EPS Bearer ID Allocation
This section describes the EPS Bearer ID Allocation procedure.

Note | Not all the steps in the preceding call flow are supported. For more details, see the descriptions in the following table. |
Step | Description | ||||
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1 |
The EBI Assignment procedure is initiated as specified in the relevant sections of 3GPP TS 23.502. The relevant steps of the procedure are executed as specified in the preceding call flow.
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2 | If the PGW-C+SMF (or H-SMF for home-routed cases) determines that EPS bearer IDs (based on operator policies, S-NSSAI, User Plane Security Enforcement information) need to be assigned to the QoS flows in the PDU session, the PGW-C+SMF invokes Namf_Communication_EBIAssignment Request (PDU Session ID, ARP list). | ||||
Step 3 through Step 6 apply only when the AMF needs to revoke EBI that was previously allocated for a UE to serve a new SMF request of EBI for the same UE. | |||||
3 | (Conditional) If the AMF has no available EBIs, the AMF may revoke an EBI that was assigned to QoS flows based on the ARPs and S-NSSAI stored during PDU Session Establishment, EBI information in the UE context and local policies. If an assigned EBI is to be revoked, the AMF invokes Nsmf_PDUSession_UpdateSMContext (EBI(s) to be revoked) to request the related SMF (called “SMF serving the released resources”) to release the mapped EPS QoS parameters corresponding to the EBI to be revoked. The AMF stores the association of the assigned EBI, ARP pair to the corresponding PDU Session ID and SMF address. | ||||
4 |
The “SMF serving the released resources” that receives the request in Step 3 invokes Namf_Communication_N1N2Message Transfer (N2 SM information (PDU Session ID, EBI(s) to be revoked), N1 SM container (PDU Session Modification Command (PDU Session ID, EBI(s) to be revoked))) to inform the (R)AN and the UE to remove the mapped EPS QoS parameters corresponding to the EBI(s) to be revoked. In home-routed roaming scenario, the H-SMF includes EBI(s) to be revoked to V-SMF to inform V-SMF to remove the mapped EPS bearer context corresponding to the EBI(s) to be revoked. The SMF can also decide to remove the QoS flow if it is not acceptable to continue the service when no corresponding EPS QoS parameters can be assigned. For home-routed roaming scenario, the "SMF serving the released resources" sends an N4 Session Modification Request to request the PGW-U+UPF to release the N4 session corresponding to the revoked EBI(s). In home-routed roaming case, the V-SMF starts a VPLMN-initiated QoS Modification for the PDU session. The V-SMF invokes the Namf_Communication_N1N2Message Transfer based on the corresponding QoS modification message received from H-SMF. | ||||
5 |
If the UE is in CM-CONNECTED state, the AMF sends N2 PDU Session Request (N2 SM information received from SMF, NAS message (PDU Session ID, N1 SM container (PDU Session Modification Command))) message to the (R)AN. If the UE is in CM-IDLE state and an ATC is activated, the AMF updates and stores the UE context based on the Namf_Communication_N1N2MessageTransfer and Step 5 and Step 6 are skipped. When the UE is reachable, for example, when the UE enters CM-CONNECTED state, the AMF forwards the N1 message to synchronize the UE context with the UE. | ||||
6 | The relevant steps of the procedure are executed as specified in the preceding figure. | ||||
7 |
If the AMF successfully assigns EBI(s), it responds with the assigned EBI(s). Otherwise, it responds with a cause indicating EBI assignment failure. If a PDU session from another SMF already exists towards the same DNN, the AMF either rejects the EBI assignment request, or revokes the EBI(s) from the existing PDU session(s) to the same DNN but different SMF. The AMF makes the decision based on the operator policy.
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8 |
The PGW-C+SMF sends an N4 Session Establishment/Modification Request to the PGW-U+UPF. For home-routed roaming scenario, if the EBI is assigned successfully, the PGW-C+SMF prepares the CN Tunnel Info for each EPS bearer. If the CN Tunnel info is allocated by the PGW-C+SMF, the PGW-U tunnel info for the EPS bearer may be provided to PGW-U+UPF. If the CN Tunnel info is allocated by PGW-U+UPF, the PGW-U+UPF sends the PGW-U tunnel info for the EPS bearer to the PGW-C+SMF. The PGW-U+UPF is ready to receive the uplink packets from E-UTRAN.
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9 |
If the PGW-C+SMF receives any EBI(s) from the AMF, it adds the EBI(s) received into the mapped EPS bearer context(s). In home-routed roaming scenario, the PGW-C+SMF generates EPS bearer context, which includes per EPS bearer PGW-U tunnel information. In addition, if the default EPS bearer is generated for the corresponding PDN Connection of PDU Session (that is, during the PDU Session establishment procedure), the PGW-C+SMF generates the PGW-C tunnel information of the PDN connection and includes it in UE EPS PDN connection. | ||||
9a | (Conditional) In non-roaming or LBO scenario, the PGW-C+SMF includes the mapped EPS bearer context(s) and the corresponding QoS Flow(s) to be sent to the UE in the N1 SM container. PGW-C+SMF also indicates the mapping between the QoS flow(s) and mapped EPS bearer context(s) in the N1 SM container. PGW-C+SMF also includes the mapping between the received EBI(s) and QFI(s) in the N2 SM information to be sent to the NG-RAN. The PGW-C+SMF sends the N1 SM container and N2 SM information to the AMF via Namf_Communication_N1N2MessageTransfer. | ||||
9b | (Conditional) In home-routed roaming scenario, the PGW-C+SMF sends the mapped EPS bearer context(s), the mapping between the received EBI(s) and QFI(s), and EPS bearer context to the V-SMF via Nsmf_PDUSession_Create Response during PDU Session Establishment, or via Nsmf_PDUSession_Update Request during PDU Session Modification. The V-SMF stores the EPS bearer context, and generates N1 SM container and N2 SM information, and forwards them to the AMF via Namf_Communication_N1N2MessageTransfer. | ||||
10 | The N1 SM container and N2 SM information are sent to the UE and NG-RAN respectively. The relevant steps of the procedure are executed as specified in the preceding figure. |