1. Network Selection Issues
Pasi Eronen

2. Network Selection -- Goals
Assist AAA routing in global roaming, when full routing information not available or ambiguous
Allow the user to select which broker to use, in case there are price or other differences
Allow the intended service providers to be a part of the transaction business-wise

3. Network Selection -- Some Solutions
AAA layer: some mechanism to provide a better AAA routing / roaming table
Link layer: advertise an SSID for the broker/intermediate network, then use that in AAA routing, using virtual AAA clients and proxies
EAP layer: provide some hints in EAP identity request, select a NAI based on those hints
A regular NAI
A NAI with the broker’s name added
Another alternative decoration:

4. Issues with NAI Prefix / EAP Solution
All proxies have to know about this
Diameter routing and Diameter-RADIUS problems
Does not work this way according to the current RFCs
APs have to be modified to get the initial ID request from the proxy, or identity re-queries are needed, lengthening the network attachment time
Does not help in selecting the AP
Need to scan of all APs and running EAP before deciding which AP to choose
EAP Identity Req/Resp contents are not secured

5. The SSID Solution No AAA protocol implications
No EAP or NAI interoperability issues
Does require APs to support multiple SSIDs
If the number of advertised networks is large, can consume a lot of beacon bandwidth
At 1 mbps, all bandwidth used for 100 network advertisements!
A similar issue with the EAP/scan solution, but not dependent on number of networks -- instead, the number of logins per second x number of APs
However, in the EAP/scan solution a higher speed can be chosen for the unicast communications
For instance, 10 logins per second with 10 APs and 100 networks, with 10 mbps unicast speed would result in 10 * 10 * = 1 mbps or 10% of the bandwidth used

6. Feedback on Network Selection
If an EAP-layer based solution is used, EAP identity request hints are probably OK
Prefix-based NAI decoration is problematic
AAA routing instructions from RFCs are violated
All proxies have to recognize the decoration
Suffix-based NAI decoration would be better
Neither the hints or the decorations are authenticated
Applies to SSIDs in part too, at least for dishonest AP case
Scanning APs and trying EAP is problematic
Particularly hard if there are multiple APs and fast roaming
And particularly if identity re-query is used
Consider combining AP selection and network selection?
Beacon-based approach is limited to ~dozen brokers
Particularly if lowest beaconing speed is small