Not entirely sure of that exact setup but usually the "monopoly" ISP will terminate the connection to the "resselling ISP" in some sort of IP tunnel. The underl

Not entirely sure of that exact setup but usually the "monopoly" ISP will terminate the connection to the "resselling ISP" in some sort of IP tunnel. The underlying physical connection is basically invisible to the reselling ISP and it just looks like a normal IP tunnel they can route to and from. The ISP providing the physical connection bills the reselling ISP a wholesale rate for the connection, which then bills the end customer.