Broadcasting scheme with low client buffers and bandwidths for video-on-demand applications

Efficient data broadcasting is independent of request arrivals, and is thus highly promising when transmitting popular videos. A conventionally adopted broadcasting method is periodic broadcasting, which divides a popular video into segments, which are then simultaneously broadcast on different data channels. Once clients want to watch the video, they download the segments from these channels. The skyscraper broadcasting (SkB) scheme supports clients with small bandwidths. An SkB client requires only two-channel bandwidths to receive video segments. This work proposes a reverse SkB (RSkB) scheme, which extends SkB by reducing buffering spaces. The RSkB is mathematically shown to achieve on-time video delivery and two-channel client bandwidths. A formula for determining the maximum number of segments buffered by an RSkB client is presented. Finally, an analysis of RSkB reveals that its client buffer requirements are usually 25–37% lower than SkB. Extensive simulations of RSkB further demonstrate that RSkB yields lower client buffer demand than other proposed systems.

Design and analysis of a look-ahead scheduling scheme to support pause-resume for video-on-demand applications

In a video-on-demand (VOD) system, subscribers can choose both the movie they wish to view and the time they wish to view it. In such an environment there are invariably hot videos which are requested by many viewers. The requirement that each viewer be able to independently pause the video at any instant and later resume the viewing with little delay can cause difficulties in batching viewers for each showing. Under batching, a single video stream is shared by multiple concurrent viewers and a resume request has to wait for additional stream capacity to become available before actual resumption can occur. The conventional approach to the support of on-demand pause-resume provides one video access stream to disks for each video request. This can greatly increase the disk arm requirements of a VOD system. In this paper, we propose a more efficient mechanism to support the pause-resume feature usinglook-ahead scheduling withlook-aside buffering. The idea is to use buffering to increase the number of concurrent viewers supportable. The concept of look-ahead scheduling is not to back up each viewer with a real stream capacity so he can pause and resume at any time, but rather with a (look-ahead) stream that is currently being used for another showing which is close to completion. Before the look-ahead stream becomes available, the pause and resume features have to be supported by the original stream through (look-aside) buffering of the missed content. It is shown via simulations that the proposed scheme can provide a substantially greater throughput than the approach without batching. Furthermore, for a given amount of buffer, the improvement in throughput grows more than linearly with the stream capacity of the server. In other words, the look-ahead stream scheduling scheme operates with good economy of scale because it is easier to form look-ahead streams for video servers with larger stream capacity.     

A circular skip-cluster scheme to support video-on-demand services

The major drawback of the existing cluster placement scheme is the long response time caused by admission control if the number of clusters and the number of users are large. A circular skip-cluster placement scheme is proposed to reduce the size of the data buffer as well as the system response time. Furthermore, the popularity of each video is different in the real world. We propose a new popularity-based data allocation scheme to allocate data units within a cluster such that the corresponding data units of these popular videos are stored in those cylinders at one end of each cluster. Due to a higher spatial locality within these hot cylinders, some data units requested by the users are stored in the same cylinder such that one seek operation, one rotation, and one transfer operation are required to retrieve these data units. Therefore, the time required to retrieve data for these requests can be reduced, thus also reducing the system response time. Based on our results, the buffer size and the system response time can be reduced by half or more. These findings are essential for constructing video-on-demand systems that provide satisfactory performance.     

Extension of practical channel transition broadcasting for near video-on-demand applications

Periodic broadcasting is a cost-effective solution for the large-scale distribution of popular videos. This strategy guarantees constant worst service latency to all clients, regardless of the number of video requests. The practical channel transition broadcasting (PCTB) scheme is an essential periodic broadcasting method that can dynamically add or release broadcasting channels (i.e., channel transition) according to video popularity. However, PCTB experiences bandwidth waste when performing channel transition. This study further finds that PCTB yields transition playback latency during channel addition. Therefore, an enhanced version referred to as PCTB+ is proposed to cause less bandwidth waste and lower transition playback latency. The applicability of this new scheme is verified, and an analytical evaluation is provided to demonstrate its performance advantage. The new scheme reduces bandwidth waste by 50 % to 100 % compared to the original PCTB scheme. Moreover, PCTB+ yields 50 % smaller transition playback latency than PCTB. The proposed scheme outperforms the seamless fast broadcasting (SFB) scheme for bandwidth waste under most conditions. No extra startup latency and client buffer demand are required when using PCTB+.     

