Saturday, November 5, 2011

RRC Connection Release

Direction: E-UTRAN => UE
Signalling Radio Bearer: SRB1
RLC Mode: AM
Logical Channel: DCCH
Transport Channel: DL-SCH

The RRC CONNECTION RELEASE message is used to command the release of an RRC connection. E-UTRAN initiates the RRC connection release procedure to an UE in RRC_CONNECTED state

The RRC CONNECTION RELEASE procedure with redirection information can also be used for CS-fallback to GERAN or UTRAN

The RRC CONNECTION RELEASE procedure can also be used for MME load balancing. If an MME feels overloaded, it can simply move the calls to other MME in the MME pool. The source MME releases the S1 connections of the UE towards the eNodeB asking the UE to perform a “load balancing TAU”. Then the eNodeB sends RRC CONNECTION RELEASE message to the UE with cause ‘load balancing TAU required'. After receiving this message, the UE initiates Tracking Area Updating procedure which is redirected to another MME

The eNodeB may provide a cell reselection priority for each frequency, by means of separate lists for each RAT (including E-UTRA) in the RRC CONNECTION RELEASE message

There is no RRC CONNECTION RELEASE COMPLETE message defined in LTE. So, UE leaves RRC_CONNECTED state without transmitting RRC CONNECTION RELEASE COMPLETE message

Some of the IEs in RRC CONNECTION RELEASE message
ReleaseCause: The IE releaseCause is used to indicates the reason for releasing the RRC Connection (Ex:- loadBalancingTAUrequired, cs-FallbackHighPriority, or other)
RedirectedCarrierInfo: The redirectedCarrierInfo indicates a carrier frequency which is used to redirect the UE to an E-UTRA or an inter-RAT carrier frequency
IdleModeMobilityControlInfo: This IE provides dedicated cell reselection priorities. 
FreqPriorityListX: Provides a cell reselection priority for each frequency, by means of separate lists for each RAT (including E-UTRA)
SystemInformation: Container for system information of the GERAN cell. Each OCTET STRING in ‘SystemInfoListGERAN’ contains one complete System Information (SI) message as defined in TS 44.018
cellInfoList: Used to provide system information of one or more cells on the redirected inter-RAT carrier frequency. The system information can be used if, upon redirection, the UE selects an inter-RAT cell indicated by the physCellId and carrierFreq (GERAN) or by the physCellId (other RATs).
utra-BCCH-Container: Contains System Information Container message as defined in TS 25.331

 Reference: 3GPP TS 36.331

Example1: Simple RRC CONNECTION RELEASE message

Example2: RRC CONNECTION RELEASE message IdleModeMobilityControlInfo

Example3: RRC CONNECTION RELEASE message with redirection from E-UTRAN to UTRAN

Example4: RRC CONNECTION RELEASE message with redirection from E-UTRAN to GERAN


  1. HI,
    I am having one doubt, when the connection is being disconnected by the UE, then all the bearers and resources from the UE side get released.
    How the eNb side comes to know about the disconnection and releases its resources and transmits the "RRCConnectionRelease" messege to the UE?

  2. Hi,

    The UE can only release resources after receiving RRC Connection release message from the NW.

  3. Swamy,
    so what is the OTA message for that in QXDM


  4. Replies
    1. OTA is over the air,QXDM does not show LTE message like 3G.You may have to decode and see what type of message.
      If QCAT is installed you can see the decoded content in QXDM directly.

    2. I have latest QCAT installed in my PC, but still its not showing the decoded message in QXDM. Still i need to decode it manually. Can any one please tell? Is there any settings we need to set it QXDM?

  5. Someone can clarify what means IE ?

  6. IE is an Information Element in an RRC Message in ASN.1 terminalogy. These IEs can be individual fields, a particular structures and so on...For example in the above RRC Connection Release message, 'release cause' is an IE

  7. Is it possible to redirect from UMTS to LTE?

  8. Hi,

    I have a question.
    I am able to do MO call in both and idle and connected mode in CSFB
    But for MT its happening for idle mode only.

    Can it be due CSFB priority handling.
    Can you tell me what parameters are responsible for it.

  9. Hi,
    I am doing Volte testing, My question is I don't see RRC message between UE and network in qxdm log. Where should it be seen?

  10. Hi,
    I have a question,when UE will go to idle mode ? UE itself will decide or EUTRAN will decide ?

    1. The UE does not decide to go into idle. It is directed to do so by the eNodeb, after an inactivity timer expires. The value of the timer is set by the operator.

