> By Assia Hamzaoui and Matthieu Latapy
As explained in this paper, radar measurements of the internet topology consist in periodic measurements of the routes followed by packets from a machine, called monitor, to a given set of other machines, called destinations, on the internet. By merging all these routes, one obtains a map of the internet arount the measurement machine, which we call an ego-centered view of the internet topology.
The video above represents such an ego-centered view, with a restricted set of destination (for readability). All nodes and links seen at one round of the periodic measurement are shown; in white we display the ones seen at the last round (the others being gray).
One may first notice the stable part: most nodes and links are seen at each round, which shows that, in this case, most routes do not change at the time-scale of the measurement (a few minutes between consecutive rounds).
Another remarkable feature is the presence some regularity in the dynamics: some parts of the graph blink almost periodically, which reflects the presence of load balancing: some routers (called load-balancers) alternatively forward the packets for a given destination to several routers, thus balancing the load between several paths to reash the destination.
Another kind of dynamics is observable, with no apparent regular behavior: at some specific rounds, the route towards some destinations changes, thus leading to the discovery of previously unknown nodes. This is responsible for the presence of nodes and links which are almost never in white on the video: those are nodes and links that we rarely see. This kind of dynamics reflects the occurrence of events in the dynamics: unusual changes in routing tables possibly due to failures, congestion, addition or removel of material, etc.