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.     

区分服务网络基于测量的接纳控制方案的设计与应用

提出了一种分布式可扩展的接纳控制方案，其目的是为区分服务网络提供端到端服务质量（Quality of Services,QoS)保证，该方案主要由以下部分构成：（1）连接接纳控制协议，主要负责主机和网络节点以及网络节点和带宽代理之间的信息传送，实现对连接请求的串行操作；（2）位于网络核心节点的可用带宽估计算法；（3）位于网络边缘节点的接纳控制算法；给出了该方案在视频传输方面的应用实例；利用多种网络拓扑结构和QoS指标评价该方案的性能，实验结果表明该方案能准确地控制可接纳区域和提高网络资源的利用率。     

Traffic characterization algorithms for VBR video in multimedia networks

A network that offers deterministic, i.e., worst case, quality-of-service guarantees to variable-bit-rate (VBR) video must provide a resource reservation mechanism that allocates bandwidth, buffer space, and other resources for each video stream. Such a resource reservation scheme must be carefully designed, otherwise network resources are wasted. A key component for the design of a resource reservation scheme is the traffic characterization method that specifies the traffic arrivals on a video stream. The traffic characterization should accurately describe the actual arrivals, so that a large number of streams can be supported; but it must also map directly into efficient traffic-policing mechanisms that monitor arrivals on each stream. In this study, we present a fast and accurate traffic characterization method for stored VBR video in networks with a deterministic service. We use this approximation to obtain a traffic characterization that can be efficiently policed by a small number of leaky buckets. We present a case study where we apply our characterization method to networks that employ a dynamic resource reservation scheme with renegotiation. We use traces from a set of 25–30-min MPEG sequences to evaluate our method against other characterization schemes from the literature.     

The probability relationship between video’s instantaneous and average aggregate rates

The growing demand for video applications and services has contributed substantially to the increase of video traffic on the Internet. Measurement-based admission control was proposed with the primary aim of eliminating or reducing the need of flow state information; also to control overhead for admission decision and maximize utilization at the potential cost of QoS degradation. Some of the admission algorithms depend on the instantaneous rate for its operation. On the other hand, the average aggregate rate has been proposed to better suit variable rate such as video traffic. In this paper, we investigate the probability relationship between the instantaneous and average aggregate rates for video traffic. A mathematical model has been developed to quantify the probability relationship between both rates and validated through extensive simulations using real video sequences. The average rate was found to be lower than instantaneous for a small number of flows, however there was no pronounced difference for a large number of flows. Furthermore, the difference between both rates increases for fast moving content such as sport or longer measurement time window.     

Above packet level admission control and bandwidth allocation for IEEE 802.16 wireless MAN

IEEE 802.16 wireless Metropolitan Area Network (MAN) is expected to revolutionize the broadband wireless access technology. Efficient resource management is essential in providing scalability in such large IEEE 802.16-based wireless network and Quality of Service (QoS) for multimedia applications (VoIP, MPEG, FTP, WWW) is usually achieved by appropriate classification of scheduling services and grant/request mechanism. In this paper, we firstly discuss the QoS issue in IEEE 802.16 wireless MANs and propose a dynamic admission control scheme for scheduling services defined in the 802.16 specification. The proposed scheme provides the highest priority for Unsolicited Grant Service (UGS) connections and maximizes the bandwidth utilization by employing bandwidth borrowing and degradation. We develop an approximate analytical model to evaluate the system performance by assuming that the traffic processes of all scheduling services are Poisson processes. In fact, the self-similarity of non-voice traffic makes its traffic process far from Poisson process and should be modeled by Poisson Pareto Burst Process (PPBP). Therefore, in the later part of the paper, we analyze upper bound blocking probabilities of all scheduling services above the packet level using PPBP model for fractal traffic and Gaussian model for aggregated traffic in large wireless network as well as using the Chernoff bound method. Based on the analytical results, we give another admission control and bandwidth allocation mechanism above the packet level so as to minimize the blocking probability of each type of service in IEEE 802.16 wireless MAN. Analytical and simulation results are obtained and compared to demonstrate the effectiveness of proposed schemes and validate our analytical models.     

