DIAMETER Totally Explained

ť For the geometric term, see DiameterDIAMETER is a computer networking protocol for AAA (Authentication, Authorization and Accounting). It is a successor to RADIUS.

Upgrade from RADIUS

The name is a pun on the RADIUS protocol, which is the predecessor (a diameter is twice the radius). Diameter isn't 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 network or 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's 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 state machines (RFC 3539)
it has error notification
it has better roaming support
it's more easily extended; new commands and attributes can be defined
it's 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 isn't a program, but a protocol based on Diameter. Diameter security is provided by IPSEC or TLS, both well-regarded protocols.

Packet format

Commands

Each command is assigned a command code, which is used for both requests and answers. 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 doesn't 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

3GPP GBA (Generic Bootstrapping Architecture): Bootstrapping Server Function

External results

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