Failure and Error Handling Support

Feature Summary and Revision History

Summary Data

Table 1. Summary Data

Applicable Product(s) or Functional Area

cnSGW-C

Applicable Platform(s)

SMI

Feature Default Setting

Enabled - Always-on

Related Documentation

Not Applicable

Revision History

Table 2. Revision History

Revision Details

Release

Added support for the Information Elements (IE):

  • Failure Cause Code

  • Cause Source (Bit 1 – CS)

  • Bearer Context IE error (Bit 2 – BCE)

2021.02.3

First introduced.

2021.01.0

Overview

cnSGW-C supports:

  • Attach and Detach failure and error handling.

  • Create, Update, Delete Bearer Request and Response failure and error handling.

  • Radio Access Bearer or Modify Beare Request failure and error handling.

The different types of failures that can occur during the call processing are as follows, except for Session Setup timer:

  • Advance validation failure on request and response.

  • Retransmission timeout.

  • Transaction service level agreement (SLA).

  • Failure reported from peer (UP, PGW, or MME depending on the stage of message process).

For Session Setup timer during attach procedure, following failures can happen:

  • Ongoing PDN establishment and Modify Bearer Request from MME isn’t received for Initial Attach and multi-PDN.

Attach and Detach Failure and Error Handling

cnSGW-C supports the following:

  • Setup timeout functionlaity

  • Failure response handling for:

    • Clear Session Request as a part of the Initial Attach and additional PDN setup procedures

    • Delete Beare Request and Delete Session Request processing for the PGW and UPF

Create Session Request Failure Handling

This section covers the Create Session Request procedure failure scenarios.

When failure occurs during Initial Attach procedure, subscriber context isn’t created,

When another PDN setup fails, PDN isn’t created in subscriber context.

The following table summarizes cnSGW-C behavior during different stages in the call processing for various failure types:

Table 3. cnSGW-C Behavior for Create Session Request Proceudure Failure Scenarios

Scenarios

Sx Signaling (Revert)

S11 Signaling (Revert)

S5 Signaling

  • Create Session Request advance validation failure

  • Sx Session Establishment Response failure from User Plane (UP)

No

Negative - Create Session Response

No

  • Create Session Response failure

Yes

Delete traffic endpoint for newly created bearers

Negative - Create Session Response

No

  • Sx Modify Response process failure

Yes

Delete traffic endpoint for newly created bearers

Negative - Create Session Response

Delete Session Request to delete newly created session

Delete Default Bearer Procedure Failure Handling

This section covers the PGW-initiated default bearer deletion procedure failure scenarios.

The following table summarizes cnSGW-C behavior during different stages of call processing for various failure types:

Table 4. cnSGW-C Behavior for Delete Default Bearer Procedure Failure Scenarios

Scenarios

SGW-service Behavior

Signaling

Output

Delete Bearer Request advance validation failure

Send failure/No signaling over Sx/PGW

Negative - S5 Delete Bearer Response

Session/PDN is not deleted

Sx Session Modify failure

Skip failure and continue

Send S11 Delete Bearer Request towards MME

S5 Delete Bearer Response (Cause = Accepted)

Sx Delete Request (to Delete traffic endpoint) depends upon Sx Session Modify Response

Session/PDN is deleted

S11 Delete Bearer Request failure

Skip failure and continue

Send Delete Bearer Response (Cause = Accepted) to PGW

Sx Delete Request (to Delete traffic endpoint)

Session/PDN is deleted

Sx Session Delete Request failure

Skip failure and continue

Send Delete Bearer Response (Cause = Accepted) to PGW

Session/PDN is deleted

Delete Session Procedure Failure Handling

This section covers the MME-initiated Deletion Session procedure failure scenarios.

The following table represents cnSGW-C behavior for the failure scenarios:

Table 5. cnSGW-C Behavior for Delete Session Procedure Failure Scenarios

Scenarios

SGW-service Behavior

Signaling

Output

Delete Session Request advance validation failure

Send failure/No signaling over Sx/MME

Negative - S11 Delete Session Response

Session/PDN is not deleted

Sx Session Modify Request failure

Skip failure and continue

Send Delete Session Request towards PGW

Send Delete Session Response (Cause = Accepted) to MME

Sx Delete Request (to Delete traffic endpoint) depends upon Sx Session Modify Response

Session/PDN is deleted

S5 Delete Session Request failure

Skip failure and continue

Send Delete Session Response (Cause = Accepted) to MME

Sx Delete Request (to Delete traffic endpoint)

Session/PDN is deleted

Sx Session Delete Request failure

Skip failure and continue

Send Delete Session Response (Cause = Accepted) to MME

Session/PDN is deleted

Session Setup Timer during Attach Procedure

This section covers the session setup timer during attach procedure.

