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Applications of Game Theory Part II(b)
John C.S. LuiComputer Science & Eng. Dept
The Chinese University of Hong Kong
On the interaction between Overlay Routing and Underlay
Routing
Y. Liu, H. Zhang, W. Gong, D. Towsley
INFOCOM 2005
First course
Motivation: Interactions Between Application Level Network and Physical
Network physical network control
– routing, congestion control,…
Control Control
Control
Result?– interactions?– controllers mismatch?
add an overlay
and another……
Outline
Problem Formulation Simulation Study Game-theoretic Study Conclusions
Routing on physical network level Inter-domain: BGP, etc. Intra-domain: OSPF, MPLS, etc.
– determine routes for all source-destination traffic demand pairs
– minimize network-wide delay, cost, etc.
Routing in Underlay Network
traffic demand pair: A->Btraffic demand pair: A->Ctraffic demand pair: C->B
A
C
E
B
D
An overlay network choose routes at application level to minimize its own delay or cost
Routing in Overlay Network
A
C
E
B
D
A
C
B
Overlay demand: A->B
logical routes: A->C->B and A->B
demand pair: A->C
Overlay gains
advantagebetter path: delay, loss, throughput, etc
is selfishpotential performance degradation to other non-overlay traffic
demand pair: C->Bdemand pair: A->B
Considering overlay and underlay
together ?
How do they interact with each other? How does selfish behavior of overlay routing
– affect overall network performance?– affect non-overlay traffic performance?– affect its own performance?
Interactions Between Overlay Routing and Underlay
Routing
Overlay Routing OptimizerTo minimize overlay cost
Underlay Routing OptimizerTo minimize overall network cost
flow allocation on logical links: “X”traffic demand for underlay
flow allocation on physical routes: “Y”
non-overlaytraffic demand
overlaytraffic demand
Iterative Dynamic Process equilibrium: existence? uniqueness? dynamic process: convergence? oscillations? performance of overlay and underlay traffic?
Approach by authors
Focusing interaction in a single AS Considering two routing models for overlay
and one routing model for underlay Simulating the interaction dynamic
process Studying this process in a Game-theoretic
framework
Routing Models Overlay routing model
– Selfish source routing Individual user controls infinitesimal amount of
traffic, to minimize its own delay
– Optimal overlay routing A central entity minimizes the total delay of all
overlay traffic demands
Underlay routing model Optimal underlay routing
A central entity minimizes the total delay of all network traffic, e.g. Traffic Engineering MPLS
Node without overlay
LinkNode with overlay
47
9
10
8
6
2
13
5
1
12
14
11
3
Simulation Study: Optimal Overlay and Optimal
Underlay14 node tier-1 POP network (Medina et.al. 2002)bimodal normal model of traffic demand3 overlay nodes
Simulation Study ( case 1: 8% overlay traffic) Optimal Overlay and Optimal Underlay
after underlay takes turnafter overlay takes turn
Iterative process Underlay takes turn at step 1, 3, 5, …
Overlay takes turn at step 2, 4, 6, … ,...5,4,3,2,1
%100)1Delay(
)1Delay(-)Delay(
=k
k
iteration
average delay of overlay traffic
perc
enta
ge
%
overlay performance improvement
iteration
average delay of all traffic
perc
enta
ge
%
underlay performance degradation
iteration
perc
enta
ge
%
overlay performance degradation
average delay of overlay traffic
after underlay takes turnafter overlay takes turn
Iterative process Underlay takes turn at step 1, 3, 5, … Overlay takes turn at step 2, 4, 6, … ,...5,4,3,2,1
%100)1Delay(
)1Delay(-)Delay(
=k
k
iteration
perc
enta
ge
%
underlay performance degradation
average delay of all traffic
Simulation Study (case 2: 10% overlay traffic) Optimal Overlay and Optimal Underlay
Game-theoretic Study Two-player non-zero sum game
overlay Underlay
X: strategy of “overlay” traffic allocation on logical linksY: strategy of “underlay” traffic allocation on physical links
: Cost of “overlay”
: Cost of “underlay”
: Constraints of “overlay”
: Constraints of “underlay”
Game-theoretic Study
• Best-reply dynamics
• Nash Equilibrium
Optimal Underlay Routing v.s. Optimal Overlay Routing
Overlay – One central entity calculates routes for all
overlay demands, given current underlay routing
– Assumption: it knows underlay topology and background traffic
A B
C
X(k)
Denote overlay’s routing decision with a single variable X(k): overlay’s flow on path ACB after round k
1-X(k)
There exists unique Nash equilibrium x*, x* globally stable: x(k) x*, from any initial x(1)
Best-reply Dynamics
iteration k iteration k
Overlay Routing Evolution Overlay Delay Evolution
x(k)
x*x(k)<x(k+1)<x*
dela
y
Underlay’s turn
Overlay’s turn
When x(1)=0, overlay performance improves
Round k Round k
x(k)
x*
Underlay’s turn
Overlay’s turn
BAD INTE
RACTION!
