This procedure will be initiated by UE on below scenarios:
1. Upon re-entry into service area after radio link failure
2. Handover failure
3. When lower layers detect problems as specified in TS 36.322
4. upon an RRC connection reconfiguration failure
5. upon integrity check failure indication from lower layers
6. upon mobility from E-UTRA failure
7. RRC connection reconfiguration failure
UE in RRC Connected state can initiate RRC Connection Re-Establishment procedure in order to keep the RRC connection while security is activated.
Once this procedure is initiated, the UE will perform below steps:
1. stop T310
2. Start T311
3. reset MAC
4. apply default physical channel configuration
5. apply the default MAC main configuration
1) RRC Connection Reestablishment Request
This message is used to request the reestablishment of an RRC connection.
It will involve resumption of SRB1 services and re-activating the security without changing the algorithms.
Signalling radio bearer: SRB0
RLC-SAP: TM
Logical channel: CCCH
Transport Channel: UL-SCH
Direction: UE to E-UTRAN
RRCConnectionReestablishmentRequest message
RRCConnectionReestablishmentRequest-r8-IEs ::= SEQUENCE {
ue-Identity
reestablishmentCause
spare
}
Identity Elements are:
ue-identity: C-RNTI [As the mobile has already RRC connected, it will get C-RNTI]
reestablishmentCause:
Possible values: reconfigurationFailure, handoverFailure, otherFailure
2) RRC Connection Reestablishment
This message is used to re-establish SRB1.
Signalling radio bearer: SRB0
RLC-SAP: TM
Logical channel: CCCH
Transport Channel: DL-SCH
Direction: E-UTRAN to UE
The purpose of this is:
1. Resumption of SRB1
2. Re-activation of security and configuration of only PCell
3. It is similar to RRC Connection Setup
RRCConnectionReestablishment message
RRCConnectionReestablishment-r8-IEs ::= SEQUENCE {
radioResourceConfigDedicated
nextHopChainingCount
nonCriticalExtension
}
3) RRC Connection Reestablishment Complete
This message is used to confirm the successful completion of an RRC connection reestablishment.
After confirmation SRB1 operation is resumed.
Once this is completed all the subsequent messages are send ciphered and integrity protected using previously configured (respective) algorithms and newly derived keys KRRCenc and KRRCint respectively.
Signalling radio bearer: SRB1
RLC-SAP: AM
Logical channel: DCCH
Transport Channel: UL-SCH
Direction: UE to E-UTRAN
4) RRC ConnectionReestablishment Reject
This message is used to indicate the rejection of an RRC connection reestablishment request.
Signalling radio bearer: SRB0
RLC-SAP: TM
Direction: E-UTRAN to UE
Logical Channel: CCCH
Transport Channel: DL-SCH
Once UE receives RRC ConnectionReestablishment Reject, the UE shall leave RRC_CONNECTED state with release cause “RRC Connection failure”
Reference: 3GPP TS 36.331