Enhancing aggregate QoS for video streaming

The IETF's Differentiated Services architecture is designed to provide different types or levels of service for Internet traffic. One of its key features is that traffic flows are aggregated so that routers in the core network only need to distinguish a relatively small number of aggregate flows, even if those flows consist of hundreds or thousands of individual flows. However, network-level QoS differentiation may not satisfy the requirements of many QoS-sensitive applications such as live video streaming, where end-to-end delay and reliability must be guaranteed.

This paper investigates application-level service differentiation for MPEG video streaming in a Diff-Serv-aware MPLS network infrastructure, along with routing support at the network layer. Based on the fact that MPEG video has become one of the most popular formats for Internet (wired and wireless) users, our approach enhances aggregate QoS for video streaming by employing existing application-level knowledge of the MPEG video structure; therefore it requires neither a new video compression algorithm nor additional bandwidth. Several MPEG video dispersion models are proposed and analyzed. Simulation results show that two such strategies are superior to the other tested. In addition, a new routing scheme is proposed to support searching the ‘best’ paths for efficient multi-path video streaming. Through extensive simulations, we demonstrate that our approaches improve the aggregate QoS of MPEG video streams, as well as overall network efficiency.     

Methodologies for bandwidth allocation,transmission scheduling,and congestion avoidance in broadband ATM networks

The call types supported in high-speed packet networks vary widely in their bandwidth requirements and tolerance to message delay and loss. In this paper, we classify various traffic sources which are likely to be integrated in broadband ATM networks, and suggest schemes for bandwidth allocation and transmission scheduling to meet the quality and performance objectives. We propose ATM cell-multiplexing using a Dynamic Time-Slice (DTS) scheme which guarantees a required bandwidth for each traffic class and/or virtual circuit (VC), and is dynamic in that it allows the different traffic classes or VCs to share the bandwidth with a soft boundary. Any bandwidth momentarily unused by a class or a VC is made available to the other traffic present in the multiplexer. The scheme guarantees a desired bandwidth to connections which require a fixed wide bandwidth. Thus, it facilitates setting up circuit-like connections in a network using the ATM protocol for transport. The DTS scheme is an efficient way of combining constant bit-rate (CBR) services with variable bit-rate (VBR) stastically multiplexed services. We also described methodologies to schedule delivery of delay-tolerant data traffic within the framework of the DTS scheme. Important issues such as buffer allocations, guarantee of service quality, and ease of implementation are also discussed.     

Impact of video scheduling on bandwidth allocation for multiplexed MPEG streams

We present efficient schemes for scheduling the delivery of variable-bit-rate MPEG-compressed video with stringent quality-of-service (QoS) requirements. Video scheduling is being used to improve bandwidth allocation at a video server that uses statistical multiplexing to aggregate video streams prior to transporting them over a network. A video stream is modeled using a traffic envelope that provides a deterministic time-varying bound on the bit rate. Because of the periodicity in which frame types in an MPEG stream are typically generated, a simple traffic envelope can be constructed using only five parameters. Using the traffic-envelope model, we show that video sources can be statistically multiplexed with an effective bandwidth that is often less than the source peak rate. Bandwidth gain is achieved without sacrificing the stringency of the requested QoS. The effective bandwidth depends on the arrangement of the multiplexed streams, which is a measure of the lag between the GOP periods of various streams. For homogeneous streams, we give an optimal scheduling scheme for video sources at a video-on-demand server that results in the minimum effective bandwidth. For heterogeneous sources, a sub-optimal scheduling scheme is given, which achieves acceptable bandwidth gain. Numerical examples based on traces of MPEG-coded movies are used to demonstrate the effectiveness of our schemes.     

