The%20structure%20of%20the%20Internet

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The structure of the Internet
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How are routers connected?

• Why should we care?
• While communication protocols will work correctly
  on ANY topology
• .they may not be efficient for some topologies
• Knowledge of the topology can aid in optimizing
  protocols

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The Internet as a graph

• Remember the Internet is a collection of
  networks called autonomous systems (ASs)
• The Internet graph
• The AS graph
• Nodes ASs, links AS peering
• The router level graph
• Nodes routers, links fibers, cables, MW
  channels, etc.
• How does it looks like?

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Random graphs in Mathematics The Erdös-Rényi
model

• Generation
• create n nodes.
• each possible link is added with probability p.
• Number of links np
• If we want to keep the
  number of links linear,
  what happen to p as
  n???

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The Waxman model

• Integrating distance with the E-R model
• Generation
• Spread n nodes on a large enough grid.
• Pick a link uar and add it with prob. that
  exponentially decrease with its length
• Stop if enough links
• Heavily used in the 90s

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1999

• The Faloutsos brothers
• Measured the Internet AS and router graphs.
• Mine, she looks different!

• Notre Dame
• Looked at complex system graphs social
  relationship, actors, neurons, WWW
• Suggested a dynamic generation model

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The Faloutsos Graph1995 Internet router
topology3888 nodes, 5012 edges, ltkgt2.57
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SCIENCE CITATION INDEX
Nodes papers Links citations
Witten-Sander PRL 1981
1736 PRL papers (1988)
P(k) k-?
(? 3)
(S. Redner, 1998)
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Sex-web
Nodes people (Females Males) Links sexual
relationships
4781 Swedes 18-74 59 response rate.
Liljeros et al. Nature 2001
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Web power-laws
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GROWING SCALE-FREE NETWORKS
(1) The number of nodes (N) is NOT fixed.
Networks continuously expand by the addition of
new nodes
Examples
WWW addition of new documents
Citation publication of new papers
(2) The attachment is NOT uniform. (Rich get
Richer)
A node is linked with higher probability to a
node that already has a large number of links.
Examples

WWW new documents link to well known sites
(CNN, YAHOO, NewYork Times, etc)

Citation well cited
papers are more likely to be cited again
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Barabasi Scale-free model
(1) GROWTH
At every timestep we
add a new node with m edges (connected to the
nodes already present in the system). (2)
PREFERENTIAL ATTACHMENT
The probability ? that a new node will be
connected to node i depends on the connectivity
ki of that node
A.-L.Barabási, R. Albert, Science 286, 509 (1999)
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The Faloutsos Graph
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The Internet Topology as a Jellyfish
Shells
Core
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• Core High-degree clique
• Shell adjacent nodes of previous shell, except
  1-degree nodes
• 1-degree nodes shown hanging
• The denser the 1-degree node population the
  longer the stem

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But is it?
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Not necessarily
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ER in disguise?

• Our sampling practices are far from being
  perfect
• Few traceroute hosts measure multitude of
  addresses
• The problem of the blind mice
• However, the Internet is probably much more broad
  scale than ER (the Jellyfish still stands)

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Past Attempts

• Measurements were done from a few (up to 10s)
  points
• ?too many links are missed especially in the
  periphery - Hidden peer connections
• ?measurements traffic was too dense
• Some maps were created based on central databases
• ?data was not up to date

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Past Measurements
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DIMES_at_HomeDistributed Internet MEasurement
Simulation

• Creating a distributed platform that will enable
• Global scale measurement of Internet graph
  structure, packet traffic statistics, demography
• Simulation of Internet behavior under different
  conditions (let the net simulate itself)
• Simulation of the Internet future
• Active networks
• Novel routing algorithms
• Distributed resource allocation grid computing
• P2P

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DIMES_at_Home
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Challenges

• Get A growing community of users to download and
  install our DIMES agent
• Optimize the architecture
• Minimize the number of measurements
• Expedite the discovery rate
• Flying under the NOC radar screens
• Study self-emerging agent collaboration
• Data analysis
• and more .

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When will DIMES solve the puzzle?

• Connectivity statistics (links power law)
  including hidden links 12 months
• Delay map 12 months
• Topology (K-Core, small worldness) including
  hidden links 18 months
• Corresponding I/O traffic statistics 24 months
• Usage mode statistics (e.g. HTTP vs. P2P)
• Traffic flow mapping
• youll just have to wait and see