RTSP协议在视频点播系统中的应用

实时流协议是一个专门为传输实时数据而设计的应用层控制协议,而视频点播系统是当前Internet上的一个重要的多媒体应用。本文介绍了实时流协议在视频点播系统中的应用及具体实现。     

A scalable cost-effective video broadcasting system for on-demand video services

Recent years have seen intensive investigations of Periodic Broadcast, an attractive paradigm for broadcasting popular videos. In this paradigm, the server simply broadcasts segments of a popular video periodically on a number of communication channels. A large number of clients can be served simultaneously by tuning into these channels to receive segments of the requested video. A playback can begin as soon as a client can access the first segment. Periodic Broadcast guarantees a small maximum service delay regardless of the number of concurrent clients. Existing periodic broadcast techniques are typically evaluated through analytical assessment. While these results are good performance indicators, they cannot demonstrate subtle implementation difficulty that can prohibit these techniques from practical deployment. In this paper, we present the design and implementation of a video broadcasting system based on our periodic broadcast scheme called Striping Broadcast. Our experience with the system confirms that the system offers a low service delay close to its analytical guaranteed delay while requiring small storage space and low download bandwidth at a client.     

A taxonomy of multicast protocols for Internet applications

The continuous growth in applications that require communications among a group of hosts or simultaneous dissemination of data to multiple sites on the Internet has led to considerable interest in multicast communication. These applications have different quality of service requirements such as deadlines to response time and tolerance to data loss. Internet multicast protocols provide a spectrum of services to cater for the needs of a wide array of multicast applications. The design alternatives of a multicast protocol for a particular application may lead to different performance characteristics, for example higher utilization of network bandwidth vs lower protocol processing requirements. Therefore a framework is required to various design choices available to design multicast protocols and evaluate the performance tradeoffs associated with these alternatives. Motivated by such a need and by the evolution of multicast applications over the Internet, this article presents a taxonomy of multicast protocols and a common framework to evaluate their performance.     

一种基于调度的VOD系统的研究与实现

传统的视频点播(Video-On-Demand,VOD)系统中,服务器为每个用户请求分配一个独立的信道。这样过多的用户经常会造成系统的服务器I/O带宽或网络带宽的瓶颈。对服务器信道调度方案的设计是缓解这一瓶颈问题的一种有效方法。介绍了一种采用了可控多播(Controlled Multieast,CM)信道调度方案的系统的实现。测试结果表明,该系统可以节约带宽,增大视频点播服务的用户数目,较好地缓解传统VOD系统中的服务器I/O或网络带宽瓶颈问题。     

基于DVB和IP双结构传输模式流媒体视频点播系统的设计与实现

针对互联网流媒体视频点播传输带宽问题,对数字广播协议原理和多协议封装技术做了简单介绍,提出了一种基于IPOVERDVB传输模式互联网-广播网双结构流媒体视频点播系统的设计方案,并给出了一种Web网页视频点播应用具体实现方法;该系统综合了互联网和广播网的网络特性,具有双向交互、稳定可靠,不受用户规模限制等诸多优点。     

Designing an effective P2P system for a VoD system to exploit the multicast communication

