102203228-10-a-Drop-Call-Analysis-v1-7

E-UTRA

RRC_IDLE

E-UTRA

RRC_CONNECTED

TA

UL in-sync

TA

UL out-of-sync

RRC Connection Release

Expiry of Short Inactivity Timer (intentional)

Timing maintenance issue (unintentional)

Contention-based RA success after UL data arrival

PDCCH order success after DL data arrival

PDCCH order success after Inactivity timer expiration

RRC Connection Reestablishment

RRC Connection Setup


Radio link failure

Radio L2 SFS (dec10): for RLT/RL10/RL05TD/RL15TD/RL20 non-contention based RA for the DL data arrival case is not yet supported.RAN2#65 decided that a UE processes UL grants only if TA timer is running, i.e., UL grant when TAT is not running does not trigger a random access procedure (see, e.g., R2-090967 CR0252)

Soc Classification level * Nokia Siemens Networks

Presentation / Author / Date TA timer expiry at UE3GPP TS 36.321: When timeAlignmentTimer expires at UE, UE MAC layer shall:flush all HARQ buffers;notify RRC layer to release PUCCH/SRS;clear any configured downlink assignments and uplink grants

3GPP TS 36.331: Upon receiving a PUCCH/ SRS release request from MAC layer, the UE RRC shall:release periodic CQI reporting config, ie it stops CQI reporting on PUCCHrelease Scheduling Request Config

Radio L2 SFS: For RL20/RL15 the approach is to keep the UE always in-sync in UL. For later releases an alignment with RRC may be required in order to indicate to reassign PUCCH and SRS resources (i.e., at least on expiry of the timing alignment timer). The details are FFS yet.Bearer Management SFS: L1 reconfiguration to recover from TA expiry is not supported in RL20/RL15

Presentation / Author / Date Random access procedure for UEs being UL Out-of-Sync (RL30)If MAC has been triggered by higher layers (layer 3) to perform a random access procedure for a UE being UL Out-of-Sync in order to gain timing alignment for this UE again (see TF_LTE_SFS_RL2_1236), MAC entity in eNB shall select one of the free dedicated RA preambles that can be used for non-contention based RA (see TF_LTE_SFS_RL2_1269) and signal the selected RA preamble to the UE in order to command a non-contention base RA procedure to the UE . If there are no dedicated preambles available, then the eNB shall command a contention based RA procedure for the UE instead. The preamble signalling shall be via PDCCH using DCI format 1A as specified in [3GPP-36.212], section 5.3.3.1.3.The dedicated preamble can be reused as soon as MAC detects the success or failure of the RA procedure. The RA procedure is considered to be successful if following the transmission of the Random Access Response message containing the respective preamble within the Random Access Response Window, there was successful transmission of data in DL (or UL). The RA procedure is considered to have failed if, following the assignment of the dedicated preamble on PDCCH, MAC has to assume that the UE has exceeded the configured maximum number of preamble transmissions while no transmission of the assigned dedicated preamble was detected by eNB. A timer with configurable value (O&M parameter DedPreambleReuseTimer, see TF_LTE_SFS_RL2_1060) may be used as worst case condition after which the failure of the RA procedure can be assumed by MAC.Note that an optimized value of the timer setting for detection of an RA failure may be derived from settings for the RA response window size, PRACH configuration, and maximum number of preamble transmissions.Any necessary alignments with layer 3 requirements for RLD x releases are left to entity specification and implementation.

