Video-on-Demand

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Video-on-Demand

• Nick Caggiano
• Walter Phillips

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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

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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

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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

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Video-on-Demand

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

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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

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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

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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

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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

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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

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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

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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

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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

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Industry Perspective
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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

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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

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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/

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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

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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

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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

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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?
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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

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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

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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

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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

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Conclusion

• Its here now

• Is it all that exciting?

• Could it do more?