Peer-assisted VoD for set-top box based IP network

1. Peer-assisted VoD for set-top box based IP network Vaishnav Janardhan & Henning Schulzrinne Dept. of Computer Science Columbia University New York, NY P2P-TV 2007 @ SIGCOMM

2. Overview • Costs in providing video content • DVRs • Architecture • local DHTs and pre-fetching • Challenges P2P-TV 2007 @ SIGCOMM

3. Economics of VoD • Transit bandwidth $40/Mb/s/month ~ $0.125/GB • US colocation providers charge $0.30/GB to $1.75/GB • Netflix postage cost: $0.70 round-trip • Typical PPV charges: $4/movie (7 GB) P2P-TV 2007 @ SIGCOMM

4. Cost for providing content cost across provider boundaries possibly another step when crossing oceans within campus/AS (multiple L2s) same L2 switch (non-blocking) distance within home P2P-TV 2007 @ SIGCOMM

5. Broadcast Video Voice, Data, IP TV Voice, Data, IP TV Serving Office Fiber Fiber Super Headend Hub Office Serving Office Splitter Serving Office Super Headend Example: FiOS TV architecture • 2 national super headends • 9 video hub offices • 292 video serving offices J. Savage (Telecom ThinkTank), Nov. 2006 P2P-TV 2007 @ SIGCOMM

6. Verizon’s FTTP Architecture CUSTOMER PREMISE Voice & Data Downstream 1490 nm Voice, Data & Video 1490 nm, 1310 nm, 1550 nm OLT Optical Line Terminal ONT Optical Network Terminal Optical Couplers (WDM) Optical Splitter Upstream 1310 nm Video 1550 nm 1x32 CENTRAL OFFICE EDFA Erbium Doped Fiber Amplifier Bandwidth & Services Upstream Downstream 1310 nm 1490 nm 1550 nm Voice & Data at 155 to 622 Mbps Voice, Data & VOD at 622 Mbps Broadcast Video 54 MHz 864 MHz Analog TV Digital TV and HDTV Brian Whitton, Verizon P2P-TV 2007 @ SIGCOMM

7. Properties of DVRs • Storage of 80-250 GB (Tivo 3) • Probably on-line 24/7 already • Often, directly connected to network (“home gateway”) • May be owned by cable or DSL company P2P-TV 2007 @ SIGCOMM

8. (P2P) video variants • Lots of variants - with very different requirements P2P-TV 2007 @ SIGCOMM

9. VoD approaches network servers P2P-TV 2007 @ SIGCOMM

10. VoD requirements short clips < 10’ (long tail) • Example: Superbad grossed $33M during August 17 weekend (in US) • = roughly 3M viewers • = roughly 1% of US population •  if VoD, each neighborhood has likely one copy • 2 problems: • get initial copy to neighborhood • multicast, OTA • distribute in neighborhood • only viable for top 1000 content feature-length • avoid Netflix queue • avoid stocking 20,000 DVDs P2P-TV 2007 @ SIGCOMM

11. Assumptions • Every P2P scheme needs to address those • DRM is orthogonal • i.e., access to bits  access to content • may not work if DRM assumes individualized content • keying or fingerprinting • Upstream bandwidth is sufficient to deliver >= 1 stream • true for modern FTTH and FTTC networks • if not, P2P systems only work if ∑ upstream > ∑ consumption • if near-VoD, averaging interval may be whole day, rather than peak viewing period • but still need time to buffer content  delay and no feedback on FF • DVRs have spare capacity • likely true for PCs • may be optimistic for DVRs using LRU-style storage management • may be able to leverage content having been viewed by user • if owned by ISP, cheating problems disappears (no need for tit-for-tat) • DVRs can’t store all content • 85,000 DVDs  595 TB P2P-TV 2007 @ SIGCOMM

12. Notes on cost shifting • Servers vs. bandwidth • Fixed vs. incremental costs • for VoD providers, each (peak) stream incurs additional cost • for end systems, generally $0 • Bandwidth • providers - ~ peak usage • ISP - want to avoid paid (= non-local) traffic • users - may not care, but may be rate-limited or violate contract • no cost impact as long as downstream >> upstream bandwidth • e.g., Columbia severely limits student bandwidth • “Quotas are 350M/hr download and 180M/hr upload” (= 400 kb/s) • not much extra upstream bandwidth left P2P-TV 2007 @ SIGCOMM

13. Example: Columbia University ratio 1.5 - not much upstream capacity left P2P-TV 2007 @ SIGCOMM

14. Network architecture Los Angeles New York Chicago National Backbone Dallas Regional Data Center • Server services: • DNS • DHCP P2P-TV 2007 @ SIGCOMM

15. Architecture • Try to find content locally (AS) • using a local (provider-internal) DHT by identifier • identify peer with available capacity • cf. Aggarwal (CCR 7/07) to identify candidate nodes • If local, stream from peer • assume single server upstream bandwidth is sufficient • otherwise, piece together multiple servers • could use standard RTSP VCR controls • Use extra upstream capacity for pre-fetching content • first, retrieve key frames and anchor points for fast-forward • MPEG: 1/15th of frames • then, rest of video • handles bandwidth variability & releases server earlier for other uses • If not local, contact ISP (caching) video server • e.g., RTSP redirect P2P-TV 2007 @ SIGCOMM

16. Pre-fetching Adjust to anchor point Adjust to anchor point t (sec) 5 sec 5 sec 5 sec Seek point Anchor point Anchor point Seek point Anchor point 60 seconds 60 seconds 60 seconds P2P-TV 2007 @ SIGCOMM

17. Tracker Peer 3 [leech] Peer 5 [leech] Peer 1 [seed] Peer 2 [leech] Peer 4 [leech] Sliding Window module Pre-fetching module Pre-fetching P2P-TV 2007 @ SIGCOMM

18. Conclusion • Need careful analysis of cost trade-off • P2P may only be optimal if you ignore network costs • compare to classical proxy architectures • clearly identify assumptions -- more than one “P2P video” • Presented combination of different approaches • Locally popular content remains local • Mid-list content at end users • “Long tail” content at ISP • Back list at content provider • What is the minimal set of tools and building blocks? P2P-TV 2007 @ SIGCOMM

19. Admission control • DVR has small upload capacity • during busy time, may have > 50% DVR utilization • Content replication converges to popularity • But also hosts rare content only available once in network • Allow client displacement • new client indicates rare content (“last resort”) • DVR tries to find alternative source for existing user • and serves new client P2P-TV 2007 @ SIGCOMM