Content for  TS 23.401  Word version:  18.4.0

The UE sends NAS message Service Request towards the MME encapsulated in an RRC message to the eNodeB. The RRC message(s) that can be used to carry the S-TMSI and this NAS message are described in TS 36.300. The Multi-USIM UE in ECM-CONNECTED state may include the Release Request indication and optionally Paging Restriction Information in the Service Request message, if the UE intends to return to ECM-IDLE state.

The eNodeB forwards NAS message to MME. NAS message is encapsulated in either an S1-AP: Initial UE Message (NAS message, TAI+ECGI of the serving cell, S-TMSI, CSG ID, CSG access Mode, RRC establishment cause), or another S1-AP message (e.g. Uplink NAS Transport Message) used for the UE in ECM-CONNECTED. Details of this step are described in TS 36.300. If the MME can't handle the Service Request it will reject it. CSG ID is provided if the UE sends the Service Request message via a CSG cell or a hybrid cell. CSG access mode is provided if the UE sends the Service Request message via a hybrid cell. If the CSG access mode is not provided but the CSG ID is provided, the MME shall consider the cell as a CSG cell. If a CSG ID is indicated and CSG access mode is not provided, and there is no subscription data for this CSG ID and associated PLMN or the CSG subscription is expired, the MME rejects the Service Request with an appropriate cause. The UE shall remove the CSG ID and associated PLMN of the cell where the UE has initiated the service request procedure from the Allowed CSG list, if present. For UEs with emergency EPS bearers, i.e. at least one EPS bearer has an ARP value reserved for emergency services, if CSG access restrictions do not allow the UE to get normal services the MME shall deactivate all non-emergency bearers and accept the Service Request. If LIPA is active for a PDN connection and if the cell accessed by the UE does not link to the L-GW where the UE initiated the LIPA PDN Connection, the MME shall not request the establishment of the bearers of the LIPA PDN connection from the eNodeB in step 4 and shall request disconnection of the LIPA PDN connection according to clause 5.10.3. If the UE has no other PDN connection then the MME shall reject the Service Request with an appropriate cause value resulting in the UE detaching, skip the following steps of the procedure and initiate the release of the core network resources with the implicit MME-initiated Detach procedure according to clause 5.3.8.3. If there is a "Availability after DDN Failure" monitoring event or a "UE Reachability" monitoring event configured for the UE in the MME, the MME sends an event notification (see TS 23.682 for further information). To assist Location Services, the eNodeB indicates the UE's Coverage Level to the MME. If the MME supports RACS, and the MME detects that the selected PLMN is different from the currently registered PLMN for the UE, the MME provides the UE Radio Capability ID of the newly selected PLMN in the UE context to the eNodeB as described in clause 5.11.3a. If the Service Request message is received from a UE in ECM-IDLE state without a Release Request indication, the MME shall delete any stored Paging Restriction Information for this UE and stop restricting paging accordingly and the procedure continues form the next step 3. If the Service Request message includes a Release Request indication or Reject Paging Indication, then:

• If the Service Request message includes Paging Restriction Information, the MME may accept or reject the Paging Restriction Information requested by the UE based on operator policy. If the MME rejects the Paging Restriction Information, the MME removes any stored Paging Restriction Information from the UE context and discards the UE requested Paging Restriction Information. If the MME accepts the Paging Restriction Information from the UE, the MME stores the received Paging Restriction Information from the UE in the UE context. The MME informs the UE about the acceptance/rejection of the requested Paging Restriction Information in the Service Accept message. If no Paging Restriction Information is provided, no paging restrictions apply;
• no S1 bearer is established (steps 4-7 are skipped);
• the MME Triggers the S1 release procedure as described in clause 5.3.5 and no further steps of this procedure are executed. The MME may however trigger the NAS Authentication/Security in step 3 before releasing the UE.

In the case of satellite access for Cellular IoT, the MME may verify the UE location and determine whether the PLMN is allowed to operate at the UE location, as described in clause 4.13.4. If the UE receives a Service Reject message with cause value indicating that the selected PLMN is not allowed to operate at the present UE location, the UE shall attempt to select a PLMN as specified in TS 23.122.

