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Incentives for Cooperation in Distributed Systems Beverly Yang Stanford University
Incentives for Cooperation in Distributed Systems
Beverly Yang
Stanford University
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Value from consolidating resources across autonomous nodes
Emerging applications
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Value from consolidating resources across autonomous nodes Web Services
Emerging applications
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Value from consolidating resources across autonomous nodes Web Services Grid Computing
Emerging applications
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Value from consolidating resources across autonomous nodes Web Services Grid Computing File-Sharing
Emerging applications
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a.k.a “peer-to-peer” Consolidating
resources across autonomous nodes
Additional features Massive replication,
scale, loose coupling Robust, self-
organizing, “autonomic” behavior
Emerging applications
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In research Focus on performance and functionality…
SIGCOMM 2003 (5/33) SOSP 2003 (3/21) SIGMOD 2004 (2/69)
…but overlook autonomy Who says nodes will contribute resources? Who says nodes will cooperate? Who says data/service is authentic?
How useful are techniques without incentives?
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Incentives
First-class problem How to get nodes to cooperate to achieve
functionality? What is effect on performance?
This talk: Our work on incentives inpeer-to-peer systems
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Outline
Introduction Context/Example RTR Protocol EigenTrust PPay
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Example
Alice wants to find a document-translation web service Web
ServicesAlice
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Example
1. Submit query
?
WebServices
Alice
Receive list ofproviders
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Example
1. Submit query
Receive list of providers
2. Select providers
WebServices
Alice
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Example
1. Submit query
Receive list of providers
2. Select providers
3. Invoke services
WebServices
Alice
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A second look
1. Submit query
Receive list of providers
?Web
ServicesAlice
Opportunistic approach: Participants route • Who says nodes will route? • What if you have competing nodes?
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A second look
1. Submit query
Receive list of providers
2. Select providers
WebServices
Alice
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A second look
1. Submit query
Receive list of providers
2. Select providers
3. Invoke services
WebServices
Alice
$$
$$
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Our contributions
1. Submit query
Receive list of providers
2. Select providers
3. Invoke services
RTR Protocol: Resource discovery incompetitive networks
EigenTrust
PPay: Efficient micropayments
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Outline
Introduction Context/Example RTR Protocol EigenTrust PPay
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Example of Non-Cooperation
“Document Translation”?
Provider 1Provider 2
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RTR Protocol
RTR: “Right To Respond” Queries as commodities Buy and sell RTRs
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Basic Exchange
2) ReqA B
3) RTR
RTR = {Q, TS, QueryString}Q
A B
Offer = {Reputation(Q), TS, QueryString, Price}
1) OfferA BQ ….
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Filters Specify query content
Exact service Categories Nothing
Sell query to neighbor only if query matches filter
sdfsdf gasq gsg sabw heaw
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Pricing
Simple pricing model Understand factors that
influence value Pinpoint parameters that
need to be estimated
∑∈
•+••=
+=
nbN
ffN
AA
AAA
NRTRENRTREIE
fpricepI
RESENE
),()),(|(
)(
)()()(
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Example of Non-Cooperation
“Document Translation”?
Provider 2Provider 1
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Functionality
0
0.5
1
1.5
2
2.5
3
3.5
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Query Score
Cooperative Competitive
No Forward RTR
Query Score
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Efficiency?
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Efficiency
0
20
40
60
80
100
120
140
160
# Messages
Cooperative Competitive
No Forward RTR
•Intelligent Routing• Content Clusters
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Many details
See paper [YKG 03] “Addressing Non-Cooperation in Competitive
Peer-to-Peer Systems” Workshop on Economics in P2P
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Outline
Introduction Context/Example RTR Protocol EigenTrust PPay
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Reputation
Not all providers are good
Evaluate using past experience
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Reputation
Not all providers are good
Evaluate using past experience
Problem: Sparse experience
−−
0
0
0
0
0
0
Node 0
Node 1
Node 2
Node 3
Node 4
Node 5
Node 6
Node 7
Node 8?
