5.3.5A Connection Resume procedure

23.4013GPPGeneral Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) accessRelease 18TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

This procedure is used by the UE to resume the ECM-connection if the UE and the network support User Plane CIoT EPS Optimisation and the UE has stored the necessary information to conduct the Connection Resume procedure (see TS 36.300 [5]) otherwise the Service Request procedures are used, see clause 5.3.4.

Figure 5.3.5A-1: UE initiated Connection Resume procedure

1. The UE triggers the Random Access procedure to the eNodeB, see TS 36.300 [5].

2. The UE triggers the RRC Connection Resume procedure including information needed by the eNodeB to access the UE’s stored AS context, see TS 36.300 [5]. The E-UTRAN performs security checks. 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 bearer is setup and which is not a Control Plane CIoT EPS bearer. 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.

3. The eNodeB notifies the MME that the UE’s RRC connection is resumed in the S1-AP UE Context Resume Request message which includes an RRC resume cause. If the eNodeB is not able to admit all suspended bearers, the eNodeB shall indicate this in the list of rejected EPS bearers, see TS 36.413 [36].

When the UE attempts to establish a signalling connection and the following conditions are met:

the eNodeB serves more than one country (e.g. it supports E-UTRA satellite access); and

– the eNodeB knows in what country the UE is located; and

– the eNodeB is connected to MMEs serving different PLMNs of different countries; and

– the UE provides an S-TMSI or GUMMEI, which indicates an MME serving a different country to where the UE is currently located; and

– the eNodeB is configured to enforce selection of the MME based on the country the UE is currently located;

then the eNodeB shall select an MME serving a PLMN corresponding to the UE’s current location and send the S1-AP UE Context Resume Request message to that MME (this is intended to cause the resume procedure to fail).

If there is a Service Gap timer running in the MME for the UE and the MME is not waiting for a MT paging response from the UE and the RRC Connection Establishment Cause for the Connection Resume Request is not ‘mo-Signalling’, the MME rejects the resume request by sending a S1-AP UE Context Resume Reject message to eNodeB.

NOTE: If the UE then sends a subsequent Service Request while the Service Gap timer is running, the MME will send a Service Reject NAS message to the UE with a Mobility Management back-off timer corresponding to the remaining time of the current Service Gap timer (see procedure in clause 5.3.4).

The MME enters the ECM-CONNECTED state. The MME identifies that the UE returns at the eNodeB for which MME has stored data related to the S1AP association, UE Context and bearer context including the DL TEID(s), necessary to resume the connection, see Connection Suspend procedure in clause 5.3.4A.

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 and non-established bearers by triggering the bearer release procedure as specified in clause 5.4.4.2.

To assist Location Services, the eNodeB indicates the UE’s Coverage Level to the MME.

3a. If the S1-U connection is resumed and the UE is accessing via the NB-IoT RAT with the RRC resume cause set to "MO exception data", the MME should notify the Serving Gateway of each use of this establishment cause by the MO Exception Data Counter. The MME maintains the MO Exception Data Counter and sends it to the Serving GW as indicated in TS 29.274 [43].

3b. The Serving Gateway should notify the PDN GW if the RRC establishment cause "MO Exception Data" has been used by the MO Exception Data Counter (see TS 29.274 [43]). The Serving GW indicates each use of this RRC establishment cause by the related counter on its CDR.

3c. The PDN GW indicates each use of the RRC establishment cause "MO Exception Data" by the related counter on its CDR.

4. MME acknowledges the connection resumption in S1-AP UE Context Resume Response message. If the MME is not able to admit all suspended E-RABs the MME shall indicate this in the E-RABs Failed To Resume List IE.

5. If the MME included in step 4 a list of E-RABs failed to resume, the eNodeB reconfigures the radio bearers.

6. 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 stored during the Connection Suspend procedure, see clause 5.3.4A. The Serving GW forwards the uplink data to the PDN GW.

7. 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) 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 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.

8. 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 deployement 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.