NAS authentication/security procedures as defined in clause 5.3.10 on "Security function" may be performed. If the MME is configured to support RLOS and the UE indicated Attach Type "RLOS", based on local regulation and operator policy, the MME may skip the authentication and security setup, or the MME may perform authentication if security information is available or obtainable from a HSS, and continue the Service Request procedure regardless of the authentication result.

If there is a Service Gap timer running in the MME MM Context for the UE and the MME is not waiting for a MT paging response from the UE, the MME rejects the Service Request with an appropriate cause. In addition, MME may also provide a UE with a Mobility Management Back-off timer set to the remaining value of the Service Gap timer. The MME deletes S11-U related information in UE context if there is any, including TEID(DL) for the S11-U for Control Plane CIoT EPS Optimisation if data buffering is in the MME, ROHC context for Control Plane CIoT EPS Optimisation, etc, but not the Header Compression Configuration. The MME sends S1-AP Initial Context Setup Request (Serving-GW address, S1-TEID(s) (UL), EPS Bearer QoS(s), Security Context, MME Signalling Connection Id, Handover Restriction List, CSG Membership Indication) message to the eNodeB. If there is a PDN connection established for Local IP Access, this message includes a Correlation ID for enabling the direct user plane path between the HeNB and the L-GW. If there is a PDN connection established for SIPTO at the Local Network with L-GW function collocated with the (H)eNB, this message includes a SIPTO Correlation ID for enabling the direct user plane path between the (H)eNB and the L-GW. This step activates the radio and S1 bearers for all the active EPS Bearers. The eNodeB stores the Security Context, MME Signalling Connection Id, EPS Bearer QoS(s) and S1-TEID(s) in the UE RAN context. The step is described in detail in TS 36.300. Handover Restriction List is described in clause 4.3.5.7 "Mobility Restrictions". If the UE included support for restriction of use of Enhanced Coverage, the MME sends Enhanced Coverage Restricted parameter to the eNodeB in the S1-AP message. The MME shall only request to establish Emergency EPS Bearer if the UE is not allowed to access the cell where the UE initiated the service request procedure due to CSG access restriction. If the MME receives multiple TAIs from E-UTRAN in step 2 and determines that some, but not all, TAIs in the received list of TAIs are forbidden by subscription or by operator policy, the MME shall include the forbidden TAI(s) as in the Service Reject message. If the Service Request is performed via a hybrid cell, CSG Membership Indication indicating whether the UE is a CSG member shall be included in the S1-AP message from the MME to the RAN. Based on this information, the RAN can perform differentiated treatment for CSG and non-CSG members. If RACS is supported and MME has UE Radio Capability ID in UE context, valid for the PLMN the UE is currently in, it signals the UE Radio Capability ID to the eNodeB as defined in clause 5.11.3a. If the eNodeB does not have mapping between the specific UE Radio Capability ID and the UE radio capabilities, it shall use the procedure described in TS 36.413 to retrieve the mapping from the Core Network.

The eNodeB performs the radio bearer establishment procedure. The user plane security is established at this step, which is described in detail in TS 36.300. When the user plane radio bearers are setup. EPS bearer state synchronization is performed between the UE and the network, i.e. the UE shall locally remove any EPS bearer for which no radio bearers are setup and, if the radio bearer for a default EPS bearer is not established, the UE shall locally deactivate all EPS bearers associated to that default EPS bearer.

The uplink data from the UE can now be forwarded by eNodeB to the Serving-GW. The eNodeB sends the uplink data to the Serving-GW address and TEID provided in the step 4. The Serving-GW forwards the uplink data to the PDN-GW.

The eNodeB sends an S1-AP message Initial Context Setup Complete (eNodeB address, List of accepted EPS bearers, List of rejected EPS bearers, S1 TEID(s) (DL)) to the MME. This step is described in detail in TS 36.300. If the Correlation ID or SIPTO Correlation ID is included in step 4, the eNodeB shall use the included information to establish a direct user plane path to the L-GW and forward uplink data for Local IP Access or SIPTO at the Local Network with L-GW function collocated with the (H)eNB accordingly.

