For the geometric term, see diameter.
Diameter is an Authentication, Authorization and Accounting (AAA) protocol for applications such as network access or IP mobility. It is intended to work in both local and roaming situations. The name is a pun on the RADIUS protocol, which is the predecessor (a diameter is twice the radius). Diameter is not directly backwards compatible, but provides an upgrade path for RADIUS.
The Diameter Base Protocol is defined by RFC 3588, and complies with the AAA Transport Profile (RFC 3539). Examples of Diameter applications currently in preparation are:
- Mobile IPv4 Application (MobileIP)
- Network Access Server Application (NASREQ)
- Extensible Authentication Protocol Application (EAP)
- Credit-Control Application (CC)
- Session Initiation Protocol Application (SIP)
- various applications in the 3GPP IP Multimedia Subsystem (IMS)
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