS definition found in recent studies. Existing QoS routing algorithms focus on resource conservation or load balancing as the key objective to attain in addition to guaranteed QoS. No works have yet focused on the preemption problem of on-going IR calls at routing stage in the presence of BA calls. We present a mathematical formulation to compute the preemption probability of an incoming IR call at routing stage based on the current IR and future BA load information. We propose a routing strategy by formulating a link cost function comprising of the calculated preemption probability of the incoming IR call and hop count. Simulation results confirm that QoS routing based on the proposed link cost function significantly outperforms widely recommended shortest path and widest path routing algorithms in terms of IR call preemption and blocking rate. The proposed approach also yields higher network utilization and IR effective throughput.     

Integrated connection-level and packet-level QoS controls over wireless mesh networks

This paper focuses on integrating connection-level and packet-level QoS controls over wireless mesh network (WMN) to support applications with diverse QoS performance requirements. At the connection-level, the dynamic guard based prioritized connection admission control (DG-PCAC) provides prioritized admission with relative connection blocking probabilities and end-to-end deterministic minimum bandwidth allocation guarantees. DG-PCAC is enabled by dynamic guard based logical link configuration controls (LCCs), which provides relative differentiated capacity limits for prioritized admission classes. At the packet-level, the optimal rate delay scheduler (ORDS) dynamically allocates link bandwidth to the admitted flows of prioritized traffic classes; with the objective to minimize deviation from relative delay targets with minimum bandwidth guarantees according to traffic classes. Two realizations of the ORDS are presented, namely optimal scheduling policy via dynamic programming (DP) algorithm, and neural network (NN) based heuristic to alleviate computational complexity. Performance results show that the DG-PCAC enables consistent performance guarantees under non-stationary arrivals of connection requests. Performance results also show that the performance of the NN based scheduling heuristic approaches to that of the DP based optimal ORDS scheme.     

Real-time transport of MPEG video with a statistically guaranteedloss ratio in ATM networks

Unlike deterministic real-time communication in which excessive resources may be required for “absolute” performance guarantees, statistical real-time communication seeks to achieve both probabilistic performance guarantees and efficient resource sharing. This paper presents a framework for statistical real-time communication in ATM networks, providing delay-guaranteed transport of MPEG-coded video traffic with a statistically-guaranteed cell-loss ratio. Delay-guaranteed communication is achieved with a modified version of Traffic-Controlled Rate-Monotonic Priority Scheduling (TCRM). A set of statistical real-time channels that share similar traffic characteristics are multiplexed into a common macrochannel. Those statistical real-time channels which are multiplexed together share the resources of a macrochannel, and individual statistical real-time channels are given timeliness and probabilistic cell-loss guarantees. A macrochannel is serviced by the modified TCRM which improves link utilization and makes channel management simpler. Based on the analysis of an M/D/1/N queueing system, we propose a procedure for determining the transmission capacity of a macrochannel necessary to statistically guarantee a cell-loss ratio bound. Our extensive trace-driven simulation has shown the superiority of the proposed framework to the other approaches. The overall cell-loss ratios for multihop statistical real-time channels are shown to be smaller than the predetermined bounds, thus verifying our analytical results     

片上网络带宽资源QoS调度算法

提出一种片上网络带宽资源QoS调度算法。通过分布式地动态调整有保障服务(GS)连接在每个路由器中的优先级,解决共享同一物理链路的不同GS连接之间的传输冲突问题,从而保障时延、带宽和时延抖动等QoS。通过给尽力而为服务(BE)通道分配动态优先级和监控GS流量2种方法的应用,有效提高了BE数据流的服务质量及链路利用率。     

一种新的Ad Hoc网络QoS框架

提出一种新的Ad Hoc网络QoS保障框架。该框架能够区分不同优先级的业务和不同QoS要求的业务。能够保障在网络可用资源不足的情况下,高优先级的业务通过“抢占”的方式接入网络,而同时保障低优先级的业务使用网络资源的最低容限。仿真显示该框架具有区分业务优先级和保障业务不同QoS要求的能力。     