The MME sends a Modify Bearer Request message (eNodeB address, S1 TEID(s) (DL) for the accepted EPS bearers, Delay Downlink Packet Notification Request, RAT Type, MO Exception data counter) per PDN connection to the Serving-GW. If the Serving-GW supports Modify Access Bearers Request procedure and if there is no need for the Serving-GW to send the signalling to the PDN-GW, the MME may send Modify Access Bearers Request (eNodeB address(es) and TEIDs for downlink user plane for the accepted EPS bearers, Delay Downlink Packet Notification Request) per UE to the Serving-GW to optimise the signalling. The Serving-GW is now able to transmit downlink data towards the UE. The usage of the Delay Downlink Packet Notification Request Information Element is specified in clause 5.3.4.2 below. If the PDN-GW requested UE's location and/or User CSG information and the UE's location and/or User CSG information has changed, the MME also includes the User Location Information IE and/or User CSG Information IE in this message. If ISR is activated or if the Serving Network IE has changed compared to the last reported Serving Network IE then the MME also includes the Serving Network IE in this message. If the UE Time Zone has changed compared to the last reported UE Time Zone then the MME shall include the UE Time Zone IE in this message. If the internal flag Pending Network Initiated PDN Connection Signalling is set, the MME indicates UE available for end to end signalling in the Modify Bearer Request message and reset the flag. The MME only includes the MO Exception data counter if the RRC establishment cause is set to "MO exception data" and the UE is accessing via the NB-IoT RAT. The MME maintains the MO Exception Data Counter for Serving PLMN Rate Control purposes (see clause 4.7.7.2). The MME may immediately send the MO Exception Data Counter to the Serving-GW. Alternatively, in order to reduce signalling, the MME may send the MO Exception Data Counter to the Serving-GW as described in TS 29.274. The MME and the Serving-GW clears the DL Data Buffer Expiration Time in their UE contexts if it was set, to remember that any DL data buffered for a UE using power saving functions has been delivered and to avoid any unnecessary user plane setup in conjunction with a later TAU. If a default EPS bearer is not accepted by the eNodeB, all the EPS bearers associated to that default bearer shall be treated as non-accepted bearers. The MME releases the non-accepted bearers by triggering the bearer release procedure as specified in clause 5.4.4.2. If the Serving-GW receives a DL packet for a non-accepted bearer, the Serving-GW drops the DL packet and does not send a Downlink Data Notification to the MME.

If the RAT Type has changed compared to the last reported RAT Type or if the UE's Location and/or Info IEs and/or UE Time Zone and/or if ISR is not activated and Serving Network id and/or the indication UE available for end to end signalling are present in step 8, the Serving-GW shall send the Modify Bearer Request message (RAT Type, MO Exception data counter) per PDN connection to the PDN-GW. User Location Information IE and/or User CSG Information IE and/or Serving Network IE and/or UE Time Zone and/or the indication UE available for end to end signalling are also included if they are present in step 8. If the Modify Bearer Request message is not sent because of above reasons and the PDN-GW charging is paused, then the SGW shall send a Modify Bearer Request message with PDN Charging Pause Stop Indication to inform the PDN-GW that the charging is no longer paused. Other IEs are not included in this message. If the Modify Bearer Request message is not sent because of above reasons but the MME indicated the MO Exception data counter, then the Serving Gateway should notify the PDN-GW that this RRC establishment cause has been used by the MO Exception Data Counter (see TS 29.274). The Serving-GW indicates each use of this RRC establishment cause by the related counter on its CDR.

If dynamic PCC is deployed, the PDN-GW interacts with the PCRF to get the PCC rule(s) according to the RAT Type by means of a PCEF-initiated IP-CAN Session Modification procedure as defined in TS 23.203. If dynamic PCC is not deployed, the PDN-GW may apply local QoS policy. The PDN-GW indicates each use of the RRC establishment cause "MO Exception Data" by the related counter on its CDR.

The PDN-GW sends the Modify Bearer Response to the Serving-GW.

