jellyfish, and other interesting creatures of the internet scott kirkpatrick, hebrew university with...
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Jellyfish, and other Interesting creaturesOf the Internet
Scott Kirkpatrick, Hebrew University
withAvishalom Shalit, Sorin Solomon, Shai Carmi, Eran Shir, and Yuval Shavitt
8 August, 2005
Copyright, Pixar, Inc. 2003
DIMES – Internet topology map
• Previous efforts to measure the Internet have used:– One machine + Traceroute to many destinations– Many* machines, specially deployed to traceroute to many destinations
• * Many <= 50 because of management headaches
• Sites restricted to academic or gov’t labs, on network backbone
• General perception was that Law of Diminishing Returns has set in
• http://www.netdimes.org seems to have made a breakthrough– Don’t manage machines, offer a very lightweight, limited purpose client, and
collect its measurements centrally• 100 – 1000 clients via word-of-mouth (Sep04 to April05)
• 1000 – 5000 clients achieved via press, slashdot, still in the geek community – (May05 -- ?)
• 5000 – 50000 clients in the general public by offering services in return
– Somewhere in the 5000-10000 client range, we have the network monitoring itself, and the possibility that it can also manage itself in real time.
AS map for July 2005
BGP• 20585 nodes• 45720 edges• <k> = 4.44
DIMES• 14332 nodes• 60134 edges• <k> = 8.39
33,862 edges 24,182 in both maps
35,952 new edges11,858 edges
+
81,672 edges <k> > 7.80
Exploring the DIMES AS-graph
• We consider the Internet at the level of its autonomous systems (ASes)• Previous studies have used degree as indicator to decompose networks
– In particular, the Faloutsos’ “jellyfish model”• Identify core of network as maximal clique (not a robust criterion)• Shells around network labeled by hop count from core (a small world)• Find that sites with few links often connect to those with high degree
• We consider longer-range connectivity, using k-pruning.• K-core, K-shell, and K-crusts result
– K-shell is “derivative” of K-core, K-crust is union of K-shells– Near power-law structure of a new “inflow” region is observed– K-shells are not connected, but K-crusts have a giant cluster
• For Erdos-Renyi graphs, K-core is w.h.p. K-connected. For scale free?
• Result – focus attention on the capabilities of the inflow region, in support of P2P, chat, local traffic.
• Next steps – reachability is much harder than percolation.
K-crusts show percolation threshold
Data from 01.04.2005
These are the hanging tentacles of our (Red Sea)Jellyfish
Largest cluster in each shell
Michalis Faloutsos’ Jellyfish
• Highly connected nodes form the core
• Each Shell: adjacent nodes of previous shell, except 1-degree nodes
• Importance decreases as we move away from core
• 1-degree nodes hanging• The denser the 1-degree
node population the longer the stem
CoreShells 12
3
Meduza (מדוזה) model
In January, the inner core was at K = 30, but this picture persists to the present day, when core is >40. The precise definition of the tendrils: those sites isolated from the largest cluster in all the crusts – they connect only to the core.
Where do the links go in Medusa?
Early shells (1-10) link to intermediate shells as well as to the core.
Random scale-free graphs produce the same structure
• Seen in both Barabasi-style and Molloy-Reed models of scale free networks
Next steps
• New data permits reexamining the clustering behavior– Much data not seen in previous BGP-based studies– This is the major deviation from simple random models– Analyze as a function of k-shell, instead of simply degree
• Reachability is not percolation, but can be evaluated – Decision to transmit a message depends on sender and
destination, not simply on the existence of a link– Cost of evaluating uphill-downhill reachability is comparable to
shortest path