Video Data Delivery using Slotted Patching

In the request-based scheme, a patching channel is initiated on arrival of a request in an interarrival time of two adjacent multicast channels. If two requests are received in a short duration in an interarrival time, two patching channels are needed to service them. Both these channels deliver almost the same data, thus, wasting the bandwidth. This problem may be addressed in two ways: using higher level patching technique, or forcing the first request to wait for the second one. Using higher level patching technique makes the system more complex and thus usually not preferred. In the second case, the bandwidth usage certainly reduces, but the length of the waiting time by the first request for the second request is the main issue. In this paper, this issue is addressed by dividing the video duration into uniform time slots such that there is at least one request in a time slot for initiating the patching channel. The proposed scheme is named as Video Data Delivery using Slotted Patching. In this scheme, the patching channels download much less video data than the request-based scheme and thus require less bandwidth. This scheme may not provide immediate services to all users unlike the request-based scheme, but the user's waiting can be made arbitrarily small without using much resources unlike the request-based scheme.     

A speculative load adaptive streaming scheme for efficient video delivery

Video on demand services require video broadcast schemes to provide efficient and reliable performance under various client request loads. In this paper, we have developed an efficient request load adaptive broadcast scheme, speculative load adaptive streaming scheme (SLAS), that requires lower service bandwidth than previous approaches, regardless of request rate. We have provided both analysis and simulation to show the performance gain over previous schemes. In this paper, we provide the theoretic upper bound of the continuous segment allocations on channels. We found that the number of allocated segments of the SLAS is close to the theoretic upper bound when compared with other schemes over various numbers of stream channels. Our analysis of client waiting time is almost identical to simulation results about all client requests. By simulation, we compared the required service bandwidth and storage requirements of the SLAS scheme and other schemes and found the SLAS scheme is an efficient broadcast scheme as compared to well known seamless channel transition schemes.     

基于patching的P2P VoD频道间协作策略

在P2P点播系统中,“冷播”频道往往节点较少且分布分散,各个节点形成多个独立的“播放链”,服务器往往需要为每个播放链单独提供一路数据流,负载很大。为此,提出了一种P2P VoD冷热播频道间协作策略,通过利用“热播”频道中具有富余服务能力的节点为“冷播”频道节点提供patching服务,从而连接“冷播”频道各个独立的“播放链”,进而减轻了多频道P2P点播系统中由于频道冷热播的不均衡导致“冷播”频道给服务器带来巨大的负载压力。仿真结果证明了该策略能有效提高多频道点播系统的并发服务能力。     

P2MCMD: A scalable approach to VoD service over peer-to-peer networks

In this paper, we deal with the problem of providing Video-on-Demand service under Scheduled Video Delivery (SVD) paradigm, which allows users to request a video for instant viewing or later viewing. In this paradigm, a major concern for the server is how to schedule the delivery of requested videos to assure users a continuous playback while utilizing its limited channels more efficiently. We propose a novel approach, P2MCMD, to deal with this problem. P2MCMD treats the service of video delivery in finer granularity. What is scheduled is segment-based multicast groups instead of video-based multicast groups. With the aid of dynamic multicast, the server is enabled to allocate its delivery resources flexibly and efficiently. The uneven popularity of provided videos are also taken into account and exploited so that the produced delivery schedule has the potential to boost the degree of multicast, thereby making the server achieve higher channel utilization. Moreover, peer-to-peer cooperation is employed to alleviate the workload at the server. The server can be relieved of the retransmission of duplicate video segments by enabling a latecomer to appeal to early arriving peers for the missing initial video segments. The performance of P2MCMD is evaluated through simulation. The experimental results show that our proposed approach can scale to a larger number of requests and allow the provision of a wider variety of videos at the server as compared to the existing approaches for SVD paradigm.     

一种新的视频点播方案——扩展幂级方案

提出一种适合于热门节目的分块广播(partition broadcasting)方案——扩展幂级方案，分析了该方案的资源需求包括服务器信道、用户端缓存、用户端I／O带宽等，并根据方案的周期性分析了用户点播时间与缓存空间及用户端I／O带宽的关系．结论表明它比现有的许多其它同类方案有着更好的兼容性，能很好地权衡用户端的I／O带宽及缓存空间，而且更易于实现。     

采用新的流调度策略的视频点播系统研究

客户多播补块流调度策略——CMP(Client Multicast Patching)——是基于代理缓存的有效的视频点播策略,它采用用户参与流调度的方式,某些用户在播放节目的同时,又作为服务器为后续用户多播一部分节目,因此,在不增加用户I／O带宽的前提下,通过利用局域网络丰富的带宽．有效地节省了服务器及主干网络的资源,并对用户请求提供即时服务,该文给出CMP方案的实现算法,并对系统进行仿真及性能分析,结果表明了CMP方案的有效性和可行性。     