  11. Hi,

    Anyone can help me, I have a question
    we are facing below command & release message but still we can't know the exact reason for receiving it

    [82] [2013-12-10 15:18:24:100] [MME -> eNB_2115] : UEContextReleaseCommand

    1 msgS1apUEContextReleaseCommand_type.uE_S1AP_IDs.choice = 1
    2 msgS1apUEContextReleaseCommand_type.uE_S1AP_IDs.u.uE_S1AP_ID_pair.mME_UE_S1AP_ID = 16853291 (0x101292b)
    3 msgS1apUEContextReleaseCommand_type.uE_S1AP_IDs.u.uE_S1AP_ID_pair.eNB_UE_S1AP_ID = 4401 (0x1131)
    4 msgS1apUEContextReleaseCommand_type.cause.choice = 1
    5 msgS1apUEContextReleaseCommand_type.cause.u.radioNetwork = 21 (0x15)
    7 msgS1apUEContextReleaseCommand_type.rawdata.numocts = 25
    9 =
    10 00 17 00 15 00 00 02 00 63 00 08 0c 01 01 29 2b ........c.....)+
    11 40 11 31 00 02 40 02 02 a0 @.1..@...

    [83] [2013-12-10 15:18:24:100] [eNB_2115 -> UE] : RRCConnectionRelease

    1 value DL-DCCH-Message ::=
    2 {
    3 message c1 : rrcConnectionRelease :
    4 {
    5 rrc-TransactionIdentifier 0,
    6 criticalExtensions c1 : rrcConnectionRelease-r8 :
    7 {
    8 releaseCause other
    9 }
    10 }
    11 }
    13 RRCConnectionRelease.rawdata.numocts = 2
    15 =
    16 28 02 (.

    Thanks everyone

  12. Hi,

    I have a question. If there is no uplink and downlink transmission for a long time, RRC connection will be released. How long should it be? Is any timer counting for that in spec and which spec can find it? I am appreciated for your help.

  13. Yes there is a timer running at eNB and the value of the timer is not specified by 3GPP. This value is operator specific

  14. Hi Kumar Swamy
    As per 23401,i always see CSFB happened with Extended service request and S1AP request & responce with CSFB indicator.(as LTE do attach & default bearer procedure from very begining).could you please explain when CSFB will trigger with RRC connection release with CSFB indicator.please explain with call flow and pratical scenario.

    Thanks in Advance
    Vijay T

  15. I have a question, RRC RELEASE COMMAND with cause as "mmeloadbalancingTAUrequired" is sent to UE from ENB only after the ENB receives UE CONTEXT RELEASE COMMAND with cause as "mmeloadbalancingTAUrequired" right?? is there any scenario where UE receives RELEASE COMMAND from ENB with the cause "mmeloadbalancinfTAUrequired" but the ENB received UE CONTEXT RELEASE COMMAND with an cause "miscellaneous unspecified".
    Could you help me on these as we saw this case from last 2 weeks, I am confused as the specs say something and i am seeing something.

  16. Agree with you and even I think that the UE get RRC Connection Release with cause 'loadBalancingTAUrequired' only when eNB gets the release command for the same but not for unspecified cause.

  17. Hi All,
    I have scenario where in i have to gracefully shutdown/disconnect all UE's in connected state at RRC and go for reboot of the complete system. Here are the steps that i have follwed
    1. Find all UE's in RRC which are in connected state
    2. Send UE Context Release Request to MME for the UE with Cause as Misc_Cause_O_M_Intervention.
    3. Once we receive UE Context Release Command from MME, Start UE Release procedure at eNodeb.
    4. When we send RRC Connection Release Use Cause as "other"
    5. Send UE Context Release Complete to MME.
    6. Repeat Above steps for all UE's.
    7. Go for reboot.

    Here in this scenario. After sending RRC Connection Release to UE, UE immediately trying to connect with message RRC Connection Request with establishmentCause as "HighPriorityAccess" and MME is releasing the UE again.

    I wanted to know why UE is trying to connect again.

    UE was just in connected state and it was doing any data transfer (Both in Uplink and Downlink).

  18. This comment has been removed by the author.

  19. I have one Question...How the eNb will know that UE has release the resource properly or not, after receiving the RRC connection Release message as we don't have RRC connection release complete message in LTE?

    1. The RRC Connection Release message is transmitted using AM RLC. So the reception of RLC ACK confirms the eNB that the UE has received RRC Connection Release message (at least RLC entity in the UE). Moreover, the eNB could release RRC connection internally even if it doesn't receive an RLC ACK for example in the case of very weak signal.

