Multipath routing for video delivery over bandwidth-limited networks

The delivery of quality video service often requires high bandwidth with low delay or cost in network transmission. Current routing protocols such as those used in the Internet are mainly based on the single-path approach (e.g., the shortest-path routing). This approach cannot meet the end-to-end bandwidth requirement when the video is streamed over bandwidth-limited networks. In order to overcome this limitation, we propose multipath routing, where the video takes multiple paths to reach its destination(s), thereby increasing the aggregate throughput. We consider both unicast (point-to-point) and multicast scenarios. For unicast, we present an efficient multipath heuristic (of complexity O(|V|3)), which achieves high bandwidth with low delay. Given a set of path lengths, we then present and prove a simple data scheduling algorithm as implemented at the server, which achieves the theoretical minimum end-to-end delay. For a network with unit-capacity links, the algorithm, when combined with disjoint-path routing, offers an exact and efficient solution to meet a bandwidth requirement with minimum delay. For multicast, we study the construction of multiple trees for layered video to satisfy the user bandwidth requirements. We propose two efficient heuristics on how such trees can be constructed so as to minimize the cost of their aggregation subject to a delay constraint.published_or_final_versio

Key management approaches to offer data confidentiality for secure multicast

Multicasting is an efficient way to deliver data to large of users in applications such as Internet stock quotes, audio and music delivery, file and video distribution, etc. Many of these applications. require the security feature of data confidentiality, which is not readily offered by the "open" nature of multicast. In order to offer such confidentiality, the encryption and decryption keys must be constantly changed upon a membership change. In this article, after discussing some performance criteria to offer secure multicast, we present a number of the proposed key management schemes for data confidentiality. We categorize these schemes into four groups: key tree-based approaches, contributory key agreement schemes supported by the Diffie-Hellman algorithm, computational number theoretic approaches, and secure multicast framework approaches. Through examples, we describe the operation of the schemes and compare their performances

Broadcasting video with the knowledge of user delay preference

In designing a video broadcasting system, the delay preference of a user is traditionally regarded as unknown. In fact, such preference can be known upon user's arrival by employing some techniques such as i) delay-dependent charging, where users are offered different levels of pay-per-view (PPV) depending on the maximum delay they are willing to tolerate; or ii) reservation, where a user specifies the exact play-time of a movie in advance, and he/she is charged according to the length of the reservation period. We explore, for the first time, the impact of such delay knowledge on request scheduling and system cost in terms of user loss and stream requirement. For delay-dependent charging, we propose "Delay-Aware Broadcasting" (DAB) and its variant based on reservation (DAB-r), where allocation of server streams is driven by the delay tolerance of a user. DAB-r offers differentiated grade of services according to user PPVs (and thereof classes). As compared with a system where user delay preference is not known, our schemes achieve substantially lower user loss rate, higher revenue, and better fairness. Regarding reservation system, we consider a scheme where clients can pre-buffer video data. Unicast streams are used to merge requests back to the on-going broadcast streams. We show that a reservation system achieves substantially lower stream requirement as compared to an on-demand system based on "patching."

Tradeoff between system profit and user delay/loss in providing near video-on-demand service

In a near video-on-demand (near-VOD) system, requests for a movie arriving in a period of time are grouped (or "batched") together and served with a single multicast stream. In this paper, we consider providing near-VOD services when there is a cost associated with using a network multicast channel. We address the tradeoff between system profit, given by the total pay-per-view collected minus the total channel cost, and user delay or user loss (due to reneging). We first analyze and compare the tradeoff of two traditional "basic" schemes, namely, the window-based schemes in which a maximum user delay can be guaranteed, and the batch-size based scheme in which system profit can be guaranteed. By combining these basic schemes, we present a scheme which can adaptively balance system profit and user delay when the underlying request rate fluctuates. We then consider the case in which delayed users may renege and determine how system profit can be maximized by sizing the batching period given user's reneging behavior. We show that maximizing profit can lead to excessively high user loss rate, especially when the channel cost is high and users are not very patient. Therefore, a shorter suboptimal batching period should be used for this case in reality. We finally introduce schemes which are able to offer high profit or low user loss when the underlying arrival rate fluctuates

TCP and UDP performance for Internet over optical packet-switched networks

Optical packet-switched (OPS) network is a strong candidate for the future Optical Internet. In this paper, we study packet aggregation and deflection routing as employed in OPS networks on the performance of upper layer Internet protocols represented by TCP and UDR Regarding packet aggregation schemes, we study no aggregation, mixed-flow aggregation, and per-flow aggregation. Our results show that for both TCP and UDP, mixed-flow aggregation achieves the highest throughput, and per-flow aggregation significantly decreases the fairness at large aggregation intervals. Both aggregation schemes increase UDP delay jitter. Regarding deflection routing, we show that deflection routing significantly improves TCP throughput in spite of the out-of-order packet delivery. However, the congestion of the deflection path significantly affects the improvement that can be achieved. UDP throughput does not suffer from out-of-order packet delivery, and hence its throughput improvement by deflection routing can be even more prominent The larger the deflection cost (delay difference between the deflection path and the shortest path) is, the larger UDP delay jitter results. Deflection cost, however, does not affect the throughput and fairness very much for both TCP and UDP

Modeling and dimensioning hierarchical storage systems for low-delay video services

