Internet
Arcs Around The Globe
By Martin
Dodge, CASA
The globe is one of the most powerful visual
metaphors to map the geographical dimensions of large
networks like shipping lines, trade flows, airline
routes and communications such as the Internet. A team
of researchers, Tamara Munzner, K. Claffy, Eric Hoffman
and Bill Fenner produced visually striking, interactive
maps of part of the Internet using arcs encircling an
Earth globe [1].
They were mapping the global topology of a particular
subset of the Internet known as the MBone (see sidebar)
from the mid 1990s using essentially the same style of
arc-node representation used to map
the ARPANET, except projected into three-dimensional
space around a globe.
Other scientists have also done significant
research into interactive mapping of communications
networks using three-dimensional global models, most
notably Stephen G. Eick and colleagues at Bell Labs [2].
While the MBone has also been mapped by others, for
example Elan Amir's abstract graph of the MBone[3]
from the August 1996 and the CAIDA
research group developed an interactive MBone
mapping tool called Manta Ray, but it uses flat,
two-dimensional representations[4].
The infrastructure of the MBone has grown into
a very complex and inefficient topological structure,
with many duplicate, redundant tunnels. The inefficient
structure is a problem because it causes unnecessary
waste of scarce Internet capacity and undermines the
very principle of multicasting. What was needed to make
sense of the global MBone topology was some form of map.
Munzner and her colleagues grasped the
challenge of mapping the MBone, using curving arcs
between node routers geographically positioned on a
three-dimensional globe. They comment that, “… one
strong advantage to our current 'arcs on globe'
geographical layout is that viewers understand it
immediately with little explanation.”. The graphical
framework for their visualizations
was provided by a 3d globe, with country boundaries,
along with US state and Canadian provincial borders, to
provide suitable geographical context. Curving lines
between router locations were employed to represent the
actual MBone tunnels, with colour and thickness used to
show characteristics of the tunnels, while the height of
the arcs above the surface of the globe was simply a
function of distance. The longest tunnels were drawn as
the highest arcs, as can be seen in the figures below.
This makes sense in the context of understanding the
MBone topology because long links that span large parts
of the Internet are most important and are highlighted
on the visualizations by
the facts that high arcs are afforded greater visual
prominence. It should be noted that these MBone visualizations
only show the structure of this network and not any data
on traffic actually flowing over the links.
A significant problem they faced was
determining the geographic location of the MBone
routers. This proved to be a time-consuming process,
involving considerable amounts of manual effort. This is
symptomatic of a wider problem of the lack of a
reliable, automatic means of geographically locating
Internet infrastructure which is the key impediment to
mapping the Internet.
One of the aims in their MBone mapping
endeavors
was to make the results as widely available as possible
and, also, make the maps as interactive as possible, so
people could really explore the topology for themselves
rather than being presented with predetermined, static
images. To achieve these aims Munzner et al produced
their 3d “arcs on the globe” maps in VRML. So rather
than just producing static maps, they made 3d models
that can be downloaded from the Web and viewed
interactively, using an appropriately configured
browser, on the end-users computer. It is possible to
download and explore their maps for yourself from the
“Planet
Multicast” Web site.
The figures give two screen-shots of the 3d
global maps. The first is a view of the whole globe,
from several hundred miles out in space, with a dense
mesh of arcs criss-crossing the USA from coast to coast,
along with higher, longer transcontinental tunnels
curving around the globe. This shows many hundreds of
different tunnels, from the MBone topology for early
1996.
The second figure is a view taken from a low
angle, close to the surface of the globe off the coast
of California. Looking across the continental US from
this angle the density of looping arcs of varying
heights is apparent. Lateral links along the West coast,
as well longer tunnels from the East coast, can be
discerned. Certain tunnels are highlighted using
different colour and thickness of lines indicating that
they are of a different specification.
Two of the principle “cartographers” -
Tamara Munzner and K. Claffy - who created the 3d MBone
maps, are pioneers in mapping the Internet. Munzner is a
graduate student in the computer graphics laboratory at
Stanford University and her principle research has been
in visualizing
information. K. Claffy is a leading
researcher in Internet data analysis and
© 1996 Tamara Munzner
(Stanford University), Eric Hoffman (Ipsilon Networks),
K. Claffy(NLANR), and Bill Fenner (Xerox PARC)