Statistical real-time channels on multiaccess bus networks

Real-time communication with performance guarantees is expected to become an important and necessary feature of future computer networks. In this paper, we present a scheme which can provide real-time communication services with both absolute and statistical performance guarantees on multiaccess bus networks for given input traffic characteristics and performance requirements. The proposed scheme reserves network bandwidth for real-time connections according to their needs. It also allows for independent addition and deletion of real-time connections while preserving existing guarantees. Our extensive simulation results for motion video communication have shown the proposed scheme to outperform the other well-known schemes     

CStream: neighborhood bandwidth aggregation for better video streaming

Despite the popularity of watching videos online, challenges still remain in video streaming in many scenarios. Limited home broadband and mobile phone 3G bandwidths mean many users stream videos at compromised quality. To provide additional bandwidth for streaming, we propose CStream, a system that aggregates bandwidth from multiple cooperating users in a neighborhood environment for better video streaming. CStream exploits the fact that wireless devices have multiple network interfaces and connects cooperating users with a wireless ad-hoc network to aggregate their unused downlink Internet bandwidth. CStream dynamically generates a streaming plan to stream a single video using multiple connections, continuously adapting to changes in the neighborhood and variations in the available bandwidth. CStream is developed and evaluated on a test bed of computers, allowing for a detailed, controlled evaluation of performance. Analysis of the results shows a linear increase in throughput over single-connection streaming and improved video quality as the number of cooperating users in a neighborhood increase.     

Adaptive bandwidth allocation based on playback tunnel to support video on demand service over ATM networks

This paper focuses on adaptive bandwidth allocation (ABA) for transporting pre-stored VBR compressed video data across networks in support of video-on-demand (VoD) service. Two key issues are addressed. Firstly, a simplified dynamic programming method based on playback tunnel is proposed to predict the bandwidth which can be dynamically allocated for transporting video segment to guarantee that the playback buffer neither underflows nor overflows. Secondly, ABA schemes with different criteria including middle-tunnel ABA (MT-ABA) and reduced-bandwidth-variability ABA (RBV-ABA) are investigated. The proposed ABA schemes are evaluated by a set of real-life MPEG video traces. The obtained results show that the RBV-ABA scheme outperforms MT-ABA scheme in terms of peak rate, traffic burstiness and bandwidth variability. On the other hand, the MT-ABA scheme is more significant for avoiding the playback buffer overflow or underflow than that of RBV-ABA.     

异构无线网络中基于非合作博弈论的资源分配和接入控制

对异构无线网络中无线资源分配和呼叫接入控制进行研究.基于非合作博弈理论,提出了不同无线资源的带宽和连接数量分配的理论模型.结合网络连接的效用函数,对非合作博弈的无线资源分配中的纳什均衡点的存在性和唯一性进行论证.而且,进一步对业务量与阻塞率之间的关系进行分析,提出了能够保证通信可靠性的接入控制算法.仿真结果表明,基于非合作博弈论的无线资源分配机制能够有效地解决带宽和连接数量的分配问题,并能在整体上保证分配的合理性和公平性.接入控制算法根据需要能够动态地调整在某一区域分配的连接数量,从而保证通信的可靠性.     

基于模糊控制的ATM网络VBR视频传输平滑策略

VBR视频传输的突发性是影响ATM网络服务质量的关键因素,文中通过模糊控制方法对视频传输流量的阈值进行监控,实现了接入的平滑并可动态调整传输速度。文中以传输流量及这发级作为评价指标进行分析,结果表明VBR视频传输自适应平滑策略的实效性。     

基于在线测量的视频服务器接纳控制

实时多媒体系统中,有限的磁盘I/O带宽和缓存空间使得接纳控制显得更为重要。针对传统算法接纳控制方面的不足,论文提出基于在线测量的VBR视频服务器接纳控制算法。通过在线测量系统所剩资源和周期容限的幅度变化来实时调节调度周期的大小,不但简化了接纳过程,节约了系统资源,提高了算法的可实现性,而且也使得系统的所剩资源达到更优的“等量”平衡。结果表明,系统的综合性能指标明显提高。     

Joint rate control for VBR MPEG video on PVC ATM links

A joint rate control algorithm for variable bit rate (VBR) MPEG-compressed digital video on point-to-point permanent virtual circuit (PVC) ATM links is proposed. The algorithm controls the encoding mode of a number of video encoders that operate either on VBR or constant bit rate (CBR) mode. The algorithm selects the encoding mode based on the buffer occupancy of a multiplexer co-located with the encoders that interfaces them to the PVC link. VBR encoding is the predominant encoding mode used during congestion-free periods. CBR mode is used only during congested periods. When CBR is selected, new bit rates are jointly assigned to the encoders based on their relative encoding complexities. The bit rate assigned to the encoders are enforced by a CBR rate control local to each encoder. The performance of the joint rate control algorithm is evaluated through simulation of a packet multiplexer, where a number of connections are multiplexed onto a fixed-capacity channel. The performance is compared to that of multiplexing conventional CBR and open-loop VBR from the video quality and bandwidth efficiency points of view. Simulation results show that the proposed algorithm improves performance over multiplexed conventional CBR or open-loop VBR MPEG video, without significantly increasing implementation complexity. The application of the algorithm to video-on-demand over ATM is discussed.     

