As a new generation AAA (Authentication, Authorization and Accounting) protocol, Diameter has been used widely and will be used more and more widely in 3GPP. Since several 3GPP WGs are developing Diameter based interfaces, e.g. CT3, CT4, etc, so in order to ensure correctness and consistency of using Diameter within all 3GPP WGs, a common set of principles, rules and recommendations across 3GPP WGs are necessary to be given clearly and followed. The present is to describe existing status of Diameter usage within 3GPP, find existing inconsistency of rules used for Diameter based interfaces which were specified in 3GPP and propose common recommendations of using Diameter to all 3GPP WGs to follow. With more and more Diameter deployment, an inter-operator Diameter signalling network infrastructure will become necessary, so the present document will also study Diameter inter-operator considerations with brief guidelines on how to deploy & realize the inter-operator Diameter-based roaming infrastructure.

The present document contains a common set of principles, rules and recommendations across 3GPP WGs to ensure Diameter-based interfaces have the same treatment for release control and generating new applications-id. Also to address in a unified manner the use/re-use of AVPs, and other Diameter BASE (see IETF RFC 3588 [x]) related decisions. The present document covers all aspects of Diameter usage within 3GPP, including description of the current situation of Diameter usage in different 3GPP WGs (CT3, CT4, SA5) in Release 6/7, describe recommendations and conditions to re-use existing Diameter applications (3GPP or IETF application-id), commands, AVPs and/or AVP values, describe recommendations and conditions to define new Diameter applications, commands, AVPs and/or AVP values, and any other related issues, e.g. the cross-release issue, whether to apply proposed guideline back to existing Diameter applications or not, or only new SAE Diameter interfaces, etc. To achieve maximum benefit from this work it is strongly recommended that all 3GPP Diameter-based protocols follow the recommendations in the present document. The present document also serves a placeholder for Diameter inter-operator considerations with brief guidelines on how to deploy & realize the inter-operator Diameter-based roaming infrastructure.