Download - sigcomm-p2ptv.ppt
August 31, 2007 P2P-TV 2007 @ SIGCOMM
Peer-assisted VoD for set-top box based IP network
Vaishnav Janardhan & Henning SchulzrinneDept. of Computer Science
Columbia UniversityNew York, NY
August 31, 2007 P2P-TV 2007 @ SIGCOMM
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• 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 contentcost
distance
possibly another step
when crossing oceans
within home
within campus/AS(multiple L2s)
same L2 switch(non-blocking)
across provider boundaries
August 31, 2007 P2P-TV 2007 @ SIGCOMM
Example: FiOS TV architecture
Fiber
ServingOffice
ServingOffice
HubOffice
SuperHeadend
Broadcast Video
Voice, Data, IP TV
Voice, Data, IP TV
SuperHeadend
ServingOffice
Splitter
Fiber
J. Savage (Telecom ThinkTank), Nov. 2006● 2 national super headends
● 9 video hub offices
● 292 video serving offices
August 31, 2007 P2P-TV 2007 @ SIGCOMM
Verizon’s FTTP Architecture
ONTOptical Network
Terminal
OLTOptical
Line Terminal
Optical Couplers (WDM)
Voice & Data Downstream 1490 nm
Upstream 1310 nm
Voice, Data & Video 1490 nm, 1310 nm, 1550
nm
1x32
Optical Splitte
r
EDFAErbium Doped Fiber Amplifier
Video 1550 nm
Bandwidth & ServicesUpstream Downstrea
mVoice, Data & Voice, Data &
VOD VOD at 622 Mbpsat 622 Mbps
Voice & Data Voice & Data at 155 to at 155 to
622 Mbps622 MbpsBroadcast VideoBroadcast Video
1310 nm 1490 nm 1550 nm
Analog TV Digital TV and HDTV54 MHz 864 MHz
CENTRAL OFFICE
CUSTOMER PREMISE
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 requirementsMode start-up time VCR controls contentnear VoD minutes - hours (~
BlockBuster)full, including skip ahead
movies, UGC
VoD seconds full movies, UGC
live streaming none TiVo-like (pause, rewind)
news, sports
August 31, 2007 P2P-TV 2007 @ SIGCOMM
VoD approaches
WAN LAN
content provider
Internet video(YouTube, Netflix, ...)
ISP-provided VoD
end users
Classical P2P (BitTorrent, ...) this approach
servers
network
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
•avoid Netflix queue•avoid stocking 20,000
DVDs
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
ratio 1.5 - not much upstream capacity
left
August 31, 2007 P2P-TV 2007 @ SIGCOMM
Regional Data Center
Server services:•DNS•DHCP
Chicago
Dallas
New YorkLos Angeles
National Backbone
Network architecture
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
5 sec 5 sec 5 sec
60 seconds 60 seconds 60 seconds
Anchorpoint
Anchorpoint
Anchorpoint
Seek pointSeek point
t (sec)
Adjust to anchor point Adjust to anchor point
Pre-fetching
August 31, 2007 P2P-TV 2007 @ SIGCOMM
Peer 1[seed]
Peer 2[leech]
Peer 4[leech]
Peer 3[leech]
Peer 5[leech]
Tracker
Sliding Window module Pre-fetching module
Pre-fetching
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