5G (NR) roaming refers to a terminal (UE) that moves from its Home Public Land Mobile Network (HPLMN) to a Visited PLMN (VPLMN) and continues accessing 5G services through other operator's network.
5G (NR) roaming process works as below:
Step 1: UE powers on and searches for a signal.
Step 2: UE selects the VPLMN based on roaming agreements.
Step 3: UE sends an attach request to VPLMN through the RAN.
Step 4: AMF in VPLMN sends an authentication request to HPLMN.
Step 5: AUSF and UDM in HPLMN authenticate UE.
Step 6: Home Security Edge Protection Proxy (hSEPP) ensures secure communication with VPLMN.
Step 7: Visited SEPP (vSEPP) receives an authentication response, ensuring secure inter-network communication.
Step 8: AMF and SMF in VPLMN establish sessions for the UE.
Step 9: NSSF selects the appropriate network slice.
Step 10: PCF manages session application policies and billing rules.
Step 11: Data is routed via UPF, which in VPLMN routes data from the UE directly to the data network (DN), enabling local breakout.
Step 12: UE accesses the internet through the DN.
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