Section: 5.19.2 Attach, TAU and RAU procedure for Dedicated Core Network
Content: When DCNs are used, the Attach, TAU and RAU procedures in this clause apply. Figure 5.19.2-1: Attach,TAU and RAU procedure for Dedicated Core Network 1. Attach, TAU, or RAU procedure is initiated as specified in the relevant clauses of this specification and TS 23.060[ General Packet Radio Service (GPRS); Service description; Stage 2 ]  [7]. The relevant steps of the procedure as specified in the figure above are executed. The following modifications apply: - In the RRC Connection Complete message transferring the NAS Request message, the UE provides the DCN-ID, if available. If the UE has a PLMN specific DCN-ID the UE shall provide this value and if no PLMN specific DCN-ID exist the pre-provisioned default standardized DCN-ID shall be provided, if pre-provisioned in the UE. The RAN node selects a DCN and a serving MME/SGSN within the network of the selected core network operator based on the DCN-ID and configuration in the RAN node. The NAS Request message is sent to the selected node. The DCN-ID is provided by the RAN to the MME/SGSN together with the NAS Request message. - E-UTRAN Initial Attach Procedure (clause 5.3.2.1 (Figure 5.3.2.1-1)) and Combined GPRS/IMSI Attach procedure (TS 23.060[ General Packet Radio Service (GPRS); Service description; Stage 2 ]  [7] clause 6.5.3 (Figure 22)): In the Identification Response message, the old MME/SGSN provides UE Usage Type parameter, if available. - Tracking area update procedure (clause 5.3.3.1 (Figure 5.3.3.1-1) and 5.3.3.2 (Figure 5.3.3.2-1)): In the Context Response message, the old MME/SGSN provides UE Usage Type parameter, if available. - Routing area update procedure (clause 5.3.3.3 (Figure 5.3.3.3-1) and 5.3.3.6 (Figure 5.3.3.6-1), TS 23.060[ General Packet Radio Service (GPRS); Service description; Stage 2 ]  [7] clauses 6.9.1.2.2 (Figure 33), 6.9.1.2.2a (Figure 33a), 6.9.1.3.2 (Figure 35), 6.9.2.1 (Figure 36), 6.9.2.1a (Figure 36a), 6.13.1.1.1 (Figure 52), 6.13.2.1.1 (Figure 54), 6.13.2.1.2 (Figure 54-2), 6.13.2.2.1 (Figure 55), 6.13.2.2.2 (Figure 55-2)): In the Context Response message, the old MME/SGSN provides UE Usage Type parameter, if available. 2. If the (first) new MME/SGSN, i.e. the MME/SGSN that has not received any MMEGI or Null-NRI/SGSN Group ID from RAN, does not have sufficient information to determine whether it should serve the UE, it sends an Authentication Information Request message to the HSS requesting UE Usage Type by adding the parameter "Send UE Usage Type" flag in the message. The MME/SGSN may also request one or more authentication vectors in addition to the UE Usage Type. The (first) new MME/SGSN has sufficient information in the following cases and may then skip this step and step 3: i. The (first) new MME/SGSN has received the UE Usage Type from the old MME/SGSN in the Identification Response (for Attach) or Context Response (for TAU/RAU) message or Forward Relocation Request (for Handover). ii. Based on configuration in the (first) new MME/SGSN and UE context information, the MME/SGSN is able to determine whether it should serve the UE. This step and redirection of NAS message (i.e. step 5 onwards) shall not be performed for TAU/RAU procedure triggered in connected mode, e.g. during handover. 3. The HSS, if supporting DCNs, provides the UE Usage Type in the Authentication Information Answer message, if any is stored for the UE. The UE Usage Type is returned by the HSS in addition to requested authentication vectors. 4. If the (first) new MME/SGSN determines that it shall not reroute the NAS message to another CN node, the MME/SGSN either continues from the designated step as stated in the figure above or depending on operator configuration rejects the NAS request message and the NAS procedure ends in this step. The NAS message is rejected with parameters, e.g. backoff timer, such that the UE does not immediately re-initiate the NAS procedure. The MME/SGSN sends the DCN-ID, if available, for the DCN to the UE in the NAS Accept message. The UE updates its stored DCN-ID parameter for the serving PLMN if DCN-ID for serving PLMN is changed. 