A kinetic scheme for the one-dimensional open channel flow equations with applications on networks

In this paper, a kinetic method to compute approximative solutions of the one-dimensional open channel flow equations with a varying cross-sectional area and a varying bottom profile is proposed. The scheme preserves the steady states at rest, keeps the water height non-negative and is able to handle dry channel beds. These three properties are essential indicators for the quality of a numerical scheme. The ability of the scheme to treat varying cross-sectional areas along the channel is an important advancement in comparison to previous papers. Further the same equations are considered on a network by coupling the equations at the nodes. The main difference to the majority of common numerical hydraulic models is the usage of the energy equality as coupling condition which seems to be more realistic than conditions based on the water height. Moreover, we set up a numerical method for computing subcritical flow on such networks. Several examples are treated to illustrate the results.     

A cross-layer framework for video-on-demand service in multi-hop WiMax mesh networks

In this work, we introduce a cross-layer framework to favor the video-on-demand service in multi-hop WiMax mesh networks. We first propose a joint solution of admission control and channel scheduling for video streams. The proposed approach guarantees that the required data rate is achieved for video streams, which is crucial for multimedia streaming applications. An efficient and light-weight multicast routing technique is also proposed to minimize the bandwidth cost of joining a multicast tree. Furthermore, we adopt the Patching technique in the application layer to improve the capacity of the video server. Overall, the quality of the video-on-demand service is dramatically improved with the help of the efficient cooperation between the techniques proposed in different layers of the network. Simulation study shows that with the proposed approach, true video-on-demand in WiMax mesh networks can be achieved under high video request arrival rate.     

An inter-PAN mobility support scheme for IP-based wireless sensor networks and its applications

Mobility support for Wireless Sensor Networks (WSN) can significantly extend the use of WSN in many fields, such as industrial control, healthcare and smart home. And high-efficiency mobility support schemes are essential for WSN because this is a typical energy constrained network. This paper proposes a LoW cost inter-PAN Mobility Support Scheme (LoWMS) for IPv6 based WSN, which follows the network based idea. The scheme aims at reducing signaling cost when sensor nodes move between two Personal Area Networks. In order to realize it, the handoff related control messages are designed to transmit in link layer, and resolution for ping-pong handoff is also given. Simulation results show the novel scheme efficiently reduces the amount of handoff messages, which is benefit for energy saving of WSN. At the end of the paper, we illustrate two possible application scenarios which could be beneficial from LoWMS, one is healthcare system, and another is logistics and storage.     

Communication support for distributed collaborative applications

The development of distributed, multimedia, collaborative applications requires the resolution of communication issues such as concurrency control and temporal and causal synchronization of traffic over related data streams. Existing transport and/or session-layer protocols do not include the desired support for multistream, multipoint communication. In this paper, we propose new communication abstractions and mechanisms that facilitate the implementation of the necessary coordination and concurrency control semantics in a collaborative application. We propose a protocol suite called themultiflow conversation protocol (MCP) for the realization of these abstractions and describe its prototype implementation in an internetwork of workstations. The paper also describes our experience with the prototype and results of a performance evaluation.     

A specification model for context-based collaborative applications

This paper presents a model for building context-based systems in pervasive computing environments from high level specifications. A pervasive computing environment is viewed as a collaboration space consisting of mobile users, system services, and sensors and resources embedded in the physical environment. The approach presented here is developed for building collaborative activities in which users and environment services cooperate towards some shared objectives and tasks. The specification model allows expression of policies related to context-based discovery and secure access of resources, and role-based interactions among users and environmental services. Using several examples we illustrate the capabilities of our specification model for expressing various kinds of context-based requirements for resource access and user interactions.     

