1	Improving Deployability of Peer-assisted
CDN Platform with Incentive	 
GLOBECOM 2009
Dec 2, 2009
Tatsuya Mori, Noriaki Kamiyama, Shigeaki Harada,Haruhisa Hasegawa, and Ryoichi Kawahara
NTT Service Integration Laboratories	 2	Background	  The great popularity of large-scale video services on theInternet; e.g., YouTube

Cisco Systems, Visual Networking Index
Forecast and Methodology, 2008-2013

 Managing ultimately huge video traffic is an important andchallenge task

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Existing approach -- Peer-assisted CDN	  Key idea:
 Make use of resources of participating peers
 100,000 users x 10GB / 10 % of CPU  100TB of storage capacity,
10,000 CPU power Distribute the workload on several peers/locations
 good scalability and robustness

 Effective to the large-scale video sharing services; YouTube [imc07]
 MSN Video [sigcomm06]

 Already deployed in the real world Joost, BBC iPlayer, P2P-next

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Drawback of Peer-assisted CDN	  Random peer selection
 It does not consider underlying network topology
 Traffic can be unnecessarily scattered Increase cross-domain traffic, which in general requires cost todeliverA	 B	 C	 ISP3	ISP1	ISP2	

transit cost	transit cost	Existing approach– Managed Peer-assisted CDN (MP-CDN)	 
 The idea:
 Make use of “Oracle” to avoid inefficient peer selection
 “optimize” traffic based on the knowledge collected by Oracle Extensively studied in the past year
 P4P: SIGCOMM 2008
 Taming the Torrent: SIGCOMM 2008
 IETF ALTO WG

A	 B	 
ISP1	C	 Oracle	

ISP2	

ISP3	5	

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Open issue of MP-CDN	  MP-CDN works gracefully in theory or in a controlledenvironment
 There have been no general studies that address how peers
can be incentivized in MP-CDN

 Question:
 What is the motivation for peer nodes to participate in thesystem and contribute their resources?

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Our solution: a new business model	  ISP manages Oracle (PM server) and provides users with
explicit incentive if they are cooperative to the system Incentive can be virtual currency or some “points” that can beused in the system Incentive can be fixed charge or calculated charge

 ISP provides CDN platform and Content provider and endusers use it Principle: End-users would prefer candy (incentive) rather
than whip (bandwidth cap) 	 

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Key Idea of our business model	 

Sell electricity back	

Why not using this model in the network context?	

Model of MP-CDN in an ISP	 
Original Server

ISP	
direct download
PM Server

peer-assisted
download

End-hosts

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10	Analysis of the model	  Show the intrinsic trade-off between cacheperformance and cost for incentive
 Increasing incentive
 increase in the # of participating users
 improve the cache performance  save the traffic cost
BUT…
 increase the cost for incentive as well

 Study how external factors such as #of users, #of files,
and storage capacity of each user, affect the cacheperformance.
 Goal: To obtain design implications

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Simulation setup	  Nodes are identical Content requests arrive with the Poisson process Nodes keep content files with LFU cache algorithm
 The nodes and content files are fixed (no churn) There are no resource constraints on bandwidth and CPU ofnodes	 12	

File access pattern	  Stretched Exponential Distribution (Discrete Weibull) Realistic model of modern web workload	 

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Acceptance of Incentive	  Logit model Given incentive of x, a node becomes cooperative with theprobability:	 14	

Simulation Setup cont’	  10 independent experiments for each parameter setting N: # of end-hosts m: # of content files
 S: cache capacity of each node (# of files)
 Simulation time T = 10000
 Corresponds to a month in real time	 15	

Role of incentive in the system	 
N=100, m=1000
T=10000	

Cost factor= Cost for incentive- θ Cost of saved traffic	

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The effect of # of nodes (N)	 

Incentive x = 10 	

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Other external factors	 

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Design implications	  There exists optimal amount of incentive (should bedesigned carefully) It is better to keep # of nodes in a P2P NW small
 It is better to keep # of distinct content files small User storage capacity can be fairly small

19	Conclusion and future work	  A new business model – selling bandwidth back to ISP Solve the incentive problem

 Design implications through the simulation analysis
 Studying more realistic model, e.g., heterogeneous setting isfor our future work

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Roles of PM (peer mgmt) server	  Acts as “virtual cache server”
 Keeps the list of peer nodes and their files Storage space is given by peer nodes
 Acts as “Oracle”
 Select peers according to the underlay network
information
 Provides “AAA” functions
 Accounting, authentication, and authorization	 

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Business model	 	User	 Service, Ad.	

Payment forcontent		Content
Provider	 Sell
MachineResources
Bandwidth
Incentive(discounting)	

Service Agreement
Cheap, ISP-oriented service		ISP	 Can establish “Win-win-win” situation	

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Other issues:	  Scalability
 Avoid making PM server be a single point of failure Underlying network structure Upload bandwidth bottleneck (CATV) Privacy Introduce some randomness in the peer selection More efficient content delivery
 Introduce the pipelining model like BitTorrent, i.e., files arechopped into pieces and transferred simultaneously