5. If the (first) new MME/SGSN determines that it should reroute the NAS request message to another CN node, the procedure is a TAU or RAU procedure and UE context was received from the old MME/SGSN, the (first) new MME sends a Context Acknowledge message with cause code indicating that the procedure is not successful. The old MME/SGSN shall continue as if Context Request was never received. 6. If the (first) new MME/SGSN determines that it should reroute the NAS request message to another CN node, it uses the "NAS Message Redirection Procedure" in clause 5.19.1. The NAS message is re-routed to a (second) new MME/SGSN. If the IMSI was retrieved unencrypted from the UE by the (first) new MME/SGSN in step 1, the (first) new MME/SGSN shall include the IMSI in the Reroute Message Request. 7. The (second) new MME/SGSN, i.e. the MME/SGSN that receives the rerouted NAS message from RAN with MMEGI or Null-NRI/SGSN Group ID, performs NAS procedure as stated for E-UTRAN in this specification and for GERAN/UTRAN in TS 23.060[ General Packet Radio Service (GPRS); Service description; Stage 2 ]  [7] from the steps shown in the figure above. The following modifications apply: - E-UTRAN Initial Attach Procedure (clause 5.3.2.1 (Figure 5.3.2.1-1)) and Combined GPRS/IMSI Attach procedure (TS 23.060[ General Packet Radio Service (GPRS); Service description; Stage 2 ]  [7] Clause 6.5.3 (Figure 22)): In the Identification Response message, the old MME/SGSN provides UE Usage Type parameter, if available. - Tracking area update procedure (clause 5.3.3.1 (Figure 5.3.3.1-1) and 5.3.3.2 (Figure 5.3.3.2-1)): In the Context Response message, the old MME/SGSN provides UE Usage Type parameter, if available. - If the IMSI was received from the first (new) MME/SGSN as part of the NAS Message Redirection Procedure, the second (new) MME/SGSN does not have to retrieve the IMSI from the UE. - Routing area update procedure (clause 5.3.3.3 (Figure 5.3.3.3-1) and 5.3.3.6 (Figure 5.3.3.6-1), TS 23.060[ General Packet Radio Service (GPRS); Service description; Stage 2 ]  [7] clauses 6.9.1.2.2 (Figure 33), 6.9.1.2.2a (Figure 33a), 6.9.1.3.2 (Figure 35), 6.9.2.1 (Figure 36), 6.9.2.1a (Figure 36a), 6.13.1.1.1 (Figure 52), 6.13.2.1.1 (Figure 54), 6.13.2.1.2 (Figure 54-2), 6.13.2.2.1 (Figure 55), 6.13.2.2.2 (Figure 55-2)): In the Context Response message, the old MME/SGSN provides UE Usage Type parameter, if available. - The MME/SGSN sends the DCN-ID, if available, for the new DCN to the UE in the NAS Accept message. The UE updates its stored DCN-ID parameter for the serving PLMN if DCN-ID for serving PLMN is changed. If network sharing and the Selected PLMN information is not provided by the UE, the SGSN may also include the PLMN ID of selected CN operator in the NAS Accept message. The (second) new MME/SGSN shall not reroute the NAS message to another CN node since the Initial UE message/UL-Unitdata message from RAN includes MMEGI or Null-NRI/SGSN Group ID. The (second) new MME/SGSN either completes the NAS procedure as stated above or depending on operator configuration rejects the NAS request message and the NAS procedure ends. When rejecting the NAS request, an appropriate cause and backoff time should be included. In the case of TAU or RAU procedure, the (second) new MME/SGSN may check (e.g. based on the indication that the NAS message has been rerouted and on local configuration) if the PDN GW (for one or more PDN connection(s)) of the UE needs to be changed. If the PDN GW needs to be changed, the (second) new MME/SGSN initiates Detach with reattach required or PDN disconnection with reactivation required procedure after the completion of the TAU or RAU procedure.