5G Terminal and AMF/SMF Interaction Information (2)

In the 5G system, the AMF is responsible not only for terminal (UE) access and mobility management, but also for processing and notifying other units about terminal (UE) service requests and data transmission. The key points of the interaction with related networks during this process are as follows:

I. The AMF is responsible for SMF selection according to the procedures described in clause 6.3.2; for this purpose, it obtains subscription data from the UDM as defined in that clause. In addition, it obtains the subscribed UE-AMBR from the UDM and, based on the operator's local policy, obtains the dynamic service network UE-AMBR (optional) from the PCF; then it sends it to the (R)AN as defined in clause 5.7.2; AMF-SMF interaction supporting LADN is defined in clause 5.6.5.

To support billing and meet regulatory requirements (NPLI (Network Provided Location Information) as defined in TS 23.228 [15]) related to IMS voice call establishment, modification and release or SMS transfer, the following provisions apply:

• If the AMF possesses the UE's PEI during PDU session establishment, the AMF will provide the PEI to the SMF.
• When the AMF forwards UL NAS or N2 signaling to a peer NF (such as SMF or SMSF) or during PDU session UP connection activation, it will provide any user location information received from the 5G-AN, as well as the AN access type (3GPP-non 3GPP) of the received UL NAS or N2 signaling.

The AMF will also provide the corresponding UE time zone. In addition, to meet regulatory requirements (i.e., providing Network Provided Location Information (NPLI) as defined in TS 23.228 [15]); when the access method is non-3GPP, if the UE is still connected to the same AMF for 3GPP access (i.e., user location information is valid), the AMF can also provide the last known 3GPP access user location information and its validity period.

II.The SMF may further provide user location information, access type, and UE time zone to the PCF. The PCF can obtain this information from the SMF to provide NPLI to applications that have requested NPLI (such as IMS). User location information may include:

• For 3GPP access: Cell ID, even if the AMF receives the primary cell ID from the auxiliary RAN node in NG-RAN, the AMF only includes the primary cell ID.
• For untrusted non-3GPP access: The local IP address used by the UE to connect to the N3IWF, and (if NAT is detected) the UDP source port number (optional).

III.Trusted non-3GPP

For trusted non-3GPP access: TNAP/TWAP identifier, the local IP address used by the UE/N5CW device to connect to the TNGF/TWIF, and (if NAT is detected) the UDP source port number (optional). When the UE connects to the TNGF using WLAN based on IEEE 802.11 technology, the TNAP identifier should include the SSID of the access point to which the UE is connected. The TNAP identifier should include at least one of the following elements, unless otherwise specified by the TWAN operator's policy:

• BSSID (see IEEE Std 802.11-2012 [106]);
• Address information of the TNAP to which the UE is connected.

IV. The TWAP identifier should include the SSID of the access point to which the NC5W is connected; unless otherwise specified by the TWAN operator's policy, the TWAP identifier should also include at least one of the following:

• BSSID (see IEEE Std 802.11-2012 [106]);
• Address information of the TWAP to which the UE is connected.

In addition:

• Multiple TNAPs/TWAPs may use the same SSID, and the SSID alone may not provide location information, but may be sufficient for billing purposes.
• It is assumed that the BSSID associated with the TNAP/TWAP is static.

V. User location information for W-5GAN access is defined in TS 23.316 [84]. When the SMF receives a request to provide access network information report, and there are no operations required to be performed on the 5G-AN or UE (e.g., no QoS flows need to be created/updated/modified), the SMF may request user location information from the AMF. The interaction between the AMF and SMF for the insertion, relocation, or removal of the I-SMF in a PDU session is described in Section 5.34.