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1
GENESIS: An agent-based model of interdomain network formation,
traffic flow and economics
Aemen Lodhi (Georgia Tech)
Amogh Dhamdhere (CAIDA)
Constantine Dovrolis (Georgia Tech)
31st Annual IEEE International Conference on Computer Communications (IEEE INFOCOM 2012)
2
Outline
• GENESIS: Introduction & Motivation• The model: Key features• Results– Validation– Analysis of results
• Case study• How to use GENESIS in your research
3
INTRODUCTION
4
Motivations for an interdomain network formation model
• Insight into dynamics of interdomain network
• Study pricing schemes• Study increasing asymmetry in
interdomain traffic matrix• Evaluate peering strategies• Impact of actions on economic
fitness• Internet “ecosystem” in the future?
5
What is GENESIS• Agent based interdomain network
formation model• Autonomous Systems (AS) as
independent agents acting in a distributed asynchronous manner
Enterprise
customer
Transit Provide
r
Transit Provide
r
Internet
Enterprise
customer
Content Provider
Content Provider
6
What is GENESIS
• Actions by ASes– Transit provider selection– Peering strategy selection– Peering and Depeering decisions
• Outcome of these actions– Formation of an interdomain network
starting from a random initial state–Mostly ending in equilibrium
7
What GENESIS is not
• Not a topology generation model• Not a crystal ball to accurately
predict the economic fitness or hierarchical status of a single specific AS in future
• Use GENESIS for – computing statistical properties of
network topology + economic fitness of different categories of ASes
8
THE MODEL
9
Model features
• Geographic co-location constraints in provider/peer selection
• Traffic matrix• Public & Private peering• Set of peering strategies• Transit provider selection mechanism• Economic attributes: Peering costs,
Transit costs, Transit revenue
Model features
Fitness = Transit Revenue – Transit Cost – Peering cost
• Objective: Maximize economic fitness• Optimize connectivity through peer
and transit provider selection
11
Geographic presence & constraints
Regions corresponding to unique
IXPs
Geographic overlap
12
Traffic Matrix• Traffic for ‘N’’ size network represented
through an N * N matrix• Illustration of traffic matrix for a 4 AS
network
0
0
0
0
30
20
10
030201
t
t
t
ttt
Traffic sent by AS 0 to other ASes in
the network
Traffic received by AS 0 from
other ASes in the network
Intra-domain traffic not
captured in the model
13
Traffic components
Autonomous system
Inbound traffic
Traffic consumed in
the ASTraffic
transiting through the AS
Traffic generated
within the AS
Outbound traffic
• Transit traffic = Inbound traffic – Consumed trafficsame as
• Transit traffic = Outbound traffic – Generated traffic
14
Peering strategies
• Restrictive: Peer only to avoid network partitioning
• Selective: Peer with ASes of similar size
• Open: Every co-located AS except customers
15
Peering strategy selection
• Default model– Tier 1 Transit providers: Restrictive– All other transit providers: Selective– Stubs: Open
16
Execution of a sample path
1 2 N
Iteration
1. Depeering2. Peering3. Transit provider
selection4. Peering strategy
update
1. Depeering2. Peering3. Transit provider
selection4. Peering strategy
update
1. Depeering2. Peering3. Transit provider
selection4. Peering strategy
update
1 2 N
Iteration
Time
• No exogenous changes• Finite states
17
RESULTS
18
Stability of the model
1 2 N
Iteration
1 2 N
Iteration
Time
• Equilibrium: No topology, peering strategy changes in two consecutive iterations
• 90% simulations reach equilibrium• Short time scales• Average time to equilibrium: 6
iterations
19
Oscillations: An artifact?
1 2 N
Iteration
1 2 N
Iteration
Time
• 10% simulations oscillate• Always involve Tier-1 ASes• Resemble real Tier-1 peering disputes• GENESIS captures that endogenous
dynamics cannot always produce stable network
• Exogenous intervention required
20
Validation
• Comprehensive validation not possible• Should be viewed as proof of concept• 10% ASes end up being transit providers• Average path length 3.7 (500 nodes) vs.
Average Internet measured path length 4• Path length does not increase significantly
as GENESIS scales from 500 to 1000 nodes
21
Validation• Highly skewed degree distribution• Not exactly a power law owing to limited
number of nodes• Few links carry several orders of magnitude
more traffic
22
Variability across equilibria
• Sources of variation in a single population: Initial topology, Playing order
• Same population but different initial topology: 85% distinct equilibria
• Same population & initial topology but different playing order: 90% distinct equilibria
• Distinct equilibria quite similar in terms of topology
• Coefficient of variation of fitness close to zero for 90% ASes
23
Variability across equilibria
• Most predictable ASes– Stubs: Enterprise customers, Small ISPs– Very large transit providers
• Most unpredictable ASes–Midsize (regional) transit providers
24
Case study: Peering Openness• How does peering openness affect the
properties of the network?• Optimal fitness in range of peering ratios
observed in the real world (1.5 to 5)
25
Case study: Peering Openness
• Widespread peering: Saving on costs not the only outcome
• Results in loss of transit revenue
26
Summary of GENESIS findings
• Individual AS status hard to predict• Regional transit providers most
sensitive to network level changes• Overall network characteristics more
predictable• Internet a stable network (mostly) in
the absence of exogenous factors• Increased peering may result in loss of
transit revenue
How can I use GENESIS in my research?
• Flexible & Modular
27
Peering strategi
es
Resulting network
Traffic matrix
Pricing schemes
Presence at IXPs
Presence at IXPs
Peering strategi
es
28
How can I use GENESIS in my research?
• C++ single thread implementation• Fast: average simulation time for 500 nodes: 1.25
hours• Scales up to 1000 nodes• Used in “Analysis of peering strategy adoption by
transit providers in the Internet” NetEcon 2012• Available at:
www.cc.gatech.edu/~dovrolis/Papers/genesis.zip
29
THANK YOU