Commonly accepted model of the internet is that it is hierarchical… In reality, it is a peering mesh of the biggest ISPs, and lots of local peerings. Check out this blog. And the direct links to the two PDF files for the paper, and the slides. Or a local copy of the slides, and the full paper.
Ok, I’ll paste the blog below for your convenience.
Anatomy of a Large European IXP
The Internet is still evolving and measurements allow us to better understand its evolution. In , Craig Labovitz and his colleagues used extensive measurements to show the growing importance of large content providers such as google, yahoo or content distribution networks such as Akamai. This paper forced researchers to reconsider some of their assumptions on the organisation of the Internet with fully meshed Tier-1 ISPs serving Tier-2 ISPs that are serving Tier-3 ISPs and content providers.  showed that many of the traffic sources are directly connected to the last mile ISPs.
In a recent paper  presented during SIGCOMM 2012 , Bernard Ager and his colleagues used statistics collected at one of the largest Internet eXchange Points (IXP) in Europe. IXPs are locations were various Internet providers place routers to exchange traffic via a switched network. While the first IXPs where simple Ethernet switches in the back of a room, current IXPs are huge. For example, AMS-IX gathers more than 500 different ISPs on more than 800 different ports. As of this writing, its peak traffic has been larger than 1.5 Terabits per second ! IXPs play a crucial role in the distribution of Internet traffic and in particular in Europe where there are many large IXPs.  highlights many unknown factors about these IXPs such as the large number of peering links that exist on each ISP, the application mix or the traffic matrices.  will become a classic paper for those willing to understand the organisation of the Internet.