Building an AS topology graph from BGP data


directed from backbone downstream to router
more hierarchical, captures less `lateral' peering 
Gao e.a. find 90%  provider-customer links
In reality, # peers ~ #customers (order of magnitude)

Zocalo: medium-sized ISP in Bay Area
8 transit providers
100 downstream networks
12 have their own AS
225 peers
=> total degree ~ 250
in sum of 43 backbone tables: indeg.11, outdeg.63, total 74
=> 3 times less