As a matter of fact, it is quite doable. Aimnet developed a roaming
server (check www.aimnet.com) that allows international ISPs to
use each other's network to provide dialup services. A group of
ISPs have joined a consortium GRIC (Global Reach Internet
Consortium) lead by Aimnet. The roaming server is based
on Radius protocol.
A telco company can install modems and route the authentication to
the specific ISP for authentication.
I just came back from Montreal INet 96 last week and a new roaming
IETF group will be started. We are working on the IETF draft
for the roaming and stay tuned.
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