My 3GPP 23.501 Notes

My 3GPP 23.501 Notes

Definition and abbreviations

See My 3GPP definition notes for definitions

See My 3GPP abbreviation notes for abbreviations

§ 4.2.1 General

23.501 describes the architecture for the 5G System. The 5G architecture is defined as service-based and the interaction between network functions is represented in two ways.

• A service-based representation, where network functions (e.g. AMF) within the Control Plane enables other authorized network functions to access their services. This representation also includes point-to-point reference points where necessary.
• A reference point representation, shows the interaction exist between the NF services in the network functions described by point-to-point reference point (e.g. N11) between any two network functions (e.g. AMF and SMF).

Service-based interfaces are listed in clause 4.2.6. Reference points are listed in clause 4.2.7.

Network functions within the 5GC Control Plane shall only use service-based interfaces for their interactions.

NOTE 1: The interactions between NF services within one NF are not specified in this Release of the specification.

NOTE 2: UPF does not provide any services in this Release of the specification, but can consume services provided by 5GC Control Plane NFs.

NFs and NF services can communicate directly, referred to as Direct Communication, or indirectly via the Service Communication Proxy (SCP), referred to as Indirect Communication. For more information on communication options, see Annex E and clauses under 6.3.1 and 7.1.2.

In addition to the architecture descriptions in clause 4, the following areas are further described in other specifications:

• NG-RAN architecture is described in TS 38.300 and TS 38.401.
• Security architecture is described in TS 33.501 and TS 33.535.
• Charging architecture is described in TS 32.240.
• 5G Media streaming architecture is described in TS 26.501.

NOTE 3: The NFs listed in clause 4.2.2 are described in the following clauses or in the specifications above.

§ 4.2.6 Service-based interfaces

See spec for full list. The 5G System Architecture contains the following service-based interfaces that are of interest to me:

Service-based interfaces

Reference	Exhibited by	Notes
Namf	AMF
Nsmf	SMF
Nudm	UDM

§ 4.2.7 Reference Points

The 5G System Architecture reference points:

Reference Points

Reference	Endpoints	Notes
N1	UE and AMF
N2	(R)AN and AMF
N3	(R)AN and UPF
N4	SMF and UPF
N6	UPF and Data Network
N9	UPF and UPF

The following reference points are of interest to me and show the interactions that exist between the NF services in the NFs. See spec for full list of reference points. These reference points are realized by corresponding NF service-based interfaces and by specifying the identified consumer and producer NF service as well as their interaction in order to realize a particular system procedure.

Reference Points

Reference	Endpoints	Notes
N8	UDM and AMF
N10	UDM and SMF
N11	AMF and SMF
N12	AMF and AUSF
N14	AMF and AMF

§ 4.2.8 Support for non-3GPP access

4.2.8.0 General

The following types of non-3GPP access networks are defined (as of V17.5.0):

• Untrusted non-3GPP access networks;
• Trusted non-3GPP access networks; and
• Wireline access networks.

The architecture to support Untrusted and Trusted non-3GPP access networks is defined in clause 4.2.8.2. The architecture to support Wireline access networks is defined in clause 4.2.8.2.4 and in TS 23.316.

4.3 Interworking with EPC

4.3.1 Non-roaming architecture

See figure 4.3.1-1 in specification, it represents the non-roaming architecture for interworking between 5GS and EPC/E-UTRAN.

N26 interface is an inter-CN interface between the MME and 5GS AMF in order to enable interworking between EPC and the NG core. Support of N26 interface in the network is optional for interworking. N26 supports subset of the functionalities (essential for interworking) that are supported over S10.

4.3.2 Roaming architecture

See figure 4.3.2-1 in specification, it represents the Roaming architecture with local breakout and Figure 4.3.2-2 represents the Roaming architecture with home-routed traffic for interworking between 5GS and EPC/E-UTRAN.

§ 5.2.1 General

Network access is the means for user to connect to 5G Core Network (CN). Network access control comprises the following functionality:

• Network selection,
• Identification and authentication,
• Authorization,
• Access control and barring,
• Policy control,
• Lawful Interception.

