7.3b MO-EDT

36.3003GPPEvolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN)Overall descriptionRelease 17Stage 2TS

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

7.3b.1 General

MO-EDT allows one uplink data transmission optionally followed by one downlink data transmission during the random access procedure.

MO-EDT is triggered when the upper layers have requested the establishment or resumption of the RRC Connection for Mobile Originated data (i.e., not signalling or SMS) and the uplink data size is less than or equal to a TB size indicated in the system information. MO-EDT is not used for data over the control plane when using the User Plane CIoT EPS/5GS optimisations.

MO-EDT is only applicable to BL UEs, UEs in enhanced coverage and NB-IoT UEs.

7.3b.2 MO-EDT for Control Plane CIoT EPS/5GS optimisations

MO-EDT for Control Plane CIoT EPS optimisation, as defined in TS 24.301 [20], and Control Plane CIoT 5GS Optimisation, as defined in TS 24.501 [91], are characterized as below:

– Uplink user data are transmitted in a NAS message concatenated in UL RRCEarlyDataRequest message on CCCH;

– Downlink user data are optionally transmitted in a NAS message concatenated in DL RRCEarlyDataComplete message on CCCH;

– There is no transition to RRC CONNECTED.

The MO-EDT procedure for Control Plane CIoT EPS optimisation and Control Plane CIoT 5GS Optimisation are illustrated in Figure 7.3b-1 and Figure 7.3b-1a respectively.

Figure 7.3b-1: MO-EDT for Control Plane CIoT EPS Optimisation

Figure 7.3b-1a: MO-EDT for Control Plane CIoT 5GS Optimisation

0. Upon connection establishment request for Mobile Originated data from the upper layers, the UE initiates the MO-EDT procedure and selects a random access preamble configured for EDT.

1. UE sends RRCEarlyDataRequest message concatenating the user data on CCCH. For EPS if enabled in the cell, or for 5GS, the UE may indicate AS Release Assistance Information.

2. For EPS, the eNB initiates the S1-AP Initial UE message procedure to forward the NAS message and establish the S1 connection. For 5GS, the ng-eNB initiates the NG-AP Initial UE message procedure to forward the NAS message.The (ng-)eNB may indicate in this procedure that this connection is triggered for EDT.

3. For EPS, the MME requests the S-GW to re-activate the EPS bearers for the UE. For 5GS, the AMF determines the PDU session contained in the NAS message.

4. For EPS, the MME sends the uplink data to the S-GW. For 5GS, the AMF sends the PDU Session ID and the uplink data to the SMF and the SMF forwards the uplink data to the UPF.

5. For EPS, if downlink data are available, the S-GW sends the downlink data to the MME. For 5GS, if downlink data are available, the UPF forwards the downlink data to SMF and the SFM forwards the downlink data to AMF.

6. If downlink data are received from the S-GW or SMF, the MME or AMF forwards the data to the eNB or ng-eNB via DL NAS Transport procedure and may also indicate whether further data are expected. Otherwise, the MME or AMF may trigger Connection Establishment Indication procedure and also indicate whether further data are expected.

7. If no further data are expected, the (ng-)eNB can send the RRCEarlyDataComplete message on CCCH to keep the UE in RRC_IDLE. If downlink data were received in step 6, they are concatenated in RRCEarlyDataComplete message.

8. For EPS, the S1 connection is released and the EPS bearers are deactivated. For 5GS, the AN release procedure is started.

NOTE 1: If the MME/AMF or the (ng-)eNB decides to move the UE in RRC_CONNECTED mode, RRCConnectionSetup message is sent in step 7 to fall back to the legacy RRC Connection establishment procedure; the (ng-)eNB will discard the zero-length NAS PDU received in RRCConnectionSetupComplete message.

NOTE 2: If neither RRCEarlyDataComplete nor, in case of fallback, RRCConnectionSetup is received in response to RRCEarlyDataRequest, the UE considers the UL data transmission not successful.