x(k)>x(k+1)>x*
x(k)<x(k+1)<x*
Overlay Delay Evolution
dela
y
Overlay Routing Evolution
Best-reply Dynamics
There exists unique Nash equilibrium x*, x* globally stable: x(k) x*, from any initial x(1)
When x(1)=0.5, overlay performance degrades
Conclusions & Open Issues
Selfish overlay routing can degrade performance of network as a whole
Interactions between blind optimizations at two levels may lead to lose-lose situation
Future work:– larger topology: analysis/experimentation– overlay routing and inter-domain routing– interactions between multiple overlays (****)– implications on design overlay routing– regulation between overlay and underlay (****)
On the Interaction of Multiple Overlay Routings
Performance 2005
Joe W.J. Jiang, D.M. Chiu, John C.S. Lui
Second course
Questions• These overlays tend to fully utilize available
resource.• So, is there any anarchy?• How do overlay networks co-exist with each
other?• What is the implication of interactions?• How to regulate selfish overlay networks via
mechanism design?• Can ISPs take advantage of this?
Outline
• Motivation• Mathematical Modeling• Overlay Routing Game• Implications of Interaction• Pricing• Conclusion
Motivation
• Overlays provide a feasibility for users to control their own routing.
• Routing, possible multi-path, becomes an optimization problem.
• Interaction occurs (due to same underlay)• Interaction between one overlay and
underlay traffic engineering, Zhang et al, Infocom’05.
• Interaction between co-existing overlays ?
Adaptive routing controls on multiple layers (overlays, underlay TE --traffic engineering) over one common physical network
Simultaneous feedback controls over one system
Stability ?
Performance ?
Performance Characteristics
• Objective: minimize end-to-end delay (e.g., RON)• Delay of a physical link e:
• Performance Characteristics (Underlay)
de(le)
le – aggregate traffic traversing link e
Average delay ( f : flow)
( )( )∑∈
⋅tsf
fdf,
Performance Characteristics
• Objective: minimize end-to-end delay• Delay of a physical link e:
• Performance Characteristics (Underlay)
de(le)
le – aggregate traffic traversing link e
Average delay (multipath routing)
( )( )( )
∑ ∑∈ ∈
⋅tsf fPr
rr fdf,
Performance Characteristics
• Objective: minimize end-to-end delay• Delay of a physical link e:
• Performance Characteristics (Underlay)
de(le)
le – aggregate traffic traversing link e
Average delay (multipath routing)
( )∑ ⋅e
eee ldl
System Objectives
• Network Operators– Min average delay in the whole underlay network
• Overlay Users– Min average delay experienced by the overlay
( )∑ ⋅e
eee ldl min
( )∑ ⋅e
eeoverlaye ldl min
How do Overlays Interact?
