Table 1 Offline evaluation metrics

Mapping cost

The cost of mapping a CDN on the testbed

equals the amount of required bandwidth

for all content distribution substrate paths

as defined by the surrogate placement

solution augmented by the computing

resources allocated to each surrogate node.

CDN deployment cost

The overall cost of deploying a CDN is based

on the adopted cost models (retrieval, update,

storage[9]). The cost is essentially comprised

by (i) the cost for storing the content at the

selected sites (ii) the access cost of CDN

end users within the area of service (iii)

the cost of updating the content at the

transit/surrogate servers

Number of surrogate

The number of nodes that are selected by

servers

the placement algorithm to host a

surrogate server.

Path length

The average number of hops between

CDN end users and the origin server in a

particular CDN solution.

Shortest path

Shortest path betweenness centrality for a

betweenness centrality

particular CDN solution is defined as the

average of individual SPBCs of the selected

surrogates comprising the final CDN solution.