Channel Allocation under Batching and VCR Control in Video-on-Demand Systems

In order to guarantee continuous delivery of a video stream in an on-demand video server environment, a collection of resources (referred to as a logical channel) are reserved in advance. To conserve server resources, multiple client requests for the same video can be batched together and served by a single channel. Increasing the window over which all requests for a particular video are batched results in larger savings in server capacity; however, it also increases the reneging probability of a client. A complication introduced by batching is that if a batched client pauses, a new stream (which may not be immediately available) needs to be started when the client resumes. To provide short response time to resume requests, some channels are set aside and are referred to as contingency channels. To further improve resource utilization, even when a nonbatched client pauses, the channel is released and reacquired upon resume. In this paper, we first develop an analytical model that predicts the reneging probability and expected resume delay, and then use this model to optimally allocate channels for batching, on-demand playback, and contingency. The effectiveness of the proposed policy over a scheme with no contingency channels and no batching is also demonstrated.     

Efficient staircase scheme with seamless channel transition mechanism

Video applications require large amount of bandwidth and also storage space. The Fast Broadcasting (FB) scheme is one of the simplest schemes to provide video services, but it requires considerably large buffer storage. This scheme assumes constant video popularity and thus has fixed amount of bandwidth requirement. The popularity of videos generally does not remain the same. It varies over a period of time and accordingly the bandwidth allocation should be adjusted. The variability in bandwidth requirement for videos based on popularity is overcome by incorporating seamless channel transition mechanism in a broadcasting scheme. After incorporating seamless channel transition mechanism, the scheme still delivers continuous video data to old and new users without jerks and hiccups. The FB scheme with seamless channel transition mechanism requires less buffer storage than the FB scheme. The staircase scheme also allocates a fixed amount of bandwidth to a video. The FB and staircase schemes divide a video into same number of segments; thus have same user’s waiting time. The basic difference between the FB and staircase schemes is that in the staircase scheme the segments are further divided into subsegments in order to reduce the buffer requirement. To consider variability of video popularity in the staircase scheme, seamless channel transition for staircase (SCTS) scheme has been discussed. The SCTS scheme performs better than the seamless Fast Broadcasting scheme as regard the buffer storage, while maintaining the same user’s waiting time. In this paper, we propose an efficient staircase scheme with seamless channel transition mechanism that performs better than the SCTS scheme. In the proposed scheme, the video (ESS scheme) data is downloaded at slower rate than that in the SCTS scheme without disrupting the user services and requiring less buffer storage.     

A double patching technique for efficient bandwidth sharing in video-on-demand systems

Patching is an efficient bandwidth-sharing technique for video-on-demand systems. In this environment, a client joins an on-going regular multicast to receive and cache the data in a local buffer. The server needs to send only the leading portion of the video in a patching stream. When the client finishes playing back the patching data, it continues the playback using the data already cached in the buffer. Although this strategy enables stream sharing without the service delay, the performance of Patching has limitation: as the time distance to the last regular multicast enlarges, the patching cost for new requests increases and eventually, a new regular multicast must be scheduled to balance the cost. In this paper, we address this problem by proposing a new technique called Double Patching. Our research is based on the observation that a patching stream can be shared by the video requests arriving in the next w _p time units if it delivers an additional 2 · w _p time units of video data. With these extra data, the patching cost for these requests can be dramatically reduced. In the new technique, a client uses no more than two download channels at any one time. Thus, its implementation cost is the same as that of the original Patching. As for its performance, our study shows that the improvement achieved by the proposed technique is significant. In many cases, Double Patching doubles the performance of the original Patching. This work is partially supported by National Science Foundation under Grant No. 0092914.     

流内容分送中的媒体后缀动态缓存技术研究

基于带前缀缓存的流调度方案OBP(optimized batch patching)提出了媒体后缀的增量缓存算法IC-BP和预分配缓存算法PA-BP,推导出两种算法下传输单一流媒体对象各自所需的平均骨干带宽、服务器平均使用输出通道数和代理所需最大缓存容量,并分析了以上两种缓存算法的综合传输代价.结果表明,两种缓存算法均有效降低了骨干带宽消耗和服务器负载,传输代价均明显低于带前缀缓存的OBP. 而PA-BP克服了IC-BP算法中每次批处理调度时都至少需请求一个批处理长度补丁的缺点,因而具有更低的传输代价,其性能优于IC-BP缓存算法.     

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+.     

