| 1. |
- Carlsson, Niklas, et al.
(författare)
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Modeling Priority-based Incentive Policies for Peer-assisted Content Delivery Systems
- 2008
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Ingår i: NETWORKING 2008 Ad Hoc and Sensor Networks, Wireless Networks, Next Generation Internet. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 3540795480 - 9783540795483 ; , s. 421-432
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Bokkapitel (refereegranskat)abstract
- Content delivery providers can improve their service scalability and offload their servers by making use of content transfers among their clients. To provide peers with incentive to transfer data to other peers, protocols such as BitTorrent typically employ a tit-for-tat policy in which peers give upload preference to peers that provide the highest upload rate to them. However, the tit-for-tat policy does not provide any incentive for a peer to stay in the system beyond completion of its download.This paper presents a simple fixed-point analytic model of a priority-based incentive mechanism which provides peers with strong incentive to contribute upload bandwidth beyond their own download completion. Priority is obtained based on a peer's prior contribution to the system. Using a two-class model, we show that priority-based policies can significantly improve average download times, and that there exists a significant region of the parameter space in which both high-priority and low-priority peers experience improved performance compared to with the pure tit-for-tat approach. Our results are supported using event-based simulations.
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| 2. |
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| 3. |
- Carlsson, Niklas, et al.
(författare)
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Multicast Protocols for Scalable On-demand Download
- 2006
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Ingår i: Performance evaluation (Print). - : Elsevier Science Publishers B. V.. - 0166-5316 .- 1872-745X. ; 63:9/10, s. 864-891
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Tidskriftsartikel (refereegranskat)abstract
- Previous scalable protocols for downloading large, popular files from a single server include batching and cyclic multicast. With batching, clients wait to begin receiving a requested file until the beginning of its next multicast transmission, which collectively serves all of the waiting clients that have accumulated up to that point. With cyclic multicast, the file data is cyclically transmitted on a multicast channel. Clients can begin listening to the channel at an arbitrary point in time, and continue listening until all of the file data has been received.This paper first develops lower hounds on the average and maximum client delay for completely downloading a file, as functions of the average server bandwidth used to serve requests for that file, for systems with homogeneous clients. The results show that neither cyclic multicast nor batching consistently yields performance close to optimal. New hybrid download protocols are proposed that achieve within 15% of the optimal maximum delay and 20% of the optimal average delay in homogeneous systems.For heterogeneous systems in which clients have widely varying achievable reception rates, an additional design question concerns the use of high rate transmissions, which can decrease delay for clients that can receive at such rates, in addition to low rate transmissions that can be received by all clients. A new scalable download protocol for such systems is proposed, and its performance is compared to that of alternative protocols as well as to new lower bounds on maximum client delay. The new protocol achieves within 25% of the optimal maximum client delay in all scenarios considered.
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| 4. |
- Carlsson, Niklas, et al.
(författare)
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Non-Euclidian Geographic Routing in Wireless Networks
- 2007
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Ingår i: Ad hoc networks. - : Elsevier Science Publishers B. V.. - 1570-8705 .- 1570-8713. ; 5:7, s. 1173-1193
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Tidskriftsartikel (refereegranskat)abstract
- Greedy geographic routing is attractive for large multi-hop wireless networks because of its simple and distributed operation. However, it may easily result in dead ends or hotspots when routing in a network with obstacles (regions without sufficient connectivity to forward messages). In this paper we propose a distributed routing algorithm that combines greedy geographic routing with two non-Euclidean distance metrics, chosen so as to provide load balanced routing around obstacles and hotspots. The first metric, Local Shortest Path, is used to achieve high probability of progress, while the second metric, Weighted Distance Gain, is used to select a desirable node among those that provide progress. The proposed Load Balanced Local Shortest Path (LBLSP) routing algorithm provides loop freedom, guarantees delivery when a path exists, is able to efficiently route around obstacles, and provides good load balancing.
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| 5. |
- Carlsson, Niklas, 1977-, et al.
(författare)
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Optimized Dynamic Cache Instantiation and Accurate LRU Approximations under Time-varying Request Volume
- 2023
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Ingår i: IEEE Transactions on Cloud Computing. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2168-7161 .- 2372-0018. ; 11:1, s. 779-797
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Tidskriftsartikel (refereegranskat)abstract
- Content-delivery applications can achieve scalability and reduce wide-area network traffic using geographically distributed caches. However, each deployed cache has an associated cost, and under time-varying request rates (e.g., a daily cycle) there may be long periods when the request rate from the local region is not high enough to justify this cost. Cloud computing offers a solution to problems of this kind, by supporting dynamic allocation and release of resources. In this paper, we analyze the potential benefits from dynamically instantiating caches using resources from cloud service providers. We develop novel analytic caching models that accommodate time-varying request rates, transient behavior as a cache fills following instantiation, and selective cache insertion policies. Within the context of a simple cost model, we then develop bounds and compare policies with optimized parameter selections to obtain insights into key cost/performance tradeoffs. We find that dynamic cache instantiation can provide substantial cost reductions, that potential reductions strongly dependent on the object popularity skew, and that selective cache insertion can be even more beneficial in this context than with conventional edge caches. Finally, our contributions also include accurate and easy-to-compute approximations that are shown applicable to LRU caches under time-varying workloads.
