In 5G networks, id-RAN-UE-NGAP-ID refers to the RAN UE NGAP ID—an identifier used in the NGAP (Next Generation Application Protocol) interface between the gNB and the AMF. The main purpose this ID is :
- Uniquely identifies a UE within the context of the RAN node (e.g., gNodeB) during communication with the 5G Core Network (5GC) via the NG interface.
- Ensures proper management of UE-specific procedures (e.g., handovers, session setup, release) between the RAN and the AMF.
Key Characteristics and Functions
In short, id-RAN-UE-NGAP-ID is simply the RAN’s unique identifier for a UE in NGAP signaling, ensuring correct association of messages with the appropriate UE context on the gNB side.
Unique RAN-Side Identifier
- The gNB allocates RAN UE NGAP ID when a new UE-associated signaling connection is set up over the NG interface.
- This ID uniquely identifies a particular UE for all NGAP messages on the RAN side (i.e., within the gNB).
Pairing with AMF UE NGAP ID
- On the core network side, the AMF allocates another unique ID called AMF UE NGAP ID.
- Together, the (RAN UE NGAP ID, AMF UE NGAP ID) pair provides a globally unique context reference for a given UE across the gNB and AMF.
Usage in NGAP Procedures
- Once assigned, the RAN UE NGAP ID is included in subsequent NGAP messages—such as Initial UE Message, Uplink/Downlink NAS Transport, and other UE-associated signaling—to ensure the UE is correctly identified at the RAN.
- It ensures that both gNB and AMF can correlate all signaling and data to the correct UE context.
Significance
- Efficient, unambiguous UE identification is critical for mobility management, paging, handover, and session management procedures.
- By maintaining this ID, the RAN can handle multiple UEs simultaneously and direct messages properly.
id-RAN-UE-NGAP-ID in Signaling
At the first NGAP message from gNB to AMF, gNB assigns a id-RAN-UE-NGAP-ID for the UE. From this point on, all the NGAP messages from gNB to AMF for this UE uses this ID.
Message: 127.0.1.1:33620 Initial UE message
initiatingMessage: {
procedureCode id-InitialUEMessage,
criticality ignore,
value {
protocolIEs {
{
id id-RAN-UE-NGAP-ID,
criticality reject,
value 1
},
{
id id-NAS-PDU,
criticality reject,
value '7E014295C6102E7...0530101'H
},
{
id id-UserLocationInformation,
criticality reject,
value userLocationInformationNR: {
nR-CGI {
pLMNIdentity '00F110'H,
nRCellIdentity '001234501'H
},
tAI {
pLMNIdentity '00F110'H,
tAC '000064'H
}
}
},
{
id id-RRCEstablishmentCause,
criticality ignore,
value mo-Signalling
},
{
id id-UEContextRequest,
criticality ignore,
value requested
}
}
}
}
At the first NGAP message from AMF to gNB, gNB assigns a id-AMF-UE-NGAP-ID for the UE. From this point on, all the NGAP messages from AMF to gNB for this UE uses this ID.
Message: 127.0.1.1:33620 Downlink NAS transport
initiatingMessage: {
procedureCode id-DownlinkNASTransport,
criticality ignore,
value {
protocolIEs {
{
id id-AMF-UE-NGAP-ID,
criticality reject,
value 100
},
{
id id-RAN-UE-NGAP-ID,
criticality reject,
value 1
},
{
id id-NAS-PDU,
criticality reject,
value '7E005B01'H
}
}
}
}
Reference :
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