The present document analyses the CT4 aspects of the 5G System (5GS) - Phase 1, based on the service requirements defined in TS 22.261, the stage 2 system architecture requirements defined in TS 23.501 and the stage 2 procedures and flows defined in TS 23.502. These CT4 aspects include the study and selection of the protocols and the definition of the procedures and services that will be used in the 5GS, including:

• the protocol and procedures for User Plane interfaces;
• the protocols, procedures and services for Control Plane interfaces (excluding PCC interfaces);
• the User Plane management procedures over N4;
• the interworking with E-UTRAN connected to EPC;
• specific services in the 5GS (SMS, PWS, LCS, IMS, Emergency Services, MPS, PEI checking);
• numbering, addressing and identification in the 5GS;
• subscriber data in 5GS;
• Network slicing impacts;
• Impacts due to Virtualization.

The present document also helps assessing the appropriate CT4 specifications structure for documenting the CT4 impacts for the 5GS. It is used as a place holder for CT4 5GS materials to be moved to appropriate 3GPP technical specifications when the TR is sufficiently stable. SA2 or SA3 status is added as a note when unstable topics in SA2 or SA3 are described in this document.