9.7 S101 Tunnel Redirection Procedure

23.4023GPPArchitecture enhancements for non-3GPP accessesRelease 18TS

S101 Tunnel Redirection Procedure is used when the UE performs TAU with MME change while the UE has already triggered a pre-registration procedure from LTE to the HRPD as described in clause 9.3.1 and the S101 session exists between the MME and the HRPD Access Network.

The detail procedure for the idle case is depicted as figure 9.7-1.

Figure 9.7-1: S101 tunnel redirection during TAU with MME change

1. UE performs pre-registration over the old MME while in ECM-CONNECTED state, followed by transition to ECM-IDLE state. The S101 tunnel exists between the old MME and the HRPD Access Network.

2. TAU procedure with MME change is executed as described in TS 23.401 [4], figure 5.3.3.1-1, up to the step where the new MME receives Update Location Ack from the HSS. The HRPD Access Network IP address is transferred to the new MME via the Context Response message.

3. The new MME sends Notification Request (Redirection, S101 Session ID) message to the HRPD Access Network. After receiving this message, the HRPD Access Network associates the S101 tunnel for this specific UE with the new MME. Then the HRPD Access Network releases any context associated with the old MME.

4. In response to the Notification Request message, the HRPD Access Network sends a Notification Response (S101 Session ID) message to the target MME.

5. The TAU procedure is completed.

The detailed procedure for the active case is depicted as figure 9.7-2.

Figure 9.7-2: S101 tunnel redirection during inter-eNodeB handover with MME relocation

1. UE performs pre-registration over the old MME while in ECM-CONNECTED state. The S101 tunnel exists between the old MME and the HRPD Access Network.

2. Inter-eNodeB handover with MME relocation procedure is executed as described in TS 23.401 [4], figure 5.5.1.2.2-1, steps up to TAU. The HRPD Access Network IP address is transferred to the new MME via the Forward Relocation Request message.

3. The new MME sends Notification Request (Redirection, S101 Session ID) message to the HRPD Access Network. After receiving this message, the HRPD Access Network associates the S101 tunnel with the new MME. Then the HRPD Access Network releases any context associated with the old MME.

4. In response to the Notification Request message, the HRPD Access Network sends a Notification Response (S101 Session ID) message to the target MME.

5. The TAU procedure occurs.