RRC Connection ReEstablishment
- What is this
- How it work
- When it happens
- Causes of RRC Reconfiguration Re-establishment Request
- Common UE side Process
It is a kind of mechanism to make a recovery when radio link got broken for some reason. (See "When it happens" section for these reason)
< How it work >
it works in three steps as shown below (refer to 36.331 5.3.7 RRC connection re-establishment for the details)
i) UE --> NW : RRCConnectionReestablishmentRequest
ii) UE <-- NW : RRCConnectionReestablishment
iii) UE --> NW : RRCConnectionReestablishmentComplete
I think most of those who read this page may be pretty familiar with LTE protocol, so just by looking at the contents of these RRC messages, they would figure out a lot of details without much explanation.
RRCConnectionReestablishmentRequest
c1: rrcConnectionReestablishmentRequest (0)
rrcConnectionReestablishmentRequest
criticalExtensions: rrcConnectionReestablishmentRequest-r8 (0)
rrcConnectionReestablishmentRequest-r8
ue-Identity
c-RNTI: 0000 [bit length 16, 0000 0000 0000 0000 decimal value 0]
physCellId: 0
shortMAC-I: 0000 [bit length 16, 0000 0000 0000 0000 decimal value 0]
reestablishmentCause: reconfigurationFailure /handoverFailure/otherFailure/ spare1
spare: 00 [bit length 2, 6 LSB pad bits, 00.. .... decimal value 0]
RRCConnectionReestablishment (An example based on 36.508 - RRCConnectionReestablishment)
c1: rrcConnectionReestablishment (0)
rrcConnectionReestablishment
rrc-TransactionIdentifier: 0
criticalExtensions: c1 (0)
c1: rrcConnectionReestablishment-r8 (0)
rrcConnectionReestablishment-r8
srb-ToAddModList: 1 item
Item 0
SRB-ToAddMod
srb-Identity: 1
rlc-Config: defaultValue (1)
defaultValue: NULL
logicalChannelConfig: defaultValue (1)
defaultValue: NULL
mac-MainConfig: explicitValue (0)
explicitValue
ul-SCH-Config
maxHARQ-Tx: n5 (4)
periodicBSR-Timer: sf20 (3)
retxBSR-Timer: sf320 (0)
..0. .... ttiBundling: False
drx-Config: release (0)
release: NULL
timeAlignmentTimerDedicated: sf750 (1)
phr-Config: setup (1)
setup
periodicPHR-Timer: sf500 (5)
prohibitPHR-Timer: sf200 (5)
dl-PathlossChange: dB3 (1)
physicalConfigDedicated
pdsch-ConfigDedicated
p-a: dB-3 (2)
pucch-ConfigDedicated
ackNackRepetition: release (0)
release: NULL
pusch-ConfigDedicated
betaOffset-ACK-Index: 9
betaOffset-RI-Index: 6
betaOffset-CQI-Index: 6
uplinkPowerControlDedicated
p0-UE-PUSCH: 0dB
deltaMCS-Enabled: en0 (0)
..1. .... accumulationEnabled: True
p0-UE-PUCCH: 0dB
pSRS-Offset: 3
filterCoefficient: fc4 (4)
cqi-ReportConfig
cqi-ReportModeAperiodic: rm30 (3)
nomPDSCH-RS-EPRE-Offset: 0dB (0)
soundingRS-UL-ConfigDedicated: setup (1)
setup
srs-Bandwidth: bw0 (0)
srs-HoppingBandwidth: hbw0 (0)
freqDomainPosition: 0
..1. .... = duration: indefinite
srs-ConfigIndex: 20
transmissionComb: 0
cyclicShift: cs0 (0)
antennaInfo: explicitValue (0)
explicitValue
transmissionMode: tm3 (2)
codebookSubsetRestriction: n2TxAntenna-tm3 (0)
n2TxAntenna-tm3: c0 [bit length 2, 6 LSB pad bits, 11.. .... decimal value 3]
ue-TransmitAntennaSelection: release (0)
release: NULL
schedulingRequestConfig: setup (1)
setup
sr-PUCCH-ResourceIndex: 60
sr-ConfigIndex: 30
dsr-TransMax: n4 (0)
nextHopChainingCount: 0
HEX string : 00 12 9B 3E 86 03 B5 79 E8 96 6C 30 64 99 80 20 A0 28 68 3C 1E 00
There are several cases where this process get triggered. According to 36.331 5.3.7.2, there are several cases as described below.
Case 1 : When radio link failure happened
Case 2 : when Handover failure happened
Case 3 : when mobility from E-UTRA failure happened
According to 36.331 5.4.3.5 Mobility from E-UTRA failure,
revert back to the configuration used in the source PCell, excluding the configuration configured by the physicalConfigDedicated, mac-MainConfig and sps-Config;
initiate the connection re-establishment procedure as described in How it works and Common UE side Process
Case 4 : when integrity check failure indication was received from lower layers
Case 5 : when RRC connection reconfiguration failure happened (UE cannot comply to the configuration set by
RRC Connection Reconfiguration message)
< Causes of RRC Reconfiguration Re-establishment Request >
When anything happens where UE need to trigger RRC Connection Re-establishment process as described above, UE sends RRC Connection Re-establishment Request with the cause of one of the followings (36.331-5.3.7.4).
ReconfigurationFailure : if the re-establishment procedure was initiated due to reconfiguration failure (the UE is
unable to comply with the reconfiguration) - Case 5 in previous section
HandoverFailure : the re-establishment procedure was initiated due to handover failure as in intra-LTE handover failure or inter-RAT mobility from EUTRA failure - Case 2, 3 in previous section
OtherFailure : Any failure caused by other than two mentioned above - Case 1, 4 and others.
Whatever the case is, overall process on UE side is similar as follows. (36.331 5.3.7.5)
i) stop timer T301
ii) consider the current cell to be the PCell
iii) re-establish PDCP for SRB1
iv) re-establish RLC for SRB1
v) perform the radio resource configuration procedure in accordance with the received radioResourceConfigDedicated
vi) resume SRB1