A distributed video-on-demand system (DVoD) with multiple server-nodes is a cost-effective and fault-tolerant solution for a high scalable enterprise video-on-demand (VoD) system. However, such a server-oriented design is highly vulnerable to workload variations given that the service capacity is limited. Peer-to-Peer (P2P) has been introduced as an architectural solution with self-growing capacity. However, the characteristics of a pure P2P system such as the peer transient nature and high network overhead make this kind of architecture unsuitable for a fully interactive VoD system. In this paper, we propose a new efficient integrated VoD architecture, called DPⁿ2P^m$D{P}^{n}2P^m$, that combines DVoD with a P2P system and multicast communications. The DVoD’s server-nodes provide a minimum required quality of service (QoS) and the P2P system is able to offer the mechanism to increase the system service capacity according to client demands. Multicast communication, wherever it is possible, is effectively exploited by our P2P system. In our design, each client is able to send video information to a set of m$m$ clients using only one multicast channel. Furthermore, the collaboration mechanism is able to coordinate a set of clients to create one collaboration group to replace the server, providing an extensive, efficient and low network-overhead collaboration mechanism from n$n$-peers to m$m$-peers. Regardless of the video the client is watching, our P2P scheme allows every active client to collaborate with the server. The P2P scheme is complemented with recovery mechanisms that are able to replace the failed client before affecting the QoS, offering continuous playback. The proposed approach has been broadly evaluated, firstly using a mathematical model to derive the theoretical performance and secondly using a simulation environment to analyze the system’s dynamic behavior, the VCR interaction impact and the client failures. Comparing DPⁿ2P^m$D{P}^{n}2P^m$ with other DVoD architectures and the most relevant P2P delivery policies, we show that our design is an improvement on previous solutions, providing a higher scalability.     

视频点播网站的设计与实现

视频点播系统是集通信网络技术、多媒体技术、计算机和数据库技术于一体的崭新的视频服务系统。此系统还运用了智能视频流技术,针对不同的网络带宽和传输速度采取不同的传输方式。     

Optimal server allocations for streaming multimedia applications on the Internet

In this paper, we address the server selection problem for streaming applications on the Internet. The architecture we consider is similar to the content distribution networks consisting of geographically dispersed servers and user populations over an interconnected set of metropolitan areas. Server selection issues for Web-based applications in such an environment have been widely addressed; the selection is mostly based on proximity measured using packet delay. Such a greedy or heuristic approach to server selection will not address the capacity planning problem evident in multimedia applications. For such applications, admission control becomes an essential part of their design to maintain Quality of Service (QoS). Our objective in providing a solution to the server selection problem is threefold: first, to direct clients to the nearest server; second, to provide multiple sources to diffuse network load; third, to match server capacity to user demand so that optimal blocking performance can be expected. We accomplish all three objectives by using a special type of Linear Programming (LP) formulation called the Transportation Problem (TP). The objective function in the TP is to minimize the cost of serving a video request from user population x using server y as measured by network distance. The optimal allocation between servers and user populations from TP results in server clusters, the aggregated capacity of each cluster designed to meet the demands of its designated user population. Within a server cluster, we propose streaming protocols for request handling that will result in a balanced load. We implement threshold-based admission control in individual servers within a cluster to enforce the fair share of the server resource to its designated user population. The blocking performance is used as a trigger to find new optimal allocations when blocking rates become unacceptable due to change in user demands. We substantiate the analytical model with an extensive simulation for analyzing the performance of the proposed clustered architecture and the protocols. The simulation results show significant difference in overall blocking performance between optimal and suboptimal allocations in as much as 15% at moderate to high workloads. We also show that the proposed cluster protocols result in lower packet loss and latencies by forcing path diversity from multiple sources for request delivery.     

一种基于IP网络流媒体传输的码流平滑算法

提出了一个视频点播解决方案,给出了服务器和客户机的系统实现和工作时序,重点描述了基于客户机预测分段的码流平滑实现机制(PPSA),包括理论模型和实验仿真结果。它有效地屏蔽了解码器读取码流速率的抖动,使得服务器输出码流速率平稳,减少了对网络的冲击。该方案适用于对延迟不敏感的视频点播系统。     