• Overlapping physical links.• Performance dependent on each
other.• Selfish routing optimization.• Overlays are transparent to each
other.• Lack of information exchange
between overlays.
Contribution
• What is the form of interaction?• Is there routing instability (oscillation),
or there is an equilibrium ?• Is the routing equilibrium efficient?• What is the price of anarchy?• Fairness issues• Mechanism design: can we lead the
selfish behaviors to an efficient equilibrium?
Mathematical Modeling
• Overlay routing: An optimization problem Decision variable: routing policy
( )Tfssss yyyy ),()2,()1,()( ,,, L=
( )),(),(2
),(1
),( ,,, fsr
fsfsfs yyyy L=
s: overlay f: flow r: path
Mathematical Modeling
• Overlay routing: An optimization problem Objective: average weighted delay (matrix form)
⎥⎦
⎤⎢⎣
⎡⎟⎠
⎞⎜⎝
⎛= ∑
i
iiTsTss yADAydelay )()()()()(
( )
( )∑ ∑
∈
⋅=f fRr
rfs
rs delayydelay ,)(
Routing Matrix Delay Function (vector form)
Overlay Routing Optimization
[ ]
0 ,
, s.t.
Minimize
,,,,; OVERLAY
)(
),(
)()()()()(
)()()(
≥≤
=∈∀
⎥⎦
⎤⎢⎣
⎡⎟⎠
⎞⎜⎝
⎛=
∑
∑
∈
−
s
fRr
fsrs
i
iiTsTss
sss
yCAy
xyFf
yADAydelay
yxCHAy
f
Convex programming
Demand constraint
(fixed transmission demand)
Capacity Constraint
Non-negative Flow Constraint
Algorithmic Solution
• Unique optimizer – Convex programming– feasible region: convex– delay function: continuous, non-decreasing,
strictly convex
• Solution– Apply any convex programming techniques.– Marginal cost network flow (probabilistic routing
ICNP’04).– This is solved in an independent, and
distributed fashion by each overlay.
But will independent optimization leads to system instability (route flop)?
Overlay Routing Game
• Nash Routing Game– Player -- N
all overlays
– Strategy -- s
feasible routing policy: feasible region of OVERLAY(s)
– Preference relation -- ≥s
low delay: player’s utility function is -delay(s)
Strategic Game: Goverlay<N, (s), (≥s)>
Illustration of Interaction
Routing Underlay
Overlay 1
Overlay 2
Overlay n
…
Routing decision on logical paths in overlay 1
Routing decision on logical paths in overlay 2
Routing decision on logical paths in overlay n
Aggregate overlay traffic
… Underlay (non-overlay) traffic
Aggregate traffic on physical links
Overlay probing
Delay of logical paths in overlay 1
Delay of logical paths in overlay 2
Delay of logical paths in overlay n
∑
Existence of Nash Equilibrium
• Definition – Nash equilibrium point (NE)
A feasible strategy profile y=(y(1),…, y(s),…, y(n))T
is a Nash equilibrium in the overlay routing game if for every overlay s∈N,
delay(s)(y(1),…y(s),…y(n)) ≤ delay(s)(y(1),…y’(s),…y(n))
for any other feasible strategy profile y’(s) .
Existence of Nash Equilibrium
• Theorem
In the overlay routing game, there exists a Nash equilibrium if the delay function
delay(s)(y(s) ; y(-s))
is continuous, non-decreasing and convex.
Good News: NO ROUTE FLOP !!!
Fluid Simulation
Six overlays
One flow per overlay
Congested network
Asynchronous routing update
Overlay performance
Transient period
Quick convergence
Overlay routing decisions
The Price of Anarchy
0 ∞1 2 3 4 5 6 7 8 ... ...
Global Performance (average delay for all flows)
• GOR: Global Optimal Routing
• NOR: Nash equilibrium for Overlay Routing Game
• NSR: Nash equilibrium for Selfish Routing
GOR
NOR
NSR
Efficiency Loss ?