The Serving-GW shall return a Modify Bearer Response (Serving-GW address and TEID for uplink traffic) to the MME as a response to a Modify Bearer Request message, or a Modify Access Bearers Response (Serving-GW address and TEID for uplink traffic) as a response to a Modify Access Bearers Request message. If the Serving-GW cannot serve the MME Request in the Modify Access Bearers Request message without S5/S8 signalling other than to unpause charging in the PDN-GW or without corresponding Gxc signalling when PMIP is used over the S5/S8 interface, it shall respond to the MME with indicating that the modifications are not limited to S1-U bearers, and the MME shall repeat its request using a Modify Bearer Request message per PDN connection. If SIPTO at the Local Network is active for a PDN connection with stand-alone GW deployment and the Local Home Network ID for stand-alone accessed by the UE differs from the Local Home Network ID where the UE initiated the SIPTO@LN PDN Connection, the MME shall request disconnection of the SIPTO at the local network PDN connection(s) with the "reactivation requested" cause value according to clause 5.10.3. If the UE has no other PDN connection, the MME initiated "explicit detach with reattach required" procedure according to clause 5.3.8.3. If SIPTO at the Local Network is active for a PDN connection with collocated LGW deployment and the L-GW CN address of the cell accessed by the UE differs from the L-GW CN address of the cell where the UE initiated the SIPTO at the Local Network PDN Connection, the MME shall request disconnection of the SIPTO at the local network PDN connection(s) with the "reactivation requested" cause value according to clause 5.10.3. If the UE has no other PDN connection, the MME initiated "explicit detach with reattach required" procedure according to clause 5.3.8.3.

When the Serving-GW receives a downlink data packet/control signalling for a UE known as not user plane connected (i.e. the S-GW context data indicates no downlink user plane TEID), it buffers the downlink data packet and identifies which MME or SGSN is serving that UE. If that MME has requested the Serving-GW to throttle downlink low priority traffic and if the downlink data packet is received on a low priority bearer to be throttled (see clause 4.3.7.4.1a), the SGW drops the downlink data. The steps below are not executed. If that MME has requested the S-GW to delay sending the Downlink Data Notification (see clause 5.3.4.2 on "Handling of abnormal conditions in UE triggered Service Request"), the Serving-GW buffers the downlink data and waits until the timer expires before continuing with step 2. If the DL-TEID and eNodeB address for that UE is received before the expiry of the timer, the timer shall be cancelled and the Network triggered Service Request procedure is finished without executing the steps below, i.e. DL data are sent to the UE. If the Serving-GW receives additional downlink data packets/control signalling for this UE before the expiry of the timer, the Serving-GW does not restart this timer.