The following table represents cnSGW-C behavior for the session timeout scenarios:

Table 6. cnSGW-C Behavior for Session Timeout Failure Scenarios

Scenarios

Sx Signaling (Revert)

S11 Signaling (Revert)

S5 Signaling

Output

Session setup timeout expired after SGW sends Create Session Response to MME and waits for the Modify Bearer Request from MME.

Sx Delete Request (To delete traffic endpoint for newly created bearers)

Delete Session Request

Delete Bearer Request

Session/PDN is deleted

Create-Update-Delete Bearer Request and Response Failure and Error Handling

This section describes create, update, and deletge bearer request and response failure and error handling scenarios.

Create Bearer Procedure Failure Handling

This section covers the PGW-initiated dedicated bearer creation procedure failure scenarios.

The following table summarizes cnSGW-C behavior during different stages of call processing for various failure types:


Note

During processing of create dedicated Bearer Request and Response, if SGW receives Context Not Found from peer (MME/UP) it deletes the PDN without performing any signaling towards the peer which sent this cause.

Table 7. cnSGW-C Behavior for Create Bearer Procedure Failure Scenarios

Scenarios

Sx Signaling

(Revert)

S11 Signaling

(Revert)

S5 Signaling

Output

  • Create Bearer Request advance validation failure

  • Sx Session Modify Request failure (request sent to UP to allocate tunnel endpoint and GTPU TEIDs).

No

No

Negative - Create Bearer Response to PGW

New Bearer Context is not created.

Create Bearer Request is sent to MME and SGW is waiting for the Response.

Yes

To remove traffic endpoint for newly created bearers.

No

Negative - Create Bearer Response to PGW

New Bearer Context is not created.

Optional parameters of Create Bearer Response are ignored.

SGW receives Create Bearer Resposne from MME and sends Sx Modify to UP to connect GTPU tunnel between eNodeB and SGW-U.

Yes

To remove traffic endpoint for newly created bearers.

Yes

To delete newly created bearers.

Negative - Create Bearer Response to PGW

New Bearer Context is not created.

Optional parameters of Create Bearer Response are ignored.

Failure in Revert handling for the Delete Bearer Request or Sx Modify Request.

No

No

Negative - Create Bearer Response

Bearer Context is not created.

Optional parameters of Create Bearer Response are ignored.

Delete Dedicated Bearer Procedure Failure Handling

This section covers the PGW-initiated dedicated bearer deletion procedure failure scenarios.

The following table summarizes cnSGW-C behavior during different stages of the call processing for various failure types:


Note

During processing of delete dedicated Bearer Request and Response if SGW receives Context Not Found from peer (MME/UP), it deletes the PDN without performing any signaling towards the peer which sent this cause.

Table 8. cnSGW-C Behavior for Delete Dedicated Bearer Procedure Failure Scenarios

Scenarios

SGW-Service Behavior

Signaling

Output

Delete Bearer Request advance validation failure

Send failure/No Signaling over Sx/MME

Negative - Delete Bearer Response to PGW

Dedicated Bearer is not deleted.

Partial Accepted: Delete Bearer Request received with multiple EBI’s, where:

  • Some EBIs belong to PDN

  • Some EBIs don't belong to PDN/Invalid EBIs

Continue DBR Procedure and delete all existing bearers for which Delete Bearer Request is received.

S11 Delete Bearer Request should carry only existing EBIs information

Sx Session Modification Request should carry existing EBIs information (Remove Traffic Endpoint)

S5 Delete Bearer Response (Cause = Partially Accepted )

S5 Delete Bearer Response where message level cause is Partially Accepted and bearer level cause is:

  • Some EBIs belong to PDN: S11 Delete Bearer Response

  • Some EBIs does not belong to PDN/Invalid EBIs: Context Not Found

CDL is updated (Remove all existing bearers)

Sx Session Modify to set action as DROP

Skip failure and continue

S5 Delete Bearer Response (Cause = Accepted)

Skip failure and continue with DBR Procedure Call Flow: Yes

S5 Delete Bearer Response (Cause = Accepted)

CDL is updated

S11 Delete Bearer Request Failure

Skip failure and continue

S5 Delete Bearer Response (Cause) = Accepted

Skip failure and continue with DBR Procedure Call Flow: Yes

CDL is updated

Sx Session Modify Request failure (Request to remove traffic endpoint on UP)

Skip failure and continue

S5 Delete Bearer Response (Cause = Accepted)

Skip failure and continue with DBR Procedure Call Flow: Yes

CDL is updated

Update Bearer Procedure Failure Handling

This section covers the PGW-initiated update bearer procedure failure scenarios.