In order to cost-effectively accommodate a large number of titles in a video system, a hierarchical storage system can be used. In this system, not-so-popular video files are stored in a tertiary level such as a disk/tape library. These files are transferred, or "staged," to a secondary level composed of magnetic disks before being streamed to the users. This system overcomes the current limitations in using disk/tape libraries to stream videos and resolves the bandwidth difference between staging and streaming. In this paper, we present, via analysis, a model of the system and determine the minimum storage and bandwidth required, at each level, to meet a given user delay goal. We also analyze a number of system operations pertaining to whether or not a file is played while it is being staged (i.e., stage-streaming) and whether or not the displayed segments are deleted (i.e., trail-deletion). We show that stage-streaming and trail-deletion can achieve substantially lower bandwidth and storage requirements. In order to further increase the streaming and storage scalability, a distributed storage system can be used where multiple local servers are put close to user pools and get their files from one of the libraries through a network. We extend the models developed to such a system and specify the resource requirements to meet a given delay goal

Improving Delaunay Triangulation for application-level multicast

In recent years, there has been increasing interest in application-level multicast (ALM), where the multicast related functionalities are moved to end-hosts. One of the promising ALM protocols is Delaunay Triangulation (DT), which constructs an overlay mesh using 2-D Delaunay Triangulation (DT) and makes use of compass routing to forward packets. However, DT protocol as it is originally proposed suffers from several weaknesses: 1) it requires users to input its, geographic location, and assumes that the location correlates well with network distance; 2) it tends to form multiple connections across two domains, and hence has a high usage of long delay (interdomain) links; 3) it does not consider the fanout of a host, therefore some less-powerful hosts may serve too many users, leading to degradation of service. To address these problems, we propose to use Global Network Positioning (GNP) for host location estimation and Forward Delegation to limit the fanout of a host explicitly and efficiently trade off the network resource usage with latency. Using Internet-like topologies, we show that our scheme, as compared to the original DT protocol, can substantially reduce average relative delay penalty, physical link stresses and network resource usage while meeting the processing capability of the hosts in the network

Client buffering techniques for scalable video broadcasting over broadband networks with low user delay

In traditional near-VOD (NVOD), the number of streams required is high if the user delay goal is low (say, 2 minutes). In this paper, we study the use of client buffering to reduce such bandwidth requirement. We first study a scheme based on streaming approach termed "join-and-stream" (JAS), which broadcasts a movie in a staggered manner and uses short unicast streams to recover the time difference between the broadcast point and the arrival time. We show that such a technique is effective for movies with intermediate arrival rate. We then propose a broadcasting scheme for popular movies termed "stream-bundling." The scheme groups (i.e., "bundles") the server streams into channels of incrementally increasing bandwidth. Such high-speed bundled channels are used to deliver the beginning portion of the videos to the clients, so that the clients can merge with an on-going broadcast stream quickly. By comparing with other previously proposed broadcasting schemes (such as Pyramid Broadcasting, Skyscraper Broadcasting and Harmonic Broadcasting), stream-bundling is shown to achieve similar level of performance with much lower complexity (without many channels to manage and to hop). Using our two schemes, the bandwidth requirement of a system can be reduced significantly (by more than 50\% in our examples) as compared with the traditional NVOD, with the cost of only a little client buffering (less than or equal to20\% of the movie length)

TCP performance with deflection routing in the Internet

Deflection routing has been well studied for optical networks with regular topologies. In this paper, we propose using deflection routing in the Internet and study its TCP performance. In particular, we show that when the difference between the delay of the deflection path and the shortest path (i.e., the deflection cost) is in a certain range, deflection routing can make almost full use of the free bandwidth in the deflection path and hence achieve substantial throughput improvement. In the worst case when the deflection cost is large, deflection routing can achieve an aggregate throughput no less than that without deflection routing. We analyze the underlying mechanisms of these characteristics. In order to extend the usefulness of deflection routing, we also propose a deflection routing scheme with adaptive deflection point and show via simulation that this scheme can achieve very high throughput as long as the deflection cost is no larger than a certain value. We show that deflection routing is friendly to the existing traffic in the deflection path. One possibly unfavorable requirement of deflection routing is that it should be enabled for either all or none of the flows contending for the same outgoing (congested) link

Multipath routing for video delivery over bandwidth-limited networks

The delivery of quality video service often requires high bandwidth with low delay or cost in network transmission. Current routing protocols such as those used in the Internet are mainly based on the single-path approach (e.g., the shortest-path routing). This approach cannot meet the end-to-end bandwidth requirement when the video is streamed over bandwidth-limited networks. In order to overcome this limitation, we propose multipath routing, where the video takes multiple paths to reach its destination(s), thereby increasing the aggregate throughput. We consider both unicast (point-to-point) and multicast scenarios. For unicast, we present an efficient multipath heuristic (of complexity O(\textbackslash{}V\textbackslash{}(3))), which achieves high bandwidth with low delay. Given a set of path lengths, we then present and prove a simple data scheduling algorithm as implemented at the server, which achieves the theoretical minimum end-to-end delay. For a network with unit-capacity links, the algorithm, when combined with disjoint-path routing, offers an exact and efficient solution to meet a bandwidth requirement with minimum delay. For multicast, we study the construction of multiple trees for layered video to satisfy the user bandwidth requirements. We propose two efficient heuristics on how such trees can be constructed so as to minimize the cost of their aggregation subject to a delay constraint