The Serving-GW sends a Downlink Data Notification message (ARP, EPS Bearer ID, Paging Policy Indication) to the MME and SGSN nodes for which it has control plane connectivity for the given UE. The ARP and EPS Bearer ID are always set in Downlink Data Notification. The MME and SGSN respond to the S-GW with a Downlink Data Notification Ack message. When supporting Paging Policy Differentiation, the Serving-GW indicates in the message the Paging Policy Indication related to the downlink data that triggered the Downlink Data Notification message, as described in clause 4.9. An MME and an SGSN that detects that the UE is in a power saving state (e.g. Power Saving Mode or extended idle mode DRX) or is only in coverage intermittently (e.g. the UE is using satellite access with a known maximum interval between coverage occasions) and cannot be reached by paging at the moment, shall invoke extended buffering depending on operator configuration, except for cases described in next paragraphs. MME/SGSN derives the expected time before radio bearers can be established to the UE. The MME/SGSN then indicates DL Buffering Requested to the Serving-GW in the Downlink Data Notification Ack message and includes a DL Buffering Duration time and optionally a DL Buffering Suggested Packet Count. The MME/SGSN stores a new value for the DL Data Buffer Expiration Time in the MM context for the UE based on the DL Buffering Duration time and skips the remaining steps of this procedure. The DL Data Buffer Expiration Time is used for UEs using power saving state or if the UE is only in coverage intermittently (e.g. the UE is using satellite access with a known maximum interval between coverage occasions) and indicates that there are buffered data in the Serving-GW and that the user plane setup procedure is needed when the UE makes signalling with the network. When the DL Data Buffer Expiration Time has expired, the MME/SGSN considers no DL data to be buffered and no indications of Buffered DL Data Waiting are sent during context transfers at TAU procedures. If there is a "Availability after DDN Failure" monitoring event configured for the UE in the MME/SGSN, the MME/SGSN does not invoke extended buffering. Instead, the MME/SGSN sets the Notify-on-available-after-DDN-failure flag to remember to send an "Availability after DDN Failure" notification when the UE becomes available. If there is a "UE Reachability" monitoring event configured for the UE in the MME/SGSN, the MME/SGSN should not need to invoke extended buffering. The MME/SGSN may use additional information based on a SLA with the MTC user for when to invoke extended buffering, e.g. only invoke it for a certain APN, do not invoke it for certain subscribers, invoke extended buffering in conjunction with "Availability after DDN failure" and "UE reachability" monitoring events, etc. A Serving-GW that receives a DL Buffering Requested indication in a Downlink Data Notification Ack message stores a new value for the DL Data Buffer Expiration Time based on the DL Buffering Duration time and does not send any additional Downlink Data Notification if subsequent downlink data packets are received in the Serving-GW before the buffer time DL Data Buffer Expiration Time has expired for the UE. If the Serving-GW, while waiting for the user plane to be established, is triggered to send a second Downlink Data Notification for a bearer with higher priority (i.e. ARP priority level) than the first Downlink Data Notification was sent for, the SGW sends a new Downlink Data Notification message indicating the higher priority to the MME. If the Serving-GW receives additional downlink data packets for a bearer with same or lower priority than the first Downlink Data Notification was sent for or if the Serving-GW has sent the second Downlink Data Notification message indicating the higher priority and receives additional downlink data packets for this UE, the Serving-GW buffers these downlink data packets and does not send a new Downlink Data Notification. If the Serving-GW, while waiting for the user plane to be established, receives a Modify Bearer Request message from MME or SGSN other than the one it sent a Downlink Data Notification message to, the Serving-GW re-sends the Downlink Data Notification message only to the new MME or SGSN from which it received the Modify Bearer Request message even if ISR is active. If the Tracking Area Update procedure with MME change or the Routing Area Update procedure is in progress when the old MME receives a Downlink Data Notification message, the old MME may reject a Downlink Data Notification message with an indication that the Downlink Data Notification message has been temporarily rejected. Similarly, if the Routing Area Update procedure with SGSN change or the Tracking Area Update procedure is in progress when the old SGSN receives a Downlink Data Notification message, the old SGSN may reject a Downlink Data Notification message with an indication that the Downlink Data Notification message has been temporarily rejected. If the MME holds stored Paging Restriction Information (see clause 4.3.33.6) for the UE that restricts the Downlink Data from causing paging, the MME sends Downlink Data Notification Ack message with an indication that the Downlink Data Notification message has been temporarily rejected. Upon reception of a Downlink Data Notification Ack message with an indication that the Downlink Data Notification message has been temporarily rejected and if the Downlink Data Notification is triggered by the arrival of downlink data packets at the Serving-GW, the Serving-GW may start a locally configured guard timer and buffers all downlink user packets received to the given UE and waits for a Modify Bearer Request message to come. Upon reception of a Modify Bearer Request message, the Serving-GW re-sends the Downlink Data Notification message only to the new MME or SGSN from which it received the Modify Bearer Request message even if ISR is active. Otherwise the Serving-GW releases buffered downlink user packets at expiry of the guard timer or receiving the Delete Session Request message from MME/SGSN. Upon reception of a Downlink Data Notification Ack message with an indication that the Downlink Data Notification message has been temporarily rejected and if the Downlink Data Notification is triggered by the arrival of signalling messages at the Serving-GW, the Serving-GW may reject the PDN-GW initiated EPS bearer(s) request with the same indication that the request has been temporarily rejected. Upon reception of a rejection for an EPS bearer(s) PDN-GW initiated procedure with an indication that the request has been temporarily rejected, the PDN-GW may start a locally configured guard timer. The PDN-GW may re-attempt, up to a pre-configured number of times, when either it detects the UE accesses via a new SGW or at expiry of the guard timer.

If the UE is registered in the MME and considered reachable for paging, the MME sends a Paging message (NAS ID for paging, TAI(s), UE identity based DRX index, Paging DRX length, list of CSG IDs for paging, Paging Priority indication, Enhanced Coverage Restricted, CE mode B Restricted, Assistance Data for Recommended Cells, WUS Assistance Information, Voice Service Indication) to each eNodeB belonging to the tracking area(s) in which the UE is registered. The step is described in detail in TS 36.300 and TS 36.413. Steps 3-4 are omitted if the MME already has a signalling connection over S1-MME towards the UE but the S1-U tunnel has not yet been established. If the MME holds stored Paging Restriction Information for the UE, the MME may block the paging for this UE, based on local policy and the stored Paging Restriction Information (see clause 4.3.33.6). If extended idle mode DRX is enabled for the UE, the MME pages the UE just before the occurrence of the UE's next paging occasion, which is determined as described in TS 23.682. Paging priority indication is included only:

• if the MME receives a Downlink Data Notification or Create/Update Bearer Request with an ARP priority level associated with MPS or other priority services, as configured by the operator.
• One Paging Priority level can be used for multiple ARP priority level values. The mapping of ARP priority level values to Paging Priority level (or levels) is configured by operator policy.

