I will present the Infocom 2002 paper by Subramanian, Agarwal, Rexford and
Katz,  "Characterizing the Internet Hierarchy from Multiple Vantage
Points"  

The abstract from the paper:

The delivery of IP traffic through the Internet depends on the complex
interactions between thousands of autonomous systems (ASes) that exchange
routing information using the Border Gateway Protocol (BGP). This paper
investigates the topological structure of the Internet in terms of
customer-provider and peer-peer relationships between ASes, as manifested
in BGP routing policies.  We describe a technique for inferring AS
relationships by exploiting partial views of the AS graph available from
different vantage points.  Next we apply the technique to a collection of
ten BGP routing tables to infer the relationships between neighboring
ASes.  Based on these results, we analyze the hierarchical structure of
the Internet and propose a five-level classification of ASes.  Our
characterization differs from previous sutides by focusing on the
commercial relationships between ASes rather than simply the connectivity
between the nodes.