VideoonDemand - PowerPoint PPT Presentation

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VideoonDemand

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Time Warner is a big company so why would San Diego use Concurrent, Palm Desert ... Not all Time Warner locations use the same equipment configuration ... – PowerPoint PPT presentation

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Title: VideoonDemand


1
Video-on-Demand
  • Nick Caggiano
  • Walter Phillips

2
Video-on-Demand
  • What is Video-on-Demand?
  • Storage, transmission, and display of archived
    video files in a networked environment
  • Most popularly used to watch movies offered by
    cable provider
  • Many companies banking on prospect of bringing
    Video-on-Demand to educational institutions

3
Video-on-Demand
  • Components of Video-on-Demand system
  • Client
  • e.g. Set-top box
  • Buffers signals sent from server
  • More buffering leads to less expensive decoding
    hardware
  • Decoding can be done while displaying, as opposed
    to real-time decoding
  • Decodes (usually from MPEG-2) signals
  • Ensures synchronization of audio and video
  • Also acts as interface between user and server
  • Set-top box sends STOP, PAUSE, and REWIND
    signals upstream to the server

4
Video-on-Demand
  • Components of Video-on-Demand system
  • Network
  • Continuous and long-lived connections
  • unlike traditional bursty, short-lived computer
    connections
  • Require bandwidths in the range of 1.5Mbps to
    5Mbps.
  • Delay and jitter must be minimized to preserve
    presentation.
  • Packets which miss deadline must be dropped

5
Video-on-Demand
  • Components of Video-on-Demand
  • Server
  • Random access
  • Short seek time
  • Reliability
  • Availability
  • Scalability

6
Video-on-Demand
  • Server architectures
  • Centralized system
  • Server and archives stored in central location
  • Easy to manage
  • Doesn't scale well
  • Low throughput
  • May add local servers with video buffers
  • no archives at local servers, but can forward
    requests to central server
  • Matrix stored at local server, Police Academy
    12 kept in archive
  • Similar to Blockbuster New Releases section

7
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8
Video-on-Demand
  • Server architectures
  • Distributed system
  • Local processing servers with archives
  • Reduced delay/congestion
  • Scales well
  • Higher availability and throughput
  • More difficult to manage

9
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10
Video-on-Demand
  • Berkeley Distributed Video-on-Demand System
  • Composed of
  • Database
  • Stores metadata for each video
  • Keyword (for searches), genre, cast, runtime, etc
  • Where the video is currently stored/cached
  • Video Manager (VMGR)
  • Locates video and prepares for playback
  • Initiates billing to user account
  • Video File Server (VFS)
  • Stores video on magnetic disks
  • May be replicated for availability/reliability

11
Video-on-Demand
  • Berkeley Distributed Video-on-Demand System
  • Composed of
  • Archive Server (AS)
  • Stores video on inexpensive storage (magnetic
    disk, tape, etc)
  • May be replicated
  • User selects video from supplied UI
  • VMGR locates video on AS or VFS
  • May select best server due to locality, network
    load, etc
  • VMGR initiates and dynamically manages playback

12
Video-on-Demand
  • Video storage architectures
  • One movie per disk
  • Disk is random access good for rewind,
    fast-forward, etc
  • Disk failure only affects one movie (and
    therefore it's streams)
  • Can easily move to another replicated disk
  • Easy scheduling
  • Under-utilizes resources (disk bandwidth)
  • some movies more popular than others (Matrix v.
    Police Academy 12)
  • Creates bottlenecks
  • Can achieve an order of mag. in response time
    with replication

13
Video-on-Demand
  • Video storage architectures
  • Stripe video across array of disks
  • Each disk can service a small number of requests
    for different movies
  • Less popular videos don't waste disk bandwidth
  • Load balancing
  • Scheduling is much more difficult
  • New video must wait for disk scheduling window
  • Fast-forward or rewind must wait for scheduling
    window in next disk
  • Disk failure affects many movies, not just one
  • Best cost/stream of two architectures

14
Video-on-Demand
  • Viola Chinese University of Hong Kong
  • Video striping across servers
  • RAIS Redun. Array of Inexpensive Servers
  • Provides additional hardware to merge video
    blocks into a single data stream
  • Good scalability
  • Simply add another server
  • Good reliability
  • Same parity protection as RAID

