Modeling Internet Topology
Kenneth L. Calvert
Matthew B. Doar
Ellen W. Zegura
Presented by Kiran Komaravolu
Why do we need to model the Internet
Topology
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Large networks abstracting the real Internet are rarely
available to work with.
Simulations
 Simulation tools need a model of the internet to work
with.
Analysis of new protocols.
 It is easier to develop new protocols and test them
on a simulation testbed rather than on the real
Internet.
Building blocks of the Internet.
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Transit Domains
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Stub Domains
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Wide Area Networks
E.g.., MCI’s backbone network.
Campus networks, Corporate networks.
Wont route other stub domain traffic.
LANs
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Eg., Research labs in the CSE department.
What the user provides.
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T: Total number of transit domains.
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S: Avg number of stub domains per transit
domain.
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NT: Average number of nodes per transit domain.
NS: Avg number of nodes per stub domain
L: Avg number of LANs attached to a stub
node.
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NL: Avg Number of nodes per LAN
# Routing nodes = T*NT(1+S*NS)
# Host nodes = T*NT*S*NS*L*NL
.
What the user provides.
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ET: Avg number of edges between transit nodes
of same domain.
ETT: Avg number of edges between transit
nodes of different domains.
ES: Avg number of nodes between stub nodes.
EST: Avg number of nodes between a stub
domain and its transit domain.
ELS: Avg number of nodes from a LAN to a
stub node.
Generation process.
1.
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6.
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Create the transit domains and connect them while
satisfying ETT.
For each transit domain create the transit nodes
and interconnect them. Each transit domain has on
average NT nodes.
Select end points in transit domains.
Locations for the stub domains are chosen. Each
stub domain on average has NS nodes. Edges are
generated within each stub domain as to satisfy Es
requirement.
Each stub domain is connected to one or more
transit domains.
Locations for the LANs are chosen. For each LAN
on average NL nodes are inserted.
Each LAN is connected to a stub node by an edge
from the centre router to the stub node.
Implementation details.
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Transit-Stub model.
Supports only two level hierarchy.
 Generates connected sub-graphs
according to given specifications.
 Extra nodes (Nodes available after
satisfying connectivity) are added
randomly.
 Edges are given weights, used while
determining routing policies.
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Implementation details.
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Tiers
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WAN, MAN, LAN hierarchies are supported.
Number of WANs = 1
Produces connected sub-graphs by joining all nodes
in one domain using a minumum span tree.
Gateways are shown as two inter-connected nodes
(a LAN node and a MAN node)
Single layer Tiers
N/W
3 layer Tiers N/W
Questions