A fairness analysis of LAN/WAN protocol relays

Functional standardization activities in ISO and in regional workshops are currently addressing network layer relays for the interconnection of several types of subnetworks. Relay systems are critical systems in the overall performance of the network because they are the points where network congestion can be built up or avoided. Particularly, when the interconnected subnetworks have very dissimilar bandwidths, congestion control becomes a very important issue in relay systems design. This paper addresses the problem of congestion control in relay systems for LAN/WAN interworking. Congestion control deals with the avoidance of collapse situations in intermediate systems due to traffic overload. It deals also with the guarantee of fairness in resource utilization, considering user needs of communication services expressed in terms of Quality of Service (QoS) parameters. To ensure congestion collapse avoidance and fairness, a channel service algorithm is proposed. Simulation results show that, in a situation of overload and for different traffic patterns with different QoS requirements, the relay's channel service and acknowledgment algorithms can guarantee justice in resource utilization and the expected QoS among the active channels.     

A core stateless bandwidth broker architecture for scalable support of guaranteed services

We present a novel bandwidth broker architecture for scalable support of guaranteed services that decouples the QoS control plane from the packet forwarding plane. More specifically, under this architecture, core routers do not maintain any QoS reservation states, whether per-flow or aggregate. Instead, the QoS reservation states are stored at and managed by a bandwidth broker. There are several advantages of such a bandwidth broker architecture. Among others, it avoids the problem of inconsistent QoS states faced by the conventional hop-by-hop, distributed admission control approach. Furthermore, it allows us to design efficient admission control algorithms without incurring any overhead at core routers. The proposed bandwidth broker architecture is designed based on a core stateless virtual time reference system developed recently. This virtual time reference system provides a unifying framework to characterize, in terms of their abilities to support delay guarantees, both the per-hop behaviors of core routers and the end-to-end properties of their concatenation. We focus on the design of efficient admission control algorithms under the proposed bandwidth broker architecture. We consider both per-flow end-to-end guaranteed delay services and class-based guaranteed delay services with flow aggregation. Using our bandwidth broker architecture, we demonstrate how admission control can be done on a per domain basis instead of on a "hop-by-hop" basis. Such an approach may significantly reduce the complexity of the admission control algorithms. In designing class-based admission control algorithms, we investigate the problem of dynamic flow aggregation in providing guaranteed delay services and devise a new apparatus to effectively circumvent this problem. We conduct detailed analyses to provide theoretical underpinning for our schemes as well as to establish their correctness. Simulations are also performed to demonstrate the efficacy of our schemes.     

Performance bounds for rate envelope multiplexing

In QoS guaranteed communication networks, such as ATM, several classes of traffic streams with widely varying characteristics share common transmission resources. To achieve high utilization of these networks, while providing appropriate grade of service for all connections, the development of powerful traffic management algorithms is a central issue. Due to scalability reasons traffic control functions like flow, congestion and admission control often need simple and efficient characterization of traffic using mainly aggregate characteristics instead of using information about all the individual flows. In this paper, the saturation probability as a possible performance measure of aggregate traffic on a communication link is discussed. This performance metric, also referred to as the tail distribution of aggregate traffic, is essential in traffic control and management algorithms of high-speed networks including also the prospective QoS Internet. In this paper, using the Chernoff bounding method, efficient closed-form bounds have been derived for the saturation probability for the case when little information is available on the aggregate traffic. The performance of these estimates is also shown by means of numerical examples.     

