Admin assisstance

I am running a Radius server using Gnu Radius and I am having trouble with checking for multiple dial-up connections.  The dial-up service I obtain through another company that uses Cisco 5800 AS.  The default installation does not support this type of access server and so it does not get the response back on whether or not the user is already connected.  How do I go about determining how the request is supposed to be formatted and how the response is going to be formatted?  And then how do I get this information into the Radius configuration so that it can use it?