Ningning HuCarnegie Mellon University7 Methodology Measurement sources: 18 nodes from a large tier-1 ISP  14 in the US, 3 in Europe, and 1 in East-Asia  Large fraction of paths cover other ISPs  Play the role of possible replica sites Measurement destinations: 164,130 IP addresses from different prefixes  67,271 IPs correspond to real online hosts  Firewalls etc sometime require us to use intermediate node as virtual destination  Play the role of clients accessing the web
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