Jehan-Francois Paris

Efficient broadcasting protocols for video on demand

Broadcasting protocols can improve the efficiency of video on demand services by reducing the bandwidth required to transmit videos that are simultaneously watched by many viewers. We present two broadcasting protocols that achieve nearly the same low bandwidth as the best extant broadcasting protocol while guaranteeing a lower maximum access time. Our first protocol, cautious harmonic broadcasting, requires somewhat more bandwidth than our second protocol, quasi-harmonic broadcasting, but is also much simpler to implement.

A low bandwidth broadcasting protocol for video on demand

Broadcasting protocols can improve the efficiency of video on demand services by reducing the bandwidth required to transmit videos that are simultaneously watched by many viewers. We present a polyharmonic broadcasting protocol that requires less bandwidth than the best extant protocols to achieve the same low maximum waiting time. We also show how to modify the protocol to accommodate very long videos without increasing the buffering capacity of the set-top box.

Hybrid broadcasting protocol for video on demand

Broadcasting protocols can improve the efficiency of video on demand services by reducing the bandwidth required to transmit videos that are simultaneously watched by many viewers. It has been recently shown that broadcasting protocols using a very large number of very low bandwidth streams for each video required less total bandwidth than protocols using a few high-bandwidth streams shared by all videos. We present a hybrid broadcasting protocol that combines the advantages of these two classes of protocols. Our pagoda broadcasting protocol uses only a small number of high-bandwidth streams and requires only slightly more bandwidth than the best extant protocols to achieve a given maximum waiting time.

Design issues for a shingled write disk system

If the data density of magnetic disks is to continue its current 30–50% annual growth, new recording techniques are required. Among the actively considered options, shingled writing is currently the most attractive one because it is the easiest to implement at the device level. Shingled write recording trades the inconvenience of the inability to update in-place for a much higher data density by a using a different write technique that overlaps the currently written track with the previous track. Random reads are still possible on such devices, but writes must be done largely sequentially. In this paper, we discuss possible changes to disk-based data structures that the adoption of shingled writing will require. We first explore disk structures that are optimized for large sequential writes with little or no sequential writing, even of metadata structures, while providing acceptable read performance. We also examine the usefulness of non-volatile RAM and the benefits of object-based interfaces in the context of shingled disks. Finally, through the analysis of recent device traces, we demonstrate the surprising stability of written device blocks, with general purpose workloads showing that more than 93% of device blocks remain unchanged over a day, and that for more specialized workloads less than 0.5% of a shingled-write disks capacity would be needed to hold randomly updated blocks.

Peer-to-Peer Multimedia Streaming Using BitTorrent

We propose a peer-to-peer multimedia streaming solution based on the BitTorrent content-distribution protocol. Our proposal includes two modifications that allow it to deliver multimedia data on time. First, we replace the rarest-first chunk downloading policy of BitTorrent by a policy requiring peers to download first the chunks that they will watch in the near future. Second, we introduce a new randomized tit-for-tat peer selection policy that gives free tries to a larger number of peers and lets them participate sooner in the media distribution. Our simulations indicate that both changes are required to achieve a good streaming quality.

A simple low-bandwidth broadcasting protocol for video-on-demand

Broadcasting protocols can reduce the cost of video-on-demand services by using much less bandwidth to transmit videos that are simultaneously watched by many viewers. Unfortunately, the most efficient broadcasting protocols are also the most difficult to implement because they allocate a multitude of very low bandwidth streams to each video. We present a protocol that uses between three and seven high-bandwidth streams per video and never requires more than five percent more bandwidth than any other protocol to guarantee a given average waiting time.

A fixed-delay broadcasting protocol for video-on-demand

Broadcasting protocols reduce the cost of video-on-demand services by distributing more efficiently videos that are likely to be simultaneously watched by many viewers. Rather than answering individual customer requests, they broadcast the contents of each video according to a fixed schedule. We present a fixed-delay pagoda broadcasting protocol that requires all users to wait for a small fixed delay before watching the video they have selected. The protocol uses this delay to reduce the bandwidth required to transmit the first minutes of each video. As a result, our protocol provides the lowest waiting times of all protocols using segments of equal duration and channels of equal bandwidth. In addition, its performance is not very far from the theoretical minimum. We also show how to modify our protocol to restrict the set-top, box receiving bandwidth to two times the video consumption rate.

Providing High Reliability in a Minimum Redundancy Archival Storage System

Inter-file compression techniques store files as sets of references to data objects or chunks that can be shared among many files. While these techniques can achieve much better compression ratios than conventional intra-file compression methods such as Lempel-Ziv compression, they also reduce the reliability of the storage system because the loss of a few critical chunks can lead to the loss of many files. We show how to eliminate this problem by choosing for each chunk a replication level that is a function of the amount of data that would be lost if that chunk were lost. Experiments using actual archival data show that our technique can achieve significantly higher robustness than a conventional approach combining data mirroring and intra-file compression while requiring about half the storage space.

An interactive broadcasting protocol for video-on-demand

Broadcasting protocols reduce the cost of video-on-demand services by distributing more efficiently videos that are likely to be simultaneously watched by several viewers. Unfortunately, they do not allow the customer to pause, move fast forward or backward while watching a video. We present an interactive pagoda broadcasting protocol that provides these functions at a very reasonable cost. Our protocol is based on the pagoda broadcasting protocol and requires a set-top box buffer large enough to keep in storage all video data until the customer has watched the entire video. As a result, rewind and pause interactions do not require any server intervention. To minimize the bandwidth requirements of fast forward interactions, the server only transmits the segments that are not available on any of the server broadcasting channels. We evaluate the overhead of these fast forward operations through a probabilistic model. Our data indicate that the most costly fast forward operations are those starting at the beginning of the video and jumping to the beginning of the second half of the video while most fast-forward operation taking place during the second half of the video require little or no additional data.

Data Management and Layout for Shingled Magnetic Recording

Ultimately the performance and success of a shingled write disk (SWD) will be determined by more than the physical hardware realized, but will depend on the data layouts employed, the workloads experienced, and the architecture of the overall system, including the level of interfaces provided by the devices to higher levels of system software. While we discuss several alternative layouts for use with SWD, we also discuss the dramatic implications of observed workloads. Example data access traces demonstrate the surprising stability of written device blocks, with a small fraction requiring multiple updates (the problematic operation for a shingled-write device). Specifically, we discuss how general purpose workloads can show that more than 93% of device blocks can remain unchanged over a day, and that for more specialized workloads less than 0.5% of a shingled-write disks capacity would be needed to hold randomly updated blocks. We further demonstrate how different approaches to data layout can alternatively improve or reduce the performance of a shingled-write device in comparison to the performance of a traditional non-shingled device.