Selfish Routing
• (User) selfish routing: a single packet’s selfishness• Every single packet chooses to route via a shortest
(delay) path.• A flow is at Nash equilibrium if no packet can
improve its delay by changing its route.
)~
()(
~
if ],,0[ ,
21
1 2
1
21
fdfd
otherwisef
PPiff
PPiff
ffPP
PP
P
P
P
PP
≤
⎪⎩
⎪⎨
⎧=+=−
=∈≠ δδ
δ
Selfish Routing
• Also a Nash equilibrium of a mixed strategic game– Player: flow { f }
– Strategy: p Pf
– Preference: low delay
• System Optimization Problem
( )( )
0 , , , s.t.
min
,,,; SELFISH
0
≥=≤=
∑∫yAyLCAyxHy
dttd
xCHAy
e
l
e
e
Performance Comparison
Overlay One
Overlay Two
Average Delay
Centralized Global Optimal Routing
2.50 2.38 2.44
NE of Overlay Optimal Routing
2.46 2.53 2.50
NE of Selfish Routing 2.63 2.75 2.69
Inspiration
• Is the equilibrium point efficient (at least Pareto optimal) ?
• Fairness issues of resource competition between overlays.
Example Network
3
21
5
src1 src2
sink1 sink2
4
6
Overlay 2
Overlay 1
3
21
5
src1 src2
sink1 sink2
4
6
1 unit
1 unit
y11-y1 y2 1-y2
Sub-Optimality
3
21
5
src1 src2
sink1 sink2
4
6
Overlay 2
Overlay 1 physical link delay function
de(le)
1-5 1+l
3-4 l
2-6 2.5+l
Routing
(y1, y2)
Average Delay(overlay1, overlay2
)
NE (0.5, 1.0) (1.5, 1.5)
Pareto Curve
(0.4, 0.9) (1.4, 1.4)
y1 y2
Non Pareto-
optimal !
Fairness Paradox
3
21
5
src1 src2
sink1 sink2
4
6
Overlay 2
Overlay 1physical link delay function
de(le)
1-5 a+l
3-4 bl
2-6 c+ly1 y2
a, b, c, are non-negative parameters
Everything is symmetric except two private links – a & c
Fairness Paradox
3
21
5
src1 src2
sink1 sink2
4
6
Overlay 2
Overlay 1physical link delay function
de(le)
1-5 a+l
3-4 bl
2-6 c+ly1 y2
⎪⎪⎪
⎩
⎪⎪⎪
⎨
⎧
⎟⎠
⎞⎜⎝
⎛+⎟⎠
⎞⎜⎝
⎛=
=
−⎟⎠
⎞⎜⎝
⎛+⎟⎠
⎞⎜⎝
⎛=
−
−
1
1
2
3
2
3
1
,12
3
22
3
αα
αα
α
α
c
b
a
a < c
Overlay 1 has a better “private” link !
