new notion: policy-constrained dual AS graph


nodes: peering sessions
links: pairs of sessions w/common AS and followed by traffic in skitter or BGP data
derived from observed AS triples
example:
1909   195 1740 - AS path (skitter,BGP)
CAIDA SDSC CERF
nodes: 1909-195 and 195-1740
ordered AS pairs
directed link: from 1909-195 to 195-1740
allows for capturing more policy