?
?
?
?
?
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Friends of Friends Ask for the opinions
of the people who you trust.
−−
0
0
0
0
0
0
Node 4
Node 1
−−
0
0
0
0
0
0
0
Node 2
Node 6
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The Math∑ ⋅=j
jkij cccik
'
Ask your friends j
What they think of node k.
And weight each friend’s opinion by how much you
trust him.
TC'ic ic=
.1
.5 0 0 0.2
0 .2 0 .3 0 .5 .1 0 0 0
.1
.3
.2
.3
.1
.1
.2 =
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Knowing All Peers Ask your friends:
t=CTci. Ask their friends:
t=(CT)2ci. Keep asking until the
cows come home: t=(CT)nci.
−−
0
0
0
0
0
0
−−
0
0
0
0
0
0
−−
0
0
0
0
0
0
−−
0
0
0
0
0
0
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EigenTrust Luckily, trust vector t, if computed in this
manner, converges to the same thing for every node!
Show how the whole network can cooperate to store and compute t
Show how to handle trust in computation See paper [KSG 02]
“The EigenTrust Algorithm for Reputation Management in P2P Systems”
WWW 2002
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Outline
Introduction Context/Example RTR Protocol EigenTrust PPay
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PPay Need money to enable
general resource sharing
Transactions Lightweight No long-term
vendor/buyer relationship
Micropayments
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$Broker Expenses Handle accounts Distribute and cash coins Security (e.g., double-spend
detection)
Load is O(n) in the number of transactions
Scalability and performance bottleneck
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Open Account
$U
Cert = {U, AddrU, PKU, Expiry}SKB
Cert
Name, Phone, AddressPayment Account (CC#)PKU
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Minting Coins
$U
C = {U, sn}SKB
C
“Owner”
PO
PO = {“Buy”, Qty}SKU
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Assigning Coin
U
AUV = {V, seq1, C}SKU
AUV
V
C $
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Reassigning Coin
U V X
RUVX = {X, AUV}SKV
RUVX
AUX
AUX = {X, seq2, C}SKU
AUX
RUVX
$
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Downtime Protocol
U V X
RUVX AUX
AUX = {X, seq2, C}SKB
RUVX
RUVX
UU
$
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Observations
Peer load higher, broker load lower Leverage resources at peers Broker involvement is linear in coins printed
Peer load scales “perfectly”
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PPay vs. Electronic Check
1 10 20
x 21
x 8
(BrokerLoad)
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Additional Details
Security Guarantees Performance Extensions See paper [YG 03]
“PPay: Efficient Micropayments for P2P Systems”
ACM CCS (Communication and Computer Security)
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Conclusion Incentives: first-order problem
RTR Protocol: Incentive-compatible resource discovery
EigenTrust: Distributed and secure reputation PPay: Efficient micropayment scheme
http://www-db.stanford.edu/peers(Google: stanford peers)
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Value from consolidating resources across autonomous nodes Web Services Grid Computing File-Sharing Ubiquitous Computing
Emerging applications
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Flow of Payment
A$$
PurchaseRTR
Q
$$Provide Service
M
N
$$
$$
Resell RTR
•A has service?•Q picks A?•Price of service?
•N buys RTR?•Value of RTR to N?
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Pricing Model
∑∈
•+••=
+=
nbN
ffN
AA
AAA
NRTRENRTREIE
fpricepI
RESENE
),()),(|(
)(
)()()(
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Efficient Routing Content filters (if specified) serve as
“routing hints”
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Communities (“clusters” in topology) will form around content
Content Clusters
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Characteristics
Vendors AND buyers
Massive resources at nodes
$PPay: Exploit characteristicswhile maintaining security
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“Good Enough” Security Micropayments are small
Utmost security not required
Must be lightweight
“Good Enough” (def): Fraud is detectable, traceable, and unprofitable
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Pico Payments
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