Regarding the AMF discovery and selection procedure

[Lakshmirnr]

I am using Open5GS V2.7.1 and UERANSIM v3.2.6 for a 5G setup. In the ‘amfconfigs’ section of the open5gs-gnb.yaml file in UERANSIM, it appears that only one AMF is configured to be selected by the particular gNB. I also checked a list of AMFs, but only the first one was selected.

According to the 3GPP document TS 23.501, "System Architecture for the 5G System" (3GPP TS 23.501 version 17.4.0 Release 17), the (R)AN selects an AMF set and an AMF from the AMF set under different circumstances. Is this functionality implemented in UERANSIM? Could you provide more information about the AMF selection procedure in UERANSIM?

[Lakshmirnr]

According to the 3GPP TS 23.501, section 6.3.5 AMF discovery and selection, the following factors should be considered for selecting an AMF by the RAN.

The AMF selection functionality in the 5G-AN may consider the following factors for selecting the AMF Set:

• AMF Region ID and AMF Set ID derived from GUAMI;
• Requested NSSAI;
• Local operator policies;
• 5G CIoT features indicated in RRC signalling by the UE;
• IAB-indication;
• NB-IoT RAT Type; and
• Category M Indication.

AMF selection functionality in the 5G-AN or CP NFs or SCP considers the following factors for selecting an AMF
from AMF Set:

• Availability of candidate AMF(s).
• Load balancing across candidate AMF(s) (e.g. considering weight factors of candidate AMFs in the AMF Set).
• In 5G-AN, 5G CIoT features indicated in RRC signalling by the UE.

So there should be algorithm designed for AMF selecton, from the gNb side (apart from selecting one AMF), which is missing.