Fairness Paradox
3
21
5
src1 src2
sink1 sink2
4
6
Overlay 2
Overlay 1
y1 y2
⎪⎪
⎩
⎪⎪
⎨
⎧
⎟⎠
⎞⎜⎝
⎛=
−⎟⎠
⎞⎜⎝
⎛+⎟⎠
⎞⎜⎝
⎛=−
2
3
4
1
2
3
42
3
2
1
1
delay
delay
a < c delay1 < delay2
∞=→<∞→2
1 delay
delayca
Unbounded
Unfairness
War of Resource Competition
1 unit 1 unit
y1
1-y1
y2
1-y2
poil(y1+y2)
pusa(1-y1) pchn(1-y2)pusa< pchn
USA
China
Min Costusa(y1 ; y2) =
y1poil(y1+y2)+(1-y1)pusa(1-y1)
War of Resource Competition
1 unit 1 unit
y1
1-y1
y2
1-y2
poil(y1+y2)
pusa(1-y1) pchn(1-y2)pusa< pchn
USA
China
Min Costchn(y2 ; y1) =
y2poil(y1+y2)+(1-y2)pchn(1-y2)
War of Resource Competition
1 unit 1 unit
poil(y1+y2)
pusa(1-y1) pchn(1-y2)
pusa< pchn
Costusa > Costchn
USA
China
Pricing (opportunity for ISP)
Inefficient Nash equilibrium
Desired equilibrium
Mechanism Design
Performance degradation (sub-optimal)
Fairness paradox
Global optimality
Improve fairness
payment new
Nash equilibrium
Pricing I – Improve Delay
• Objective: to achieve global optimality
• NE of overlay routing game
• Global optimal
( )∑ −+⋅e
se
see
se lldl )()()( min
le(s) : traffic of
overlay s
le(-s) : traffic other
than overlay s
( )∑ ⋅e
eee ldl min
)()( se
see lll −+=
Pricing I – Improve Delay
• Objective: to achieve global optimality
• New NE of overlay routing game
• Global optimal
( )[ ]
∑
∑⋅+
+⋅ −
e
se
se
e
se
see
se
pl
lldl
)()(
)()()(
min
( )∑ ⋅e
eee ldl min
)()( se
see lll −+=
)()( min ss paymentdelay +
Heterogeneous pricing
Pricing I – Improve Delay
• New NE of overlay routing game
• Global optimal
( )[ ]∑ ++⋅ −
e
se
se
see
se plldl )()()()( min ( )∑ ⋅
eeee ldl min
KKT condition:
( )( )( )( ) ( )
r
reee
se
seee
re
se
se
se
se
u
ldlpld
plldl
=
⋅++=
++⋅
∑
∑
∈
∈
−
')()(
')()()()(
KKT condition:
( )( )
( ) ( )
r
reeeeee
reeee
u
ldlld
ldl
=
⋅+=
⋅
∑
∑
∈
∈
'
'
pe(s)=le
(-s) de’(le)
Pricing II – improve fairness
• Cause of unfairness:– Over-utilize good common resources– Unfair resource (bandwidth) allocation
• Pricing Scheme
ISP
maximize profit
Improve performance &
Reduce cost
Overlay
price
p
routing decision
Incentive Resource Allocation
• For overlays:
( )( ) ∑∑ ⋅+⋅⋅=
+⋅=−
e
see
eee
ses
sss
sss
lpldl
paymentdelayyy)()(
)()()()()(
;Cost min
α
α
s : sensitivity factor
new Nash equilibrium {le}
Revenue Distribution
• For ISPs (links):
( ) ( )eeeee lclplP −⋅= max
( ) ( )( )ee
ee
eeee
e ld
ld
llcp
dl
dP '' 1
0 +==→=
: profit of link e
: revenue
: operating cost --
ee lp ⋅( )ee lP
( )ee lc ( )( )eee ldl ⋅log
Effectiveness of Pricing
Conclusion• Study the interaction between multiple co-
existing overlays.• Non-cooperative Nash routing game.• Prove the existence of NEP.• Show the anomalies and implications of the
NEP.• Present two distributed pricing schemes to
address the anomalies.
Third Course
Interaction of ISPs: Distributed Resource Allocation and Revenue Maximization
Sam C.M. Lee, Joe W.J. Jiang, D.M Chiu, John C.S. Lui
View of ISPsTier-1 ISP
Tier-2 ISP
Local ISP
Peering link
Tier-2 ISP
Local ISP
Peering link
ISP
Peer
ISP link
ISP
Peer
Peer
PeerPeer
Peer
Peer kPeer j
Tier-2 ISP(ISP)
Peer i 1. performance of the link2. charge of the link
Issues to consider:
Optimization problem of peers
Optimization problem of peers
Happiness obtained from sending traffic to peers
Delay cost in ISP link
Payment to ISP
Delay costs in peering links
Payments to peers
Constraints of peers
1.
