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Multimedia Information Systems

Jan 18, 2016

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Multimedia Information Systems. Shahram Ghandeharizadeh Computer Science Department University of Southern California. Reading. First 11 (until Section 3.2) pages of: - PowerPoint PPT Presentation

  • Multimedia Information SystemsShahram Ghandeharizadeh Computer Science DepartmentUniversity of Southern California

  • ReadingFirst 11 (until Section 3.2) pages of:

    S. Ghandeharizadeh and R. Muntz, Design and Implementation of Scalable Continuous Media Servers, Parallel Computing, Elsevier 1998.

  • MULTIMEDIAMultimedia now:

    Multimedia in a few years from now:

    Remaining:

  • Continuous Media: Audio & VideoDisplay of a clip as a function of time.Constant Bit RateVariable Bit RateTimeTimeBytesBytes

  • Continuous Media: Audio & VideoA clip has a fixed display time.Constant Bit RateVariable Bit RateTimeTimeBytesBytesClip display time

  • Continuous Media: Audio & VideoA clip has a fixed size.Constant Bit RateVariable Bit RateTimeTimeBytesBytesClip size

  • Continuous Media: Audio & VideoAverage bandwidth for continuous display is clip size divided by the clip display time.Constant Bit RateVariable Bit RateTimeTimeBytesBytesDisplay bandwidth requirementsBW = Line slope

  • Time and spaceOne may manipulate the bandwidth required to display a clip by prefetching a portion of the clip.Constant Bit Rate MediaTimeBytesStartup latencyPrefetch portion

  • Continuous display from magnetic diskTarget architectureMemoryCPUDisplaySystem Bus

  • Continuous displayOnce display is initiated, it should not starve for data. Otherwise, display will suffer from frequent disruptions and delays, termed hiccups.MemoryCPUDisplaySystem Bus

  • Continuous display: using memoryGiven the low latency between memory and display, stage the entire clip from disk onto memory and then initiate its display.MemoryCPUDisplaySystem Bus

  • Continuous display: using memoryLimitations: Forces the user to wait un-necessarily.Requires a large memory module in the order of Gigabytes for 2 hour movies.

    MemoryCPUDisplaySystem Bus

  • Continuous display: pipeliningPartition a clip X into n fixed size blocks: X1, X2, X3, , XnStage Xi in memory and initiate its display.Stage Xi+1 in memory prior to completion of the display of XiDisplay X1Display X2DisplayDiskX1X2Time Period

  • Pipelining: multiple displaysWith multiple displays, disk is multiplexed between multiple requests, resulting in disk seeks.Display XiDisplay Xi+1DisplayDiskXiXi+1Time PeriodWjSeek + Rotational delayZkWj+1Zk+1

  • How to manage disk seeks?Live with it:Assume the worst seek time in order to guarantee hiccup-free displayAssume average seek time if hiccups are acceptable.

    Use the elevator algorithm by delaying display of a block to the end of a time period, termed Group Sweeping Scheme (GSS):Display X1DisplayDiskX1Wj+1Time PeriodWjZkZk+1X2Zk+2

  • Impact of block sizeDisk service time with transfer-rate tfr and block size B is:Tdisk = Tseek + TRotLatency + (B / tfr)

    Number of simultaneous displays supported by a single disk is: N = Tp/Tdisk

    Simple pipelining requires (N+1)B memory, GSS requires 2NB.

    The observed transfer rate of a disk drive is a function of B and its physical characteristics: tfrobs = tfr ( B / [B + (Tseek + Tlatency) tfr] )

    Percentage of wasted disk bandwidth: 100 * (tfr tfrobs) / tfr

  • Impact of block sizeMPEG-1 clips with 1.5 Mbps bandwidth requirementsTarget disk characteristics:Seek: max = 17 msec, min = 2 msecRotational latency: Max = 8.3 msec, min = 4.17 msecDisk tfr = 68.6 MbpsThroughput and startup latency as a function of block size:

    Block sizeNMemory RequiredLatency Sec (2 Tp)Wasted disk BW (%)8 KB580 KB0.01288.916 KB10320 KB0.16777.732 KB161 MB0.33364.764 KB243 MB0.6747.5128 KB328 MB1.3330256 KB3718.5 MB2.6719.1512 KB4141 MB5.3310.31 MB4396 MB10.666

  • Modern disks are multi-zonedEach zone provides a different storage capacity (number of tracks and sectors per track) and transfer rate.Outermost zone is typically twice faster than the innermost zone.

  • Seagate ST31200W zones

  • Seagate ST31200WConsists of 2697 cylinders. One may model its seek characteristics as follows:

  • Seagate ST31200W

  • IBMs Logical TrackLet Zmin denote the zone with fewest track, TminA disk with Z zones is collapsed into a logical disk consisting of one zone with Tmin tracks. Size of each track is Z * TavgThe size of a block must be a multiple of the logical track sizeDisadvantage: Z+1 seeks to retrieve a logical trackLogical Track 1Logical Track 2Logical Track 3

  • HPs Track PairingLet Zmin denote the zone with fewest track, TminPair outermost track with the innermost one and continue inward.A disk with Z zones is collapsed into a logical disk consisting of one zone with (Z*Tmin)/2 tracks.The size of a block must be a multiple of a track pairDisadvantage: 2 seeks to retrieve a logical trackLogical Track 1Logical Track 2Logical Track 3Logical Track 8...

  • USCs region-based approachPartition the Z zones into R regions. A region may consist of 1 or more consecutive zones. The slowest participating zone dictates transfer rate of its assigned region.Assign blocks of a clip to regions in a round-robin manner.Display of clips requires visiting regions one at a time, multiplexing their bandwidth between N active requests. Both fix sized blocks and variable length blocks are supported.Region 1Region 2

  • Multi-zone disk drivesWith all 3 techniques, one may selectively drop zones: sacrifice storage for bandwidth!Example: USCs region-based approachRegion 1Region 2

  • FIXBPartition a clip into fix sized blocks and assign them to the regions in a round-robin manner.During a time period, retrieve blocks from one region at a time.Display starts when sufficient data is in main memory.

  • FIXBAmount of data produced during (1 maximum seek + TScan) is identical to the amount of data displayed during TScan.

  • FIXB

  • VARBVariable size blocks dictated by the transfer rate of each zone.Amount of data produced during one TMUX is identical to the amount of data displayed during TMUX.Limitation: complex to implement due to variable block sizes.

  • ComparisonFIXB and VARB waste space due to:Round-robin assignment of blocks to zonesDifferent zones offer different storage capacities.

  • Comparison

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