Non-Contention Based RA Preamble Assignment (DL data arrival case), RL30When there are DL data for an UE awaiting transmission and the eNB has detected that the UL synchronization status of the UE is Out-of-Sync, the MAC entity in eNB shall select one of the free dedicated RA preambles that can be used for non-contention based RA (see TF_LTE_SFS_RL2_1269). The selected RA preamble shall be signalled to UE with PDCCH signalling. If there are no dedicated preambles available, then the eNB shall command a contention based RA procedure for the UE.The preamble signalling shall be via PDCCH using DCI format 1A as specified in [3GPP-36.212], section 5.3.3.1.3.The dedicated preamble can be reused as soon as MAC detects the success or failure of the RA procedure. The RA procedure is considered to be successful if following the transmission of the Random Access Response message containing the respective preamble within the Random Access Response Window, there was successful transmission of data in DL (or UL). The RA procedure is considered to have failed if, following the assignment of the dedicated preamble on PDCCH, MAC has to assume that the UE has exceeded the configured maximum number of preamble transmissions while no transmission of the assigned dedicated preamble was detected by eNB. A timer with configurable value (O&M parameter DedPreambleReuseTimer, see TF_LTE_SFS_RL2_1060) may be used as worst case condition after which the failure of the RA procedure can be assumed by MAC.Note that an optimized value of the timer setting for detection of an RA failure may be derived from settings for the RA response window size, PRACH configuration, and maximum number of preamble transmissions.


Presentation / Author / Date TA timer expiry at eNBPresentation / Author / Date Maintenance of UL Time Alignment by eNB (source: Radio L2 SFS) UL TA update is done periodically and in addition on per-need basis. MAC entity provides PHY layer the information when a TA update is needed together with the TA update value. MAC entity in eNB shall send it to UE via Timing Alignment MAC control element. As UE detects Out-of-Sync status using a Timing Alignment Timer, the timer shall be started or restarted whenever an initial TA or a TA update command is received (see [3GPP-36.321], section 5.2). If the timer expires, the UE detects out-of-sync status. eNB needs to prevent UE TA timer from expiring, because in RL20/RL15 there is no way to bring UE back in-sync (without dropping call) if TA timer expires The interval between periodic TA update commands is based on the Timing Alignment Timer reduced by a configurable offset taTimerMargin. Radio L2 SFS: TA command period = TimeAlignTimer taTimerMargin A configurable parameter TimeAlignmentMaxOffset is used to determine the maximum allowed timing alignment offset before a per-need timing alignment update is required.

Presentation / Author / Date


Presentation / Author / Date TA timer expiry at eNBPresentation / Author / Date If the TA offset measured by the UL PHY layer is greater than the configurable threshold TimeAlignmentMaxOffset then a TA command is sent to the UE. If the reported TA offset also exceeds a threshold calculated as taSchedulingThreshold = max(taOffsetSchedMgn, TimeAlignmentMaxOffset +0.5s), the UL scheduler is informed that the UE is drifting out of alignment When HARQ ACK feedback is received for the TA command then: For a per-need TA command and when taSchedulingThreshold (see above) was exceeded: the UL scheduler is informed that the TA is OK again. The periodic timing alignment timer is (re)started. If no HARQ ACK feedback is received for a TA command within the maximum number of DL HARQ transmissions then: The TA update command shall be repeated up to a configurable maximum number of times taCommandMaxRetries or until the timing alignment timer expires; the latest available timing advance estimation shall be used for every repetition. If the maximum number of retries is exceeded or the timing alignment timer has expired, then status UE UL out-of-sync is detected TatExpiry seen in UDP Log and Emil Immediate release of RRC and S1 follows (there is no waiting for T_RLF expiry)



Presentation / Author / Date TA timer expiry at eNB

NOTE: TA out-of-sync causes immediate release (no T_RLF involved)



Presentation / Author / Date TA timer expiry at eNB, Emil examplePresentation / Author / Date TaTExpiry followed by immediate S1 + RRC release



Presentation / Author / Date TA timer expiry at eNB, user-configurable parametersPresentation / Author / Date

Always check the current values (defaults and the actual used) of the eNB sw version in use.


Parameter abbreviated Name

Description

Ac-cess

Parameter Type

Range/

Step-size

Default value

Para-meter Scope

Reference

Multi-

plicity

taTimer

Determines the number of subframes after which a UE assumes being Out-of-Sync in UL if no Time Alignment Command was received.