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| 6. |
- Carlsson, Niklas, et al.
(författare)
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Optimized Periodic Broadcast of Non-linear Media
- 2008
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Ingår i: IEEE transactions on multimedia. - : IEEE. - 1520-9210 .- 1941-0077. ; 10:5, s. 871-884
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Tidskriftsartikel (refereegranskat)abstract
- Conventional video consists of a single sequence of video frames. During a client's playback period, frames are viewed sequentially from some specified starting point. The fixed frame ordering of conventional video enables efficient scheduled broadcast delivery, as well as efficient near on-demand delivery to large numbers of concurrent clients through use of periodic broadcast protocols in which the video file is segmented and transmitted on multiple channels. This paper considers the problem of devising scalable protocols for near on-demand delivery of “nonlinear” media files whose content may have a tree or graph, rather than linear, structure. Such media allows personalization of the media playback according to individual client preferences. We formulate a mathematical model for determination of the optimal periodic broadcast protocol for nonlinear media with piecewise-linear structures. Our objective function allows differing weights to be placed on the startup delays required for differing paths through the media. Studying a number of simple nonlinear structures we provide insight into the characteristics of the optimal solution. For cases in which the cost of solving the optimization model is prohibitive, we propose and evaluate an efficient approximation algorithm.
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| 7. |
- Carlsson, Niklas, et al.
(författare)
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Peer-assisted On-demand Streaming of Stored Media using BitTorrent-like Protocols
- 2007
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Ingår i: NETWORKING 2007. Ad Hoc and Sensor Networks, Wireless Networks, Next Generation Internet. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783540726050 - 3540726055 ; , s. 570-581
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Bokkapitel (refereegranskat)abstract
- With BitTorrent-like protocols a client may download a file from a large and changing set of peers, using connections of heterogeneous and time-varying bandwidths. This flexibility is achieved by breaking the file into many small pieces, each of which may be downloaded from different peers. This paper considers an approach to peer-assisted on-demand delivery of stored media that is based on the relatively simple and flexible BitTorrent-like approach, but which is able to achieve a form of “streaming” delivery, in the sense that playback can begin well before the entire media file is received. Achieving this goal requires: (1) a piece selection strategy that effectively mediates the conflict between the goals of high piece diversity, and the in-order requirements of media file playback, and (2) an on-line rule for deciding when playback can safely commence. We present and evaluate using simulation candidate protocols including both of these components.
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| 8. |
- Carlsson, Niklas, et al.
(författare)
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Peer-assisted On-demand Video Streaming with Selfish Peers
- 2009
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Ingår i: NETWORKING 2009. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783642013980 - 3642013988 ; , s. 586-599
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Bokkapitel (refereegranskat)abstract
- Systems delivering stored video content using a peer-assisted approach are able to serve large numbers of concurrent requests by utilizing upload bandwidth from their clients to assist in delivery. In systems providing download service, BitTorrent-like protocols may be used in which “tit-for-tat” policies provide incentive for clients to contribute upload bandwidth. For on-demand streaming delivery, however, in which clients begin playback well before download is complete, all prior proposed protocols rely on peers at later video play points uploading data to peers at earlier play points that do not have data to share in return. This paper considers the problem of devising peer-assisted protocols for streaming systems that, similar to download systems, provide effective “tit-for-tat” incentives for clients to contribute upload bandwidth. We propose policies that provide such incentives, while also providing short start-up delays, and delivery of (almost) all video frames by their respective playback deadlines.
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| 9. |
- Carlsson, Niklas, et al.
(författare)
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Server Selection in Large-scale Video-on-Demand Systems
- 2010
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Ingår i: ACM Transactions on Multimedia Computing, Communications, and Applications (TOMCCAP). - : ACM. - 1551-6857 .- 1551-6865. ; 6:1, s. 1:1-1:26
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Tidskriftsartikel (refereegranskat)abstract
- Video on demand, particularly with user-generated content, is emerging as one of the most bandwidth-intensive applications on the Internet. Owing to content control and other issues, some video-on-demand systems attempt to prevent downloading and peer-to-peer content delivery. Instead, such systems rely on server replication, such as via third-party content distribution networks, to support video streaming (or pseudostreaming) to their clients. A major issue with such systems is the cost of the required server resources. By synchronizing the video streams for clients that make closely spaced requests for the same video from the same server, server costs (such as for retrieval of the video data from disk) can be amortized over multiple requests. A fundamental trade-off then arises, however, with respect to server selection. Network delivery cost is minimized by selecting the nearest server, while server cost is minimized by directing closely spaced requests for the same video to a common server. This article compares classes of server selection policies within the context of a simple system model. We conclude that: (i) server selection using dynamic system state information (rather than only proximities and average loads) can yield large improvements in performance, (ii) deferring server selection for a request as late as possible (i.e., until just before streaming is to begin) can yield additional large improvements, and (iii) within the class of policies using dynamic state information and deferred selection, policies using only “local” (rather than global) request information are able to achieve most of the potential performance gains.
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