The following table summarizes cnSGW-C behavior during different stages in call processing for various failure types:

Table 9. cnSGW-C Behavior for Update Bearer Procedure Failure Scenarios

Scenarios

S5/Sx Signaling

Output

Update Bearer Request advance validation failure

Negative - Update Bearer Response

No change in Bearer/PDN context.

Update Bearer Request with non-existing EBIs

Update Bearer Response with message level cause as REQ_PARTIALLY_ACCEPTED. Bearer level cause for non-existing EBIs as Context Not Found. (Normal handling for existing EBIs)

Update Bearer Response with message level cause as REQ_PARTIALLY_ACCEPTED.

Bearer level cause for non-existing EBIs as CONTEXT_NOT_FOUND.

Normal handling for existing EBIs.

CDL is updated for existing EBIs only.

Update Bearer Request is sent to MME and waiting for the response

Negative - Update Bearer Response

Negative - Update Bearer Response

CDL is not updated.

S11 Update Bearer Response (Message level Cause == CONTEXT_NOT_FOUND) and S5 Update Bearer Req/Rsp had default bearer in the bearer context list

Sx Delete Req/Rsp

Negative - Update Bearer Response

Negative - Update Bearer Response

CDL is not updated.

Statistics/Transactional Logs

PDN Key Release + PDN deallocation

If this is the last PDN, then resource manager is released, all subscriber keys are released and subscriber deallocation is done.

S11 Update Bearer Response (Message level Cause == CONTEXT_NOT_FOUND) and S5 Update Bearer Req/Rsp didn't have default bearer in the bearer context list

Sx Modify Req/Rsp

Negative - Update Bearer Response

CDL is not updated.

S11 Update Bearer Response (Message level Cause == REQ_PARTIALLY_ACCEPTED, Bearer Context Cause == Any failure for dedicated bearer)

Sx Modify Req/Rsp

Update Bearer Response with message level cause as REQ_PARTIALLY_ACCEPTED

Update Bearer Response with message level cause as REQ_PARTIALLY_ACCEPTED

CDL is updated for successful bearers.

S11 Update Bearer Response (Message level Cause == REQ_PARTIALLY_ACCEPTED, Bearer Context Cause == CONTEXT_NOT_FOUND for default bearer)

Sx Delete Req/Rsp

Negative - Update Bearer Response

Negative - Update Bearer Response

CDL is not updated.

PDN Key Release and PDN deallocation

If this is the last PDN, then resource manager is released, all subscriber keys are released and subscriber deallocation is done.

If Sx modify is triggered after Update Bearer Response:

  • Sx Session Modify Request (IPC/Retransmission Timeout/Internal Failure and so on)

  • Sx Session Modify Response (Cause != ACCEPTED except CONTEXT_NOT_FOUND)

Ignore failure and continue

Ignore failure and continue

If Sx Modify is triggered after Update Bearer Response:

  • Sx Session Modify Response (Cause == CONTEXT_NOT_FOUND)
1
2

If Sx Delete is triggered after Update Bearer Response:

  • Sx Session Delete Request (IPC/Retransmission Timeout/Internal Failure and so on)

  • Sx Session Delete Response (Cause != ACCEPTED)

  • Resource manager release (Internal Error)

Ignore failure and continue

Ignore failure and continue
1 As part of Update Bearer Procedure handling, SGW-service triggers new transaction for PDN deletion:

  • Sx Failure Cause received as part of Sx Session Modification Response

    • Context Not Found

SGW Behavior (New Transaction):

  • SGW triggers S11 Delete Bearer Request and S5 Delete Session Request to delete that PDN

  • No Sx Signaling

SGW Behavior (Update Bearer Transaction): SGW sends S5 Update Bearer Response with Cause as No Resource Available, as part of Update Bearer Procedure Transaction. Also, SGW doesn’t initiate any signaling towards UP as soon as it receives Sx Session Modification Response with cause as Context Not Found.