During a congestion situation the eNodeB may prioritise the paging of UEs according to the Paging Priority indications. If the MME, while waiting for a UE response to the Paging Request message sent without Paging Priority indication, receives an Update Bearer Request, Create Bearer Request or Downlink Data Notification, any of which indicates an ARP priority level associated with MPS or other priority services, as configured by the operator, the MME shall send another paging message with the suitable Paging Priority. When the MME is configured to support CSG paging optimisation in the CN, the MME should avoid sending Paging messages to those eNodeB(s) with CSG cells for which the UE does not have a CSG subscription. When the MME is configured to support CSG paging optimisation in the HeNB Subsystem, the list of CSG IDs for paging is included in the Paging message. For CSG paging optimisation, the CSG IDs of expired CSG subscriptions and valid CSG subscriptions are both included in the list. If the UE has emergency bearer service the MME shall not perform the CSG paging optimisation. When the MME supports SIPTO at Local Network and LIPA paging for traffic arriving on the PDN connection with L-GW function collocated with the (H)eNB the MME should only page this (H)eNB to avoid sending Paging messages to eNodeB(s) that are not handling this specific PDN connection. Paging strategies may be configured in the MME for different combinations of APN, Paging Policy Indication from SGW when available (see clause 4.9) and other EPS bearer context information e.g. QCI. APN and any EPS bearer context information are identified by EPS bearer ID received in Downlink Data Notification. Paging strategies may include:

• paging retransmission scheme (e.g. how frequently the paging is repeated or with what time interval);
• determining whether to send the Paging message to the eNodeBs during certain MME high load conditions;
• whether to apply sub-area based paging (e.g. first page in the last known ECGI or TA and retransmission in all registered TAs).

If extended idle mode DRX was enabled in the UE, the MME may additionally take into account the Paging Time Window length for paging retransmission schemes. The MME and the E-UTRAN may support further paging optimisations in order to reduce the signalling load and the network resources used to successfully page a UE by one or several following means:

• by the MME implementing specific paging strategies (e.g. the S1 Paging message is sent to the eNodeB that served the UE last);
• by the MME considering Information On Recommended Cells And eNodeBs provided by the E-UTRAN at transition to ECM-IDLE. The MME takes the eNodeB related part of this information into account to determine the eNodeBs to be paged, and provides the information on recommended cells within the S1 Paging message to each of these eNodeBs;
• by the E-UTRAN considering the Paging Attempt Count Information provided by the MME at paging.

When implementing such optimisations/strategies, the MME shall take into account any PSM active timer and the DRX interval for the UE. The MME shall ensure that the correct Paging DRX Length is provided based on the accepted UE Specific DRX of the current RAT. If the UE Radio Capability for Paging Information is available in the MME for the RAT corresponding to the TAI(s) in the S1 Paging message, the MME shall add the UE Radio Capability for Paging Information for that RAT in the S1 Paging message to the eNodeB. If the Information On Recommended Cells And eNodeBs For Paging is available in the MME, the MME shall take that information into account to determine the eNodeBs for paging and, when paging an eNodeB, the MME may transparently convey the information on recommended cells to the eNodeB. The MME may include in the S1AP Paging message(s) the paging attempt count information. The paging attempt count information shall be the same for all eNodeBs selected by the MME for paging. The MME may include in the S1AP Paging message(s) the WUS Assistance Information, if available. If the MME has Information for Enhanced Coverage stored and Enhanced Coverage is not restricted then the MME shall include Information for Enhanced Coverage in the Paging message for all eNodeBs selected by the MME for paging. For including the Enhanced Coverage Restricted parameter in the paging message, see clause 4.3.28. For including the CE mode B Restricted parameter in the Paging message, see clause 4.3.27a. If the network supports the Paging Cause Indication for Voice Service feature if the UE context in the MME indicates that the UE supports the Paging Cause for Voice Service feature, the MME should provide the Voice Service Indication in the S1AP Paging message only when the MME detects that the downlink data which triggers the Paging message is related to voice service, as specified in clause 4.3.