15
Video-on-Demand
  • Quality of Service and Admission Control
  • Server must maintain some quality of service
    (QoS)
  • Prompt set-up time
  • User doesn't want to wait when he selects a movie
  • Synchronization/continuity of streams
  • Minimized delay/jitter
  • Fast repsonse to VCR functions
  • In order to do so, must maintain some admission
    control
  • Disk bandwidth, memory buffers, network
    bandwidth, etc
  • Must be determined ahead of time, to ensure QoS
    throughout session

16
Industry Perspective
17
Side Note Why even bother with VOD servers?
  • Personal Alternatives
  • Tivo -- Replay TV -- VCR
  • Centrally managed benefit
  • Interactive
  • Shopping and advertisement delivery. Usage
    profiling
  • Play, pause, fast forward and rewind
  • Billing
  • Monthly billing vs. usage billing (also
    Hybrid billing)
  • Convenient access to the latest/dynamic content
  • Higher value to the user
  • Marketing ploy
  • Competition with the satellite providers

18
Who wants Video On Demand?
  • Some e-Poll findings
  • Two-thirds of those surveyed have heard of VOD
    (mostly male and younger demographics)
  • People prefer the subscription payment method vs.
    pay per view method (both methods are utilized)
  • Scheduled premium movies (every half-hour) might
    be acceptable for most viewers (sporting events)
  • Results were from December 2002
  • Time Warner San Diego released VOD in September

19
Big Names
  • SeaChange
  • ITV 12024
  • Maynard, Maryland
  • http//www.seachangeinternational.com/Products/On_
    Demand_television/
  • Concurrent Computer Corporation
  • Media Hawk
  • Duluth, Georgia
  • http//www.ccur.com/vod/
  • nCube
  • n4x
  • Beaverton, Oregon
  • http//www.ncube.com/vod/

20
Common features
  • Off the shelf processors (i.e. Pentium class)
  • High speed I/O
  • SCSI 160MBps
  • FIBRE channel 260MBps
  • All use RAID5 or some proprietary variant
  • Why RAID5?
  • Obviously fault tolerance and efficient space
    usage (compared to mirroring)
  • RAID5 gives slow write performance but good read
    performance which is what we are concerned about

21
Why such diversity?
  • Time Warner is a big company so why would San
    Diego use Concurrent, Palm Desert use nCube, and
    Los Angeles use SeaChange?
  • Answer Competition amongst VOD vendors

22
Local Industry
  • Cox Communications
  • Distributed Infrastructure
  • Servers Used?
  • Employees were not very helpful
  • Time Warner
  • Centralized Infrastructure
  • Media Servers used Concurrent Computer
    Corporation Media Hawk 2000 (7 of them)
  • Covers a large geographic area North County to
    Coronado
  • Not all Time Warner locations use the same
    equipment configuration

23
Centralized vs. Distributed
  • Centralization is easy to manage
  • Simpler
  • Requires high bandwidth throughout the system
  • Distributed replication can be a problem
  • Might be more fault tolerant
  • Better if limited bandwidth between the core and
    the hubs

What about scalability?
24
Time Warner
  • Capacity
  • Designed for 6 of digital subscriber use
  • 16 On Demand Channels (3 more planned)
  • 800 hours (expanding to 3200 hours)
  • Each coax cable can carry 10 streams
  • Each node has 4 coax outputs
  • This means 40 movies can be delivered to a
    neighborhood
  • The 41st subscriber would get a denial of service
  • Remember, this is VOD only. Regular PPV and
    digital channels still work

25
From the server to your house
  • Media comes out of the server over 160 Mbps ASI
    (Asynchronous Serial Interface) cables
  • Converted to optical signal and transmitted via a
    hub to a node in the neighborhood
  • The node converts the signal back to an RF signal
    that can be transmitted over regular coax
  • Scientific Atlanta D9477 MQAM Modulator
  • QAM ? Quadrature Amplitude Modulation

26
Side Notes
  • 160 Mbit/second ASI
  • A movie requires 3.75 Mbits/seconds
  • 40 streams per ASI cable
  • Analog coax can carry 10 movies
  • Nodes are logically grouped in 4s
  • Can be reassigned dynamically as needed
  • Groupings are dictated by the number of set top
    boxes served

27
Managing the system
  • Sunfire 280R (http//www.sun.com/servers/entry/280
    r/)
  • Business Management System (BMS)
  • Responsible for things such as
  • Billing / Ordering
  • Scheduling
  • Content management

28
Conclusion
  • Its here now
  • Is it all that exciting?
  • Could it do more?
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