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)
1
Outline
• GENESIS: Introduction & Motivation
• The model: Key features
• Results
– Validation
– Analysis of results
• Case study
• How to use GENESIS in your research
2
INTRODUCTION
3
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?
4
What is GENESIS
• Agent based interdomain network
formation model
• Autonomous Systems (AS) as
independent agents acting in a
distributed asynchronous manner
Internet
Transit
Provider
Enterprise
customer
Transit
Provider
Content
Provider
Content
Provider
Enterprise
customer
5
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
6
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
7
THE MODEL
8
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
9
Model features
Fitness = Transit Revenue – Transit Cost – Peering cost
• Objective: Maximize economic fitness
• Optimize connectivity through peer and
transit provider selection
Geographic
Geographic presence & constraints
overlap
Regions
corresponding
to unique IXPs
11
Traffic Matrix
• Traffic for ‘N’’ size network represented
through an N * N matrix
Traffic
sent by AS 0
Intra-domain
traffic
captured
in the
tofor
other
ASes
• Illustration of trafficnotmatrix
a 4
ASin the
model
network
network
Traffic received by
AS 0 from other
ASes in the network
 0 t 01 t 02 t 03
t10 0



t 20

0


0
t 30
12
Traffic components
Inbound traffic
Traffic
consumed in the
AS
Traffic generated
Traffic transiting
within the AS
through the AS
Autonomous system
• Transit traffic = Inbound traffic – Consumed traffic
Outbound traffic
same as
• Transit traffic = Outbound traffic – Generated traffic
13
Peering strategies
• Restrictive: Peer only to avoid network
partitioning
• Selective: Peer with ASes of similar size
𝑉𝑥
≤𝜎
𝑉𝑦
𝑉𝑥 = 𝑇𝑟𝑎𝑛𝑠𝑖𝑡 + 𝐺𝑒𝑛𝑒𝑟𝑎𝑡𝑒𝑑 + 𝐶𝑜𝑛𝑠𝑢𝑚𝑒𝑑
• Open: Every co-located AS except
customers
14
Peering strategy selection
• Default model
– Tier 1 Transit providers: Restrictive
– All other transit providers: Selective
– Stubs: Open
15
Execution of a sample path
• No exogenous changes
• Finite
states
1. Depeering
1. Depeering 1. Depeering
2. Peering
2. Peering 2. Peering
3. Transit
provider selection
3. Transit 3.
provider
Transitselection
provider
selection
4. Peering
strategy update
4. Peering 4.
strategy
Peeringupdate
strategy
update
Iteration
Iteration
1
2
N
1
2
N
Time
16
RESULTS
17
Stability of the model
• Equilibrium: No topology, peering strategy
changes in two consecutive iterations
• 90% simulations reach equilibrium
• Short time scales
• Average time to equilibrium: 6 iterations
Iteration
1
2
Iteration
N
1
Time
2
N
18
Oscillations: An artifact?
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
•
•
•
•
Iteration
1
2
Iteration
N
1
Time
2
N
19
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
•
•
•
•
20
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
21
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
22
Variability across equilibria
• Most predictable ASes
– Stubs: Enterprise customers, Small ISPs
– Very large transit providers
• Most unpredictable ASes
– Midsize (regional) transit providers
23
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)
24
Case study: Peering Openness
• Widespread peering: Saving on costs not
the only outcome
• Results in loss of transit revenue
25
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
26
How can I use GENESIS in my
research?
Presence
at IXPs
• Flexible & Modular
Resulting
network
Pricing
schemes
Traffic
matrix
Peering
strategies
27
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
28
THANK YOU
29