Session Initiation Protocol

In Release 15, new SIP procedures were introduced for using functional aliases in initial INVITE requests, both for client and server operations. The release also specified the use of TCP for SIP signaling during voice fallback to EPS when the N26 interface is absent and clarified the usage of SIP REFER for group calls. Furthermore, it added mechanisms for the retrieval of migration credentials to access a partner mission-critical system's SIP core and removed unified access control checks when adding or removing media during an MMTEL session.

• Retrieval of migration credentials for access to SIP core / IMS of a partner MC system TS 23.280CR0066
• Use TCP for SIP signaling in case of voice fallback to EPS without N26 interface TS 24.173CR0131
• Using functional alias in initial SIP INVITE request – client procedures TS 24.379CR0394
• Using functional alias in initial SIP INVITE request – server procedures TS 24.379CR0395
• No unified access control check when adding or removing media during MMTEL session TS 24.173CR0130
• Correction to session-type in XML schema for MCVideo Information TS 24.281CR0039

+ 13 more changes

In Release 16, key SIP enhancements introduced procedures for establishing, using, and releasing a "pre-established session" to efficiently initiate SDS and MCData communications. Furthermore, the P-CSCF's capabilities were expanded to support SIP forking, RTCP flows, and Access Type Change notifications, and its discovery was integrated with the NRF, allowing the SMF to perform it.

• eIMS P-CSCF use of NRF TS 23.228CR1199
• Allowing SMF to perform P-CSCF Discovery using NRF TS 23.228CR1202
• New IMS Management Objects for Handling of Session Timer TS 24.167CR0215
• Pre-established session – References, General details and warning updates TS 24.282CR0079
• Common procedures for initiating SDS communication using pre-established session TS 24.282CR0080
• Pre-established session – General and PF use of resource sharing TS 24.282CR0081

+ 52 more changes

In Release 17, SIP enhancements primarily focused on Mission Critical Services, introducing functional alias association protocols for MCPTT, MCVideo, and MCData groups to enable alias-based targeting within pre-established sessions. Additionally, procedures were added for upgrading, cancelling, or establishing on-network private emergency communications for MCData and SDS sessions. The release also updated SIP Digest Access Authentication to support hash values for alternate algorithms and referenced the current HTTP/1.1 protocol.

• Upgrade IMS non-MPS session to an IMS MPS session. TS 23.228CR1238
• Support for Attestation for IMS priority sessions TS 23.228CR1241
• Request for network resources at session establishment from the MC service server TS 23.280CR0278
• Update of HTTP Digest Access Authentication and reference update for HTTP/1.1 protocol TS 24.141CR0119
• Reference update for HTTP/1.1 protocol TS 24.259CR0055
• Functional alias association with MCVideo group - protocol implementation TS 24.281CR0141

+ 38 more changes

In Release 18, SIP enhancements primarily focused on standardizing procedures for Mission Critical Services (MCPTT, MCVideo, MCData), specifically for managing ad-hoc group sessions using pre-established sessions within a single system. This included defining protocols and controlling function (CF) procedures to determine users to invite or release based on specific criteria for these group communications. Additionally, the release introduced support for handling SIP MESSAGE requests for ad-hoc group emergency alert cancellation and added protocol description parameter support in the Npcf_PolicyAuthorization service API.

• Clarification regarding the protocol used on new reference points TS 23.280CR0313
• General Adhoc group call procedures using pre-established session in Single system - Protoc impl for MCVideo TS 24.281CR0229
• General Adhoc group call procedures using pre-established session in Single system - procedures at CF (mcvideo) TS 24.281CR0236
• Determine the users based on the criteria to invite, release from, an ad hoc group session - MCVideo TS 24.281CR0245
• General Adhoc group data communication procedures using pre-established session in Single system - Protoc impl for MCData TS 24.282CR0365
• General Adhoc group comm procedures using pre-established session in Single system - procedures at CF (mcdata) TS 24.282CR0378

+ 42 more changes

In Release 19, SIP enhancements introduced new procedures for Mission Critical Services (MCX), including adding a reason to leave a session in MCVideo, MCData, and MCPTT, and supporting session recording using the Session Recording Protocol. The release also added capabilities for the P-CSCF to retrieve satellite service identifiers during SIP procedures and introduced modifications for standalone IMS Data Channel sessions. Furthermore, it expanded support for ad-hoc group emergency alerts by adding criteria to SIP messages containing participant lists.

• Support of MPS priority for IMS Immediate Messaging and IMS Session-based Messaging TS 23.228CR1419
• Address ENs in IMS AS Session Management Service TS 23.228CR1483
• DCSF instructing the IMS AS to terminate the session at the IMS AS TS 23.228CR1498
• KI#2: Procedure of adding bootstrap DC to existing IMS session TS 23.228CR1589
• Add the regroup group member update during MCX session TS 23.280CR0441
• MC Recording procedures using Session Recording Protocol TS 23.280CR0630

+ 26 more changes

In Release 20, the primary change for the Session Initiation Protocol function was the removal of support for the "simultaneous session" capability. This modification streamlined the protocol by eliminating the procedures and mechanisms required for handling multiple concurrent sessions within a single communication instance. Consequently, session establishment and management logic was simplified, focusing on single-session interactions.

• Remove simultaneous session TS 23.280CR0711
• Remove simultaneous session TS 23.281CR0262
• Remove simultaneous session TS 23.379CR0502