2 As part of Update Bearer Procedure handling, SGW-SVC additionally triggers new transaction for PDN deletion:

  • Sx Failure Cause received as part of Sx Session Modification Response

    • Context Not Found

SGW Behavior (New Transaction):

  • SGW triggers S11 Delete Bearer Request and S5 Delete Session Request to delete that PDN

  • No Sx Signaling

SGW Behavior (Update Bearer Transaction): SGW sends S5 Update Bearer Response with Cause as No Resource Available, as part of Update Bearer Procedure Transaction. Also, SGW doesn’t initiate any signaling towards UP as soon as it receives Sx Session Modification Response with cause as Context Not Found.

Radio Access Bearer/Modify Bearer Request Failure and Error Handling

This section covers the Radio Access Bearers (RAB), Modify Bearer Request and Response (MBR) from PGW and User Plane (UP) failure scenarios.

The following table summarizes cnSGW-C behavior during different stages of call processing for various failure types:

Table 10. cnSGW-C Behavior for Radio access Bearer and Modify Bearer Response Procedure Failure Scenarios

Message Type

Failure Interface

Failure Response Recevied

Failure Response to be sent

Handling

MBR initial attach

Sx

CONTEXT_NOT_FOUND

EGTP_CAUSE_

NO_RESOURCES_

AVAILABLE

Cleanup PDN with DSR towards PGW and DBR towards MME

Other Failure Response

EGTP_CAUSE_

NO_RESOURCES_

AVAILABLE

Cleanup PDN with DSR towards PGW and DBR towards MME.

Sx_Modification_Req/

Sx_Session_Delete to cleanup resource on UP

Timeout

Timeout on PFCP

EGTP_CAUSE_

NO_RESOURCES_

AVAILABLE

Cleanup PDN with DSR towards PGW and DBR towards MME.

Sx_Modification_Req/

Sx_Session_Delete to cleanup resource on UP

MBR Service Request

Sx

CONTEXT_NOT_FOUND

EGTP_CAUSE_

NO_RESOURCES_

AVAILABLE

Cleanup PDN with DSR towards PGW and DBR towards MME

Other Failure Responses

EGTP_CAUSE_

NO_RESOURCES_

AVAILABLE

Do not update anything in PDN, Ignore S5 Signaling

Timeout

EGTP_CAUSE_

NO_RESOURCES_

AVAILABLE

Do not update anything in PDN, Ignore S5 Signaling

S5

EGTP_CAUSE_

CONTEXT_NOT_

FOUND

EGTP_CAUSE_

CONTEXT_NOT_

FOUND

Sx_Session_Delete send to UP

MBRsp failure to MME (No DBR/DSR)

Other Failure Responses

Failure Response received from PGW

Do not update PDN/DB

Timeout

Timeout from PGW

EGTP_CAUSE_

PEER_NOT_

RESPONDING

Do not update PDN/DB

RAB

Sx

CONTEXT_

NOT_FOUND

(Single PDN call)

EGTP_CAUSE_

REQ_ACCEPTED

Cleanup PDN with DSR towards PGW and DBR towards MME

CONTEXT_

NOT_FOUND

(Multi PDN call and context not found for one PDN)

Send RAB Resp

(EGTP_CAUSE_

REQ_ACCEPTED)

Cleanup the PDN for which context not found received with DSR towards PGW and DBR towards MME

Move other PDN/UE to IDLE

Other Failure Response

EGTP_CAUSE_

REQ_ACCEPTED

Move PDN/UE to IDLE

Timeout

EGTP_CAUSE_

REQ_ACCEPTED

Move PDN/UE to IDLE

Support for Failure Cause Code, Cause Source, and Bearer Context Error

This section describes the support for the Information Elements (IE) – Failure cause code, Cause Source (CS), and Bearer Context Error (BCE).

For more information on the technical specifications for the IEs, see 3GPP TS 29.274.

Failure Cause Code

cnSGW-Csupports handling any failure cause code received from SMF on S5 interface.

Cause Source

Bit 1 – CS (Cause Source) value ‘0’ indicates that the error is originated by the node sending the message.

Bit 1 – CS (Cause Source) value ‘1’ indicates that the error is originated by the remote node (MME/SGSN to a PGW, or PGW to an MME/SGN).

Bearer Context Error

The default value of Bit 2-BCE (Bearer Context IE Error) is ‘0’. If the BCE Bit is 1, it indicates that the corresponding rejection clause is due to the error in the Bearer Context IE. This bit is discarded if the cause value is one of Acceptance cause value.