Call Flow

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

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.