7.3b.3 MO-EDT for User Plane CIoT EPS/5GS optimisations

MO-EDT for User Plane CIoT EPS optimisation, as defined in TS 24.301 [20], and for User Plane CIoT 5GS Optimisation, as defined in TS 24.501 [91], are characterized as below:

– The UE has been provided with a NextHopChainingCount in the RRCConnectionRelease message with suspend indication;

– Uplink user data are transmitted on DTCH multiplexed with UL RRCConnectionResumeRequest message on CCCH;

– Downlink user data are optionally transmitted on DTCH multiplexed with DL RRCConnectionRelease message on DCCH;

– The short resume MAC-I is reused as the authentication token for RRCConnectionResumeRequest message and is calculated using the integrity key from the previous connection;

– The user data in uplink and downlink are ciphered. The keys are derived using the NextHopChainingCount provided in the RRCConnectionRelease message of the previous RRC connection;

– The RRCConnectionRelease message is integrity protected and ciphered using the newly derived keys;

– There is no transition to RRC CONNECTED.

The MO-EDT procedure for User Plane CIoT EPS optimisation is illustrated in Figure 7.3b-2.

Figure 7.3b-2: MO-EDT for User Plane CIoT EPS Optimisation

0. Upon connection resumption request for Mobile Originated data from the upper layers, the UE initiates the MO-EDT procedure and selects a random access preamble configured for EDT.

1. The UE sends an RRCConnectionResumeRequest to the eNB, including its Resume ID, the establishment cause, and an authentication token. The UE resumes all SRBs and DRBs, derives new security keys using the NextHopChainingCount provided in the RRCConnectionRelease message of the previous RRC connection and re-establishes the AS security. The user data are ciphered and transmitted on DTCH multiplexed with the RRCConnectionResumeRequest message on CCCH. If enabled in the cell, the UE may indicate AS Release Assistance Information.

2. The eNB initiates the S1-AP Context Resume procedure to resume the S1 connection and re-activate the S1-U bearers.

3. The MME requests the S-GW to re-activate the S1-U bearers for the UE.

4. The MME confirms the UE context resumption to the eNB.

5. The uplink data are delivered to the S-GW.

6. If downlink data are available, the S-GW sends the downlink data to the eNB.

7. If no further data are expected, the eNB can initiate the suspension of the S1 connection and the deactivation of the S1-U bearers.

8. The eNB sends the RRCConnectionRelease message to keep the UE in RRC_IDLE. The message includes the releaseCause set to rrc-Suspend, the resumeID, the NextHopChainingCount and drb-ContinueROHC which are stored by the UE. If downlink data were received in step 6, they are sent ciphered on DTCH multiplexed with the RRCConnectionRelease message on DCCH. The procedure ends with the reception of the HARQ feedback (ARQ) acknowledging the successful DL transmission.

The MO-EDT procedure for User Plane CIoT 5GS Optimisation is illustrated in Figure 7.3b-2a.

Figure 7.3b-2a: MO-EDT for User Plane CIoT 5GS Optimisation

0. Upon connection resumption request for Mobile Originated data from the upper layers, the UE initiates the MO-EDT procedure and selects a random access preamble configured for EDT.

1. The UE sends an RRCConnectionResumeRequest to the ng-eNB, including its I-RNTI, the resume cause, and an authentication token. The UE resumes all SRBs and DRBs, derives new security keys using the NextHopChainingCount provided in the RRCConnectionRelease message of the previous connection and re-establishes the AS security. The user data are ciphered and transmitted on DTCH multiplexed with the RRCConnectionResumeRequest message on CCCH. The UE may indicate AS Release Assistance Information.

2. The uplink data are delivered to the UPF.

3. The ng-eNB sends a NG-AP Context Resume Request message to the AMF to resume the connection. If the UE included AS Release Assistance information indicating No further UL/DL higher layer PDU in step 1, ng-eNB may request for immediate transition to RRC IDLE with Suspend.

4. If the AMF does not receive a request for immediate transition to RRC IDLE with Suspend in step 3 or the AMF is aware of downlink data or signalling pending, the AMF requests the SMF to resume the PDU session.

5. The AMF sends a NG-AP Context Resume Response to the ng-eNB. If the AMF receives a request for immediate transition to RRC IDLE with Suspend in step 3 and there is no downlink data or signalling pending, the AMF includes a Suspend indication, and keeps the UE in CM-IDLE with Suspend.

6. If the AMF includes Suspend indication in step 5, the ng-eNB proceeds to step 8. If the AMF does not include Suspend indication and the UE included AS Release Assistance information indicating Only a single Downlink Data transmission subsequent to the Uplink transmission in step 1, the ng-eNB may wait for the DL data to arrive, and proceeds to step 7.