A preemptive channel allocation scheme for multimedia traffic in mobile wireless networks

This paper presents a channel allocation model with both partial and full preemptive capabilities for multimedia traffic in mobile wireless networks. The different types of multimedia traffic in transmitting through next-generation networks possess different characteristics and demand an adequate channel allocation scheme to fulfill individual Quality of Service (QoS) requirements. In the proposed model, multimedia traffic is classified into three classes corresponding to different priority levels in a decreasing order. To effectively reduce the dropping probability, a higher-priority handoff call is allowed to fully or partially preempt any lower-priority ongoing calls when the channel capacity becomes insufficient. In addition, to prevent from possible starvation of the lowest-priority traffic, a portion of system channels are purposely reserved. Performance measures, including the dropping probability of handoff calls, the call-interruption probability that an ongoing call is forced to termination due to full preemption, and the bandwidth reduction ratio due to partial preemption, are investigated through an analytical model built with 4-D Markov chains. The numerical results demonstrate the effectiveness of our model.     

Integrated Multimedia Personal Communications with Asymmetric Services for Mobile Users in Cellular Systems

Wireless personal communication networks are evolving to provide integrated multimedia services to mobile users. An important issue in their design is the accommodation of various services each having predefined Quality-of-Service (QoS) requirements. Efficient resource utilization can be achieved using a medium access scheme that allows various traffic components to be statistically multiplexed and a call admission control to prevent overload. Some multimedia services have asymmetric resource needs. For example, web browsing generally requires more downlink bandwidth than uplink bandwidth. We present a medium access scheme and a call admission control algorithm for guaranteed QoS provisioning in asymmetric integrated multimedia personal communication networks. An overall performance analysis model is developed. Performance characteristics are calculated and presented for an example system.     

Linux环境下路由器中的网络带宽管理

Linux是目前广泛用于路由设备中的操作系统,而流量管理是这种网络操作系统的一个重要功能.研究了Linux系统的流量管理机制,发现当前Linux系统所采用的在网络接口的出口实现的基于网络包调度的流量管理机制缺乏对于网络带宽在系统范围的全局性的管理,也缺乏对于输入流的网络处理的有效管理和调度,从而造成不必要的CPU资源的浪费.为解决这一问题,提出了一种新颖的网络带宽管理机制,它通过调度网络协议处理所占用的CPU时间来实现带宽管理.这种新的机制将网络带宽的管理和调度从网络接口的出口点转移到处理接收到的网络包的系统软件中断处理程序中,从而克服了原来的流量管理机制的缺点.通过系统实现和对比实验,发现该机制本身给系统带来的负载小于Linux原来的流量管理机制,同时可以提供更好的流量隔离,并且能够有效地节省用于网络处理的CPU资源.     

QoS in InfiniBand subnetworks

The InfiniBand architecture (IBA) has been proposed as an industry standard both for communication between processing nodes and I/O devices and for interprocessor communication. It replaces the traditional bus-based interconnect with a switch-based network for connecting processing nodes and I/O devices. It is being developed by the InfiniBand/sup SM/ Trade Association (IBTA) in the aim to provide the levels of reliability, availability, performance, scalability, and quality of service (QoS) required by present and future server systems. For this purpose, IBA provides a series of mechanisms that are able to guarantee QoS to the applications. In previous papers, we have proposed a strategy to compute the InfiniBand arbitration tables. In one of these, we presented and evaluated our proposal to treat traffic with bandwidth requirements. In another, we evaluated our strategy to compute the InfiniBand arbitration tables for traffic with delay requirements, which is a more complex task. In this paper, we evaluate both these proposals together. Furthermore, we also adapt these proposals in order to treat VBR traffic without QoS guarantees, but achieving very good results. Performance results show that, with a correct treatment of each traffic class in the arbitration of the output port, all traffic classes reach their QoS requirements.     

异构分层无线网络中基于业务QoS保证的切换策略研究

针对异构分层无线网络提出了一种保证业务QoS的切换策略。该策略在层间呼叫双向溢出基础上,为实时业务切换设置了保护信道,为非实时业务切换设置了缓冲队列。为了进一步降低实时业务切换的掉线率,还使用了信道侵占技术,原理是实时业务切换呼叫可以侵占数据业务正在使用的信道资源。仿真结果表明,提出的切换方法能够显著降低各类切换业务的掉线率,同时整个异构分层系统的信道利用率也略有提高。