Transcript Video-on-Demand Nick Caggiano Walter Phillips

Video-on-Demand
Nick Caggiano
Walter Phillips
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
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 realtime 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
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
Video-on-Demand
• Components of Video-on-Demand
– Server
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Random access
Short seek time
Reliability
Availability
Scalability
Video-on-Demand
• Server architectures
– Centralized system
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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
Video-on-Demand
• Server architectures
– Distributed system
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Local processing servers with archives
Reduced delay/congestion
Scales well
Higher availability and throughput
More difficult to manage
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
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
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
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
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
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
Industry Perspective
Side Note: Why even bother with
VOD servers?
• Personal Alternatives
– Tivo
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Replay TV
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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
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
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/
Common features
• Off the shelf processors (i.e. Pentium class)
• High speed I/O
– SCSI
– FIBRE channel
~160MBps
~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
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
Local Industry
• 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
• Cox Communications
– Distributed Infrastructure
– Servers Used?
– Employees were not very helpful
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?
• Capacity
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Time Warner
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
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
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Scientific Atlanta D9477 MQAM Modulator
QAM  Quadrature Amplitude Modulation
Side Notes
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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 4’s
• Can be reassigned dynamically as needed
• Groupings are dictated by the number of set top
boxes served
Managing the system
• Sunfire 280R (http://www.sun.com/servers/entry/280r/)
• Business Management System (BMS)
• Responsible for things such as:
– Billing / Ordering
– Scheduling
– Content management
Conclusion
• Its here now
• Is it all that exciting?
• Could it do more?