RW

BTS restart

O

{500, 750, 1280, 1920, 2560, 5120, 10240}

1280

cell

36.331

timeAlignmentTimer

1

taMaxOffset

Determines the maximum allowed time alignment offset. If value is exceeded the need for time alignment update is given.

RW

O

0..5/0.01

Unit: s

0.52

(corresponds to 16*Ts)

cell

TF_LTE_SFS_RL2_697

1


Presentation / Author / Date TA timer expiry at eNB, vendor parametersPresentation / Author / Date

Always check the current values (defaults and the actual used) of the eNB sw version in use.


Parameter abbreviated Name

Description

Ac-cess

Parameter Type

Range/

Step-size

Default value

Para-meter Scope

Reference

Multi-

plicity

taTimerMargin

Used to control the interval between periodic timing alignment commands being sent to the UE.

The actual time interval between updates will be TimeAlignTimer taTimerMargin

The upper value is constrained by the value of TimeAlignTimer.

RW

O

0..2560/1

Unit: subframes

89

Cell

TF_LTE_SFS_RL2_697

1

taOffScheMarg

Used to determine when to no longer consider a UE that is drifting out of time alignment in uplink scheduling;

R

V

1.54/0.1unit: s

2

BTS

TF_LTE_SFS_RL2_697

1

taCmdMaxRetry

The number of times the TA command will be retried before MAC assumes the UE has gone out-of-sync.

R

V

0..10/1

1

BTS

TF_LTE_SFS_RL2_697

1


Presentation / Author / Date eNB differentiation between in-sync and out-sync (RL30)RRC connected substates: UL in-sync and UL out-of-sync

Uplink RA SR or downlink PDCCH order to bring UE back in-sync (RL30)


E-UTRA

RRC_IDLE

E-UTRA

RRC_CONNECTED

TA

UL in-sync

TA

UL out-of-sync

PDCCH order failure after DL data arrival

PDCCH order failure after Inactivity timer expiration

Expiry of Short Inactivity Timer (intentional)

Timing maintenance issue (unintentional)

Contention-based RA success after UL data arrival

PDCCH order success after DL data arrival

PDCCH order success after Inactivity timer expiration

RRC Connection Reestablishment

RRC Connection Setup


Radio link failure

Radio L2 SFS (dec10): for RLT/RL10/RL05TD/RL15TD non-contention based RA for the DL data arrival case is not yet supported.RAN2#65 decided that a UE processes UL grants only if TA timer is running, i.e., UL grant when TAT is not running does not trigger a random access procedure (see, e.g., R2-090967 CR0252)

eNB has inactivity timer parameter to get UE to IDLEMME also has has a mobile reachable timer, mme default = 58min, periodic TA timer=54min default, implicit detach timer = 58min (default) (checked Dec 2010).


Presentation / Author / Date Ue out-of-sync recovery (RL30)If UE goes loses timing alignment, it listens to PDCCH but is allowed to transmit only on PRACH

Periodic CQI reporting is stopped, SR and UL ACK/NACK cannot be sentNOTE: pending UL ACK/NACK transmission will not trigger RA Scheduling RequestIf there is DL data to be sent, eNB uses PDCCH order to trigger RAIf there is UL data to be sent, UE uses RA SRAfter UE has valid TA, eNB re-establishes CQI/SR/SRS config via RRC Conn Reconfig

Note: following successful UE resynchronization, higher layers will reassign dedicated resources on PUCCH and for SRS to the UE. As long as these are the same resources or at least resources with the same periodicity and reporting instances, there is no need to reconfigure the DRX Start Offset. Further development: As soon as this is not the case any more, configuration of dedicated resources on PUCCH will require reconfiguration of UEs DRX Start Offset; this in turn will require to enhance DRX reconfiguration procedure substantially as the restrictions as defined in RRM.2504 may no longer apply.Note: it is not foreseen that MAC control elements for the DL also trigger a resynchronization of a UE as there should be no need to transmit those in UL out-of-sync state.

