The present document defines a transport protocol for use in the IP multimedia (IM) Core Network (CN) subsystem based on Diameter.

The present document is applicable to:

- The Sh interface between an SIP AS and the AAA.

- The Sh interface between an SCS and the AAA.

Whenever it is possible this document specifies the requirements for this protocol by reference to 8 specifications produced by the IETF within the scope of Diameter. Where this is not possible, extensions to 9 Diameter are defined within this document.