An access server may have a mixture of analog and digital interfaces and support hundreds of simultaneous users.
A NAS consists of a communications processor that connects asynchronous devices to a LAN or WAN through network and terminal emulation software.
The NAS is meant to act as a gateway to guard access to a protected resource.
Although not required, NASs are almost exclusively used with authentication, authorization, and accounting (AAA) servers.
The Diameter base protocol extends RADIUS services by providing error handling and inter-domain communications.