The following call flow illustrates the IDFT support with S-GW Relocation.

The above call flow describes the IDFT tunnels establishment and deletion with S-GW relocation and without MME change.

If IDFT tunnels are not deleted by MME, then S-GW initiates the local delete of IDFT tunnels.

This feature supports the following scenarios for the Pure-S and Collapse calls:

• S-GW relocation with same MME

• S-GW relocation with same MME and different eNodeB

• S-GW relocation with different MME

• S1-based eNodeB Handoff

• EUTRAN to UTRAN Handoff

• EUTRAN to UTRAN Handoff with S-GW relocation

• UTRAN to EUTRAN Handoff

• UTRAN to EUTRAN Handoff with S-GW relocation

• Tracking Area Update (TAU) with S-GW change and indirect data forwarding

• Radio Access Bearer (RAB) during Active IDFT

• Sx transaction timeout during IDFT setup or removal

• Pending Sx transaction (event from PCRF or OCS) and IDFT request comes in

• Create Bearer Request (CBR) during Active IDFT

• Update Bearer Request (UBR) during Active IDFT

• Delete Bearer Request (DBR) during Active IDFT

• Modify Bearer Request (MBR) behavior on other PDN during Active IDFT

• Source MME path failure

• Target MME path failure

• MME path failure with NTSR enabled

• eGTP-C S5 path failure

• eGTP-C S5 path failure with P-GW restart notification enabled

• Sx path failure (clean IDFT and calls)

• Abort session (clear sub all, local abort, and so on.)

• CBR, UBR on other PDN during Active IDFT

• DBR on other PDN/bearer during Active IDFT

• S1-u path failure for target eNodeB

• S1-u path failure for source eNodeB

• S-GW path failure for source S-GW

• S-GW path failure for target S-GW

• S1-u error indication on the default bearer while Active IDFT

• S1-u error indication on the dedicated bearer while Active IDFT

• S1-u error indication from the target S-GW to source S-GW bearer

• S1-u error indication from the target eNodeB to target S-GW bearer

• Sending End Marker when tearing down IDFT tunnel after failure

• If SMF ICSR/SR leads to the cleanup of IDFTs, the UPF also cleans the IDFT PDRs/FARs

5G to 4G Handover with IDFT

In compliance with 3GPP TS 23.502 v15.5.1, the 5G to 4G handover with IDFT is supported in UPF. Refer the "5GS to EPS handover using N26 interface" section in the 3GPP specification for details about call/datapath flow for IDFT.

This functionality isn't CLI-controlled in UPF.

4G to 5G Handover with IDFT

In compliance with 3GPP TS 23.502 v15.5.1, the 4G to 5G handover with IDFT is supported in UPF. Refer the "EPS to 5GS handover using N26 interface" (preparation and execution phase) section in the 3GPP specification for details about the call flow.

This functionality isn't CLI-controlled in UPF.

The IDFT feature supports the following functionality:

• Create IDFT request for Collapsed, Pure-S, combination of Collapsed and Pure-S multi-PDN calls with multiple bearers.

• Data transfer on downlink and uplink IDFT bearers.

• Deletion of IDFT request from MME. Also, timer-based deletion of IDFT bearer after expiration of a default value of 100 seconds, if the MME does not send an IDFT request for deletion.

• Deletion of IDFT PDN, including Clear/Delete subscribers from MME/P-GW, when normal PDN goes down.

• IDFT creation of Sx Failure Handling for Pure-S and Collapsed PDN.

Important

Transport GTP-U address capability is assumed to be same across eNodeB and S-GW.

The IDFT feature has the following limitations:

• Message interaction and collision during IDFT PDN establishment or deletion with any other procedure is not supported.

• S11/S5 and Sx Path Failure Handling on non-IDFT PDN is not supported when IDFT PDN is Active.

• Deletion of partial dedicated bearers in IDFT connected-state is not supported.

On SMF, use the following CLI commands to enable or disable the IDFT feature.

configure 
   context context_name 
      sgw-service service_name 
         [ default | no ] egtp idft-support 
         end 

NOTES:

• idft-support : Enables/Disables the IDFT feature in UPF.

• By default, the IDFT feature is disabled and this CLI command is applicable on run-time change.

This section provides information regarding show commands and their outputs in support of the feature.