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DIAMETER is a protocol that authenticates remote dial-up users. It evolved from the popular RADIUS protocol. Both protocols are AAA (authentication, authorization, and accounting) protocols, meaning that they are used to authenticate dial-up users and provide the authorizations users need to access systems. The accounting aspect handles back-end account tracking services. RADIUS has worked well, but it has some limitations-namely, that it is limited to working over the SLIP and PPP data link protocols used with modem connections. A number of new devices are being used to access the Internet, such as smart phones and hand-held devices that use different access protocols.

DIAMETER evolves the RADIUS scheme by adding new features, such as the ability to ask for additional logon information beyond the basic authentication. For example, DIAMETER uses the initial logon and authentication to identify a user, and then can continue to query the user for additional information that might be used to strengthen the authentication or to give the user access to additional systems.

DIAMETER supports user roaming. The IETF ROAMOPS (Roaming Operations) Working Group investigated whether RADIUS could be used to support roaming and concluded that it was ill suited to handle interdomain exchange of user and accounting information. DIAMETER is a new solution to this problem. See "Roaming" for more information.

Note that the base DIAMETER protocol is not used on its own but is always extended for a particular applications. DIAMETER is being worked into extensions under development by the following IETF working groups:

• ROAMOPS (Roaming Operations) is developing procedures, mechanisms, and protocols to support user roaming among groups of Internet service providers (ISPs).


• NASREQ (Network Access Server Requirements) is taking NAS design beyond simple dial-up into VPN support, smart authentication methods, and roaming.


• MobileIP (IP Routing for Wireless/Mobile Hosts) is developing routing support to permit IP nodes (hosts and routers) using either IPv4 or IPv6 to seamlessly "roam" among IP subnetworks and media types.


• AAA (Authentication, Authorization, and Accounting) is developing DIAMETER- related protocols with added accounting, transport, security, and proxy support.

DIAMETER was under development at the time of this writing. You can obtain a list of relevant documents by going to the IETF "Internet-Drafts" Web page (see related entries page) and searching for "DIAMETER." The previously mentioned Working Groups also list drafts and RFCs related to DIAMETER.

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