Cause Description and Scenarios
This section provides information on the causes that SMF receives from AMF through N11 interface messages and the relevant scenarios of those causes.
REL_DUE_TO_HO
The following table describes the release due to handover cause and scenario.
Cause | REL_DUE_TO_HO | ||
Cause Description from 3GPP TS 29.502 | Release due to handover | ||
Scenario of occurrence | Handover from 5GS to EPG or ePDG during roaming | ||
Message Used | vsmfUpdateData | ||
Message Direction | H-SMF to V-SMF | ||
Comments and Specification References |
3GPP TS 29.502
If the request indication in the request is configured to NW_REQ_PDU_SES_REL and if the Cause IE indicates the release due to handover cause, then the V-SMF initiates the release of RAN resources reserved for the PDU session, if any. However, SMF doesn't send a PDU session release command to the UE. The V-SMF doesn't release the SM context for the PDU session.
|
EPS_FALLBACK
The following table describes the mobility due to EPS fallback for IP Multimedia Subsystem (IMS) voice cause and the scenario of occurrence of the cause:
Cause |
EPS_FALLBACK |
||
Cause description from 3GPP TS 29.502 |
Mobility due to ongoing EPS fallback for IMS voice. |
||
Scenario of occurrence |
IMS voice configuration in roaming scenario |
||
Message used |
VsmfUpdatedData This message is used in the qosFlowsFailedtoAddModList attribute, which is the Cause IE of QosFlowItem. |
||
Message direction | V-SMF to H-SMF | ||
Comments and Specification References |
SMF supports the following scenarios for this cause as per the specification:
|
REL_DUE_TO_UP_SEC
The following table describes the release due to unfulfilled security requirements from User Plane cause and the scenario of occurrence of the cause:
Cause | REL_DUE_TO_UP_SEC |
Cause description from 3GPP TS 29.502 | Release due to unfulfilled User Plane security requirements. |
Scenario of occurrence |
AMF-initiated release when the NG-RAN is unable to fulfill the required User Plane security enforcement. |
Message used | Release SM Context service operation |
Message direction | AMF to SMF |
Comments or Specification References |
3GPP 29.502, Section 5.2.2.4, Release SM Context service operation The REL_DUE_TO_UP_SEC cause is available in SM Context Release Request when NG-RAN is unable to fulfill the required User Plane security enforcement. |
DNN_CONGESTION
The following table describes the release due to the DNN-based congestion control cause and the scenario of occurrence of the cause:
Cause | DNN_CONGESTION |
Cause Description from 3GPP TS 29.502 | Release due to the DNN-based congestion control. |
Scenario of occurrence |
SMF detects congestion for the requested DNN and performs an overload control for the DNN that restricts the establishment of the PDU session. |
Message Used | SM Context Create Error and SM Context Update Error |
Message Direction |
SMF to AMF |
Comments or Specification References |
Not supported. |
S_NSSAI_CONGESTION
The following table describes the release due to the S-NSSAI-based congestion control cause and the scenario of occurrence of the cause:
Cause | S_NSSAI_CONGESTION |
Cause description from 3GPP TS 29.502 | Release due to the S-NSSAI-based congestion control. |
Scenario of occurrence |
SMF detects congestion for the requested S-NSSAI and performs overload control for the S-NSSAI that restricts the establishment of the PDU session. |
Message used |
SM Context Create Error and SM Context Update Error |
Message direction |
SMF to AMF |
Comments or specification references |
Not supported. |
REL_DUE_TO_REACTIVATION
The following table describes the release due to PDU session reactivation cause and scenario of its occurrence:
Cause | REL_DUE_TO_REACTIVATION |
Cause Description from 3GPP TS 29.502 | Release due to PDU session reactivation. |
Scenario of occurrence |
3GPP TS 29.502, Section 5.2.2.3.10, P-CSCF Restoration Procedure via AMF. The POST request contains the release IE configured to True and the cause IE configured to REL_DUE_TO_REACTIVATION. |
Message used | Update SM Context service operation |
Message direction | AMF to SMF |
Comments or specification references |
After receiving the cause from AMF, SMF sends the 5GSM cause as Reactivation Required towards UE. |
5G_AN_NOT_RESPONDING
The following table describes the cause when 5G access network (AN) doesn't respond to network-initiated request and the scenario of occurrence of the cause:
Cause | 5G_AN_NOT_RESPONDING |
Cause Description from 3GPP TS 29.502 | The 5G AN doesn't respond to the network-initiated request. |
Scenario of occurrence | None. |
Message Used | SM Context Status Notification or Status Notification |
Message Direction | SMF to AMF |
Comments or Specification References |
SMF supports the following scenarios for this cause:
|
REL_DUE_TO_SLICE_NOT_AVAILABLE
The following table describes the release due to unavailability of the associated S-NSSAI cause and the scenarios of the occurrence of the cause:
Cause | REL_DUE_TO_SLICE_NOT_AVAILABLE |
