The present document provides the protocol details for the messaging service within the IP Multimedia Subsystem (IMS) based on the Session Initiation Protocol (SIP), the Session Description Protocol (SDP) and, the Message Session Relay Protocol (MSRP). The document covers immediate messaging; session based messaging and session-based messaging conferences.

Where possible the present document specifies the requirements for this protocol by reference to specifications produced by the IETF within the scope of SIP, SDP and, MSRP, either directly, or as modified by 3GPP2 X.S0013-004.

The present document is applicable to Application Servers (ASs), Media Resource Function Controllers (MRFCs), Media Resource Function Processors (MRFPs) and to User Equipment (UE) providing messaging capabilities.

This document does not cover the signalling between a MRFC and a MRFP.