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

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
Overview
• Costs in providing video content
• DVRs
• Architecture
– local DHTs and pre-fetching
• Challenges
August 31, 2007
P2P-TV 2007 @ SIGCOMM
Economics of VoD
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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
cost
across provider boundaries
possibly
another step
when crossing
oceans
within campus/AS
(multiple L2s)
same L2 switch
(non-blocking)
distance
within home
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P2P-TV 2007 @ SIGCOMM
Example: FiOS TV architecture
Serving
Office
Super
Headend
Serving
Office
Hub
Office
Super
Headend
Serving
Office
Fiber
Splitter
Broadcast Video
Voice, Data, IP TV
Voice, Data, IP TV
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
CUSTOMER
PREMISE
Voice & Data
Downstream 1490 nm
OLT
Optical
Line
Terminal
Optical
Couplers
(WDM)
Voice, Data & Video
1490 nm, 1310 nm, 1550 nm
ONT
Optical
Splitter
Optical Network
Terminal
Upstream 1310 nm
Video
1550 nm
1x32
EDFA
CENTRAL
OFFICE
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
Brian Whitton, Verizon
August 31, 2007
Analog TV
P2P-TV 2007 @ SIGCOMM
864 MHz
Digital TV and HDTV
Properties of DVRs
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•
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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
movies, UGC
live streaming
none
TiVo-like
(pause,
rewind)
news, sports
August 31, 2007
P2P-TV 2007 @ SIGCOMM
VoD approaches
network
WAN
content provider
end users
servers
August 31, 2007
LAN
Internet video
(YouTube, Netflix, ...)
Classical P2P
(BitTorrent, ...)
ISP-provided VoD
this approach
P2P-TV 2007 @ SIGCOMM
VoD requirements
short clips < 10’
(long tail)
feature-length
• avoid Netflix queue
• avoid stocking 20,000
DVDs
• 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
August 31, 2007
P2P-TV 2007 @ SIGCOMM
Assumptions
•
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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
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DVRs have spare capacity
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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
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P2P-TV 2007 @ SIGCOMM
Network architecture
Los Angeles
New York
Chicago
National Backbone
Dallas
Regional
Data Center
Server services:
•DNS
•DHCP
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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
Adjust to anchor point
Adjust to anchor point
t (sec)
5 sec
Anchor
point
60 seconds
August 31, 2007
5 sec
Seek point
Anchor
point
60 seconds
P2P-TV 2007 @ SIGCOMM
5 sec
Seek point
Anchor
point
60 seconds
Pre-fetching
Peer 3
[leech]
Peer 1
[seed]
Peer 2
[leech]
Sliding Window module
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Peer 5
[leech]
Peer 4
[leech]
Pre-fetching module
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
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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