[奨励講演]
インセンティブによるピア協力型 CDNの運用実現性向上
NS-OCS-PN研究会
2009/6/25
森†,上山†,原田††,長谷川†,川原††NTT サービスインテグレーション基盤研究所†† NTT西日本研究開発センタ

Background The great popularity of large-scale video services on theInternet; e.g., YouTube, Youku
 Not only UGC (User-generated content) but professional
content is attracting traffic; e.g, Hulu, BBC iPlayer Dominant of Internet traffic is now shifting to videofrom P2P file sharing.
 Ratio of P2P traffic will decrease to 20% in 2013 (Cisco,May 2009)

 Managing ultimately huge video traffic is an importantand challenge taskExisting approach -- Peer-assisted CDN
 The idea:
 Make use of resources of participating peers
 100,000 users x 1GB / 10 % of CPU  10TB of storage capacity,
10,000 CPU power Distribute the workload on several peers/locations
 good scalability

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

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

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 to deliverA

BC
ISP3

ISP1

ISP2

transit costtransit 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 WGAB
ISP1COracle

ISP2

ISP3

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?

 Some apps have such function embedded implicitly,e.g., BBC iPlayer, however, will end-users be willing toaccept the implicit exploiting situation in general?

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 canbe used in the system Incentive can be fixed charge or calculated charge

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

Sell electricity backBusiness model
UserService, Ad.

Payment forcontent
ContentProvider

SellMachine
Resources
BandwidthIncentive(discounting)Service Agreement
Cheap, ISP-oriented service

ISPCan establish “Win-win-win” situation

Model of MP-CDN in an ISP
Original ServerISPdirect download
PM Server

peer-assisted
download

End-hosts

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

Analysis of the model Show the intrinsic trade-off between cacheperformance and cost for incentive
 increase incentive
 increase # 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, #offiles, storage capacity of each user, affect thecache performance.
 Goal: To obtain design implications

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

Acceptance of Incentive
 Logit model Given indentive of x, a node becomes cooperative withthe probability: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

Asymptotical property of systembehavior (N=100, m=1000, S=5)

Role of incentive in the system

Cost factor= Cost for incentive- θ Cost of traffic

The effect of # of nodes (N)Incentive x = 10

Other external factors

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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
are chopped into pieces and transferred simultaneously

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

 Design implications through the simulation analysis
 Discussed the potential issues that are essential to makethe MP-CDN deployable Studying more realistic model, e.g., heterogeneous
setting is for our future work