At power up, restart and when modifications are applied, the 5G-AN node and AMF use non-UE related N2 signalling to exchange configuration data. Full details of this configuration data are specified in TS 38.300
, but the following highlights some aspects.
The AMF supplies the 5G-AN node with information about:
the AMF Name and the GUAMI(s) configured on that AMF Name;
the set of TNL associations to be established between the NG-RAN node and the AMF;
weight factor associated with each of the TNL association within the AMF; and
weight factor for each AMF Name within the AMF set; and
(optional) for each GUAMI(s) configured on that AMF the corresponding backup AMF Name.
The weight factors are used for load distribution of the initial N2 messages. The AMF chooses whether or not to use the same TNL association for the initial N2 message and subsequent messages for that UE. TNL associations configured with a weight factor set to zero are not permitted for the initial N2 message, but can be used for subsequent N2 messages.
Deployments that rely solely on 5GC-based load balancing can set the weight factors associated with TNL associations that are permitted for the initial N2 message to the same value.