4 Messaging overview

24.2473GPPMessaging service using the IP Multimedia (IM) Core Network (CN) subsystemRelease 17Stage 3TS

The basic services for the IP Multimedia core network Subsystem (IMS), as defined in 3GPP TS 24.229 [5], allow a user to initiate, modify and terminate media sessions using the Session Initiation Protocol, as defined in RFC 3261 [7]. Although these basic mechanisms already allow the exchange of instant messaging information using SIP, this functionality can be extended to provide a richer service within the IMS.

The messaging service within the IM CN subsystem provides the means for a user to send or receive single messages immediately to / from another user and to create and participate in a messaging conference with one ore more other users. Participants to such message based communication may be internal or external to the home network.

When to use an immediate message and when to use a session-based messaging session will depend on the application.

NOTE: Some participants may always use session-based messaging, while others may use immediate messaging or a combination of session-based messaging and immediate messaging dependant of the characteristics of the messaging session. The criteria are implementation and application specific.

For immediate messaging the procedures for page-mode messaging, as defined in RFC 3428 [8] or for session-mode messaging, as defined in RFC 4975 [9], RFC 6714 [19] and RFC 6135 [18] are utilized. When to use an page-mode messaging and when to use session-mode messaging session for the purpose of immediate messaging will depend on the application.

For session-based messaging and session-based messaging conferences, the Message Session Relay Protocol (MSRP) is utilized to transport messages.

The architecture for the 3GPP messaging is specified in 3GPP TS 23.228 [6] and 3GPP TS 23.218 [3]. The 3GPP recommended media formats and codecs are specified in 3GPP TS 26.141 [14]. The 3GPP2 recommended media formats and codecs are specified in 3GPP2 C.S0050-B [17].

The functional split for session-mode messaging between an AS, MRFC and MRFP is that same as that described in clause 4 in 3GPP TS 24.147 [10] for SIP based conferences. The functional split between the AS, MRFC and MRFP for page-model messaging is out of scope of the present document.