defines the Session Management related procedures. It refers to clause 4.4
for the N4 interactions.
As defined in TS 23.501, clause 5.6.3
, considering the case of Home Routed PDU Session, the NAS SM information processing by SMF considers following kind of NAS SM information:
Information that both the V-SMF and H-SMF process: indication of the nature of the NAS SM signalling (e.g. PDU Session Establishment Request), PDU Session Type, Session-AMBR, UE addressing information (allocated IPv4 address, interface identifier).
Information that is not visible to the V-SMF, only processed by the H-SMF: SSC mode, Protocol Configuration Options, SM PDU DN Request Container, QoS Rule(s) and QoS Flow level QoS parameters if any for the QoS Flow(s) associated with the QoS rule(s).
"Information that is not visible to the V-SMF" refers to information that the V-SMF is to relay between the UE and the H-SMF (and that it can store in CDR) but that the V-SMF is not assumed to process otherwise.
The NAS SM information processing split between V-SMF and H-SMF is transparent to the UE.
Both V-SMF and H-SMF process information interpreted by the AMF as the PDU Session ID, the DNN, the S-NSSAI (with values for the Serving PLMN and HPLMN processed by the V-SMF, and with a value for the HPLMN processed by the H-SMF).
In the case of Home Routed PDU Session the H-SMF provides also the V-SMF with the IPv6 Prefix allocated to the PDU Session.
IPv6 Prefix allocated to the PDU Session is provided to allow the V-SMF fulfilling regulatory requirements for data storage in the visited country.
In non roaming and LBO cases the SMF processes all NAS SM information.
In HR roaming scenarios, in order to support SM features only requiring support from the H-SMF without impacting the V-SMF, as specified in detail in TS 29.502
The V-SMF transfers NAS SM information, which is not visible to the V-SMF, in a container towards the H-SMF;
The V-SMF transfers NAS SM information which it does not comprehend (unknown IEs or IEs with an unknown value not set to "reserved" according to the release to which the V-SMF complies), in a different container towards the H-SMF;
The H-SMF transfers NAS SM information which the V-SMF does not need to interpret, in one container towards the V-SMF;
The V-SMF appends unknown NAS SM information received in the N16 container at the end of the NAS SM message it sends to the UE.
A PDU Session establishment may correspond to:
a UE initiated PDU Session Establishment procedure.
a UE initiated PDU Session handover between 3GPP and non-3GPP.
a UE initiated PDU Session handover from EPS to 5GS.
a Network triggered PDU Session Establishment procedure. In this case the network sends the device trigger message to application(s) on the UE side. The payload included in Device Trigger Request message contains information on which application on the UE side is expected to trigger the PDU Session establishment request. Based on that information, the application(s) on the UE side trigger the PDU Session Establishment procedure. For more detail refer to clause 4.13.2.
If the UE is simultaneously registered to a non-3GPP access via a N3IWF/TNGF/W-AGF located in a PLMN different from the PLMN of the 3GPP access, the functional entities in the following procedures are located in the PLMN of the access used to exchange NAS with the UE for the PDU Session.
As specified in TS 23.501, clause 5.6.1
, a PDU Session may be associated either (a) with a single access type at a given time, i.e. either 3GPP access or non-3GPP access, or (b) simultaneously with multiple access types, i.e. one 3GPP access and one non-3GPP access. A PDU Session associated with multiple access types is referred to as Multi Access-PDU (MA PDU) Session and it may be requested by ATSSS-capable UEs.
The following clause 188.8.131.52
specifies the procedures for establishing PDU Sessions associated with a single access type at a given time. The particular procedures associated with MA PDU Sessions are specified as part of the ATSSS procedures in clause 4.22