Diameter (protocol)

Diameter is an authentication, authorization, and Accountingprotokoll ( Triple -A ) system for authentication of communication partners in a network.

The Diameter protocol is defined in RFC 6733 and fulfills the requirements of the AAA transport profile Authentication, Authorization, Accounting from the RFC 3539th

Diameter is including in the IP Multimedia Subsystem used.


The name is a pun on the previous protocol called RADIUS. The diameter ( engl. diameter) is a term used in geometry, which indicates twice the radius ( engl. radius) and thus second generation.

Upgrade from RADIUS

Diameter is not fully backward compatible with its predecessor Protocol Remote Authentication Dial- In User Service ( RADIUS). The benefits of Diameter over RADIUS include:

  • Reliable transport protocols (TCP or SCTP ​​)
  • Encryption with IPsec or TLS
  • The 32 -bit address space AVP (English: attribute value pairs) allows more than 256 different attributes, ie authenticatable entities
  • Stateful and stateless models can be used
  • Dynamic discovery of participants ( DNS SRV and NAPTR )
  • Bargaining power
  • Error Notification
  • Better roaming support
  • Easy extensibility - new commands and attributes can be defined
  • Basic support for user sessions and accounts
  • Network protocol at the application layer