Section: 5.10.3 UE or MME requested PDN disconnection
Content: The UE or MME requested PDN disconnection procedure for an E-UTRAN is depicted in figure 5.10.3-1. The procedure allows the UE to request for disconnection from one PDN. Bearers including the default bearer of this PDN shall be deleted during this procedure. The procedure also allows the MME to initiate the release of a PDN connection. This procedure is also used as part of the SIPTO function when the MME determines that GW relocation is desirable. In this situation the MME deactivates the PDN connection(s) relevant to SIPTO-allowed APN(s) using the "reactivation requested" cause value, and the UE should then re-establish those PDN connection(s). NOTE 1: The deactivation with reactivation requested does not work with pre-Rel-9 LTE UEs. It shall be possible to configure the MME to deactivate a PDN connection, for PDN GW relocation due to SIPTO above RAN, only when UE is in ECM-IDLE mode or during a Tracking Area Update procedure without established RAB(s). This procedure is not used to terminate the last PDN connection unless "Attach without PDN Connectivity is supported" in the Preferred Network behaviour indicated by the UE at attach time is supported by the network and the UE at any time it requires the last PDN connection to be disconnected. The UE uses the UE-initiated Detach procedure in clause 5.3.8.2 to disconnect the last PDN connection. The MME uses the MME-initiated Detach procedure in clause 5.3.8.3 to release the last PDN connection. Figure 5.10.3-1: UE or MME requested PDN disconnection NOTE 2: For a PMIP-based S5/S8, procedure steps (A) are defined in TS 23.402[ Architecture enhancements for non-3GPP accesses ]  [2]. Steps 3, 4 and 5 concern GTP based S5/S8. NOTE 3: If after step 6, the MME determines that PDN being disconnected has no active bearers in the E-UTRAN, (e.g. because data is transported using Control Plane CIoT EPS Optimisation) steps 7, 8. 10a and 10b are modified to only transfer the indicated ESM signalling messages and steps 9a and 9b are skipped. 1. The procedure is triggered by either step 1a or step 1b. 1a. The UE initiates the UE requested PDN disconnection procedure by the transmission of a PDN Disconnection Request (LBI) message. The LBI indicates the default bearer associated with the PDN connection being disconnected. If the UE was in ECM-IDLE mode, this NAS message is preceded by the Service Request procedure if any of the exiting PDN connections were using the User Plane without CIoT EPS Optimisation, or, if the user plane was used just with User Plane CIoT EPS Optimisations, a Resume Procedure is executed instead. 1b. The MME decides to release the PDN connection. This may be e.g. due to change of subscription, lack of resources, due to SIPTO if the PDN connection serves a SIPTO-allowed APN or on receiving a PDN GW Restart Notification from the Serving GW as specified in TS 23.007[ Restoration procedures ]  [72]. If the UE is in ECM-IDLE state and the reason for releasing PDN connection is "reactivation requested" e.g. due to SIPTO, the MME initiates paging via Network Triggered Service Request procedure in clause 5.3.4.3 from step 3a onwards in order to inform UE of the request. 2. If the PLMN has configured secondary RAT usage reporting, the MME shall perform step 7 through 10 before step 2 onwards. If the PDN connection was served by a P-GW, the EPS Bearers in the Serving GW for the particular PDN connection are deactivated by the MME by sending Delete Session Request (Cause, LBI, User Location Information (ECGI), Secondary RAT usage data) to the Serving GW. This message indicates that all bearers belonging to that PDN connection shall be released. If the UE Time Zone has changed, the MME includes the UE Time Zone IE in this message. For PDN connection to the SCEF the MME indicates to the SCEF the connection for the UE is no longer available according to TS 23.682[ Architecture enhancements to facilitate communications with packet data networks and applications ]  [74] and steps 2,3,4,5,6 are not executed. If the MME received Secondary RAT usage data in step 9b, the MME shall include it in this Delete Session Request message. 3. The Serving GW sends Delete Session Request (Cause, LBI, User Location Information (ECGI), Secondary RAT usage data) to the PDN GW. The S-GW also includes User Location Information IE and/or UE Time Zone IE if it is present in step 2. The Serving GW also includes the Secondary RAT usage data in this message if it was present in step 2 and if PDN GW secondary RAT usage data reporting is active. 4. The PDN GW acknowledges with Delete Session Response (optionally, APN Rate Control Status). 5. The PDN GW employs the PCEF-initiated IP-CAN Session Termination procedure as defined in TS 23.203[ Policy and charging control architecture ]  [6] to indicate to the PCRF that the IP-CAN session is released if PCRF is applied in the network. If requested the PDN GW indicates User Location Information and/or UE Time Zone Information to the PCRF as defined in TS 23.203[ Policy and charging control architecture ]  [6]. 6. The Serving GW acknowledges with Delete Session Response (optionally, APN Rate Control Status). If received, the MME stores the APN Rate Control Status in the MM context. 7. If the UE is in ECM IDLE state and the PDN disconnection is decided by the MME, the MME shall delete the corresponding contexts of the PDN connection locally, steps 7 to 10b are skipped except if the MME has decided to restore certain PDN connections as specified in TS 23.007[ Restoration procedures ]  [72] or for other reasons e.g. SIPTO. The MME initiates the deactivation of all Radio Bearers associated with the PDN connection to the eNodeB by sending the Deactivate Bearer Request message to the eNodeB. The MME shall re-calculate the UE-AMBR (see clause 4.7.3). This S1-AP message carries the list of EPS bearers to be released, the new UE-AMBR, and a NAS Deactivate EPS Bearer Context Request (LBI) message. The MME builds a NAS message Deactivate EPS Bearer Context Request including the EPS Bearer Identity, and includes it in the S1-AP Deactivate Bearer Request message. If the network wants to trigger GW relocation (e.g. for SIPTO), the NAS message Deactivate EPS Bearer Context Request includes the request for reactivation of the same PDN connection via the same APN by the UE. If the MME released the PDN connection due to failed bearer set up during handover, the UE and the MME deactivate the failed contexts locally without peer-to peer ESM signalling. NOTE 4: If the UE is in ECM-IDLE state and the PDN disconnection is decided by the MME, the EPS bearer state is synchronized between the UE and the network at the next ECM-IDLE to ECM-CONNECTED transition (e.g. Service Request or TAU procedure). 8. The eNodeB sends the RRC Connection Reconfiguration message including the corresponding bearers to be released and the NAS Deactivate EPS Bearer Context Request (LBI) message to the UE. 9a. The UE releases all resources corresponding to the PDN connection and acknowledges this by sending the RRC Connection Reconfiguration Complete message to the eNodeB. 9b. The eNodeB sends an acknowledgement of the deactivation to the MME. If the PLMN has configured secondary RAT usage reporting and the eNodeB has Secondary RAT usage data to report, the Secondary RAT usage data is included. 10a. The UE NAS layer builds a Deactivate EPS Bearer Context Accept message. The UE then sends a Direct Transfer (Deactivate EPS Bearer Context Accept) message to the eNodeB. If the Deactivate EPS Bearer Context Request message from the MME indicated reactivation requested, the UE starts the UE initiated PDN connection request procedure as specified in clause 5.10.2 by using the same APN of the released PDN connection. 10b. The eNodeB sends an Uplink NAS Transport (Deactivate EPS Bearer Context Accept) message to the MME. The MME determines the Maximum APN Restriction for the remaining PDN connections and stores this new value for the Maximum APN Restriction.