Callback is often used in Polish Telecom TPSA. They use Radius server for AAA. During the configuration of callback and Radius we met some problems. We didn't know which parameters should be given back to the router by Radius server.
For proper operating we have to configured the following attributes on Radius server:
ATTRIBUTE Framed-Protocol 7 integer
ATTRIBUTE Callback-Number 19 string
ATTRIBUTE Service-Type 6 integer
After configuring these attributes on Radius Server we was able to establish proper connection with Radius. These attributes were given back to the router and callback worked correctly.
Pleae use these attributes on Radius server for proper operating.