Performance-aware placement and chaining scheme for virtualized network functions: a particle swarm optimization approach

The Journal of Supercomputing - Network functions virtualization (NFV) is a new concept that has received the attention of both researchers and network providers. NFV decouples network functions...     

Virtual workflow system for distributed collaborative scientific applications on Grids

Grid computing has become an effective computing technique in recent years. This paper develops a virtual workflow system to construct distributed collaborative applications for Grid users. The virtual workflow system consists three levels: abstract workflow system, translator and concrete workflow system. The research highlight of the implementation is that this workflow system is developed based on CORBA and Unicore Grid middleware. Furthermore, this implementation can support legacy application developed with Parco and C++ codes. This virtual workflow system can provide efficient GUI for users to organize distributed scientific collaborative applications and execute them on Grid resources. We present the design, implementation, and evaluation of this virtual workflow system in the paper.     

协作译码转发中继网络中的安全能效分析

基于物理层安全理论,研究了存在窃听用户情形下协作译码转发中继网络中的安全能效问题。安全能效,即消耗单位能量所能传输的保密信息量。在满足各节点发射功率约束和中继处最小译码速率要求下,通过功率控制实现系统的安全能效最大化。针对目标函数非凸问题,利用分式规划和DC(Difference of Convex functions)规划理论把目标函数分解为子函数通过迭代来进行优化求解。仿真结果表明,能效优化可以显著提升系统的安全能效。     

Two-way chaining for non-uniform distributions

Two-way chaining is a novel hashing scheme with separate chaining that achieves O(log log n) expected maximum search time, when Θ(n) data points are hashed via two independent uniform hash functions into a table of size n. In this note, we consider the two-way chaining scheme in the fixed density model, where the hashing values behave according to two fixed but possibly different densities on [0, 1].     

无线传感器网络节能转发策略的改进与实现

基于电池供电的传感器网络的节点电源无法替换,导致能量消耗问题直接影响网络的生命周期,所以节省能源成为关键问题.由于节点沿某路径到达接收点的基于跳数的转发在交付率和节能方面是低效的,尤其在高损耗环境中,因此针对这个问题,根据有损链路模型,对通过折中交付率和能源代价来最大化能源效率的单链和多链的节能转发方法进行了研究.通过数学分析、仿真和实验评价,将该方法和其它的转发策略进行了比较,发现节能转发方案有效节约了能源.     

面向协同应用的通用协作语言研究

研究和探讨一种能够灵活定制不同协同应用方案的编程语言。对CSCW协同应用中的协作机制和交互特征进行分析，抽象出协同应用中最具共性的基本协作元素，对这些基本元素进行定义和描述。提出将协作问题从计算应用问题中分离出来的方案。对于一个给定的应用，可以构造多种协作方案。使最终用户可选择最符合自己需要的协作方案和交互规则来进行他们之间协同工作，并且还可在协同工作会话过程中改变协作交互规则。     

A reusable structural design for mobile collaborative applications

Architecting mobile collaborative applications has always been a challenge for designers. However, counting on a structural design as a reference can help developers to reduce risks and efforts involved in system design. This article presents a reusable architecture which helps modeling the communication and coordination services required by mobile collaborative applications to support collaboration among users. This architecture has been used as a basis for the design of several mobile systems. Two of them are presented in this article to show the applicability of the proposal to real world collaborative systems.     

基于分层的传感器网络密钥预分配方案

在基于部署知识的密钥预分配方案中,随着节点部署误差的增大,网络的局部连通率将显著下降,从而导致网络的全局连通率下降。为了减轻部署误差对方案性能的影响,提出了一种新的密钥预分配模型。该模型将部署区域划分成基本区和联系区,联系区根据离基本区的远近分层,并在此基础上提出了一种新的密钥预分配方案。分析和模拟表明:与直接利用部署知识的方案相比,基于分层的密钥管理方案可以显著地提高网络的性能。