Presentation / Author / Date Radio L2 SFS (dec10): When DRX is configured, it is open whether UE can be kept in UL synchronized status when UE is in active state since DRX is not supported in RLT. E.g. long DRX cycles may mean the UE's TA timer may expire. This open issue depends on how UL reference signals are configured by RRM and what is the maximum UL reference signal transmission interval (provided by PHY) in order to keep UE in UL synchronization status.


Presentation / Author / Date Random Access Scheduling Request detectionRA_SR link state notification in eNB is triggered when eNB receives a RACH msg3 which contains a C-RNTI and the UE with this C-RNTI is already active in the cell (time alignment status for the UE is in-sync). This is not a real radio link failure, but only result of UE PUCCH Scheduling Request failing multiple times and UE sending SR on PRACH



Presentation / Author / Date Random Access Scheduling Request and L1 PUCCH reconfiguration, example from RL20First RA_SR detected indicating that SR sending on PUCCH has failed and PUCCH SR and CQI config was released by UE RA SR triggered

RA SR detected from UEL1 PUCCH reconfiguration

Presentation / Author / Date In this example eNB does not reconfigure PUCCH until after third RA_SR. Until that all UE UL transmission must use RA_SR.


Presentation / Author / Date Random Access Scheduling Request and L1 PUCCH reconfiguration, example from RL20Periodic CQI reporting on PUCCH reconfiguredScheduling Request resource on PUCCH reconfigured




Outline UE-detected RF problems: RRC Connection Re-Establishment eNB-detected radio link problems

PUSCH RLFCQI RLFAck/Nack RLFSRS RLFeNB-initiated release: TA timer expiryeNB-initiated release: maximum RLC retransmissions exceededeNB-initiated release: GTP-U failureTimers and constants (3GPP)



Presentation / Author / Date RLC layer STATUS polling mechanismSource: 3GPP 36.322 v8.8.0, June 2010, Bearer Management SFS, PDDBRLC layer retransmissions only in RLC acknowledged modeRLC AM transmitter requests a STATUS PDU from RLC receiver (sets poll bit on in RLC header)

After the number of bytes transmitted since previous poll exceeds the value of amRlcPBTab3ulPollByte (uplink, ue cat3) or amRlcPBTab3dlPollByte (downlink, ue cat3), or After pollPdu RLC PDUs have been transmitted since previous pollin the last data PDU in the RLC transmit bufferThe RLC AM receiver responds to polling request by transmitting a STATUS PDU which acknowledges successfully received PDUs and also selectively nacks unsuccessfully received PDUs (selective NACK).

RLC receiver will not send STATUS PDU more often than interval defined by parameter tProhib.RLC receiver also sends STATUS PDU if tReord timer expires (but not if timer tProhib is running).NOTE: default PDDB settings tProhib=50ms and tReord=50ms.If RLC transmitter receives no STATUS PDU within tPollretr, a new poll request along with unacknowledged data will be sent to RLC receiverRLC AM window size is fixed to 512 RLC PDUs (segments of an RLC PDU are counted as one PDU).

Presentation / Author / Date PDCP status reporting should be activated for DL, to avoid TCP throughput notch during handover. Set statusRepReq=3 in bearer PDCP profile.


Presentation / Author / Date RLC layer ARQ mechanismSource: 3GPP 36.322 v8.8.0, June 2010, Bearer Management SFS, PDDBRLC transmitter will retransmit all data that is nacked in the STATUS PDUMaximum number of UL and DL RLC retransmissions is defined by vendor parameter drbAmMxRtxTh (default=16)


Text

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Rx

Tx

time

RLC PDUPoll bit set

RLC Status

Polling trigger reached

ACKed RLC PDUs can be removed from buffer

Ttransfer-1

Ttransfer-2

Twait

Documents

102203228-10-a-Drop-Call-Analysis-v1-7