Peer-assisted VoD for set-top box based IP network Vaishnav Janardhan & Henning Schulzrinne Dept. of Computer Science Columbia University New York, NY August 31, 2007 P2P-TV 2007 @ SIGCOMM

Costs in providing video content DVRs Architecture Challenges Overview Costs in providing video content DVRs Architecture local DHTs and pre-fetching Challenges August 31, 2007 P2P-TV 2007 @ SIGCOMM

Economics of VoD Transit bandwidth $40/Mb/s/month ~ $0.125/GB http://existhosting.com/colo/bandwidth.html http://www.hackingnetflix.com/netflix/2005/07/postmaster_gene.html https://www.blockbuster.com/signup/rp/regPlan 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 P2P-TV 2007 @ SIGCOMM

Cost for providing content across provider boundaries possibly another step when crossing oceans within campus/AS (multiple L2s) same L2 switch (non-blocking) distance within home August 31, 2007 P2P-TV 2007 @ SIGCOMM

Example: FiOS TV architecture Fiber Serving Office Hub Super Headend Broadcast Video Voice, Data, IP TV Splitter Joseph Savage, Nov. 29, 2006 http://www.glgroup.com/glgi-presentations/iptv-11-29-06/Savage%20NYC%2011%2029%20seminar%20(3).ppt 2 national super headends 9 video hub offices 292 video serving offices J. Savage (Telecom ThinkTank), Nov. 2006 August 31, 2007 P2P-TV 2007 @ SIGCOMM

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 by Brian Whitton, Verizon Networks 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 August 31, 2007 P2P-TV 2007 @ SIGCOMM

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 P2P-TV 2007 @ SIGCOMM

(P2P) video variants Lots of variants - with very different requirements Mode start-up time VCR controls content near VoD minutes - hours (~ BlockBuster) full, including skip ahead movies, UGC VoD seconds full live streaming none TiVo-like (pause, rewind) news, sports August 31, 2007 P2P-TV 2007 @ SIGCOMM

VoD approaches Internet video ISP-provided VoD network WAN LAN content provider Internet video (YouTube, Netflix, ...) ISP-provided VoD end users Classical P2P (BitTorrent, ...) this approach servers August 31, 2007 P2P-TV 2007 @ SIGCOMM

VoD requirements short clips < 10’ (long tail) feature-length 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 http://www.the-numbers.com/charts/thisweek.php BlockBuster has 5,192 stores in the US NetFlix has 85,000 movie titles on DVD August 31, 2007 P2P-TV 2007 @ SIGCOMM

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 August 31, 2007 P2P-TV 2007 @ SIGCOMM

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 August 31, 2007 P2P-TV 2007 @ SIGCOMM

Example: Columbia University http://www.columbia.edu/acis/networks/bandwidth.html Our commodity routers are nyser111-gw-1 which connects to Broadwing(now Level(3) at 500 Mbps), nevis-gw-1 which connects to Qwest at 45Mbps, Vortex which connects to RCN (private peering) at 100 Mbps,nyser32-gw-1 which connects to NYSERNet at 200 Mbps and Ultralight(CERN) at 1 Gbps. ratio 1.5 - not much upstream capacity left August 31, 2007 P2P-TV 2007 @ SIGCOMM

Network architecture National Backbone Los Angeles Chicago New York Dallas Regional Data Center Server services: DNS DHCP August 31, 2007 P2P-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: 1/15th 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 August 31, 2007 P2P-TV 2007 @ SIGCOMM

Pre-fetching t (sec) 60 seconds 60 seconds 60 seconds Adjust to anchor point Adjust to anchor point t (sec) 5 sec 5 sec 5 sec Anchor point Seek point Anchor point Seek point Anchor point 60 seconds 60 seconds 60 seconds August 31, 2007 P2P-TV 2007 @ SIGCOMM

Pre-fetching Peer 1 [seed] Peer 2 [leech] Peer 4 Peer 3 Peer 5 Tracker Sliding Window module Pre-fetching module August 31, 2007 P2P-TV 2007 @ SIGCOMM

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? August 31, 2007 P2P-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 P2P-TV 2007 @ SIGCOMM