    2. Do UE requires grant for SRB1 data it has to send in uplink ??for exmaple RLC ACk /NACK !

  20. hi., one question.. What are the premeties involve during PRACH to RACH MAPPING IN LTE ?
    Thanks in Advance

  21. redirectedCarrierInfo utra-FDD : 10837.

    What does 10837 denotes ?

  22. redirectedCarrierInfo utra-FDD : 10837.

    What does 10837 denotes ?

    1. It is actually ARFCN-ValueUTRA which is the carrier frequency to which redirection is intended.

      RedirectedCarrierInfo ::= CHOICE {
      eutra ARFCN-ValueEUTRA,
      geran CarrierFreqsGERAN,
      utra-FDD ARFCN-ValueUTRA,
      utra-TDD ARFCN-ValueUTRA,
      cdma2000-HRPD CarrierFreqCDMA2000,
      cdma2000-1xRTT CarrierFreqCDMA2000,

  23. what is the advantage of having idleModemobilityControlInformation in rrcConnectionRelease?

    I understand that it could be used for load balancing but anyhow we are not specifying exact cell(PCI)as it might be possible that some cells within an earfcn are heavily loaded and some are not. And anyhow eNB can't decide which earfcns are not heavily loaded at run-time and which one aren't?

    1. The network wants the UEs in Idle mode to be on a particular frequency/cell all the time => Which implies that the connection establishment to be done in that frequency/cell.
      Ex: Let us say that the network supports a particular CA combination with pCell on B1 and sCell on B2 and there is another cell on B3 (Cell3). The Network may define highest priority for the pCell on B1. So for example for the UEs going to Idle mode in Cell3, would be forced to go to pCell on B1.

      idleModemobilityControlInfo is semi static in the sense that the network wouldn't update the priorities etc..for days so it is definitely not for load balancing purpose (as you rightly said)

    2. Could you please elaborate more the scenario when ENB sends idleModemobilityControlInfo in RRC Connection Release ?

  24. Hi,
    I have a question about the use of RedirectedCarrierInfo in the RRC Connection Release message. Can this optional parameter be used for other scenarios other than CSFB? The objective is for the eNodeB to redirect the UE that attempt to connect to the eNodeB to a NodeB.


    1. Hi,

      Yes you are correct, this IE is not mandated to be used only in the case of CSFB.

      Best regards,

  25. Dear,
    Normally in RRC Release we have target frequency.
    in some logs of CSFB test, i have all these information in the same RRC Release message :
    redirectedCarrierInfo: GERAN frequencies
    idleModeMobilityControlInfo :
    composed of
    freqPriorityListEUTRA and freqPriorityListGERAN and freqPriorityListUTRA

    Does anyone can help why i have all these information?

    1. In your case, redirectedCarrierInfo: GERAN frequencies indicate to which frequency the network is trying to redirect the UE to.

      Where as idleModeMobilityControlInfo provides dedicated cell reselection priorities of EUTRA, GERAN and UTRA frequencies

    2. ok nice. Why only in Huawei log file, i have
      redirectedCarrierInfo + idleModeMobilityControlInfo ?

      In Nokia or ALU or E// LTE, i have only redirectedCarrierInfo.

      I have 2G CSFB declared in all cases as second priority after 3G first priority.

  26. During a CSFB call, What if an enodeb redirects the UE to another enodeb or UTRA cell, that does not exist, what would happen to the CS call and the call flow post this? This is kind of a corner scenario, but would like to know the UE behaviour in such case.

    1. The UE could do a store search on the specified RAT, if the UE could still not find any frequencies on that redirected RAT, the UE switch RAT.

      Ex: If the UE can't find the specified cell on UTRA, it would search for other cells/frequencies before switching to GSM. (this could be vendor specific)

    2. what is the expected UE behavior when the UE received several SI in the RRC connection release under following condition

      When UE found PSC that match with one of the SI in RRC connection release
      When UE didn’t find PSC that match with any of the SI in the RRC connection release, what is the order of search
      When UE found PSC that match with one of the SI in the RRC connection release but another PSC much stronger
      When UE found the PSC that match with one of the SI in the RRC connection release but the LAC in the SI is different than the one over the air in SIB (wrong information in SI)
      When UE receive 16 SI in the RRC connection release, and found several of them in the air (some stronger than others), which one to chose

  27. Hi, the standard UE connection release (eNB initiated) is as fallows:

    1. UE context release request
    2. UE context release command
    3. UE context release complete
    4. RRC connection release

    In case of UE connection release with REDIRECT:
    1. RRC connection release
    2. UE context release request
    3. UE context release command
    4. UE context release complete

    I'm looking for exact 3GPP source which describes this difference. Many thanks for your feedback!