What Does Diameter Mean?

Diameter is an authentication, authorization and accounting
(AAA) protocol used by computer networks. It defines the minimum requirements
that an AAA protocol must support and was built to surpass and replace the
older RADIUS protocol that preceded it. It came about because of various
developments made to address the limitations of the RADIUS gateway.


Techopedia Explains Diameter

Diameter is a base foundation protocol with routing capabilities, negotiation capabilities, error handling and transmission of diameter messages. It serves to authenticate, authorize and account for the activities of a user before being allowed into the network to use an ISP’s services.

AAA is simply a process that filters information before granting access to a client or user into a network in order to provide a secure and reliable output. One of the early standards used to implement AAA is the Remote Authentication Dial-In User Service (RADIUS) that Diameter replaced. RADIUS was quite popular, however it was very limited in security and reliability, so it was improved on by adding advanced processes and new operations such as attribute-value pairs and error notification. The base RADIUS gateway protocol plus the new added features became the Diameter protocol, which is just a pun on RADIUS since the diameter of a circle is equal to twice its radius.

The design of Diameter was started by the 3rd Generation Partnership Project (3GPP) for their IP Multimedia Subsystem (IMS). It supports interfaces such as Dx, Dh, Cx, Ro, Rh and Sh. It was not backwards compatible, so older applications utilizing RADIUS had to adapt to the new protocol.


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Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.