DIAMETER

DIAMETER is an AAA protocol (Authentication, Authorization and Accounting) succeeding its predecessor RADIUS.

Upgrade from RADIUS

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 main differences are :

it uses reliable transport protocols (TCP or SCTP, not UDP)
it can use transport level security (IPsec or TLS)
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 is a client-server protocol, with exception of supporting some server-initiated messages as well
both stateful and stateless models can be used
it has dynamic discovery of peers (using DNS SRV 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 more easily extended; new commands and attributes can be defined
it is aligned on 32 bit boundaries
it has basic support for user-sessions and accounting

Protocol description

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. An application is not a program, but a protocol based on Diameter. Diameter security is provided by IPSEC or TLS, both well-regarded protocols.

Applications

A Diameter Application is not a software application, but a protocol based on the DIAMETER Base protocol (defined in RFC 3588). Each application is defined by an application identifier and can add new command codes and/or new mandatory AVPs. Adding a new optional AVP does not require a new application.

Examples of Diameter applications :

Diameter Mobile IPv4 Application (MobileIP, RFC 4004)
Diameter Network Access Server Application (NASREQ, RFC 4005)
Diameter Extensible Authentication Protocol Application (RFC 4072)
Diameter Credit-Control Application (DCCA, RFC 4006)
Diameter Session Initiation Protocol Application (RFC 4740)
various applications in the 3GPP IP Multimedia Subsystem

External links

http://www.opendiameter.org/
http://www.cisco.com/en/US/products/ps6638/products_data_sheet09186a00804fe332.html Cisco page outlining differences between RADIUS and DIAMETER
http://www.csg.uzh.ch/staff/morariu/opendiameter/ - Debian Packages for OpenDiameter
https://jdiameter.dev.java.net/ - Diameter Base Protocols written in Java

The actual descriptive text portion of the article above (and its Contents menu) are licensed under the GNU Free Documentation License then in effect published by the Free Software Foundation. The text article uses material from http://en.wikipedia.org/wiki/DIAMETER (retrieval date: 2007-05-27) and is provided "as-is" and without warranty. Permission is granted to copy, distribute and/or modify only the actual descriptive text portion of the article above (and its Contents Box) under the GNU Free Documentation License. A copy of the license is available at: http://en.wikipedia.org/wiki/Wikipedia:Text_of_the_GNU_Free_Documentation_License. Any advertisements (or active links not embedded in the actual article) and the layout or selection thereof are excluded from such license.
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