The LTE to Wi-Fi handoff occurs as follows:

1. The P-GW delays sending the DBR to the S-GW until:

   • CSR expiry is sent to the ePDG (default behavior).

   • Uplink data is sent on the Wi-Fi tunnel.

   • Handover timer has expired. If timer expires, the ePDG does not send the Modify Bearer Request (MBR) to notify handoff completion.

2. After CSR for LTE to Wi-Fi handoff is received, Control Plane GTPv2 (GTP-C) messages from LTE access are not handled at the P-GW. These messages are blocked at the EGTPC.

3. LTE tunnel carries GTP-U traffic during the transition period. Transition period is defined as time between CSR (for LTE to Wi-Fi handoff is received) and handover completion. MBR for handoff completion is not expected in this scenario.

4. In case of multiple outstanding CCR-Us being supported, all requests before the handoff request are dropped. This is done at IMSA.

5. During the transition period:

   • If Modify Bearer Command (MBC) is received in Wi-Fi, it is rejected with Service-Denied message.

   • If Delete Bearer Command for dedicated bearer is received in LTE, it is discarded.

   • If PCRF sends RAR for policy change, it is processed after handover is complete.

   • New tunnel (that is, Wi-Fi) does not carry any GTP-U traffic. Any GTP-U traffic that is received on the Wi-Fi during the transition period is dropped or ignored. Similarly, any downlink traffic that is received on the Wi-Fi is sent on an older tunnel (that is, LTE tunnel) until DBR is sent on the Wi-Fi tunnel. This is true even when CSR is sent on the Wi-Fi tunnel. Any uplink traffic that is received on the Wi-Fi tunnel before timer expiry triggers the handover completion, and from then on all traffic is forwarded only through the Wi-Fi tunnel.

   • Any pending transactions on LTE access are discarded. For example, if CBR or UBR is sent for LTE access and handoff is initiated before completion of CBR or UBR transaction, then CBR or UBR is ignored at the P-GW. PCRF is not notified about failure.

   • If ASR is received, then call drop occurs and both tunnels go down.

   • If session-release occurs from PCRF, then call is dropped and CSR is sent with cause as “no-resources”.

   • GTP-U or GTP-C path failure over LTE leads to call drop for LTE access while the Wi-Fi call continues.

   • GTP-U or GTP-C path failure over Wi-Fi leads to call drop. Both tunnels are cleared.

   • If the user moves back to LTE (that is, back to back handoff from LTE to Wi-Fi to LTE) with HO-Ind set to 1 (after guard timer), then the HO is processed successfully and user session is moved to LTE again.

   • If the user moves back to LTE (that is, back to back handoff from LTE to Wi-Fi to LTE) with HO-Ind set to 0, then it leads to context replacement. Old call is cleared on Wi-Fi access with reason as context replacement and call is processed like a new call over LTE.

During the transition period, old access is considered as stable state and Full Checkpoint is triggered once handover is complete from LTE to Wi-Fi (S2bGTP). This is done for both Session Recovery and ICSR.

Use the following CLI commands to configure LTE to Wi-Fi handover timer.

configure 
   context context_name 
      apn apn_name 
         lte-s2bgtp-first-uplink timeout 
         { default | no } lte-s2bgtp-first-uplink 
         end 

NOTES:

• default : Enables the LTE to Wi-Fi handover completion to occur when the Create Session Response is sent on the Wi-Fi tunnel.

• no : Disables the feature and handover completion occurs on Create Session Response.

• lte-s2bgtp-first-uplink timeout : Configures LTE to S2bGTP handover completion timeout in multiples of 100 milliseconds. The valid range is from 100 to 3000. The recommended configuration is 1000 milliseconds.

• By default, the LTE to Wi-Fi handover completion happens when Create Session Response is sent on the Wi-Fi tunnel. However, after handover timeout is configured, the handover is delayed until timeout or on receipt of uplink data on the Wi-Fi tunnel.

This section provides information regarding show commands and/or their outputs in support of this feature.

The following statistics are included in support of this feature.