7 The ng-eNB initiates the NG-AP UE Context Suspend procedure to inform the AMF that the RRC connection is being suspended. The AMF requests the SMF to suspend the PDU session and the SMF requests the UPF to release the tunnel information for the UE.

8. The eNB sends the RRCConnectionRelease message to keep the UE in RRC_IDLE. The message includes the releaseCause set to rrc-Suspend, the I-RNTI, the NextHopChainingCount and drb-ContinueROHC which are stored by the UE. If downlink data were received in step 6, they are sent ciphered on DTCH multiplexed with the RRCConnectionRelease message on DCCH. The procedure ends with the reception of the HARQ feedback (ARQ) acknowledging the successful DL transmission.

NOTE 1: If the MME/AMF or (ng-)eNB decides the UE to move in RRC_CONNECTED mode, RRCConnectionResume message is sent in step 7 to fall back to the RRC Connection resume procedure. In that case, the RRCConnectionResume message is integrity protected and ciphered with the keys derived in step 1 and the UE ignores the NextHopChainingCount included in the RRCConnectionResume message. Downlink data can be transmitted on DTCH multiplexed with the RRCConnectionResume message. In addition, an RRCConnectionSetup can also be sent in step 7 to fall back to the RRC Connection establishment procedure.

NOTE 2: If neither RRCConnectionRelease nor, in case of fallback, RRCConnectionResume is received in response to RRCConnectionResumeRequest for MO-EDT, the UE considers the UL data transmission not successful.

For MO-EDT for User Plane CIoT EPS Optimisation and User Plane CIoT 5GS Optimisation, an RRC connection can also be resumed in an (ng-)eNB (the new (ng-)eNB) different from the one where the connection was suspended (the old (ng-)eNB). Inter (ng-)eNB connection resumption is handled using context fetching, whereby the new (ng-)eNB retrieves the UE context from the old (ng-)eNB over the X2 (Xn) interface. The new (ng-)eNB provides the Resume ID for EPS or I-RNTI for 5GS which is used by the old (ng-)eNB to identify the UE context. This is illustrated in Figure 7.3b-3 and Figure 7.3b-3a for the case of User Plane CIoT EPS Optimisation and for the case of User Plane CIoT 5GS Optimisation respectively.

Figure: 7.3b-3: MO-EDT for User Plane CIoT EPS Optimisations in different eNB

Figure: 7.3b-3a: MO-EDT for User Plane CIoT 5GS Optimisation in different ng-eNB

1. Same as step 1 in the intra (ng-)eNB connection resumption.

2. The new (ng-)eNB locates the old (ng-)eNB using the Resume ID (for EPS) or I-RNTI (for 5GS) and retrieves the UE context by means of the X2-AP (for EPS) or Xn-AP (for 5GS) Retrieve UE Context procedure.

3. The old (ng-)eNB responds with the UE context associated with the Resume ID (for EPS) or I-RNTI (for 5GS).

4. For EPS, the new eNB initiates the S1-AP Path Switch procedure to establish a S1 UE associated signalling connection to the serving MME and to request the MME to resume the UE context. For 5GS, the new ng-eNB initiates the NG-AP Path Switch procedure to establish a NG UE associated signalling connection to the serving AMF and to request the AMF to resume the UE context.

5. For EPS, the MME requests the S-GW to activate the S1-U bearers for the UE and updates the downlink path. For 5GS, the AMF requests requests the SMF to resume the PDU session and the SMF requests the UPF to create the tunnel information for the UE and update the downlink path.

6. MME/AMF Acks step 5.

7. For EPS, after the S1-AP Path Switch procedure the new eNB triggers release of the UE context at the old eNB by means of the X2-AP UE Context Release procedure. For 5GS, after the NG-AP Path Switch procedure the new ng-eNB triggers release of the UE context at the old ng-eNB by means of the Xn-AP UE Context Release procedure.

8. For EPS, same as step 5 in the intra eNB connection resumption. For 5GS, the uplink data are delivered to the UPF.

9. Same as step 6 in the intra (ng-)eNB connection resumption.

10. Same as step 7 in the intra (ng-)eNB connection resumption.

11. Same as step 8 in the intra (ng-)eNB connection resumption.