Tree-assisted gossiping for overlay video distribution

Given its readily deployable nature and broad applications for digital entertainment, video streaming through overlay networks has received much attention recently. While a tree topology is often advocated due to its scalability, it suffers from discontinuous playback under highly dynamic network environments. For on-demand streaming, the asynchronicity among client requests further aggravates the problem. On the other hand, gossip protocols using random message dissemination, though robust, fail to meet the real-time constraints for streaming applications. In this paper, we propose TAG, a Tree-Assisted Gossip protocol that addresses the above issues. TAG adopts a tree structure with time indexing to accommodate asynchronous requests, and an efficient pull-based gossip algorithm to mitigate the impact of network dynamicity. It seamlessly integrates these two approaches and realizes their best features, namely, low delay with a regular tree topology, and robust delivery with smart switching among multiple paths, thus making effective use of the available bandwidth in the network. We evaluate the performance of TAG under various settings, and the results demonstrate that it is quite robust in the presence of local and global bandwidth fluctuations. As compared to pure tree-based overlay VOD system, it achieves much lower and stable segment missing rates, even under highly dynamic network conditions.This research is supported by a Canadian NSERC Discovery Grant, an NSERC RTI Grant, a CFI New Oppurtunities Grant, and an SFU President's Research Grant.The author names are in alphabetical order.     

优化补丁算法的研究与设计

介绍了动态调度技术的补丁算法及其优化算法,并受周期缓存重用算法和双补丁算法的启发,提出了一种优化补丁算法的新算法。新算法既充分利用缓冲区,又以多传送t-B帧视频数据的补丁流为其后紧接着的（t-B）／2个单位时间内到达的新请求创造共享机会。     

A multicast interface for UNIX 4.3

The UNIX 4.3 operating system, like its predecessor UNIX 4.2, is designed to allow interprocess communications between pairs of processes using sockets — pairs of integers identifying specific hosts and ports — which are associated with a process. In this paper a software package which allows interprocess communications between many UNIX processes (as opposed to two) is presented.     

PVPS：P2P点播中的分布式搜索算法

PVPS系统针对P2P点播服务实现中的源节点搜索问题给出了一种实用高效的解决策略.PVPS在节点结构组织上采用了基于节目内容分簇的网状结构,每个分簇中由代理节点进行管理.在簇间搜索过程中,PVPS采用改进的启发式MPR算法、基于邻居优先级的自裁减策略和基于消息冗余度的剪枝策略对非结构化搜索进行多次优化,提高了搜索的效率.理论分析和实验结果表明,PVPS服务体系采用的搜索策略在性能上优于现有策略,在大型网络中具有良好的稳定性和扩展性.     

Distributed dynamic mobile multicast

Traditional mobile multicast schemes have either high multicast tree reconfiguration cost or high packet delivery cost. The former affects service disruption time while the latter affects packet delivery delay. Although existing region-based mobile multicast schemes offer a trade-off between two costs to some extent, most of them do not determine the size of the service range, which is critical to network performance. In this paper, we propose a novel approach, called Distributed Dynamic Mobile Multicast (D²M²), to dynamically determine the optimal service range according to the mobility and service characteristics of a user. We derive an analytical model to formulate the costs of multicast tree reconfiguration and multicast packet delivery. The model is based on a Markov chain that analyzes a mobile node’s movement in a 2D mesh network. As the complexity of computing steady probability is high, we aggregate the Markov states by leveraging mobility symmetry. Simulation shows that the network performance is enhanced through D²M².     

A hybrid multicast connectivity solution for multi-party collaborative environments

In multi-party collaborative environments, a group of users can share multiple media streams via IP multicasting. However, despite of the efficiency of IP multicast, it is not widely available and alternative application-layer multicast approaches are introduced. Application-layer multicast is advantageous, however, it incurs additional processing delays. In this paper, we present a new hybrid-style application-layer multicast solution that satisfies both network efficiency and easy deployment. We achieve this goal by connecting multicast islands through UDP tunnels employing UMTP (UDP multicast tunneling protocol). We also design a MPROBE protocol to remove multicast loop among multicast island in real Internet. We verify the feasibility of the proposed solution by implementing a prototype tool, AG Connector, that works on Access Grid multi-party collaborative environment.