无线视频通信中信道自适应差错控制策略的研究

针对无线视频通信中现有的差错控制方法的缺点和局限性，根据无线信道高误码率和高时变性的特点，提出一种基于反馈的信道自适应差错控制策略．根据反馈信号预测未来信道的状态，自适应地调整冗余信息值，优化无线视频通信系统的传输效率，使其在稳定性、功率消耗和传输效率之间达到有效的折衷．仿真结果表明，该方法能有效地提高无线视频通信系统的传输效率，尤其在无线信道误码率变化剧烈的情况下，效果更加明显．     

Dimensioning the capacity of true video-on-demand servers

The need to reduce the huge bandwidth demand of video-on-demand (VoD) services has led to the conception of both multicast and broadcast based techniques for the deployment of such services on a large scale. Interactivity, a desirable feature for video services, includes the capacity to perform VCR operations. However, whenever a viewer requests the performance of a VCR operation, his/her video stream becomes unsynchronized with that of his/her multicast group, and a new channel must be allocated for the performance of this operation. The present paper introduces a novel approach for determining the number of video channels needed to support such interactivity. Moreover, it investigates the performance of interactive systems with a pool of channels reserved for the support of VCR operations. Systems with both batching and piggybacking are analyzed. Results indicate that for a medium to high number of users performing VCR operations the number of channels required to achieve target levels of quality-of-service is lower for systems with no pool of reserved channels than it is for systems with such a pool.     

Efficient implementation of the implicit error correction nVoD schema

Implicit Error Correction is a near Video-on-Demand (nVoD) schema that trades bandwidth utilization for initial playback delay while potentially allowing an infinite number of users. Additionally, it provides error protection without further bandwidth increase by exploiting the implicit redundancy of nVoD protocols, using linear combinations of the segments transmitted in a given time slot. This paper introduces a new implementation that outperforms the original schema by adding two new mechanisms: redundancy channels and feedback error correction.     

Seamless channel transition for slotted generalized fibonacci broadcasting

Periodic Broadcasting schemes are cost- effective methods of implementation of Near Video on Demand systems. While the schemes enjoy the advantage of reducing the demand on server bandwidth, they suffer from the problem of insensitivity to the popularity of videos. However, the popularity of a video does not remain constant in the real world; it varies with time, social events, and so on. From a service provider’s viewpoint, given a set of popular videos and limited server bandwidth, it would be desirable to adjust the bandwidth allocated to each of the videos dynamically and seamlessly according to the level of its hotness. In this paper, we first re-formulate the Generalized Fibonacci Broadcasting as the Fixed-Length Segment- Scheduling problem and name the re-formulated scheme the Slotted Generalized Fibonacci Broadcasting (SGFB). We then propose a seamless channel transition enhancement on top of the SGFB scheme so that the service provider is capable of adjusting the channel allocation policy to make the most benefit out of the available bandwidth. The correctness of SGFB together with its performance analysis will be presented. Furthermore, we shall provide mathematical analysis to demonstrate its channel transition behavior. This work is partially supported by NSC-94-2213-E-260-024.     

P2P transfer of partial stream in multimedia multicast

In this paper, we propose a new multicast scheme that is based on the client-initiated-with-prefetching (CIWP) and peer-to-peer (P2P) transfer of a partial multimedia stream. In the CIWP scheme, when a new client joins an ongoing multicast channel, the server has to create an extra unicast channel to retransmit the partial stream that has already been transmitted. However, the unicast channel consumes some of the I/O bandwidth of the server, as well as some of the network resources between the server and the client's Internet Service Provider (ISP). To solve this problem, we propose the use of the P2P transfer algorithm to deliver the partial stream from a client that has already joined the ongoing multicast session to the newcomer. This P2P transfer between clients is limited to clients belonging to the same ISP. To further improve the performance, a threshold is used to control the P2P transfer. We performed analytical studies to show that the proposed multicast scheme can reduce the consumption of the network resources of the server, by utilizing the client's disk space. We also performed various simulation studies to demonstrate the performance improvement in terms of the use of the server's bandwidth and the waiting time for the clients’ requests.     

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.     

远程教学中COD的组播实现

本文提出了一种集中式管理、点播服务器分布式放置的远程教学课件点播(Courseware On Demand-COD)系统。在这一体系结构下．采用了新的批处理信道调度策略，对用户实施多播流和补丁流相结合的组播服务。提高了网络带宽利用率，增加了可服务的点播并发流数，同时降低了课件播放延迟时间。     

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.     

VoD系统中基于优先级的准入控制和带宽分配策略

本文针对VoD系统中不同客户对视频服务质量的不同要求,提出一种基于优先级的准入控制和带宽动态分配策略。在准入控制时,综合考虑请求的优先级和并发流占用的实际带宽等因素,在保证为高优先级请求预留较多固定带宽的同时提高并发流个数;在服务过程中,根据优先级和网络状况动态调整每个流的带宽,使丢包率低于一定的阈值,并保证在相同的网络状态下为高优先级请求提供较高的视频服务质量。