If the UE is registered in the SGSN, the SGSN sends paging messages to RNC/BSS, which is described in detail in TS 23.060.

If eNodeBs receive paging messages from the MME, the UE is paged by the eNodeBs. The step is described in detail in TS 36.300 and TS 36.304. If the WUS Assistance Information is included in Step 3a, the eNodeB takes it into account when paging the UE (see TS 36.300). If the UE and eNodeB support WUS, then:

• if the S1-AP Paging message contains the Assistance Data for Recommended Cells IE (see TS 36.413), the eNodeB shall only broadcast the UE's Wake Up Signal in the last used cell;
• else (i.e. the Assistance Data for Recommended Cells IE is not included in the S1-AP Paging message) the eNodeB should not broadcast the UE's Wake Up Signal.

If the Voice Service Indication is included in step 3a, the eNodeB supporting the Paging Cause Indication for Voice Service feature should include the Voice Service Indication in the paging message to the UE, see TS 36.300.

If RNC/BSS nodes receive paging messages from the SGSN the UE is paged by the RNSC/BSS, which is described in detail in TS 23.060.

When UE is in the ECM-IDLE state, upon reception of paging indication in E-UTRAN access, the UE initiates the UE triggered Service Request procedure (clause 5.3.4.1) or, if the UE is enabled to use User Plane CIoT EPS Optimisation and there is suspended access stratum context stored in the UE, the UE initiates the Connection Resume procedure (clause 5.3.5A). If the MME already has a signalling connection over S1-MME towards the UE but the S1-U tunnel has not yet been established, then the messages sequence performed start from the step when MME establishes the bearer(s). If the Multi-USIM UE is in ECM-IDLE state, upon reception of paging indication in E-UTRAN access and if the UE decides not to accept the paging, the UE attempts to send a Reject Paging Indication via the UE Triggered Service Request procedure (clause 5.3.4.1) unless it is unable to do so, e.g. due to UE implementation constraints. Upon reception of paging indication in UTRAN or GERAN access, the MS shall respond in respective access as specified TS 24.008 and the SGSN shall notify the S-GW. The MME and/or SGSN supervises the paging procedure with a timer. If the MME and/or SGSN receives no response from the UE to the Paging Request message, it may repeat the paging according to any applicable paging strategy described in step 2. If the MME and/or SGSN receives no response from the UE after this paging repetition procedure, it shall use the Downlink Data Notification Reject message to notify the Serving-GW about the paging failure, if paging was triggered by a Downlink Data Notification message, unless the MME or SGSN is aware of an ongoing MM procedure that prevents the UE from responding, i.e. the MME or SGSN received a Context Request message indicating that the UE performs TAU or RAU procedure with another MME or SGSN. If paging was triggered by control signalling from the Serving-GW and if the MME or SGSN receives no response from the UE after this paging repetition procedure, the MME or SGSN shall reject that control signalling. When a Downlink Data Notification Reject message is received, if ISR is not activated, the Serving-GW deletes the buffered packet(s). If ISR is activated and the Serving-GW receives Downlink Data Notification Reject message from both SGSN and MME, the Serving-GW deletes the buffered packet(s) or rejects the control signalling which triggers the Service Request procedure. The Serving-GW may invoke the procedure PDN-GW Pause of Charging (clause 5.3.6A) if UE is in ECM-IDLE and the PDN-GW has enabled "PDN charging pause" feature.

After receiving the Reject Paging Indication, the MME uses the Downlink Data Notification Failure Indication message to notify the Serving-GW that the UE rejected the page and no user plane radio bearers will be established. The UE remains reachable for future paging attempts based on stored (if any) Paging Restriction Information.

If ISR is activated and paging response is received in E-UTRAN access the Serving-GW sends a "Stop Paging" message to the SGSN.

If ISR is activated and paging response is received in UTRAN or GERAN access the Serving-GW sends a "Stop Paging" message to the MME.