This clause describes the procedures used for 5GS session management (5GSM) performed over an N1 NAS signalling connection. The main function of the 5GSM sublayer is to support the PDU session handling in the UE and in the SMF (transferred via the AMF). The 5GSM comprises procedures for:

• the authentication and authorization, establishment, modification and release of PDU sessions; and
• request for performing handover of an existing PDU session between 3GPP access and non-3GPP access, or to transfer an existing PDN connection in the EPS to the 5GS.

Each PDU session represents a PDU session established between the UE and an SMF. PDU sessions can remain established even if the radio and network resources constituting the corresponding PDU session between the UE and the SMF are temporarily released. 5GSM procedures can be performed only if a 5GMM context has been established between the UE and the AMF, and the secure exchange of NAS messages has been initiated by the AMF by use of the 5GMM procedures described in clause 5. Once the UE is successfully registered to a PLMN, a PDU session can be established. If no 5GMM context has been established, the 5GMM sublayer has to initiate the establishment of a 5GMM context by use of the 5GMM procedures as described in clause 5. The UE can request the network to modify or release PDU sessions. The network can fulfil such a request from the UE by modifying a PDU session or releasing a PDU session using network-requested procedures (see subclause 6.3).

Three types of 5GSM procedures can be distinguished:

1. Procedures related to PDU sessions:
   These procedures are initiated by the network and are used for authentication and authorization or manipulation of PDU sessions:
   1. PDU authentication and authorization;
   2. network-requested PDU session modification;
   3. network-requested PDU session release; and
   4. service-level authentication and authorization.
   This procedure is initiated by the UE and to request for establishment of PDU sessions or to perform handover of an existing PDU session between 3GPP access and non-3GPP access, or to transfer an existing PDN connection in the EPS to the 5GS:
   UE-requested PDU session establishment.
2. Transaction related procedures:
   These procedures are initiated by the UE to request for handling of PDU sessions, i.e. to modify a PDU session, or to release a PDU session:
   1. UE-requested PDU session modification; and
   2. UE-requested PDU session release.
   This procedure is initiated by the 5G ProSe UE-to-network relay UE and is used for the manipulation of PDU sessions:
   • remote UE report.
   A successful transaction related procedure initiated by the UE triggers the network to execute one of the following procedures related to PDU session; network-requested PDU session modification procedure or network-requested PDU session release procedure. The UE treats the start of the procedure related to the PDU session as completion of the transaction related procedure.
3. Common procedure:
   The following 5GSM procedure can be related to a PDU session or to a procedure transaction:
   5GSM status procedure.