2.
3.
4.
Solution to the peers
• Objective function is strictly concave in every transmission rate
• The optimal transmission rates and maximum utility are unique and can be found by the Lagrangian method.
Problems for an ISP
• Maximization of revenue– How to determine the optimal value of
unit price
• Resource distribution– How to determine the capacity for the
peers
Information exchange framework
ISP peer
Bandwidthallocation Bid
Compute resourcedistribution
Computeoptimalrates
Next period
ISP 1: Resource distribution
peer1
Bid = 50MBps
? ? ?
ISP
peer2 peer3
Bid = 100MBps Bid = 150MBps
Bandwidth = 600MBps
Proportional share algorithm
peer1 peer2 peer3
Bid = 50MBps Bid = 100MBps Bid = 150MBps
ISP Bandwidth = 600MBps
100MBps 200MBps 300MBps
Equal share algorithm
peer1 peer2 peer3
Bid = 50MBps Bid = 100MBps Bid = 150MBps
ISP Bandwidth = 600MBps
150MBps 200MBps 250MBps
Simulations
• When the happiness coefficients of peers are low
PSA ESA
Simulation
• When the happiness coefficients of peers are high
PSA ESA
ISP 2: Maximization of Revenue
Unit price
Demand by peer i
Determine the optimal price
Total revenue from the peers
Solution: Maximization of revenue
•Estimate the aggregate traffic ( ) from all
peers in term of the price (P)
Conclusions
• Utility maximization of a peer• Resource distribution of ISP• Revenue maximization of ISP
Fourth Course
On the Access Pricing Issues of Wireless Mesh Networks
ICDCS 2006
Ray K. Lam Dah-Ming Chiu John C.S. Lui
WMN Paints a Bright Future
• Wireless mesh network (WMN)– Wireless nodes– Multi-hop routing– Form a wireless “mesh”
• More access to the Internet– More people, rich or poor– More ubiquitous,
anywhere, anytime– More opportunities to
everyone
Internet Internet
The Critical Thing—Cooperation
Multi-hop routingRelay packets for each otherMy concerns: bandwidth, CPU time, security…
Community network with symmetric trafficHelp each other => mutual benefit
Access network with asymmetric trafficGeographically good VS poorWhy help the poor?Incentive system needed—pricing
When AP Meets a Client
• Simple analysis by Musacchio and Walrand [1]
• A game with 2 players– Access point (AP)
provides Internet access
– Client buys the service
– One deal per time slot
AP Clientp1
accept
p2
accept
p3
reject
slot 1
slot 2
slot 3
serviceduration
AP Client
p
A Beautiful Equilibrium• AP and client each maximizes
her gain– AP: guess the “right” price– Client: compare the price p with
service utility U• Web browsing utility function
• A beautiful equilibrium– AP has the same optimal price in every time slot– Client connects if her per-slot service utility is
greater than slot price (U > p)
• Encourages flat-rate pricing
To a Multi-hop Scenario
• Adding a relaying node, or “reseller” (RS)
• RS tries to mark up AP’s price to the “right” level
• AP takes note of RS’s action when setting her price
• Equilibrium is still flat-rate pricing
• Multi-hop => multiple RSs
AP Clientc1
acceptslot 1
slot 2
slot 3
serviceduration
p1
accept
c2
accept
p2
accept
c3
reject
p3
reject
RS
AP ClientRS
c
p
Drawbacks of the Simple Model
• Assuming unlimited network capacity– 2-player game represents
whole system– Treat every incoming client the
same– Unlimited admission =>
unlimited capacity• Assuming a tree-like network
– 2-hop / multi-hop linear network extension
– Does not consider multiple paths
– Pricing competition may occur
A tree-like network
A graph-like network
AP ClientRS
What If Capacity Limited?
