Video-on-Demand

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

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

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) • All use RAID5 or some proprietary variant • Why RAID5? • High speed I/O • SCSI ~160MBps • FIBRE channel ~260MBps • 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 • 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

23. 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 Centralized vs. Distributed What about scalability?

24. Time Warner • Designed for 6% of digital subscriber use • Capacity • 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 4’s • 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/280r/) • 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?