5G - id-RAN-UE-NGAP-ID

id-RAN-UE-NGAP-ID

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 :

[1]