Cause Description from 3GPP TS 29.502 | Release due to the associated S-NSSAI is unavailable. |
Scenario of occurrence |
The following are the scenarios of the occurrence of the cause:
|
Message Used |
The following are the messages used for these scenarios:
|
Message Direction | AMF to SMF |
Comments or Specification References |
SMF supports the following scenarios for this cause as per the specification:
|
REL_DUE_TO_DUPLICATE_SESSION_ID
The following table describes the release due to UE request for new PDU session establishment cause and the scenario of the occurrence of the cause:
Cause | REL_DUE_TO_DUPLICATE_SESSION_ID | ||
Cause Description from 3GPP TS 29.502 | Release due to a UE request to establish a new PDU session with an identical PDU session ID. | ||
Scenario of occurrence | AMF-requested PDU Session Release due to duplicate PDU Session ID. | ||
Message Used | Update SM Context service operation | ||
Message Direction | AMF to SMF | ||
Comments or Specification References |
SMF supports the following scenario: As defined in 3GPP TS 24.501 [7], clause 5.4.5.2.5, when the AMF receives an initial request with the existing PDU Session ID in the PDU session context of the UE, AMF requests the SMF to release the existing PDU Session. After receiving the SM context status notification indicating that the deletion of the SM context in the SMF, the AMF releases the stored context for the PDU session. Then, the AMF sends the initial request with the PDU Session ID. The POST request includes the release IE configured to True and the cause IE configured to REL_DUE_TO_DUPLICATE_SESSION_ID.
|
PDU_SESSION_STATUS_MISMATCH
The following table describes the release due mismatch of PDU session status between UE and AMF cause and the scenario of the occurrence of the cause:
Cause | PDU_SESSION_STATUS_MISMATCH |
Cause Description from 3GPP TS 29.502 | Release due to mismatch of PDU Session status between UE and AMF. |
Scenario of occurrence | UE service request procedure. |
Message Used | SM Context Release Data |
Message Direction | AMF to SMF |
Comments or Specification References |
SMF supports the following scenario: As defined in 3GPP TS 24.501, Section 5.2.2.4, Release SM Context service operation, in case of mismatch of the PDU session status between the UE and the AMF, the AMF starts Release operation towards SMF to release the PDU context from network. |
HO_FAILURE
The following table describes the handover preparation failure cause and the scenario of the occurrence of the cause:
Cause | HO_FAILURE |
Cause Description from 3GPP TS 29.502 | Handover preparation failure. |
Scenario of occurrence | 5GS to EPS handover over N26 interface and if no resources can be assigned in EPS for any attempted PDU session to be handed over. |
Message Used | SM Context Update |
Message Direction | AMF to SMF |
Comments or Specification References |
SMF supports the following scenario: AMF updates the SMF with the information that the handover preparation failed by sending a POST request with the cause attribute configured to HO_FAILURE and with an empty list of EPS bearer contexts. This procedure doesn't include the dataForwarding IE. Then, SMF releases the resources prepared for the handover and proceeds with the PDU session. |
INSUFFICIENT_UP_RESOURCES
The following table describes the activation failure for User Plane connection due to insufficient resources cause and the scenario of the occurrence of the cause:
Cause | INSUFFICIENT_UP_RESOURCES |
Cause Description from 3GPP TS 29.502 | Failure to activate the User Plane connection of a PDU session due to insufficient user plane resources. |
Scenario of occurrence | During an idle mode exit procedure. |
Message Used | SM Context Updated Data |
Message Direction | SMF to AMF |
Comments or Specification References |
3GPP TS 129.502 , Section 5.2.2.3.2.2, Activation of User Plane connectivity of a PDU session SMF supports the following scenario: As defined in 3GPP TS 38.413 [9], clause 9.3.4.16 5G-AN sends the N2 SM information to SMF including the cause of the failure or if the resources failed to establish the PDU session. After SMF receives this information, SMF considers that the activation of the User Plane connection has failed and configures the upCnxState attribute to DEACTIVATED. In case the activation of the User Plane connection fails due to insufficient resources, the cause is included in the problem details response and configured to INSUFFICIENT_UP_RESOURCES with status code as 500. |
PDU_SESSION_HANDED_OVER
The following table describes the handover of PDU session cause and the scenario of the occurrence of the cause:
Cause | PDU_SESSION_HANDED_OVER | ||
Cause Description from 3GPP TS 29.502 | The PDU session is handed over to another system or access. | ||
Scenario of occurrence |
5GC to EPS mobility without N26 interface Handover from 5GS to EPC or ePDG |
||
Message Used | SM Context Status Notification | ||
Message Direction | SMF to AMF | ||
Comments or Specification References |
SMF supports the following specification for this cause:
|