§ 5.2.2 Network Selection

To determine which PLMN to attempt registration, UE performs network selection. The network selection procedure comprises two main parts, PLMN selection and access network (AN) selection. The requirements for PLMN selection are specified in TS 22.011 and the procedures are in TS 23.122. The access network (AN) selection part for the 3GPP access networks is specified in TS 36.300 for E-UTRAN and in TS 38.300 for the NR. The network selection for Disaster Roaming is described in TS 23.122 and TS 24.501.

§ 5.2.3 Identification and authentication

The network may authenticate the UE during any procedure establishing a NAS signalling connection with the UE. The security architecture is specified in TS 33.501. The network may optionally perform an PEI check with 5G-EIR.

§ 5.2.4 Authorization

The authorization for connectivity of the subscriber to the 5GC and the authorization for the services that the user is allowed to access based on subscription (e.g. Operator Determined Barring, Roaming restrictions, Access Type and RAT Type currently in use) is evaluated once the user is successfully identified and authenticated. This authorization is executed during UE Registration procedure.

§ 5.2.5 Access control and barring see spec

§ 5.2.6 Policy control

Network access control including service authorization may be influenced by Policy control, as specified in clause 5.14.

§ 5.2.7 Lawful Interception

For definition and functionality of Lawful Interception, see TS 33.126.

§ 5.4.7 NG-RAN location reporting

NG-RAN supports the NG-RAN location reporting for the services that require accurate cell identification (e.g. emergency services, lawful intercept, charging) or for the UE mobility event notification service subscribed to the AMF by other NFs. The NG-RAN location reporting may be used by the AMF when the target UE is in CM-CONNECTED state. The NG-RAN location reporting may be used by the AMF to determine the geographically located TAI in the case of NR satellite access.

The AMF may request the NG-RAN location reporting with event reporting type (e.g. UE location or UE presence in Area of Interest), reporting mode and its related parameters (e.g. number of reporting).

If the AMF requests UE location, the NG-RAN reports the current UE location (or last known UE location with time stamp if the UE is in RRC Inactive state) based on the requested reporting parameter (e.g. one-time reporting or continuous reporting).

If the AMF requests UE location, in the case of NR satellite access, the NG-RAN provides all broadcast TAIs to the AMF as part of the ULI. The NG-RAN also reports the TAI where the UE is geographically located if this TAI can be determined.

If the AMF requests UE presence in the Area Of Interest, the NG-RAN reports the UE location and the indication (i.e. IN, OUT or UNKNOWN) when the NG-RAN determines the change of UE presence in Area Of Interest. After N2 based Handover, if the NG-RAN location reporting information is required, the AMF shall re-request the NG-RAN location reporting to the target NG-RAN node. For Xn based Handover, the source NG-RAN shall transfer the requested NG-RAN location reporting information to target NG-RAN node.

The AMF requests the location information of the UE either through independent N2 procedure (i.e. NG-RAN location reporting as specified in clause 4.10 of TS 23.502), or by including the request in some specific N2 messages as specified in TS 38.413.

5.5 Non-3GPP access specific aspects

5.5.0 General

This clause describe the specific aspects for untrusted non-3GPP access, trusted non-3GPP access and W-5GAN access.

5.5.1 Registration Management

This clause applies to Non-3GPP access network corresponding to the Untrusted Non-3GPP access network, to the Trusted Non-3GPP access network and to the W-5GAN (Wireline 5G Access Network). In the case of W-5GAN the UE mentioned in this clause corresponds to 5G-RG (5G Residential Gateway) or to the W-AGF (Wireline Access Gateway Function) in the case of FN-RG (Fixed Network Residential Gateway). In the case of N5CW (Non-5G-Capable over WLAN) devices access 5GC (5G Core Network) via trusted WLAN access networks, the UE mentioned in this clause corresponds to TWIF (Trusted WLAN Interworking Function).

To Telecommunications Info