Download Complex Networks

Internet and Overlay Networks
Ram Keralapura
ECE Dept
[email protected]
Layered Architecture

Five main layers
• Application layer
• Transport layer
• Network (IP) layer
• Link layer
• Physical/Optical layer
Applications/Computers
Application layer links
Routers
Virtual IP links
Optical switches
Optical fibers
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Introduction

Internet Routing Infrastructure
• Intra-domain routing (IGP)

RIP, OSFP, ISIS, etc.
Internet
• Inter-domain routing

BGP
Domain or
Autonomous System
3
Intra-domain Routing
Links are assigned link costs/weights
 Path between two nodes inside a
domain follows shortest path (least
cost path)

4
B
C
2
3
A
7
1
B
2
Dst D
C
A
D
1
F
1
E
F
E
4
Network Properties

Important properties of networks
that service providers look for:
• Connectivity
• Performance
• Resiliency
• Robustness in functionality

Service availability – delivering a given
packet from source to destination
5
Characterizing Networks

Main causes for concern – resiliency
and robustness
• How does the IGP protocol behave
during network component failures?
• How does the behavior impact the data
that the network carries?
6
Characterizing Networks (cont’d)
We have developed a model that
captures the dynamic behavior of the
network protocols during link failures
[Keralapura et al, 2004]
 Protocol convergence depends on:

• Topology – nodes and connectivity
• Protocol timer settings
• Number of entries to update in the
forwarding tables
7
Characterizing Networks (cont’d)

Metrics for service availability
• Service disruption time
• Traffic disruption

Based on the above metrics we
define “goodness factor” for the
network
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Ingress Node Goodness
Results (cont’d)
Ingress Node Goodness
Out Degree
Out Degree
Static properties (like node
out-degree) do not capture
operational conditions and
network dynamics
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Network Goodness
Network Diameter
Similar results were also found in the paper
“Layered Complex Networks” by Kurant and Thiran
10
Internet Architecture

Tiered hierarchy in domains
Peering relationship
Tier-2
C
Tier-1
Tier-1
A
B
Tier-2
D
Tier-2
E
Tier-2
F
Customer-Provider relationship
11
Inter-domain routing

Policy-based routing
• Ad-hoc and can change with agreements
with other domains

Can we capture these policies?
• Domains do not disclose their connectivity

Policies can obstruct views and hinder
domain-level topology discovery
• Need multiple vantage points for more
accurate topology information
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Application Layer Networks
Email Networks
 World Wide Web (WWW)
 Peer-to-Peer (p2p) Networks
 Several Content Delivery Networks
(CDN)

Overlay networks
13
Background: Overlay
Networks
B’
D’
Domain-2
A’
B
Y
X
A
D
C’
Domain-4
Domain-1
C
Domain-3
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Interaction between networks
Overlay networks compete with IP
networks to provide routing service
 IP and overlay networks are unaware
of key things happening at the other
layer
 Multiple overlay networks co-exist
and make independent decisions
 How does all this affect IP and
overlay networks?

15
Interactions between Networks

Identified some potential interactions
[Keralapura et al, 2005]
• Traffic engineering in IP networks
Load balancing issues
 IP layer traffic matrix estimation

• Coupling of multiple domains

Defeats the objective of BGP
• Multiple co-existing overlay networks
Traffic oscillations
 Cascading reactions

16
Load Balancing and TM Estimation
5
H
5
5
G
5
8
M
A
20
F
N
5
8
5
E
5
5
B
5
5
D
C
5
17
Coupling Multiple AS Domains
F
B
X
C
A
D
Domain-1
G
E
H
Domain-2
Defeats one of the objectives of BGP to
decouple different domains
18
Traffic Oscillations
Link Utilization
Traffic Oscillations
Time (ms)
Failure of link 10-12
Failure of link 2-5
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Open questions
Interactions need to be understood
better and we need to model them
 How to go about characterizing the
robustness of a network after we
model such interactions?
 Are there interactions between
networks at other layers?

• If yes, then how to we qualify, quantify,
and model them?
20