[5g NR] RRC connection release

1. RRC Introduction to connection release

RRC Connection release , success

When UE With the base station RRC Reconfiguration failed 、 Switch failed 、 When the wireless link fails and the integrity protection fails , Will launch RRC Release The process , take UE To RRC_IDLE or RRC_INACTIVE state .

Purpose of initiation ：

Release RRC Connect , Including releasing the established radio bearer and all wireless resources , Or just building SRB2 And at least one DRB Time out RRC Connect , Including suspending the established wireless bearer .

Release scenario ：

• Network initiation RRC Connect the release process to RRC_CONNECTED Medium UE The switch to RRC_IDLE;
• When SRB2 And at least one DRB stay RRC_CONNECTED When creating in , take UE stay -RRC_CONNECTED Convert to RRC_INACTIVE;
• When UE When trying to recover , take RRC_INACTIVE Medium UE Forward back RRC_INACTIVE;
• When UE When trying to recover , take UE stay RRC_INACTIVE Transit to RRC_IDLE;
• Release UE And redirect it to another frequency .

2. UE receive RRCRelease Processing flow

When UE received RRCRelease When the news , Proceed as follows ：

1. Stop timer T380 and T320
2. If not activated AS Security , Ignore RRCRelease Message except waitTime Any other field except .UE into RRC_IDLE state , Release reason ’other’, Program end
3. If RRCRelease The message contains instructions to redirect to eutra Of redirectedCarrierInfo, And includes cnType, After the cell selection , Indicate available... To the upper layer CN Type and received cnType;
4. If RRCRelease The message contains cellReselectionPriorities, Storage cellReselectionPriorities Cell reselection priority information provided ; If it includes T320, Then start the timer T320, according to T320 Set the timer value . If RRCRelease The message does not contain cellReselectionPriorities, Then the cell reselection priority information broadcast in the application system information ;
5. If you include deprioritisationReq, Then start or restart the timer T325, And set the timer value to deprioritisationTimer, And store deprioritisationReq until T325 expire ;
6. If RRCRelease contain suspendConfig, Then the application receives suspendConfig, Reset MAC And release the default MAC Cell Group To configure ; by SRB1 The reconstruction RLC Entity ;
7. If received with suspendConfig Of RRCRelease Message to respond RRCResumeRequest or RRCResumeRequest1, Stop timer T319, stay UE Inactive AS Use the current KgNB and KRRCint Replace KgNB and KRRCint; use UE received RRCRelease Temporary message C-RNTI、 community cellIdentity、 The physical cell ID replaces the current C-RNTI、cellIdentity And physical cell identification .
8. Suspend all SRB and DRB（SRB0 With the exception of ）;
9. If you include t380, Start timer T380, The timer value is set to t380;
10. If RRCRelease The message contains waitTime, Start timer T302, Set the value to waitTime; Inform the upper layer of access restrictions except “0” and “2” All access categories except ;
11. If T390 Running , Stop timer T390;
12. Pause to the upper RRC Connect , UE Get into RRC_INACTIVE state ;
13. If RRCRelease Not included suspendConfig, be UE Get into RRC_IDLE state , The reason for release is “other”.

3. T320 The timer expired

Release from cellReselectionPriorities Provided or from another RAT Inherited cell reselection priority information , The cell reselection priority information broadcast in the application system information

4. RRC Release Message structure

RRC Release structure

RRCRelease-IEs ::=                  SEQUENCE {
    
    redirectedCarrierInfo               RedirectedCarrierInfo                                                       OPTIONAL,   -- Need N
    cellReselectionPriorities           CellReselectionPriorities                                                   OPTIONAL,   -- Need R
    suspendConfig                       SuspendConfig                                                               OPTIONAL,   -- Need R
    deprioritisationReq                 SEQUENCE {
    
        deprioritisationType                ENUMERATED {
    frequency, nr},
        deprioritisationTimer               ENUMERATED {
    min5, min10, min15, min30}
    }                                                                                                               OPTIONAL,   -- Need N
    lateNonCriticalExtension                OCTET STRING                                                        OPTIONAL,
    nonCriticalExtension                    RRCRelease-v1540-IEs                                                OPTIONAL
}

• redirectedCarrierInfo： Redirect information , Allowing UE Redirect to other frequencies ;
• cellReselectionPriorities： Cell reselection priority information
• suspendConfig： Express RRC_INACTIVE Configuration of state
• deprioritisationType ： Indicates whether the object to be de prioritized is frequency or NR
• deprioritisationTimer： Indicates the waiting time for de prioritization ,5min,10min,15min,30min

Cell reselection priority parameter

CellReselectionPriorities ::=       SEQUENCE {
    
    freqPriorityListEUTRA               FreqPriorityListEUTRA                                               OPTIONAL,       -- Need M
    freqPriorityListNR                  FreqPriorityListNR                                                  OPTIONAL,       -- Need M
    t320                                ENUMERATED {
    min5, min10, min20, min30, min60, min120, min180, spare1} OPTIONAL,     -- Need R
    ...,
    [[
    freqPriorityListNRSlicing-r17       FreqPriorityListNRSlicing-r17                                       OPTIONAL        -- Need M
    ]]
}

FreqPriorityListEUTRA ::=           SEQUENCE (SIZE (1..maxFreq)) OF FreqPriorityEUTRA

FreqPriorityListNR ::=              SEQUENCE (SIZE (1..maxFreq)) OF FreqPriorityNR

FreqPriorityEUTRA ::=               SEQUENCE {
    
    carrierFreq                         ARFCN-ValueEUTRA,
    cellReselectionPriority             CellReselectionPriority,
    cellReselectionSubPriority          CellReselectionSubPriority                                          OPTIONAL        -- Need R
}

FreqPriorityNR ::=                  SEQUENCE {
    
    carrierFreq                         ARFCN-ValueNR,
    cellReselectionPriority             CellReselectionPriority,
    cellReselectionSubPriority          CellReselectionSubPriority                                          OPTIONAL        -- Need R
}

• carrierFreq： Reselect cell frequency points
• cellReselectionPriority ： Cell reselection priority
• cellReselectionSubPriority： Used to calculate the absolute priority of frequency points

RRC Suspend configuration parameters

SuspendConfig ::=                   SEQUENCE {
    
    fullI-RNTI                          I-RNTI-Value,
    shortI-RNTI                         ShortI-RNTI-Value,
    ran-PagingCycle                     PagingCycle,
    ran-NotificationAreaInfo            RAN-NotificationAreaInfo                                                OPTIONAL,   -- Need M
    t380                                PeriodicRNAU-TimerValue                                                 OPTIONAL,   -- Need R
    nextHopChainingCount                NextHopChainingCount,
    ...
}

• I-RNTI-Value：I-RNTI, length 40bit
• ShortI-RNTI-Value： Short format I-RNTI, length 24bit
• PagingCycle: The cycle of paging initiated by the access network .rf32 Corresponding to 32 Wireless frame ,rf64 Corresponding 64 A wireless frame , And so on
• RAN-NotificationAreaInfo：RAN Update area information
• PeriodicRNAU-TimerValue: stay UE Medium periodic trigger RAN The timer of the update process .min5 Corresponding to 5 minute , And so on
• NextHopChainingCount： Frequency hopping configuration