• Cannot admit unlimited clients– Client demands bandwidth guarantee– AP admission control– AP’s system capacity: m
• 2-player game not enough– AP deals with each client differently– Client arrival model: Poisson process
• Like an M/M/m/m/M queuing system
Flat-rate Pricing Fails…
• Failure scenario– AP is full; m clients admitted– An admitted client a is paying $5/slot– A new client b arrives– AP asks b for $6/slot– If b accepts
• AP raises price for a to $6/slot, OR• Simply kicks a out
• Flat-rate pricing is not optimal!
Everybody Loves Flat Rate
• Unrealistic for variable rate• More practical—fixed-rate, non-
interrupted service– AP charges a client a fixed rate p over
time– AP cannot disconnect a client unilaterally
• AP can still charge different clients at different “fixed” rates– How to set the optimal rate on different
occasions?
Best Strategy in New Service Model
• AP sets price based on remaining capacity– Raises price when becoming full– State price: at state k, AP charges next “to-be-
admitted” client at fixed rate pk
– Policy of AP characterized by price vector
• Client’s best strategy– Connect AP if service utility per unit time > price
per unit time (U > p)
System Dynamics• State transition
– Adding a factor P(U > pk) to regular arrival rate in M/M/m/m/M model
• Reward structure– Simplification: immediate expected
profit when a client connects
0 1 2 mm-1…
M P(U > p0) M-1) P(U > p1) M-m+1) P(U > pm-1)
2 m
State transition diagram
System Dynamics• State transition
– Adding a factor P(U > pk) to regular arrival rate in M/M/m/m/M model
• Reward structure– Simplification: immediate expected
profit when a client connects
Reward Structure
0 1 2 mm-1…
p0/
0 0 0
p1/ pm-1/
Finding Optimal Price Vector
• Classical optimization– Solution for queuing system gives limiting state
probability for each state k, k
– Gain of AP is a function of price vector
– Complicated to optimize with classical techniques
• Policy-iteration method in Markovian decision theory– Reduces computational complexity by iterative
algorithm– Guarantees convergence to the best policy
Numerical Results• Capacity m=5,
population M=10, departure rate =1
• Vary arrival rate from 0.2 to 10
• Utility U uniformly distributed on [0,10]
• U normally distributed with mean 5, s.d. 1.67
• Price increases number of clients in AP and with
Limited Capacity in Multi-hop Case
• Simplification– Traffic merges at AP– AP is the bottleneck– Only AP controls
admission
• AP’s policy specified by a price matrix– At each state, different prices for requests
from different distances
– pki: price at state k for a client i-hop away
AP ClientRS
Internet
bandwidthbottleneck
System Dynamics• Removing finite population
– Complicates state information– Different arrival rates for clients at different distances
0 1 …
1P(U > m1(p0,1))
m
2P(U > m2(p0,2))
nP(U > mn(p0,n))
…
m-1 m
1P(U > m1(pm-1,1))
2P(U > m2(pm-1,2))
nP(U > mn(pm-1,n))
…
Client 1-hop away arrives
Client 2-hop away arrives
Client n-hop away arrives
State transition diagram
System Dynamics
0 1 …
0 0
p0,n/
…
m-1 m
…
Client 1-hop away arrives
Client 2-hop away arrives
Client n-hop away arrives
p0,2/
p0,1/
pm-1,n/
pm-1,2/
pm-1,1/
Reward Structure
• Removing finite population– Complicates state information– Different arrival rates for clients at different distances
Conclusion• Contributions
– Show that fixed-rate pricing fails with limited capacity
– Generalize unlimited capacity model into limited capacity model
– Devise optimal pricing for fixed-rate, non-interrupted service with Markovian decision theory
• References[1] J. Musacchio and J. Walrand. WiFi access point
pricing as a dynamic game. IEEE/ACM Trans. Networking. to appear in.