Peerassisted Vo D for settop box based IP
Peer-assisted Vo. D for set-top box based IP network Vaishnav Janardhan & Henning Schulzrinne Dept. of Computer Science Columbia University New York, NY August 31, 2007 P 2 P-TV 2007 @ SIGCOMM
Overview • Costs in providing video content • DVRs • Architecture – local DHTs and pre-fetching • Challenges August 31, 2007 P 2 P-TV 2007 @ SIGCOMM
Economics of Vo. D • • 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) August 31, 2007 P 2 P-TV 2007 @ SIGCOMM
Cost for providing content cost across provider boundaries possibly another step when crossing oceans within campus/AS (multiple L 2 s) same L 2 switch (non-blocking) distance within home August 31, 2007 P 2 P-TV 2007 @ SIGCOMM
Example: Fi. OS TV architecture Serving Office Super Headend Serving Office Hub Office Super Headend Serving Office er Fiber Splitter Broadcast Video Voice, Data, IP TV J. Savage (Telecom Think. Tank), Nov. 2006 ● 2 national super headends ● 9 video hub offices ● 292 video serving offices August 31, 2007 P 2 P-TV 2007 @ SIGCOMM
Verizon’s FTTP Architecture Voice & Data Downstream 1490 nm OLT Optical Line Terminal Upstream 1310 nm Optical Couplers (WDM) CUSTOMER PREMISE Voice, Data & Video 1490 nm, 1310 nm, 1550 nm ONT Optical Splitter Video 1550 nm Optical Network Terminal 1 x 32 EDFA CENTRAL OFFICE Erbium Doped Fiber Amplifier Upstream 1310 nm Bandwidth & Services Voice & Data at 155 to 622 Mbps Brian Whitton, Verizon August 31, 2007 Downstream 1490 nm Voice, Data & VOD at 622 Mbps 54 MHz Analog TV P 2 P-TV 2007 @ SIGCOMM 1550 nm Broadcast Video 864 MHz Digital TV and HDTV
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 August 31, 2007 P 2 P-TV 2007 @ SIGCOMM
(P 2 P) video variants • Lots of variants - with very different requirements Mode start-up time VCR controls content near Vo. D minutes - hours (~ Block. Buster) full, including skip ahead movies, UGC Vo. D seconds full movies, UGC live streaming none Ti. Vo-like (pause, rewind) news, sports August 31, 2007 P 2 P-TV 2007 @ SIGCOMM
Vo. D approaches network WAN content provider end users servers August 31, 2007 LAN Internet video (You. Tube, Netflix, . . . ) Classical P 2 P (Bit. Torrent, . . . ) ISP-provided Vo. D this approach P 2 P-TV 2007 @ SIGCOMM
Vo. D requirements short clips < 10’ (long tail) feature-length • avoid Netflix queue • avoid stocking 20, 000 DVDs • Example: Superbad grossed $33 M during August 17 weekend (in US) • = roughly 3 M viewers • = roughly 1% of US population • if Vo. D, each neighborhood has likely one copy • 2 problems: – get initial copy to neighborhood • multicast, OTA – distribute in neighborhood • only viable for top 1000 content August 31, 2007 P 2 P-TV 2007 @ SIGCOMM
Assumptions • • Every P 2 P 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, P 2 P systems only work if ∑ upstream > ∑ consumption • if near-Vo. D, 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 August 31, 2007 P 2 P-TV 2007 @ SIGCOMM
Notes on cost shifting • Servers vs. bandwidth • Fixed vs. incremental costs – for Vo. D 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 350 M/hr download and 180 M/hr upload” (= 400 kb/s) • not much extra upstream bandwidth left August 31, 2007 P 2 P-TV 2007 @ SIGCOMM
Example: Columbia University ratio 1. 5 - not much upstream capacity left August 31, 2007 P 2 P-TV 2007 @ SIGCOMM
Network architecture Los Angeles New York Chicago National Backbone Dallas Regional Data Center Server services: • DNS • DHCP August 31, 2007 P 2 P-TV 2007 @ SIGCOMM
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: 1/15 th 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 August 31, 2007 P 2 P-TV 2007 @ SIGCOMM
Pre-fetching Adjust to anchor point t (sec) 5 sec Anchor point 60 seconds August 31, 2007 5 sec Seek point Anchor point 60 seconds P 2 P-TV 2007 @ SIGCOMM 5 sec Seek point Anchor point 60 seconds
Pre-fetching Tra cke Peer 1 [seed] r Peer 3 [leech] Peer 2 [leech] Sliding Window module August 31, 2007 Peer 5 [leech] Peer 4 [leech] Pre-fetching module P 2 P-TV 2007 @ SIGCOMM
Conclusion • Need careful analysis of cost trade-off – P 2 P may only be optimal if you ignore network costs – compare to classical proxy architectures – clearly identify assumptions -- more than one “P 2 P 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? August 31, 2007 P 2 P-TV 2007 @ SIGCOMM
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 August 31, 2007 P 2 P-TV 2007 @ SIGCOMM
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