map improves models
Technology Research News
As the Internet becomes an increasingly
important part of both communications and commerce, it is ever more important
to know exactly how it grows.
Scientists from Italy and Spain have analyzed three years worth of daily
maps of the Internet's
connections in an attempt to better characterize the environment of the
real Internet. The study makes a distinction between the Internet, which
connects computers around the world in a real network,
and software like the Web,
which is a virtual network that resides on the Internet.
The researchers used maps of the Internet's connections collected daily
by the Cooperative Association for Internet Data Analysis (CAIDA) and
the National Laboratory for Applied Network Research (NLANR), which is
funded by the U.S. National Science Foundation.
The researchers are looking to closely characterize the Internet because
it is an example of a complex network that can be readily analyzed. Their
past work was on modeling epidemics and immunization procedures in complex
networks like the Internet and networks of human social relationships.
"Soon we realized that the deeper analysis, going beyond the simple connectivity
properties usually considered, was needed in order to fully characterize
the Internet structure," said Romualdo Pastor-Satorras, a visiting professor
at the Polytechnic University of Catalonia.
The researchers analyzed Internet growth over time with statistical methods
usually used for physics research.
The analysis showed that the Internet grows in specific ways, said Pastor-Satorras.
"The Internet can be considered as a spontaneously growing organism. Since
there are not global entities regulating the Internet development, it
defaults as a self-organized system with high growth rate."
Despite the high growth rate, the Internet has settled into a state whose
overall topographical and geometrical properties are stationary in time,
said Pastor-Satorras. "The Internet evolved spontaneously [into] a scale-free
network characterized by wild fluctuations in the connectivity properties
of the [Internet service providers,]" he said. In scale-free networks,
a few nodes, or providers, have many connections to other nodes, while
many nodes have few connections.
The analysis also showed that nodes, or computers, on the Internet have
settled into well-defined, efficient hierarchies that have to do with
how the properties of a node are affected by those of its neighbors. "We
find that highly connected nodes are more likely connected to nodes with
lower connectivity. This allows us to distinguish different layers of
the Internet, or small providers connect to larger providers and so on,
following a connectivity and size hierarchy," said Pastor-Satorras.
The hierarchy includes stub domains, which are groups of nodes, or computers
that carry traffic only within that domain, or group, and transit domains,
which connect different stub domains. The connections inside stub domains
are usually short, while the connections among domains are usually long.
"The existence of stub and transit domains allows us to identify... a
hierarchical structure in the Internet," Pastor-Satorras said.
The growth patterns of the Internet show many short interconnections in
stub domains but just a few longer links connecting them to each other,
which is "quite [economical] in the sense of the total length of the connections
established," said Pastor-Satorras.
The information also allows for the study of properties of Internet service
providers like "how the connectivity of providers is related to their
age, and the death and replacement events occurring in the growth process,"
The hierarchy among nodes, the redundant connections that exist among
old nodes, and also the real geographical location of nodes can all influence
how the Internet evolves, according to Pastor-Satorras.
The information also allowed the researchers to predict the creation of
new connections among providers over time. "This gives information on
the forces driving the Internet demand and economical market," said Pastor-Satorras.
The information the researchers have gathered can be used to assess the
reliability and effectiveness of computer Internet models used to simulate
and test new communications protocols and routing algorithms for the Internet,
Pastor-Satorras said. It also may prove useful in developing Internet
models, he added.
The researchers are working toward more completely mapping the Internet's
characteristics, said Pastor-Satorras. "We would like to have a full characterization
of the Internet, including the load of information carried on top of the
Internet structure. Since we can consider the Internet as a natural object,
we would like to pinpoint the dynamical mechanisms driving the Internet
formation and provide a quantitative physical model for Internet growth,"
The study sheds new light on some aspects of local connectivity, said
Bosiljka Tadic, a physics professor at the Jozef Stefan Institute in Slovenia.
The researchers found in the data a correlation regarding who connects
to whom, he said. "It appears that many nodes with low connectivity are
linked to a few nodes with high connectivity, but in a way that cannot
be produced in a generic model," he said.
The research is useful for more realistic modeling of the Internet, said
The study also showed that the Internet shares many growth factors with
the Web, the virtual network that resides on the Internet. "Apart from
several important differences [like] link directions, growth of the Internet...
and the Web... are guided in part by the same dynamic rules: growth, attachment
[and] rewiring," he said.
The work shows how the topological properties of the Internet are determined
by the dynamical properties that govern the network's growth, said Albert-László
Barabási, a physics professor at the University of Notre Dame. "We are
only at the beginning of our understanding of how this topology emerges
in real systems," he said.
The work is important because it combines measurements with simulations
to shed light on the interplay between topology and growth and paves the
way towards realistic network models, Barabási said.
Pastor-Satorras' research colleagues were Alexei Vásquez of the International
School for Advanced Studies in Italy and Alessandro Vespignani of the
Abdus Salam International Center for Theoretical Physics in Italy. The
research was funded by the International Center for Theoretical Physics
(ICTP) and the Spanish Ministry of Science and Technology.
TRN Categories: Internet
Story Type: News
Related Elements: Technical paper, "Dynamical and Correlation
Properties of the Internet," posted on the arXiv physics archive at http://arXiv.org/abs/cond-mat/0105161.
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