Packet video transport in ATM networks with single-bit feedback

The promise of a broadband integrated service digital network has led to the design of mechanisms for efficient transport of real-time compressed video in packet switching networks. We examine feedback control for video transport in ATM networks where the available feedback is a single bit of information carried in the cell header. We investigate the performance of three single-bit schemes for source rate adaptation. Two were originally for congestion control of bursty data traffic and are modified to control video traffic. The third scheme conveys more information about the state of queue(s) at the bottleneck. The simulation results show that all three schemes for feedback control of VBR video streams work remarkably well. During severe network congestion, the signal quality degrades gracefully, but not uniformly across all connections. Based on insights from the initial simulations, we propose a scheme to improve the fairness of service and demonstrate its effectiveness.     

Dynamic resource allocation via video content and short-termtraffic statistics

The reliable and efficient transmission of high-quality variable bit rate (VBR) video through the Internet generally requires network resources be allocated in a dynamic fashion. This includes the determination of when to renegotiate for network resources, as well as how much to request at a given time. The accuracy of any resource request method depends critically on its prediction of future traffic patterns. Such a prediction can be performed using the content and traffic information of short video segments. This paper presents a systematic approach to select the best features for prediction, indicating that while content is important in predicting the bandwidth of a video hit stream, the use of both content and available short-term bandwidth statistics can yield significant improvements. A new framework for traffic prediction is proposed in this paper; experimental results show a smaller mean-square resource prediction error and higher overall link utilization     

Congestion prevention in broadband wireless access systems: An economic approach

While the demand for mobile broadband wireless services continues to increase, radio resources remain scarce. Even with the substantial increase in the supported bandwidth in the next generation broadband wireless access systems (BWASs), it is expected that these systems will severely suffer from congestion, due to the rapid increase in demand of bandwidth-intensive multimedia services. Without efficient bandwidth management and congestion control schemes, network operators may not be able to meet the increasing demand of users for multimedia services, and hence they may suffer an immense revenue loss. In this paper, we propose an admission-level bandwidth management scheme consisting of call admission control (CAC) and dynamic pricing. The main aim of our proposed scheme is to provide monetary incentives to users to use the wireless resources efficiently and rationally, hence, allowing efficient bandwidth management at the admission level. By dynamically determining the prices of units of bandwidth, the proposed scheme can guarantee that the number of connection requests to the system are less than or equal to certain optimal values computed dynamically, hence, ensuring a congestion-free system. The proposed scheme is general and can accommodate different objective functions for the admission control as well as different pricing functions. Comprehensive simulation results with accurate and inaccurate demand modeling are provided to show the effectiveness and strengths of our proposed approach.     

Bandwidth allocation in UWB WPANs with ECMA-368 MAC

The new ECMA-368 MAC for UWB WPANs consists of two channel access methods: the distributed reservation protocol (DRP) and prioritized contention access (PCA). The exact method of medium access slot (MAS) allocation in DRP is not specified in the standard. The contribution of this paper is twofold. First, the paper describes a distributed resource allocation method in which a number of interference–avoidance rules are used to reserve slots for devices. Devices maintain sending and receiving tables to track activities in the neighbourhood. The proposed method is a simple, effective solution to the DRP MAS allocation problem, avoiding reservation conflicts and interference from hidden terminals. Secondly, for VBR MPEG-4 video traffic, we propose a bandwidth requirement calculation method based on traffic prediction. In the proposed scheme bandwidth is allocated based on accurate traffic predictions, therefore matching network resources to the traffic demand. Application QoS is maintained while network utilization is kept high. Furthermore, the simple, adaptive linear predictor does not incur much computation overhead. Simulation results have demonstrated the accuracy of the proposed prediction algorithm and effectiveness of the bandwidth allocation method.