Efficient multicast schemes for 3-D Networks-on-Chip

3-D Networks-on-Chip (NoCs) have been proposed as a potent solution to address both the interconnection and design complexity problems facing future System-on-Chip (SoC) designs. In this paper, two topology-aware multicast routing algorithms, Multicasting XYZ (MXYZ) and Alternative XYZ (AL + XYZ) algorithms in supporting of 3-D NoC are proposed. In essence, MXYZ is a simple dimension order multicast routing algorithm that targets 3-D NoC systems built upon regular topologies. To support multicast routing in irregular regions, AL + XYZ can be applied, where an alternative output channel is sought to forward/replicate the packets whenever the output channel determined by MXYZ is not available. To evaluate the performance of MXYZ and AL + XYZ, extensive experiments have been conducted by comparing MXYZ and AL + XYZ against a path-based multicast routing algorithm and an irregular region oriented multiple unicast routing algorithm, respectively. The experimental results confirm that the proposed MXYZ and AL + XYZ schemes, respectively, have lower latency and power consumption than the other two routing algorithms, meriting the two proposed algorithms to be more suitable for supporting multicasting in 3-D NoC systems. In addition, the hardware implementation cost of AL + XYZ is shown to be quite modest.     

基于P2P的视频点播系统设计

随着计算机网络和多媒体技术的发展,人们对网络视频点播的需求越来越高,高清、流畅和互动已经成为人们对视频点播的要求,在传统的C/S模式的视频点播系统中,客户终端要观看视频都需要依赖中心化的视频服务器,而且对带宽的要求越来越大,视频服务器就容易成为网络的瓶颈,当网络规模越大时,服务器的负担就会越重,一旦服务器崩溃,整个网络就会瘫痪.另外由于服务器的能力有限,往往不能及时地对每一个客户端的请求作出响应,因此会造成资源利用率低下.P2P网络中没有中心化的服务器,不存在系统瓶颈,每个节点既充当客户端又充当服务器端,因而具有很高的资源利用率.     

网络宽带交互式视频点播系统的设计与实现

随着计算机网络和Internet的发展,宽带VOD视频点播技术因其交互式功能和流媒体传输技术已倍受教育、娱乐等行业青睐,论文结合NT平台开发实例阐述了基于WEB的实时VOD系统的协议原理、软件结构和设计实现方案,以便为基于IP的大规模多媒体点播系统的设计提供参考。     

A distributed multicast routing algorithm for real-time applications in wide area networks

The problem of constructing a minimal cost multicast routing tree (MRT) with delay constraints in wide area networks (WAN) is considered. A new distributed token-passing based algorithm that constructs a sub-optimal MRT satisfying given delay constraints for all members in the multicast group is presented. In contrast with the previous works by Jia [A distributed algorithm of delay-bounded multicast routing for multimedia applications in wide area networks, IEEE/ACM Trans. Network. 6 (1998) 828–837] and several others [Y. Im, Y. Lee, S. Wi, Y. Choi, Delay constrained distributed multicast routing algorithm, Comput. Comm. 20 (1997) 60–66; X. Jia, Y. Zhang, N. Pissinou, K. Makki, A distributed multicast routing protocol for real-time multicast applications, Comput. Networks 31 (1999) 101–110; Q. Sun, H. Langendorfer, A distributed delay-constrained dynamic multicast routing algorithm, Telecommun. Systems 11 (1999) 47–58], in which cycles may occur, we show that the multicast routing network produced by our algorithm is indeed a tree, namely, cycle free. Also the success rate of our algorithm to find a feasible solution, if one exists, is guaranteed to be 100%, while Jia's algorithm is not. Furthermore, our algorithm is fault tolerant and can also adapt to cases where the multicast group members are allowed to join or leave the multicast session dynamically. Simulations have been conducted and the results show that the MRT generated by our algorithm has better performance compared to previous methods.     

流媒体视频点播控制模型研究

流媒体点播应用越来越广泛,用户可以在浏览器窗口和媒体服务器进行交互,在嵌入式播放器中观看和控制音,视频等多媒体信息。文中介绍实时流化协议,研究以RTSP协议为核心的流媒体点播控制模型,在信令控制和媒体内容缓存等方面提出了解决方案。