For the geometric term, see DIAMETER.
Diameter is an AAA_protocol for applications such as network access or IP mobility. The basic concept is to provide a base protocol that can be extended in order to provide AAA services to new access technologies. Diameter is intended to work in both local and roaming AAA situations.
The name is a pun on the RADIUS protocol, which is the predecessor (a diameter is twice the radius). Diameter is not directly backward compatibility, but provides an upgrade path for RADIUS. The main differences are :
it uses reliable transport protocols (Transmission Control Protocol or Stream Control Transmission Protocol, not User Datagram Protocol)
it uses transport level security (IPsec or Transport Layer Security)
it has transition support for RADIUS
it has larger address space for AVPs (Attribute Value Pairs) and identifiers (32-bit instead of 8-bit)
it s a peer-to-peer protocol, not Client-server : supports server-initiated messages
both stateful and stateless models can be used
it has dynamic discovery of peers (using Domain Name System SRV record and NAPTR)
it has capability negotiation
it supports application layer acknowledgements, defines failover methods and statemachines (RFC 3539)
it has error notification
it has better roaming support
it is easier extended, new commands and attributes can be defined
basic support for user-sessions and accounting is built in
The Diameter Base Protocol is defined by RFC 3588, and defines the minimum requirements for an AAA protocol. Diameter Applications can extend the base protocol, by adding new commands and/or attributes. Examples of Diameter applications currently in preparation are:
Mobile IPv4 Application (MobileIP, RFC 4004)
Network Access Server Application (NASREQ, RFC 4005)
Extensible Authentication Protocol Application (EAP, RFC 4072)
Credit-Control Application (DCCA, RFC 4006)
Session Initiation Protocol Application (Session_Initiation_Protocol)
various applications in the 3GPP IP Multimedia Subsystem (IP_Multimedia_Subsystem)
=External links=
*
http://www.diameter.org/
*
http://www.opendiameter.org/