Service Discovery Protocol

In Release 15, the SDP function was extended to support new service discovery mechanisms, including the WebRTC Web Server Function discovery. It also introduced specific SDP body modifications for off-network Mission Critical services, such as adding an audio media level section for MCVideo group and private calls, and removing the IP address from the media-level section for MCData Standalone SDS. Furthermore, enhancements were made for ProSe direct discovery over WLAN with the addition of a Diameter AVP for charging.

• WebRTC Web Server Function discovery TS 23.228CR1173
• Add Diameter AVP for charging of WLAN-based ProSe direct discovery TS 32.299CR0796
• Clarification on PCF discovery and selection TS 29.513CR0003
• Correction to the PCF discovery and selection TS 29.513CR0016
• Correction on PCF discovery TS 29.513CR0052
• Adding audio media level section in SDP body for offnetwork MCVideo group and private call TS 24.281CR0072

+ 2 more changes

In Release 16, the SDP function was enhanced to enable new network function discovery mechanisms, specifically allowing the SMF to perform P-CSCF discovery using the NRF and updating PCF discovery procedures for the AF within the eSBA architecture. It also introduced clarifications and corrections for HSS and S-CSCF discovery processes, including interface type selection via the NRF. Furthermore, the release addressed technical corrections in areas like IP Connectivity SDP offer/answer generation and the handling of erroneous protocol data.

• HSS Discovery and Interface Type Selection TS 23.228CR1201
• Allowing SMF to perform P-CSCF Discovery using NRF TS 23.228CR1202
• Support for MCData emergency alert and communications MCC note: This CR introduces the abbreviation IMPU; MCC has added this in the list of abbreviations, choosing the most appropriate of the five variations appearing in other 3GPP Specs. Similarly, MCC has provided the expansions of abbreviations UUID and URN introduced, but not defined by, this CR. The newly introduced term "Group identity" has a circular definition. In §D.1.3,, "can" has been changed to "may" in newly introduced bullet points 11 c), 11 c) i), and 11 e). TS 24.282CR0126
• DNN Replacement as PCF discovery factor for the AMF TS 29.513CR0122
• Update of PCF discovery by the AF for eSBA TS 29.513CR0142
• Clarification for HSS Discovery and Interface Type Selection TS 23.228CR1212

+ 5 more changes

In Release 17, key SDP updates introduced specific discovery procedures for new functional entities like the TSCTSF (Transit and Screening Control Function) and the NWDAF (Network Data Analytics Function) by the PCF (Policy Control Function). Furthermore, the release enhanced the discovery mechanisms for the PCF itself, including its use for a UE, for a PDU session, and within MBS (Multicast Broadcast Service) PCC (Policy and Charging Control) deployments. It also added the functional alias association protocol implementations for critical MCPTT, MCData, and MCVideo service groups.

• Reference update for HTTP/1.1 protocol TS 24.259CR0055
• Functional alias association with MCVideo group - protocol implementation TS 24.281CR0141
• Functional alias association with MCData group - protocol implementation TS 24.282CR0265
• Functional alias association with MCPTT group - protocol implementation TS 24.379CR0747
• NWDAF discovery by the PCF TS 29.513CR0297
• Completion of PCF discovery mechanisms TS 29.513CR0300

+ 17 more changes

In Release 18, the SDP function was enhanced to support service discovery and capability exchange for new features including IMS Data Channels, V2X application servers for MBS, and RCS. Key additions involved new SDP attributes for data channel sub-protocols, direction attributes, and the encoding of configuration parameters for V2X MBS. The release also introduced clarifications and corrections for SDP offer-answer procedures in contexts like MCPTT, MCVideo, and one-to-one/group SDS communications.

• IMS DC capability discovery TS 23.228CR1268
• KI#4 Describe option to support MRF registration and discovery using NRF TS 23.228CR1265
• MCVideo support of multiplexing - SDP offers and answers TS 24.281CR0215
• MCPTT support of multiplexing - SDP offers and answers TS 24.379CR0889
• V2X application server discovery for MBS TS 24.587CR0275
• Introduction of V2X MBS parameter discovery TS 24.587CR0279

+ 20 more changes

In Release 19, the SDP function was enhanced to support the negotiation of IMS application data channels by adding an `app-dc-status` parameter to the `3gpp-req-app` attribute. It also introduced a new affiliation check procedure for handling SIP MESSAGE requests used for absolute URI discovery. Furthermore, corrections were made to bandwidth (`b=AS`) calculations and SDP examples for Immersive Voice and Audio Services (IVAS).

• Terminating local BDC establishment without BDC media component in SDP of incoming INVITE request TS 23.228CR1416
• Adding app-dc-status parameter to 3gpp-req-app attribute for SDP negotiation of IMS application data channels TS 26.114CR0590
• Affiliation check upon receiving a "SIP MESSAGE request for absolute URI discovery request" message TS 24.282CR0470
• Corrections to b=AS calculations and SDP examples for IVAS TS 26.114CR0600